Marine Mammal Scientific Support to Scottish Government

Harbour seals (Monica Arso)

Harbour seals (Monica Arso)

At the beginning of 2015 the Sea Mammal Research Unit started a major new strategic marine mammal research project funded by the Scottish Government (the Marine Mammal Scientific Support Research Programme MMSS/002/15),  This project continued with some areas of work funded under the previous project (see below) whilst also looking forward to new areas of technology, industry and research, continuing to provides advice to Scottish Ministers and stakeholders across a range of key marine policy areas. The programme comprised three major themes:

  • Marine Renewable Energy,
  • HarbourSeal Decline,
  • Seal and Salmon Interactions.

To complete the research the Sea Mammal Research Unit is working with a number of  collaborating organisations, including the Natural Environment Research Council (NERC) and Scottish Natural Heritage (SNH).  The annual reports associated with this research programme can be found below.

Marine Renewable Energy

This research theme continues to identifying and assessing possible impacts of offshore marine renewable energy developments on marine mammals, focusing mainly on seals.

MRE 1 Annual Report Year 1

The work presented under the Marine Renewable Energy (MRE) theme falls in to three tasks;
MRE 1.1 – Fine scale marine mammal behaviour around tidal energy devices.
MRE 1.2 – Harbour seal movement modelling.
MRE 1.3 – Estimating collision risk using available information.

Since MRE 1.1 will not start until year 2 of the project, and the deliverables for MRE1.3 have been amalgamated into the Marine Scotland project CR/2014/12 (which will report separately), this annual report presents on the progress for MRE 1.2 only.


– Progress is reported on the development of an Inter-Haulout Transition Rate Model to explore and characterise harbour seal population movements in the area of Orkney and the Pentland Firth.
– Data from 41 tagged seals were collated and processed. A method was developed to accurately position haulout bouts within the tracks from these tagged animals. This was particularly necessary for the Argos tags as they provide less accurate position track data than GPS/GSM tags.
– A method was also developed to cluster the large number of individual haulout sites into a smaller number of haulout site clusters. This process reduced the amount of computation time required to run the model.
– At a given haulout site, the probability of a simulated seal being associated with any one of the 41 individual haulout transition matrices generated from the tagging data will be proportional to the amount of time that the tagged animal spent at that site.
– The simulations within in this model have not yet been completed. However, all the methodological developments have been completed.
– The structure of a proposed harbour seal Individual Based Model (IBM) is presented with the aim of ultimately demonstrating proof of concept of the IBM approach. The model is based on individuals alternating between foraging at sea and hauling out ashore, based on their individual states (internal properties such as body condition). Movement models based on both memory and exploration are being developed and will be incorporated. Shortest sea-route algorithms have been developed to assist in simulating the memory-based movement of seals to specific targets.
– Whilst the major simulations within this model have not yet been optimised, illustrative movement simulations have been completed. The ultimate challenge is thus to produce a model of appropriate complexity whose predictions (emergent properties) fit well with independent tagging data. The methodology for model validation and parameter estimation is under development after which proof of concept can be demonstrated.

A copy of the MRE 1 annual report year 1 is available for download.

MRE 2 Annual Report Year 1

Following on from the work of Thompson et al. (2015), modifications were made to collision apparatus to reduce the uncertainty surrounding the effective collision speeds of seals with modelled tidal turbine blades.

A copy of the MRE2 annual report year1 is available for download.

Harbour Seal Decline

This research theme continues to try to identify and assess possible factors affecting the population levels of UK harbour seals.

HSD 2 Annual Report Year 1

Numbers of harbour seals (Phoca vitulina) have dramatically declined in several regions of the north and east of Scotland, while numbers have remained stable or have increased in regions on the west coast. For any management and mitigation plans to address this situation, the relative contribution of various factors in the decline of harbour seals in Scotland needs to be identified, understood and assessed. Potential drivers of the decline include changes in prey quality and/or availability, increasing grey seal population size which may be influencing harbour seal populations through direct predation or competition for prey resources, and the occurrence and exposure of seals to toxins from harmful algae.
Previous work by Matthiopoulos et al. (2014) and Caillat and Smout (2015) developed and fitted an age-structured population model to data from the well-studied subpopulation of harbour seals in Loch Fleet (Moray Firth), to evaluate the contributions of different potential proximate causes to the observed decline. After reviewing the existing software, this model has been re-coded directly into R, a framework that will allow for future development and maintenance, and has been designed to be adapted to different model structures and future data sets. Preliminary results are consistent with those obtained from the original OpenBUGS modelling. Future work will have as its key objective the identification of the important drivers of population change in harbour seals, from those being studied as listed above. Temporal and spatial variation in these drivers will be incorporated into the population model.
Harbour seal haulout sites located in different regions of Scotland were visited in the spring and the summer of 2015 to collect information on their suitability for long-term monitoring of harbour seal populations, including their suitability for live captures, scat sampling, aerial and ground survey counts during pupping and moulting and photo-identification. This will allow empirical data to be collected and vital rates (fecundity and survival) to be estimated, for inclusion in the population model.
A haulout site located in West Burray (Orkney) has been selected to represent a region of decline, and a haulout site by Peninver (East Kintyre) has been selected to represent a region of stability or increase. In addition, photo-identification data will also be collected in Dunvegan Loch (Isle of Skye). The regional scope of local populations at each study site (Orkney, Kintyre and Isle of Skye) has been defined to direct future collation of any relevant environmental and biological data. Existing aerial survey counts of harbour and grey seals at each of the defined areas have been collated for use in the age-structured population model.
As part of the live captures programme, female harbour seals will be fitted in 2016 with low-cost electronic location tags, developed to allow a larger number of captured seals to be tagged and designed to regularly relay GPS locations from terrestrial locations. Data from these tags and from ten SMRU GPS/GSM phone tags will inform and direct the extent of the photo-identification re-sighting effort at haulout sites in 2016.
Domoic acid (DA) concentrations have been measured in urine and faecal samples collected from harbour seals in 2015, as a continuation of the work carried out by Jensen et al. (2015). DA is still being found in harbour seals around the Scottish coast and whilst concentrations vary between the different matrices (blood, faeces and urine) and samples, due to variation in exposure and time from uptake to excretion, some individuals appear to be consuming relatively high levels of toxin. Data from the monitoring of biotoxins in shellfish by the Centre for Fisheries and Aquaculture Science (Cefas) and Harmful Algal Blooms (HABs) by the Scottish Association for Marine Science (SAMS) were available for all of 2015 and January 2016. These datasets provide some indication of the occurrence of HABs and toxin-producing blooms in the regions of interest.
To further improve understanding of potential drivers of population change, initial contacts have been made to investigate the availability of prey samples relevant to seals foraging from the study sites, as well as the availability of prey abundance data from long-term fish surveys in the different regions of interest.
An update is provided on the current state of knowledge of the causes of spiral lacerations in seals based on necropsy results of stranded individuals since November 2014. Occurrences around Scotland are summarised along with objective assessments of the cause of the wound patterns, based on a weighted scoring system.

A copy of the HSD2 annual report year 1 is available for download.

Seals and Salmon Interactions

This research theme focuses on the interactions between seals and commercial wild salmon fisheries around Scotland.

SSI Annual Report Year 1

This document reports on progress made on marine mammal research at wild salmon fisheries during 2015. The objectives of the research were: 1) to continue studies into the effectiveness and practical application of Acoustic Deterrent Devices (ADDs) and the modification of salmon nets to mitigate the effects of seals on these fisheries; 2) to collect shot seals for dietary analysis; and 3) to provide support to District Salmon Fishery Boards (DSFBs). Activities related to the first two objectives were primarily focused on two sites in the Moray Firth; Gamrie Bay and Portmahomack.
During 2015, trials on the efficacy of an Airmar ADD continued near Crovie, Gamrie Bay, as did the evaluation of net modifications at this fishery by assessing the effectiveness of two different sizes of fish court entrance. Both ADD trials and net modification trials were conducted at the same netting site, with a balanced design of ADD ‘on’ and ‘off’ periods across the deployment of the two types of net.
Underwater video equipment collected footage from inside the nets for over 1200 hours. The fishery provided salmonid catch and fish damage statistics for each haul of the net for the entire season, and environmental data were collected from a weather station deployed close to the netting site. Analysis of the collated data showed there was a significantly lower probability of detecting a seal during ADD ‘on’ treatments compared with ADD ‘off’ treatments. Furthermore, undamaged catch per unit effort was significantly greater when the ADD was ‘on’ compared with ‘off’, but also significantly greater when the wind direction was onshore compared with offshore. Net modification trials enabled the identification of a compromise that excluded seals from the fish court whilst allowing swift passage of fish through the net, reducing depredation opportunities for seals in both chambers of the net.
At Gamrie Bay (More Head) and Portmahomack, support was provided for fishery-led ADD deployments. In both instances the deployments were run entirely by the fisheries who also collected and provided catch statistics and anecdotal observations. The overall perception of the fishers towards the ADD was positive, and was supported by the data which indicated that landings were higher when the ADDs were ‘on’ and that levels of damage were lower. There was still some evidence however that seals can depredate and damage fish in the nets while ADDs were ‘on’.
During 2015, a further twelve shot seal carcasses were recovered from bag-net sites. Diet information from these seals shows that lethal control is becoming increasingly selective, with a greater proportion of the recovered seals having consumed salmonids. This may be the result of the increasing use of ADDs and net modifications which are helping to reduce the shooting of transient seals.
Presentations have been provided on these studies, along with further support to river fisheries when requested, particularly from the Dee Fishery Board. Where requests for support were received, this led to a channel of communication between those working in river fisheries and SMRU, which is beginning to form the basis of good collaborative work.
This project is continuing to produce encouraging results from the use of ADDs and net modifications at mitigating the effects of seals on these fisheries, and is maintaining positive and open relations with both net and river fisheries.

A copy of the SSI annual report year 1 is available for download.


Previous Programmes


In 2015 the Sea Mammal Research Unit (SMRU) completed a major strategic marine mammal

Harbour seals (Monica Arso)

Harbour seals (Monica Arso)

research project funded by the Scottish Government, with additional support from Scottish Natural Heritage (SNH), which provides advice to Scottish Ministers and stakeholders across a range of key marine policy areas (the Marine Mammal Scientific Support Research Programme MMSS/001/11).


The programme comprised four major themes:

  • Marine Renewable Energy,
  • Harbour (or Common) Seal Decline,
  • Unexplained Seal Deaths,
  • Seal and Salmon Interactions.

To complete the research SMRU worked with a number of  collaborating organisations, including the Joint Nature Conservation Committee (JNCC), the Department for Energy and Climate Change (DECC), the Natural Environment Research Council (NERC), the Department for Food and Rural Affairs (Defra), and the Scottish Association for Marine Science (SAMS). The final reports associated with this research programme can be found below. The Executive Summary from each report can be viewed separately and the reports downloaded as pdfs.

Marine Renewable Energy

off shore wind farm

Off shore wind farm (iStock)

The focus of this research theme was the possible impact of offshore marine renewable energy developments on marine mammals. Potential interactions between seals and cetaceans and various tidal, wind and wave devices were evaluated. An investigation into suitable mitigation measures was also included. This project recognised the need to progressively improve both marine mammal assessment and monitoring methods as well as management approaches to help minimise any apparent adverse effects.



MR1&2 Mapping out the current marine renewables research landscape and an assessing of the data gaps with regards to marine mammals

Current state of knowledge of effects of offshore renewable energy generation devices on marine mammals & research requirements. Update, September 2014

An initial review of the current state of knowledge on the effects of offshore renewable energy generators on marine mammals was provided to the Scottish Government in August 2013. This report provides an update to the 2013 report, highlighting improvements to the current state of knowledge of effects of offshore renewable energy generators on marine mammals and provides an update on progress on the prioritised list of research gaps presented in the previous report.

A total of 28 specific research gaps were identified in the previous report. Of these, 16 were at that time already under investigation to some extent with either active research projects or planned and funded future projects.

The 12 remaining projects were yet to secure funding. Of these, funding has been secured for two (AVOID and ARRY) and discussions are underway in relation to funding for a further two (TAG and MECH). The remainder remain unfunded. Largely the research priorities remain similar, but additional priorities that were not highlighted in the original report have been identified.

In parallel with this study, an analysis of research requirements for developing models to identify Population Consequences of Disturbance (PCOD) was carried out under the ORJIP programme. As part of this work, a number of research priorities were identified and this has been used to extend the list of research gaps and amend the priorities of specific projects in this update.

A copy of the updated final report MR1_and_MR2_update_VF1 is available for download.

MR3 Developing methods for tracking the fine scale underwater movements of marine mammals around tidal devices

The Scottish Government has the duty to ensure that the development of offshore renewable sectors is achieved in a sustainable manner in the seas around Scotland. There is a need to evaluate potential interactions between offshore renewables and marine wildlife as a matter of priority. One such potential interaction is the effect of underwater turbine generators on marine mammals. This report considers the possible technological methods for tracking fine scale underwater movements of marine mammals around marine tidal devices.

The target specification for interaction data as follows: a range of 100mof the turbine which have a temporal resolution of 1s and a spatial precision of 1m. These data requirements place a heavy demand on existing technology. However, we identify three generic methodologies that show potential: Animal-borne telemetry devices (tags), Passive sonar arrays to track animals that vocalise or that carry acoustic pingers, and Active sonar systems, the underwater equivalent of radar.

Animal-borne telemetry devices. These electronic ‘tags’ are attached to locally captured animals (acoustic pinger tags are discussed below). Capturing cetacea is not currently feasible and so this technique is limited to seals. The difficulty in recapturing individual tagged UK grey and harbours seals (within the six month attachment period) means that those type of tag which rely on retrieval for downloading data are not an option. The best option is a tag that relays surface GPS locations and detailed dive depth profiles through the mobile phone system (the GPS/GSM tag). GSM coverage is sufficient for most tidal devices areas. It is technically possible to incorporate dead reckoning (DR) so that the 3-D underwater track can be accurately generated in between surface GPS locations. The drawback is that water current data are required for this calculation at a level of detail that is not currently feasible.

Passive acoustic detection (PAM). PAM is essentially an array of hydrophones that can detect (to species level) and track vocalising animals (primarily toothed whales – especially porpoises and dolphins). A static array of hydrophones around a turbine should be capable of achieving the required level of precision. It is an unsatisfactory system for baleen whales that vocalise unpredictably. Whilst seals also do not regularly vocalise, they could be captured and fitted with individually coded acoustic ‘pinger’ tags. They would thus be capable of being tracked by a PAM system.

Active Sonar. Active sonar is akin to underwater acoustic radar. It has been proven to detect and track marine mammals in the vicinity of underwater turbines at sufficient spatial and temporal scales. It is good at detecting both seals and cetacea and viewing the raw data usually allows distinction between a seal and an odontocete. However we recommend that active sonar is used in conjunction with a PAM system, whereby the species (or individual, if acoustically tagged seals are used) discrimination is greatly improved. Active sonar is the only technology that will detect and track baleen whales.

To balance the strengths and weakness of the above technologies we suggest that the following generic configuration represents the best probability of achieving the overall objective:

Establish a static PAM array around one or more turbine to track vocalising odontocetes.

Tag local seals (c. 20+) with acoustic pingers so that they can also be detected and tracked by the PAM array.

Establish one or more active sonars on the turbine to detect and track all marine mammal species (including baleen whales). Generic discussions with engineers indicate that such an approach is feasible. However site-specific discussions have yet to take place.

Detection of a turbine blade actually striking a marine mammal is essential to interpret the consequences of fine scale movement. However none of the tracking technologies is likely to provide data sufficient to confidently discriminate an actual marine mammal strike from a near miss. Although high risk, we suggest that the feasibility of two possible approaches be explored. First, the physical detection of a strike using stress sensors built into the turbine blades. Second, the development of an underwater video surveillance system.

Appendix II of the report provides a case study of the proposed technology at the proposed Sound of Islay turbine array.

A copy of the final report, entitled MR3_Fine_scale, is available for download.

MR4 Advising regulators and regulatory bodies on specific issues relating to marine renewable energy devices as they arise

SMRU have had a close working relationship with various departments within Marine Scotland as well as with Scottish Natural Heritage and the Joint Nature Conservation Committee. This has previously been in the form of either informal discussions for short or easily answered questions or structured formal research contracts to answer more demanding or time consuming questions.   In developing the MMSS 001/11 research programme Marine Scotland identified a need for a flexible form of advice service that would be intermediate between these two approaches. It was required to still respond rapidly to new and emerging issues but to also be able to call on SMRU staff to respond to any questions related to marine mammals.   This task therefore aimed to deliver effective and timely advice (based on the best available information) to Marine Scotland and other public bodies upon request. The advice is based on the best available information to support Scottish Government requirements on issues relating to marine mammals and marine renewable developments.

A copy of the final report, entitled MR4_advice_function_VF1, is available for download.

MR5 Characterising seal populations

This report describes seal density maps, produced by the Sea Mammal Research Unit, University of St Andrews as a deliverable of Scottish Government Marine Mammal Scientific Support Research Programme MMSS/001/11. The report outlines how the maps can be interpreted and the extent of their limitations with a set of caveats. Appendix 1 describes methodology and software used.

Grey seal (Halichoerus grypus) telemetry data from 1991-2011 and harbour seal (Phoca vitulina) telemetry data from 1991-2012 were combined with count data from 1988-2012 to produce UK-wide maps by species of estimated density and associated confidence intervals. The usage maps are available for download as GIS shape files from the Marine Scotland Interactive website (

MR5.1 At-sea usage and activity

MR5.2 Activity classification using state space modelling

The state-space model developed for defining activity budgets on a coarse resolution (6 hours) was used to define activity budgets at a fine temporal resolution (2 hours) based on both geo-centric and hydro-centric movements. Hydro-centric movements (active movement of seals through the water) were estimated by deleting vectors of current from the geographic movement data. ARGOS data were excluded because the temporal resolution of the location data prohibits the delineation of fine resolution activity budgets.

Activity budgets at a 2 hour resolution were successfully defined using the data from 90% of the 76 GPS/GSM tags considered. Problems apparent when defining activity budgets on the coarse resolution (including the estimation of only one diving state) appeared to be reduced when considering the fine resolution. Although there were some spatial differences in apparent foraging on the two resolutions, the activity budgets defined on the coarse resolution did not appear to be subject to consistent biases.

A significantly higher proportion of time was estimated to be devoted to foraging when hydro-centric rather than geo-centric movements were considered, indicating the importance of incorporating data on water movement when modelling activity budgets in marine animals.

MR5.3 Harbour seal haul-out monitoring, Sound of Islay

The purpose of this report is to provide an overview of the current techniques available for monitoring seal haul-out sites either at the Sound of Islay or at haul-out sites elsewhere.

This report builds on existing knowledge of harbour seal behaviour in the Sound of Islay and the South-East Islay Skerries SAC based on telemetry data collected in 2011 and 2012 with an assessment of data collected by GPS phone tags deployed in April 2014.

Controlled disturbance trials were carried out to assess the effect of disturbance by increased boat activity on haul-out behaviour. Concurrent monitoring of haul-out sites using remote camera systems recorded behavioural responses to trials, as well as giving daily seal counts at particular sites.

Modelling of transition probability indicated that controlled disturbance trials did not affect the probability of harbour seals transiting from one haul-out site to another. Seals generally displayed a high degree of site fidelity. The relationship between site fidelity and transition probability varied with whether seals hauled out again on the same or on a subsequent low tide period after a disturbance. Overall seals were more likely to transit from one haul-out site to another if the trip in between included at least one high tide period.

The results of this study suggest that increased boat activity during the construction phase of the proposed tidal turbine development will not cause individual seals to transit from one haul-out site to another. If seals are flushed from their haulout they are likely to return to the same haul-out site either during the same or on a subsequent low tide period. The recommendation of this report is therefore that monitoring effort to mitigate against any perceived risk of an increase in levels of disturbance by boat need only be on a local scale relative to any proposed development.

In light of these results a simple, time lapse photography based method of haulout monitoring that should provide sufficient information to identify and characterise any boat based disturbance events is described.

MR5.4 Inter-haul-out transition rates

The aim of this study was to predict the changes in the number of seals hauled at the South-East Islay Skerries Special Area of Conservation (EIS SAC) in response to disturbance at other haul-out sites.

Telemetry data from 25 harbour seals (Phoca vitulina), tagged between 2011 and 2014 at capture sites close to the Sound of Islay, were used to populate a movement model based on individual haul-out transition matrices. This model generalised the matrices in order to represent population movements. Disturbance was modelled as the serial permanent closure of one of the 35 haul-out sites used by the tagged seals. The model excluded movement during the breeding season. The modelled response was the change in numbers hauled out at the Ardmore haul-out site within in the EIS SAC. The varying effect of disturbing different haul-out sites reflected the complexity of the haul-out network.

Most disturbances had a positive effect of the number of seals at Ardmore (range: -0.5% to +21%). Haul-out sites with the largest effects were within 50 km of Ardmore and there was little or no effect when the disturbed site was more than 150 km away. However, the response was variable and within 50km distance did not predict which disturbed haul-outs affected Ardmore, as many sites within 50km had little or no effect. Thus the power to infer the effect of remote haulout disturbance by distance alone was limited, other than to say that the effect was greatest within 50 km of the haulout of interest.

However, within a range of 50km, the shortest network path between the disturbed haul-out site and Ardmore provided more information about which sites had an effect. Haul-out site networks adjacent to Ardmore (such as Machrihanish and Eilean nan Coinein) had a larger influence. There was no significant effect when a disturbed haul-out site was more than two transition jumps (connections) from Ardmore. Such network path information can be efficiently obtained in other areas with a simplified and cheaper telemetry system.

The effect of disturbance on the entire EIS SAC depended on the representativeness of the 25 tagged seals’ usage within the EIS SAC. The distribution of haul-outs in the August moult survey differed from the haulout usage of the tagged seals in this study. However, this may be due in part to redistribution during the breeding season. If the tagged seals were representative, the proportional effect of a disturbance to the EIS SAC would be similar. If, however, seals that used other haul-out sites in the EIS SAC were part of a completely different network of haul-out sites then the effect reported here would be reduced.

Whilst useful in this study, the model that was developed was essentially mechanistic. The limitations of this approach are reviewed and recommendations about future work using Individual Based Models are made.

Copies of the final reports, entitled MR5_Seal_density_maps, MR5-1_at-sea_usage_and_activity_VF2 MR5-2_activity_classification_using_state_space_modelling_VF2 and MR5-4_inter-haul-out_transition_rates_VF1 are available for download.

MR6 Characterise cetacean populations

MR6.1 Review of methodology and main results of the JCP analysis of cetacean densities in the context of marine renewable development.

There are a number of potential issues affecting the populations of cetaceans living in or using UK waters. Without knowing the distribution and abundance of these animals the ability to assess how any of these issues could be affecting UK cetaceans is limited.

The revised Joint Cetacean Protocol (JCP) Phase III report attempted to estimate the abundance and distribution of cetaceans from a disparate data set of dedicated and platform of opportunity surveys. It also considered trends in cetacean abundance in the North Sea and waters out to the shelf-edge west of the UK and Ireland, also examining subareas within that area.

The modelling of the data involved sophisticated statistical methods and required various simplifications to be made. A formal model selection process was used but alternative models might produce very different estimates. It is recommended that work is carried out to explore whether moving to indices of abundance and/or maps of relative densities will simplify the model and reduce the risk of producing misleading results without compromising the results of the project.

For some species, the patterns identified by the models are inconsistent with other available sources of information. In particular, the JCP estimate for harbour porpoise abundance in 1994 is difficult to reconcile with that from the SCANS survey.

The JCP report contains many important caveats about the robustness and reliability of its results. It is not obvious that the results of the analyses it contains provide a suitable basis for the conservation and management of cetacean populations around the UK.

A copy of the final report, entitled MR6-1_review_of_JCP_VF2, is available for download.

MR6.2 Definition of ‘range’ in the context of marine renewable energy development and marine mammal conservation.

There are a number of potential issues affecting the populations of cetaceans living in or using UK waters. Without knowing the distribution and abundance of these animals the ability to assess how any of these issues could be affecting UK cetaceans are limited.

The area of sea, or range, specifically used by each cetacean species is an important factor when looking at issues such as Marine Renewable developments. If a development site falls within the natural range of a cetacean species, that species may be likely to be present and therefore collection of baseline data is of vital importance. However, the definition of a natural range, and whether a particular species is likely to be present at a particular site, is not straightforward as cetaceans may only be present at a site seasonally or sporadically because of their wide ranging movements.

There are a wide variety of techniques developed to explore the issue of animal range but not all of these may be suitable for cetaceans, and for some there are not adequate data. Further research will be necessary to ascertain whether there is enough existing cetacean sightings data to explore the utility of some of the measures that have been devised, and therefore to find a model that best serves the need to define the ‘natural range’ of these animals both within the context of the Habitats Directive and any other legislative obligations.

A copy of the final report, entitled MR6-2_define_range_VF2, is available for download.

MR7 Quantifying the risks to marine mammals from different types of interaction with devices in specific areas

Studies of harbour seal behaviour in areas of high tidal energy: Part 1. Movement and diving behaviour of harbour seals in Kyle Rhea.

The report presents a summary of the data collected during the initial transmitter deployments on harbour seals in the Kyle Rhea study area in 2012. As such it forms one of a series of interim reports describing the movements and diving behaviour of seals in areas of high tidal energy. It is designed simply to present the information most likely to be of use in assessing the potential impacts of any tidal turbine deployments in an easily accessible format.

Nine harbour seals caught and tagged at sites within the channel at Kyle Rhea. These seals were fitted with GPS equipped GSM phone tags that provided continuous tracking and dive behaviour data for a total of 506 seal days. The tagged seals concentrated their diving activity within the channel (57% of location fixes) at Kyle Rhea.

All of the seals tagged in Kyle Rhea swam repeatedly through the channel in the vicinity of the proposed turbine deployments. We present an example of how seals were distributed in the water column as they passed through one section of the channel. The filtered data shows a clear bimodal pattern in transits with respect to distance from the shore, with transits being less frequent in the central, deeper section of the channel. In addition, there appears to be a reduced density of transits in mid-water through the central deep channel. This would be an expected consequence of the dive profile patterns and has clear and important implications for estimating collision risk. However, the interpolation error due to timing of GPS fixes and the small but significant GPS position error mean that the transit depth and location data will still contain substantial error.

MR 7.1.1 Quantifying porpoise depth distributions and underwater behaviour in tidal rapids areas.

A vertical hydrophone array has been developed to provide new insights into harbour porpoise dive depths, underwater movements and echolocation behaviour in tidal habitats. This information is of direct relevance to understanding and reducing environmental impacts of tidal current driven turbines. Analysis of field data is on-going however we have demonstrated that it is possible to investigate the behaviour of porpoises in tidal areas using passive acoustics and further work is likely to yield reliable depth distributions.

A copy of the final report, entitled MR7-1-1_porpoise_depth_VF2, is available for download.

MR 7.1.2 The density and behaviour of marine mammals in tidal rapids.

Harbour porpoises (Phocoena phocoena) are one of Europe’s most common cetaceans and they are protected under European law. The current expansion of the tidal energy industry has highlighted concerns about anthropogenic activity in tidal habitats, particularly whether deployed turbines may pose a collision risk to animals. However, the ecological significance of tidal habitats for harbour porpoise is poorly understood and little data exists to inform on the potential risk that tidal turbines may pose. One key metric that needs to be measured to inform on this risk is the depth distribution of animals, for example, if harbour porpoises spend the majority of their time at the surface in tidal habitats then collision risk with deeper turbines will be very low. This report details the results of a three year project to develop, test and survey with a system capable of accurately determining the position of harbour porpoises underwater.

Determining the dive depths of animals is difficult. Tags are a possibility, however, there are no tagging programmes in the UK and the likelihood any one tagged animal would spend a significant time in tidal areas may be small. Passive acoustic monitoring (PAM) is a methodology which can detect the presence, classify the species and localise the position of animals, by listening to their vocalisations. Harbour porpoise use high frequency echolocation clicks almost continually for orientation, prey detection, navigation and social interactions, making them ideal candidates for studies using PAM. However, in order to achieve the accurate underwater tracking required to determine a depth distribution, a large dispersed array of multiple underwater receivers (hydrophones) is required.

Deploying such an array in a tidal habitat is difficult. Fixed structures would be inordinately expensive to deploy in areas with up to 8.5 knots of current and therefore a drifting hydrophone array was developed. The array consisted of 10-12 hydrophones, deployed between 3-45m underwater, from a small research vessel. The practical considerations for such a system are numerous; the array must be quickly recoverable and deployable, any movement underwater must be measured precisely and the delicate electronics used must be sufficiently rugged to remain operational in the particularly harsh environmental conditions present in tidal rips.

In addition to these considerations there are general issues with PAM. Porpoise have narrow beam profiles and hence are easy to miss if facing away from the hydrophone array. Noise and multiple animals clicking at the same time can also be problematic. Many of these issues were overcome by utilising new localisation and tracking methods developed during the project, however, difficulties remain in the fact that usually only fragments of tracks, rather than entire dive profiles, are detected. For the purposes of determining a depth distribution this information is adequate. However, it makes studies on the fine scale behaviour of animals more challenging.

Six tidal sites were surveyed over three years. Over 8514GB and 234 hours of data were collected resulting in 5210 tracks of animals. These were used to create depth distributions for each dive site. Two sites, Corryvreckan/the Great Race and Kyle Rhea contained by far the highest number of detected porpoise vocalisations per hour. Both sites are comparatively deep and porpoises had remarkably similar depth distributions during the day with animals spending 75% of time in the upper 38-40m of the water column. Kyle Rhea was the only site surveyed at night and showed a shift in the depth distribution, with animals spending more time in shallow waters.

The data summarised here provide the first substantial general dataset on porpoise depth distributions and underwater behaviour in tidal rapids. Given that virtually no data existed before, the data presented here can be used to improve collision risk estimates. However, the variation between sites evident in this dataset emphasises the importance of collecting data on a site by site basis.

The continual development of hardware, open source accessible software and PAM localisation methods during this project mean that a methodology now exists to determine depth distributions of harbour porpoises in tidal sites. However, this only forms a subset of the data required to inform on the ecological significance of such an area. Further work needs to focus on combining fine scale tracking of animals with visual/acoustic surveys and long term data recorders.

A copy of the final report, entitled MR7-1-2_porpoise_in_tidal_rapids_VF1, is available for download.

MR 7.2.1 Collision Risk: a brief review of available information on behaviour of mammals and birds in high tidal energy areas.

The large body of published literature focusing on the movement, habitat preference and behaviour of marine birds and mammals was examined for evidence of overlap of marine mammals and birds with sites with potential for tidal energy generation developments. From the review it is clear that there is a wide range of species that use areas of high tidal energy and there is confirmation of the overlap between ecologically important mammal and bird populations with possible tidal turbine sites.

A copy of the final report, entitled MR7-2-1_collision_risk_review_VF1, is available for download.

MR 7.2.2 Collision risk and impact study: Examination of models for estimating the risk of collisions between seals and tidal turbines.

The rate at which collisions can be expected to occur between marine mammals and tidal energy generation devices is potentially important to both the conservation of these species and the industry. Developers need to identify potential adverse effects of their proposed developments. For seals, this means demonstrating, among other things, that development and operation will not have an adverse effect upon the integrity of any SACs for which seals are a qualifying interest. Seals are seen as a particular problem in this respect because they frequent coastal locations where most tidal turbine developments have been proposed.

The major difficulty in estimating likely rates of collision is the lack of information on how animals will respond to active turbines. It is possible that they will be attracted, increasing their overall risk, though it seems more likely that they will avoid some potential collisions. Without such information, which is likely to be difficult to collect even once there are operational turbines, estimation is limited to encounter rates. Encounter rates are defined as the number of seals per unit time which turbines would strike if seals did not respond to the presence of the device. Those can be rescaled by assuming rates of avoidance, but that process will necessarily be approximate.

This report examines two models that have been proposed for estimating the rate at which seals can be expected to encounter tidal turbine blades. It also summarises a method that has been applied to calculate the risks to riverine fish from passing through hydroelectric power stations. The assumptions and implications of using the methods are discussed.

One approach was developed at SAMS Research Services Ltd (SRSL; Batty et al., 2012). It simplifies calculations by simplifying the shape of animals into spheres that would be of equivalent risk and assuming that animals’ speeds are independent of their direction relative to the turbine blade. The two versions of that model seem to have errors in the equations they present, but their overall intent is clear.

An alternative approach was a development of the Band model for the risk of birds being struck by wind turbines. That 2012 model assumed the animal’s motion was parallel to the axis of rotation of the turbine. Counterintuitively, the model’s representation of a “flapping bird” is a more appropriate approximation of a seal than is its “gliding bird” one. The model was broadly similar to the one presented by von Raben for fish passing through a hydroelectric power plant.

The two approaches produce broadly similar results from their different simplifications. Given the greater uncertainty in the animals’ responses, either could be used to give an estimate that will be less of an overestimate than simply estimating the number of animals likely to pass through the disc swept by a turbine rotor. If more detailed comparisons, such as between devices, are required, then a better estimate could be made by averaging the risks over an estimate of the likely joint distribution of animal speeds, directions and orientations throughout the tidal cycle.

In practice, the results of any assessments of overall risk are likely to be determined by the assumptions made about animals’ ability to avoid collisions. Until data on avoidance rates become available, further refinements of the models of encounter rates may be of limited value.

A copy of the final report, entitled MR7-2-2_collision_risk_impact_models_VF1, is available for download.

MR 7.2.3 Collision risk and impact study: Field tests of turbine blade-seal carcass collisions.

In the absence of any field data, collision risk models currently assume that all collisions between marine mammals and tidal turbines will be fatal. This precautionary assumption is not likely to be true and will lead to over-estimation of mortality rates. Estimated mortality rates are likely to be a serious constraint on turbine deployments and reducing the uncertainty should have the effect of reducing these rate estimates.

To address this issue a series of collision trials were carried out with grey seal (Halichoerus grypus) carcasses using a shaped, rigid bar fixed to the keel of a jet drive boat to simulate the leading edge of a turbine blade. The blade profile chosen represented a section near the tip where it is narrowest/sharpest and therefore most potentially damaging. The boat was driven at and collided with a number of previously frozen grey seal carcasses at a range of speeds. The angle at which the carcass was struck influenced the effective speed of that collision. This was accounted for by measuring the angle of the centre line of the keel to the water’s surface (which varied with the vessel’s speed) using video cameras and incorporating this into the effective speed calculations. Carcasses were impacted at a range of effective speeds from 1.95 m/s to 5.32 m/s. Resulting injuries were assessed via inspection of radiographs and by detailed post-mortem analysis. These data and the estimates of effective collision speeds were used to assess the likelihood of injury or death in real collisions.

Post-trial x-rays and post-mortems revealed no evidence of skeletal trauma. Neither were there obvious indicators of trauma such as tears, avulsions or rupture in the integument, musculature or organs, in any of the test subjects as a result of the collision trials. However, due to the difficulties in assessing soft tissue damage such as bruising and tissue oedema in previously frozen carcasses these soft tissue assessments were not considered reliable indicators of trauma in this experiment.

The results of the trials suggest that slow speed collisions with the tips of tidal turbines, at less than the maximum 5.32 m/s measured in this test, are unlikely to produce serious or fatal injuries in grey seals. It seems likely that a significant proportion of impacts would not be fatal, given the range of speeds tested in this set-up and the speeds with which wild seals will be exposed to when interacting with tidal turbines (see Data derived collision risk assessment). These are however, preliminary results and should be treated with caution as they are limited in their inability to assess soft-tissue damage or to determine potential unconsciousness as a result of collisions.

A copy of the final report, entitled MR7-2-3_collision_risk_impact_field_VF1, is available for download.

MR7.2.4 Data based estimates of collision risk: An example based on harbour seal tracking data around a proposed tidal turbine array in the Pentland Firth.

This report presents an estimate of the risk of collision between harbour seals (Phoca vitulina) and tidal turbines on the basis of observed behaviour patterns derived from targeted telemetry tracking studies and recent population survey data. The collision risk associated with a proposed turbine array development in the Pentland Firth was used as a worked example of the method.

A brief summary of the movement data collected during transmitter deployments on harbour seals in the Pentland Firth study area in 2011 was presented, with an emphasis on information that is most likely to be of use in assessing the potential impacts of tidal turbine deployments.

A process to estimate the number of times that telemetry tagged seals could pass through the area of the proposed turbine array was described. The method incorporates dive depth data to estimate the number of times tagged seals would have passed through the swept area of individual turbines in a hypothetical turbine array within the site.

Telemetry data from seals tagged at various sites in the Pentland Firth and Orkney was used to support an estimate of the number of seals likely to be at risk of interacting with such an array. The expected number of collisions between harbour seals and turbines in the array was based on details of their movements relative to the locations and movements of hypothetical tidal turbine blades, assuming that seals are oblivious to the presence of devices i.e. show no avoidance and take no evasive action.

    • It was estimated that 1.2 seals per year (approx. 95% confidence interval (C.I.) 0.8- 2.0) would collide with individual turbines.
    • Scaling that estimate up to the full 86 turbine array suggested that 103 (approx. 95% C.I. 73 – 152) collisions would occur per year.
    • This estimate was approximately 15% of the rate derived from collision risk models for the same site.

The preliminary information from collision experiments was then used to give estimated mortality rates from such collisions. The effects of interpolation error due to timing of GPS fixes and the small, but significant, GPS position error on the estimates of interaction rates are discussed and an attempt is made to incorporate estimates of variability from other sources such as population estimates. Areas where such error distributions are poorly understood and require additional research are highlighted.

A copy of the final report, entitled scottish-natural-heritage-commissioned-report-no-900, is available for download.

MR8 Identifying and testing feasible management and mitigation measures

MR 8.1 Tests of acoustic signals for aversive sound mitigation with harbour seals.

Some anthropogenic activities that produce intense sound in the marine environment present a risk of causing injury to the body tissues and auditory systems of sensitive marine life. It is an offence to kill or injure a seal under the Marine (Scotland) Act 2010 and in addition both grey and harbour seals are on Annex II of the Habitats Directive and are qualifying features for Special Areas of Conservation set up to promote their conservation. For these reasons, mitigation measures to minimise the risk of causing damage or injury are often a requirement when licences are issued to carry out risky activities in the marine environment. The traditional approach to mitigation is for observers to search for marine mammals (including seals) using visual and acoustic techniques, within a mitigation zone and to delay or halt risky activities if animals are detected. (A mitigation zone should be defined as an area within which animals are at an elevated risk of suffering damage. Joint Nature Conservation Committee (JNCC) guidance suggests that mitigation zones around piling should have a radius of at least 500m.) Such monitoring mitigation is unlikely to be fully effective when animals are difficult to sight at the surface and are rarely vocal, when mitigation ranges are large and when operations are required to continue in poor sighting conditions and at night. Mitigation monitoring can also be very costly to achieve at offshore sites. Aversive sound mitigation is a promising alternative or complimentary approach which would involve moving vulnerable animals out of the mitigation zone before activities such as pile driving commence, using appropriate aversive acoustic signals. In this project data was collected to assess how effectively aversive sound mitigation could be applied to harbour seals by conducting a series of controlled exposure experiments (CEEs).

Three sound sources (a Lofitech ADD, an Airmar ADD and broadcast killer whale calls) were assessed as potential sound sources for aversive sound mitigation. The findings suggest that, of the devices tested, the Lofitech ADD is the most effective at eliciting behavioural responses from harbour seals which should be useful for mitigation.

Our results show that out to a range of around a kilometre, all seals might be expected to show a readily identifiable change in behaviour. However, not all responses resulted in straight forward movement away from the sound source. Response also varied between CEEs in ways which may reflect the particular circumstances of the experiment as well as the motivation and status of the subjects.

Three observations from this work are particularly pertinent to those planning to use aversive sound mitigation. The first is the propensity for seals which are close to shore at the start of a CEE to move very close inshore and then move along shore in very shallow waters. This may well be a general and effective anti-predator response but the extent to which it would protect animals from exposure to intense sound needs further investigation. The second is the observation that animals that were traveling when faced with a CEE ahead of them would rarely reverse their tracks. More commonly they would “swerve” around the sound source, passing closer to it than the range at which avoidance behaviour was first noted and on occasion passing within a few hundred metres of it. Clearly, if this occurred during a mitigation exercise then animals might experience higher sound exposure. Studies should be carried out to investigate how animals respond to multiple sound sources in the field which could inform how they should be spaced to achieve effective mitigation. A final important observation is that animals apparently foraging within an area would often start to return to that area soon after a CEE. An implication of this for aversive sound mitigation is that the potentially damaging activity should start immediately after (or during) the mitigation broadcast.

It will be extremely difficult to measure behavioural response of seals to pile driving because any individual tagged animals would be unlikely to be close to pile driving when it started and it is not feasible to use or replicate pile driving as an experimental sound source. However, the observations made during this study of animals responding to what were clearly aversive signals may provide insights into how seals might react to pile driving.   Although seals showed an increase in speed during CEEs this was only modest. This limited response probably reflects energetic constraints on maximum sustainable swim speed which would also limit their escape speed from pile driving. The mean “escape” swim speeds observed during CEEs were lower than those assumed in some exposure models and, in contrast to the assumptions in most models, seals did not always swim directly away from the sound source. These considerations emphasise the desirability of moving animals to a “safe range” using a mitigation sound source whose characteristics can be controlled and measured beforehand using field CEEs.

A copy of the final report, entitled MR8-1_ADD_mitigation_VF2, is available for download.

MR 8.2 Sound Exposure Explorer Tool

The purpose of the Sound Exposure Explorer (SEE) is to provide a simple interactive utility which can be used to explore simple sound exposure scenarios, especially those involving cumulative exposures to moving animals. Using the tool, the cumulative exposure of animals can be calculated and plotted for different exposure scenarios; the “starting ranges” at which acoustic doses received over the course of an exposure scenario will exceed particular predetermined thresholds are also calculated. The intention is not to replace more sophisticated products which may incorporate complicated models of propagation loss and animal movements but to provide a straightforward, readily-understood and easy-to-use tool which can be used to make a first broad assessment of a sound exposure scenario and can provide a benchmark against which the conclusions from more complicated modelling exercises can be compared.

In its current form the utility focuses on the calculation of cumulative exposure for an animal which moves through a sound field created by one or more sound sources.

The conceptual framework of the SEE generally follows that laid out by Southall et al 2007 and many of the thresholds and parameters they propose are available as pre-set values or defaults within the utility.

SEE is open source; thus any developer can check or enhance the underlying Java source code. Our intention in planning and designing the SEE has been to provide a basic functionality within an architecture that will allow for future development and expansion as required.

A copy of the final report, entitled MR8-2_Sound_Exposure_Explorer_Tool2_Manual_VF1, is available for download.

Harbour * Seal Decline

Significant declines in many harbour seal populations on the east and north coasts of harbour sealScotland were first identified following aerial surveys carried out in 2006. The numbers of animals hauled out on land during their annual moult in August are counted by the SMRU. The dramatic reduction in the number of animals seen during these counts has caused concern, particularly in Shetland and Orkney where up to 60% of the animals have been lost and in the Firth of Tay where over a 90% decline in numbers has been observed.

This research theme provided an update on the potential causes of the decline and priorities for future research; discussed management and potential mitigation options; determined the diet of Scottish common compared to grey seals (whose populations in Scotland are not declining) and investigated the dynamics of the common seal populations using a modelling and risk assessment approach.

*also known as common seals

CSD 1 Review of the status, trends and potential causes for the decline in abundance of harbour seals around the coast of Scotland

Review of the status, trends and potential causes for the decline in abundance of harbour seals around the coast of Scotland.

A copy of the report CSD1-1_Review_of_potential_causes_for_harbour_seal_decline is available for download.

CSD 1.2 and CSD 2 Workshop report on decline in abundance of harbour seals around the coast of Scotland and discussion of mitigation and management measures

CSD 1.2 & CSD 2 Workshop report on decline in abundance of harbour seals around the coast of Scotland and discussion of mitigation and management measures

Workshop report on decline in abundance of harbour seals around the coast of Scotland and discussion of mitigation and management measures.

A copy of the updated report, entitled CSD1-2_and_CSD2_Workshop_report_on_decline_in_abundance_of_harbour_seals , is available for download.

CSD 3.1 Improved estimates of digestion correction factors and passage rates for harbour seal (Phoca vitulina) prey

CSD 3.1 Improved estimates of digestion correction factors and passage rates for harbour seal (Phoca vitulina) prey.

Diet composition estimates for pinnipeds are widely conducted using prey hard remains recovered from faeces. To estimate the size and number of prey consumed accurately, digestion correction factors must be applied to measurements and counts of fish otoliths and cephalopod beaks. We conducted 101 whole prey feeding trials with six harbour seals (Phoca vitulina) and 18 prey species to derive estimates of digestion coefficients (DC; accounting for partial digestion using otolith width (OW) or length (OL)) and recovery rates (RR; accounting for complete digestion). Greater than 98% of otoliths were passed within 3 days of consumption. All otoliths passed were recovered by day 10 and all beaks by day 14. RRs were smallest for Atlantic salmon smolts (Salmo salar, RR=0.306; SE=0.031), progressively greater for sandeels, flatfish, squid (Loligo forbesii) and large gadoids, and greatest for Trisopterus spp (RR=1.017, SE=0.002). Species-specific DCs were greatest for greater sandeel (Hyperoplus lanceolatus, DC(OW)=1.75, SE=0.049), then progressively smaller for sandeel, flatfish, large gadoids and Trisopterus species (DC(OW)=1.14, SE=0.015). The amount of erosion of each otolith was graded using a scale of 1-4. The majority of otoliths recovered (65.9%) were severely eroded (grade 4). Grade specific DCs were greatest for greater sandeel (DC=1.82, SE=0.047), then progressively smaller for large gadoids, flatfish and Trisopterus spp (DC=1.18, SE=0.016). Possible explanations for some results with RR>1 and DC<1 are discussed. In almost all cases the CV was
smaller for DCs using OW than using OL. As such, OW DCs (gradespecific) will be used to estimatethe diet of harbour seals, where possible. RRs were broadly similar to those for grey seals (Halichoerus grypus), but harbour seal species – and grade- specific DCs were generally smaller.
Differences in partial and complete digestion rates among prey species and between harbour and grey seals highlight the importance of applying predator and prey-specific digestion correction factors when reconstructing diet.
A copy of the final report, entitled CSD3-1_Harbour_seal_feeding_experiments, is available for download.
CSD 3.2 Harbour Seal Diet Composition and Diversity

Harbour seal diet composition and diversity

Previous studies of harbour seal diet around Scotland and elsewhere in Britain and Ireland have described diet composition at small spatial scales. However, these studies have been patchy in time and space, and the most recent results are from the early 2000s. In addition, declines in harbour seal numbers have been observed since 2000 in Shetland, Orkney and eastern Scotland. Reduced availability of prey is one potential contributory cause of these declines. Comparison of diet among regions that exhibit different population trajectories may shed some light on why harbour seals are declining in some parts of Scotland but not others.
The objective of this study was to provide seasonal and regional estimates of harbour seal diet composition and regional estimates of prey consumption, and to investigate how harbour seal diet (composition and/or diversity) relates to the different population trajectories observed around Scotland.
Harbour seal scats were collected seasonally throughout Scotland and along the east coast of England over a 12 month period in 2010/11. Methods used to estimate diet followed those used in previous SMRU studies of seal diet. Hard remains of prey (fish otoliths and cephalopod beaks) were recovered, identified and measured, and corrections made to account for partial and complete digestion. Diet composition was estimated as the percentage, by weight, of each species in the diet for each region and season. Sampling variability was
estimated using non-parametric and parametric bootstrap resampling methods. Diet diversity was estimated for each region within a season using estimates of prey species richness and the relative abundance of prey species (species evenness). Standard molecular methods were used to ascertain the sex of the seal corresponding to each scat. A total of 1,976 harbour seal scats containing hard prey remains were processed, yielding 65,534 otoliths and beaks.
In the Outer Hebrides, harbour seal diet was approximately evenly split between Trisopterusspecies, pelagic fish, large gadids, scorpion fish, and sandeel. In the Inner Hebrides, large gadids were the main prey; other important species were Trisopterus species and pelagic fish. Sandeel contributed little to the diet along the west coast of Scotland. In Orkney, sandeel dominated the diet in summer and spring. Large gadids were important prey in all seasons. Pelagic prey were important in autumn. In Shetland, the diet comprised primarily pelagic prey, large gadids and sandeel.
In south east Scotland the diet comprised primarily flatfish (mainly plaice) and also sandeel and large gadids. In the Moray Firth, sandeel strongly dominated the diet in all seasons. In the southern North Sea, there was considerable seasonal variation in diet composition. The diet was dominated in summer by sandy benthic species, flatfish and sandeel; in autumn by flatfish, large gadids and dragonet; in winter
by whiting, scorpion fish and sandy benthic prey; and in spring by flatfish and sandy benthic prey.
The large majority of fish consumed by harbour seals were <30 cm in estimated length and the mean size of each species was mostly below the minimum landing size for cod, haddock, whiting and plaice. The effect of harbour seal predation on fish stocks can only be assessed robustly by incorporating seal predation in fish stock assessments. However, mortality rates of the main fish species in the diet of harbour seals are mostly high so predation on the much larger younger age classes of fish is likely to have less of an effect than would
predation on much smaller older age classes. If so, this suggests that the interaction between harbour seals and commercial fisheries around Scotland may not be important for most fish species.

In all regions, except the Moray Firth, there were some differences in male and female diet across all seasons. In The Wash and Scottish west coast regions, females ate fewer large gadids than males and made up the difference in percentage contribution with sandy benthic and pelagic fish in The Wash, pelagic fish in the west coast-central region and Trisopterus species in the west coast-south region. The diet of male and female harbour seals matched most closely during the summer. This similarity in prey composition of the diet may reflect male seals mirroring the distribution of female seals at this time of year. Overall, across all seasons, species richness and evenness did not vary greatly between the diet of male and female harbour seals; however, a small degree of seasonal variation was observed across the diet of both sexes in The Wash in winter and spring.

Overall, harbour seals were estimated to have consumed 23,710 t (95% confidence interval: 21,900-26,170 t) of prey in the North Sea (ICES Subarea IV) and 29,950 t (95% confidence interval: 26,820-32,980 t) of prey west of Scotland (ICES Division VIa) in the 12 months from April 2010 to March 2011, and a grand total of53,660 t (95% confidence interval: 50,180-57,400 t).
Overall, no clear consistent pattern emerged to link estimated diet composition of harbour seals with observed population trends. Instead, variation in diet appeared to correspond largely to regional and seasonal differences in prey distribution and abundance. However, there was a pattern between diet diversity and population trend. Prey species richness and evenness were generally lower in Orkney and Shetland, where harbour seals have declined, and higher in the west coast of Scotland and The Wash, southern North Sea, where harbour seals have not declined. This relationship did not hold in the Moray Firth, where the diet was dominated by a single
prey type (sandeel).
Sandeel was an important component in harbour seal diet in Shetland, Orkney and the Moray Firth and quite important in southeast Scotland – all regions where populations have shown declines. Sandeel was not an important component of the diet west of Scotland, where populations have remained stable, nor in the southern North Sea, where the population is increasing.
Direct comparison of results with other studies was affected by methodological differences but it was possible to take this into account qualitatively and draw some inferences about changes in harbour seal diet over time. Combining this with information on estimated sandeel biomass from stock assessments revealed a general pattern regarding the relationship between diet and trends in population size of harbour seals. Where harbour seals have declined (northern and eastern Scotland) sandeel stocks have also declined and, although their contribution to the diet has declined, they remain an important component of the diet. In regions where harbour seals have not declined (west coast of Scotland, southern North Sea), sandeel were and remain unimportant in the diet and, in the southern North Sea, sandeel stocks have increased.
Overall, with the caution that information is incomplete, the diet of harbour seals is less diverse and at least partially reliant on declining sandeel stocks in regions where population declines have been observed, and is more diverse and not reliant on sandeels in regions where population declines have not been observed. A tentative conclusion is that declines in harbour seal abun
dance in northern regions may be linked to a decline in the abundance of sandeels.
A copy of the final report is availale here.
CSD 3.3 Grey Seal Diet Composition and Prey Consumption

Grey seal diet composition and prey consumption

Since the last comprehensive assessment of grey seal diet around Britain in 2002, grey seal numbers have continued to rise in the North Sea while harbour seal numbers have declined in Shetland, Orkney and southeast Scotland. Stocks of gadid fish have also
declined. In this report on task CSD3.3 of the MMSS/001/11 programme, grey seal diet is reassessed in 2010/11 and compared to previous assessments in 1985 and 2002, and estimates of prey consumed by grey seals are compared with fish stock sizes to estimate
percent predation mortality.
Grey seal scats were collected seasonally throughout Scotland and along the east coast of England over a 12 month period in 2010/11. Methods used to estimate diet followed those used in previous years. Hard remains of prey (fish otoliths and cephalopod beaks) were recovered, identified and measured, and corrections made to account for partial and complete digestion. Diet composition was estimated as the percentage, by weight, of each species in the diet for each region and seas on. Prey consumption was estimated assuming that grey seal populations met their annual energy requirements. Sampling variability was estimated using non-parametric and parametric bootstrap resampling methods.
A total of 2,205 grey seal scats containing hard prey remains were processed, yielding 68,465 otoliths and beaks. In the Western Isles, estimated diet was dominated by sandeel and gadid prey, particularly cod and ling. In the Northern Isles, the diet was also dominated by sandeel and gadid prey, particularly saithe and cod. Sandeel made up around a quarter of the diet in Shetland and around half of the diet in Orkney. In the central North Sea, diet was heavily dominated by sandeel but was more varied in the southern North Sea.
Overall, grey seals were estimated to have consumed 129,200 t (95% conf. interval: 114,800-149,400 t) of prey in the North Sea (ICES Subarea IV) and 70,300 t (95% conf. interval: 60,000-84,000 t) of prey west of Scotland (ICES Division VIa) in the 12 months from April 2010 to March 2011; a grand total of 199,500 t (95% conf. interval: 181,200-225,500 t).
Diet composition appears to have changed little in the Western Isles from 1985 to 2002 to 2010/11. In the Northern Isles, changes in diet composition were characterised by a marked decline in the contribution of sandeel in Shetland and a more gradual decline in Orkney, and an increase in the contribution of gadids. In the central North Sea, however, the change in the contribution of sandeel and gadids was the reverse of that seen in the Northern Isles. Gadids declined markedly but sandeel increased steadily between 1985 and 2010/11.
In the North Sea (ICES Subarea IV), consumption by seals as a percentage of estimated stock size is estimated to be small; the highest figure is for cod (5% in 2010). West of Scotland (ICES Division VIa), however, estimated consumption by seals as a percentage of estimated stock size is larger for whiting (10% in 2010) and very large for cod (> 100% in 2010). These figures increase to ~50% and > 200%, respectively, if harbour seal consumption is also included. The partial coverage of west coast cod by the stock assessment and the lack of overlap between the area of the fishery and the area where seals forage provide an explanation for how the estimated consumption by seals can be so large relative to the size of the assessed stock.
Ac opy of this report can be found here.
Comparing the Diet of Harbour and Grey Seals in Scotland and Eastern England

CSD 3.4: Comparing the Diet of Harbour and Grey Seals in Scotland and Eastern England

Harbour seal populations in some areas around Scotland have declined since around 2000 but the cause(s) of these declines are unknown. Reduced availability of prey is one potential contributory cause, including the possibility of competition between grey seals and harbour seals. To contribute new information regarding this question, regional and seasonal similarities and differences in the diet of harbour and grey seals in relation to regional differences in population trajectories of harbour seals, were examined.
Grey seal diet was dominated by sandeel in all regions of the North Sea. Sandeel were also dominant in the diet of harbour seals in the Moray Firth but, to the south, their diet was more varied and also included flatfish, sandy benthic and large gadid prey. In Orkney and Shetland, harbour and grey seal diet comprised mostly sandeel, large gadids and pelagic prey. The largest differences were in Orkney in spring/summer, where harbour seals ate more sandeel, and in Orkney in autumn/winter and all year in Shetland where harbour seals ate more pelagic fish. West of Scotland, large gadids were the main prey in the diet of both harbour and grey seals. Pelagic fish were also important in harbour seal diet and sandeel and sandy benthic prey in grey seal diet. Despite some differences in diet between grey and harbour seals, there was no clear evidence of seasonal variation in these differences that may be related to the different life cycles of these two species.
Although there was considerable seasonal and regional variation in the diet of both harbour and grey seals, there was no unequivocal pattern to explain differences in diet between species in regions where harbour seals have and have not declined.
However, there was some evidence that sandeel may play an important role in the diet of harbour seal populations in the North Sea a
nd Northern Isles. In regions where harbour seals have declined (northern and eastern Scotland) sandeel stocks have also declined and, although their contribution to the diet has declined, they remain an important component. In regions where harbour seals have not declined (west coast of Scotland and southern North Sea), sandeel were and remain unimportant in the diet. Grey seal populations are stable or
increasing, regardless of the importance of sandeel in the diet.
Overall, the diet of harbour seals was less diverse and at least partially reliant on declining sandeel stocks in regions where population declines have been observed, and was more diverse and not reliant on sandeels in regions where population declines have not been observed. A tentative conclusion is that declines in harbour seal abundance in northern regions may be linked to a decline in the abundance of sandeels.
More information is needed to improve the understanding of whether or not changes in prey availability, including any influence of
competition between harbour and grey seals, may have led to changes in the ability of harbour seals to meet their nutritional requirements and, hence, ultimately to population declines. This information includes, at appropriate temporal and spatial resolu
tions, prey distribution and abundance, the availability of that prey to seals, and the foraging behaviour of seals in relation to their life history.
A full copy of this report is available here.
CSD 4 Harbour seal decline: population modelling

CSD 4 Harbour seal decline: population modelling

A baseline model was developed to estimate harbour seal (Phoca vitulina) demographic rates, such as fecundity and survival for different age classes. Count data and two independent estimates of population size based on capture-recapture photo-ID studies, were used to fit the model along with historical records of shooting of seals in the area. Modifications made to an earlier model (Matthiopoulos et al., 2013) resulted in a more realistic and robust version. The estimated demographic trends are very similar to the original model but with a considerably better fit to the independent estimates. Using simulations based on the fitted model, the sensitivity of the population growth rate to different scenarios of fecundity, survival or seal management was investigated. The results of fitting the baseline model suggest that of the demographic trends, the fecundity rate appears to be the most variable in time and the parameter most sensitive to environmental changes. The most important age class in the population are the adult females (Harwood & Prime, 1978). If the adult female annual survival rate decreases by 5% per annum then the population will decline.
Next, the possible effects of other covariates that could potentially have an impact on these rates were investigated, including prey covariates: herring (Clupea harengus), Atlantic cod (Gadus morhua), sprat (Sprattus sprattus) and sandeels (Ammodytes marinus);
environmental covariates: sea surface temperature (SST), North Atlantic oscillation (NAO) winter index; interaction covariates: counts of grey seals in northern Moray Firth; andbiotoxin data: mussel concentration of saxitoxin and domoicacid. Over all the models two covariates were significantly different to zero, indicating a correlation between (a) grey seal (Halichoerus grypus) abundance and harbour seal pup survival, and (b) sandeel abundance and fecundity. With the grey seal abundance covariate included in the model the trend in
the pup survival rate is very different to the one in the baseline model, with a decreasing pup survival rate linked to an increase in the grey seal populationsize.
Finally, to explore the potential to fit such models at sites where fewer data are available, the baseline model was modified such that
only one part of the data was used to fit the model. Results were then compared with those obtained using the full data set. For the model run with only moult data eitherthe fecundity rate was fixed using the value estimated by Cordes (2011) or an informative prior to the fecundity rate was set. The model overestimated the abundance but abundance trends were similar to estimates based on the full dataset. With a minimum of one breeding survey per year the results were much better. This time the non-pups were slightly overestimated but the fecundity and the pup survival trends were very close to the credible interval of the baseline model.
In conclusion, if the objective is to understand what parameters drive harbour seal vital rates (fecundity and survival), and to predict the status of the population, it is very important, as a minimum to collect both regular harbour seal moult counts and pup counts and to collect covariate data on potential drivers at a local level.
A copy of the report, entitled CSD4_population_model_VF2, is available to download.
CSD 5 Changes in at-sea foraging trips of harbour seals and grey seals in south-east Scotland

CSD 5 Changes in at-sea foraging trips of harbour seals and grey seals in south-east Scotland

In many areas of Scotland including Orkney, Shetland and south-east Scotland, the harbour seal (Phoca vitulina) population is in rapid decline. Although the reasons for this decline are not known, nutritional stress has been postulated as a potential key factor. In south-east Scotland, telemetry data are available for multiple years for both harbour and grey (Halichoerus grypus) seals, allowing a pilot study to be conducted to investigate whether putative symptoms of nutritional stress are present in the behaviour of harbour seals. Specifically, it was hypothesised that the duration and extent of harbour seal foraging trips would have increased since the decline started. Contrary to the hypothesis, while controlling for day of year and sex, it was found that, since the start of the decline, harbour seal trip extent and duration has significantly decreased. In contrast, grey seal trip duration and extent has significantly increased, despite the grey seal population in south-east Scotland not appearing to be in decline. Although changes in the environment are likely to have driven these changes in apparent foraging effort, the underlying drivers remain unknown. Further work should focus on how robust the results are to (1) changes in how foraging trips are defined and (2) changes in the metric of foraging effort considered.
A copy of the report, entitled CSD5_at_sea_activity_report_VF1, is available to download.
CSD 6 Harbour seal decline workshop II, 24th April, 2014

CSD 6 Harbour seal decline workshop II, 24th April, 2014

The persistent decline in the abundance of harbour seals (Phoca vitulina) in some regions of Scotland continues to be of concern. Following a workshop held at the Sea Mammal Research Unit in 2012 (Hall et al., 2012) a number of key potential drivers (particularly the potential causes of the spiral seal lacerations, factors affecting prey availability and the effect of toxins from harmful algae) were highlighted as being priority areas for further research. This led to a second workshop, again hosted by the Sea Mammal Research Unit (SMRU), held in April, 2014 and which is the subject of this report. The main aim of the Workshop was to discuss the main candidate drivers responsible for the sharp decline in harbour seal numbers on the Scottish East Coast, Orkney and Shetland and develop an empirical and statistical research approach for investigating their role in future population trajectories.
The workshop acknowledged that there is a need to rapidly identify any anthropogenic drivers of the decline so that mitigation could be implemented before the situation deteriorates any further. It was agreed that the most important priority was not just to focus on candidate drivers but to estimate the vital population rates that shape the population trends, namely survival and fecundity rates. This would be critical in furthering our understanding of the most likely causes for the declines, which could be different in different regions and may be due to a combination of drivers. Because some regions are declining but others are stable or increasing, this provides a ‘natural experiment’ in which vital rates can be compared among areas of decline in abundance and those that are not.
Although the workshop participants did not set any recommendations for future research SMRU made recommendations based on the outcomes of the workshop and the discussions that were had. SMRU will now develop a focused programme of research to seek to establish the key life-cycle factors that appear to be driving the decline in some regions but not in others. This will be based around a minimum of two sites (one in an area with a population decline and another in an area with a stable population). It will include investigation of the potential contribution of grey seals (Halichoerus grypus) as competitors for prey and other interactions between the two species, the type and availability of prey in the different regions and the potential impact of exposure to toxins (such as domoic acid and saxitoxin) produced by harmful algal blooms. SMRU will continue to research the issue of spiral seal lacerations to inform revised guidance for developers and to explore potential mitigation options.
A copy of the report, entitled CSD6_harbour_seal_workshop_II_VF1, is available to download.

Unexplained Seal Deaths

Significant numbers of harbour seal and some grey seal carcasses showing unusualspiral seal photo injuries have been washing ashore at sites around the UK, many along the east coast of Scotland. The carcasses have a characteristic single, smooth-edged cut starting at the head and spiralling around the body. These trauma injuries are not consistent with any previously identified causes of death such as entanglement in fishing nets or boat propeller strikes.

This project set out to identify the mechanism(s) involved in these unexplained seal mortality events; to assess the extent and level of seal mortality due to these mechanisms and the implications for the viability of the local seal populations.

Updated USD 1 & USD 6 Current state of knowledge of the extent, causes and population effects of unusual mortality events in Scottish seals

Current state of knowledge of the extent, causes and population effects of unusual mortality events in Scottish seals

This report summarises the available information on a newly identified cause of seal deaths around the Scottish coast. All of the seals had a characteristic wound consisting of a single smooth edged c ut that started at the head and spiralled around the body. In most cases the resulting spiral strip of skin and blubber was detached from the underlying tissue. The wound was identified as the cause of death in all cases for which a detailed post mortem examination was carried out.
To date (January 2015) a total of 127 seals with confirmed spiral injuries have been recorded in Scotland; 73 grey seals, 51 harbour seals (Phoca vitulina), 1 hooded seal (Cystophora cristata) and 2 seals of indeterminate species. These numbers are minimum estimates and will probably represent only a proportion of those animals killed close to shore.
Geographical and seasonal distributions of dead seals with these characteristic wounds are patchy in Scotland. Two concentrations are apparent; one around the Scottish south east coast (mainly comprising the area around the Tay and Eden estuaries and the coast of the Firth of Forth) and the other in Orkney. These patterns indicate strong selectivity in the causal mechanism. The presence of similar injuries around Europe and in Canadian waters is presented, showing that this is a widespread problem.
A range of causal mechanisms have been investigated and the list of potential causes has been reduced to the most likely cause being a rotating blade in a tunnel or housing , i.e. ducted.
The circumstances leading to the injuries and their possible population consequences are discussed.
A copy of the report, entitled USD1and6_update_report_VF2,  and an addendum, entitled USD1and 6_addendum_report_VF2, are available for downlaod.


USD 2 Testing the hypothetical link between shipping and unexplained seal deaths

Testing the hypothetical link between shipping and unexplained seal deaths.

This investigation was driven by the need to determine the cause of spiral lacerations in seals; a cause of death which has been reported with increasing incidence in the UK for the past decade. The purpose of this study was to demonstrate the ability of certain propulsion systems used on vessels to cause these types of injuries. The effect of animal size, propeller speed and propeller type on the occurrence of seal- propeller interactions was investigated. All trials were conducted with scale models of seals comprised of silicon rubber cores and wax outer layers.

A total of 59, 80 and 75 seal models were recorded and analysed for the ducted propeller, open propeller and Voith-Schneider propeller treatment groups respectively. Each propeller type was tested at four different rotation speeds and three model sizes representing different life stages were subjected to each speed. Only scale models which were subjected to a ducted propeller (a propeller fitted with a static housing) displayed characteristic injuries similar to those seen on stranded seals in the UK and Canada. Propeller speed was a significant factor in determining damage attributes, with slower speeds producing more spiral lacerations. Model size appeared to be unimportant in determining damage characteristics. Open propellers and Voith-Schneider propellers did not produce these patterns in any of the trials.

Ducted propulsion systems were the only mechanism which produced spiral lacerations under these test conditions. Consequently observations on candidate vessels are vital to gain a better understanding of the circumstances under which these interactions can occur in coastal regions. Viable mitigation can then be developed to reduce the number of cases and protect seal populations.

A copy of the report, entitled USD2_hypothetical_link_VF2-0, isavailable for downlaod.


USD 3 Testing the hypothetical reasons for inappropriate responses to the candidate mechanisms for the unexplained seal deaths

USD 3 Testing the hypothetical reasons for inappropriate responses to the candidate mechanisms for the unexplained seal deaths

The primary aim of this investigation was to establish whether the acoustic properties of ducted propellers had an attractive quality to seals. Ducted propellers were identified as a candidate, causal mechanism for the unexplained seal deaths in Onoufriou & Thompson (2014). However, the means by which a seal would come into contact with a propeller remain unclear. The hydrodynamic qualities of a ducted propeller mean that seals must be voluntarily swimming to within a few metres for an unavoidable collision to occur.
Sound exposure experiments were carried out on both harbour seals (Phoca vitulina) and grey seals(Halichoerus grypus) in both wild and captive situations. Target seals were exposed to recordings of ducted propellers, open propellers and harbour seal mating calls.
In the wild, seal responses were monitored with active sonar to detect any approach to the sound source. In the captive trials seals choice of feeding location and behaviour close to and remote from the sound source were monitored using video recordings.
No response was detected by any seal to the exposures. In the wild, no seals approached the speaker and with the captive seals the
primary drivers appeared to be feeding rather than exploration of the sound producing device. Even with the removal of the feeding stimulus, no behavioural response as a direct result of sound exposures was observed.
If ducted propellers are a cause of thespiral injuries in seals then the results of this study would suggest the manner by which the interaction occurs is not the result of an acoustic attraction. The stranding of a grey seal test-subject with spiral lesions two days after release from the captive facility indicates either (a) at least one individual was susceptible to the attractive qualities of ducted propellers and those qualities were not replicated in this experiment, or (b) that acoustic signals are not involved in attracting seals to the mech anism causing the spiral lacerations.
A copy of the report, entitled USD3_inappropriate_response_VF1, isavailable for downlaod.


USD 4 Examining the distribution of observed carcasses to identify biological and oceanographic patterns and distribution of potential causes to assess the patterns of risk associated with these unexplained seal deaths

USD 4 Examining the distribution of observed carcasses to identify biological and oceanographic patterns and distribution of potential causes to assess the patterns of risk associated with these unexplained seal deaths

This investigation sought to establish a monitoring protocol for analysing the potential of shipping interactions as the cause of spiral lesions in grey (Halichoerus grypus) and harbour (Phoca vitulina) seals. Two major projects aimed to: (a) assess fine scale shipping behaviour on an individual stranding, case by case basis and (b) establish the nationwide overlap between vessel traffic and seal usage. Automated Identification Systems (AIS) and radar were the primary sources of data in both cases. In addition telemetry data wereused to generate seal usage maps.
A total of 26 strandings between January 2013 and January 2015 were assessed for possible, related fine-scale shipping behaviour. Candidate vessels were identified in all cases when wind-direction and estimated time-of-death were taken into account.  Sixteen
cases contained at least one identified candidate vessel which had also appeared in another case.
Shipping traffic around the UK was primarily within 100km of the coast, and the heaviest consistent densities were on the south coast of England, in the English Channel and the mouth of the Thames. For both UK species of seal areas of highest occurrence between seals and shipping are within 50km of the coast and coincide with areas of high seal usage. However, there does not appear to be a relationship
between stranding locations and areas of high occurrence between seals and shipping.
It was concluded that, although candidate vessels could be identified in all cases, shipping densities illustrate that strandings are not occurring where expected if seal-shipping interactions were the primary cause of spiral lesions. However, this could be due to lack of reporting or identification in areas of high interaction rates. As yet, with the evidence presented here, there is no further reason to assume seal-shipping interactions are causing spiral seal lacerations.
A copy of the report, entitled USD4_distribution_of_potential_causes_VF1, isavailable for downlaod.


USD 5 Assessing the impact of the observed and estimated levels of mortality on seal populations at a local, national and international level

USD 5 Assessing the impact of the observed and estimated levels of mortality on seal populations at a local, national and international level

Aerial surveys have detected alarming declines in the counts of harbour seals (Phoca vitulina) in several regions across Scotland. Available demographic data and simple models are used to examine the recent declines in the numbers of harbour seals counted in one population within a Special Area of Conservation (SAC) on the east coast of Scotland. The models suggest that the continuation of current trends would result in the species effectively disappearing from this area within the next 20 years.
While the cause of the decline is unknown, it must be reducing adult survival because the high rate of decline cannot be wholly accounted for by changes in other demographic parameters. Recovery of the population to the abundance when the SAC was designated is likely to take at least 40 years, even if the cause of the decline is immediately identified and rectified.
The models suggest that partial removal of the cause will have only limited benefits to population recovery, and there are unlikely to be any long-term benefits from introducing or reintroducing additional individuals while the problem persists. Therefore, if the population of harbour seals in this area is to recover it is essential that the sources of the increased mortality are identified and measures are put in place to manage these.
A total of 36 harbour seal carcasses with characteristic spiral wounds have been recorded in the vicinity of the Firth of Tay and Eden estuary since 2010. This level of mortality is estimated to be unsustainable and likely to be a major factor in the decline. Less information is available from other regions, but a comparison with potential biological removal (PBR) estimates suggests that the same mechanism of injury may become important in the Moray Firth and possibly Orkney if the level of reporting is low.
A copy of the report, entitled USD5_assessing_impact_of_spiral_lesions_VF1, isavailable for downlaod.


Seals and Salmon Interactions

There is a long history of conflict between salmon fisheries and seals due to highly visible damage to fish or observed depredation (seals removing fish from nets), leadiseal taking salmon from netng to a widespread belief among fishermen that seals adversely affect both salmon stocks and landings. Until recently, this conflict was often resolved by shooting individual seals. Since 2010, however, shooting has only been allowed in Scotland under licence to protect fish and fishing gear from seals. While non-lethal measures are preferred, these are still not effective in all cases and the option of killing should now be seen as a last resort.

The objectives of this study were therefore to investigate the effectiveness of acoustic deterrent devices (ADDs) and the modification of salmon nets to mitigate the effects of seals on these fisheries; to collect seal carcases for dietary analysis and provide scientific support to the district salmon fishery boards (DSFBs).

SSI: Seals and wild salmon fisheries

SSI Seals and wild salmon fisheries

This document reports on the progress made during 2014 with regard to marine mammal research at wild salmon fisheries. The objectives were: to continue studies into the effectiveness of Acoustic Deterrent Devices (ADDs) and the modification of salmon nets to mitigate the effects of seals on these fisheries; collect shot seals for dietary analysis and provide support to district salmon fishery boards (DSFBs). Activities primarily focused on two sites in the Moray Firth, Portmahomack and Crovie.

During 2013 the salmon net fishery at Portmahomack reported that seals were regularly seen at the net and that salmon landings were damaged by seals despite the use of an ADD. During 2014 seal sightings and salmon landings data were collected and photo-identification of seals from land-based photography was used to identify individual seals. Images were collected (n=1197) and all seal sightings at the net while the ADD was ‘on’ were attributed to adult male grey seals. Photo-identification revealed only two adult male grey seals were prepared to visit the salmon net while the ADD was ‘on’.

During 2013 tests began on the effectiveness of an ADD at Crovie. This work continued in 2014 through the collection and processing of underwater video footage to study the rate at which seals entered the net. The deployment of a C-POD was trialled to provide information on the presence of cetaceans during ADD ‘on’ and ‘off’ treatments; however, the elevated noise levels during ADD ‘on’ periods compromised the C-PODs ability to detect cetaceans. Dolphins and porpoises were regularly detected on the C-POD during ADD ‘off’ periods. Land-based observations recorded dolphins during both ADD ‘off’ and ‘on’ periods. Seal sightings were between five and six times higher during ADD ‘off’ periods compared to ADD ‘on’.

At Crovie in 2014 the evaluation of net modifications continued by examining the effectiveness of a different size of net entrance. Results from the 2014 study suggested that the new design increased salmon landings and reduced fish hesitation in the outer part of the net, an important aspect of reducing depredation from this area.

In April 2014 a report on the diet of seals shot at salmon nets from 2005 to 2013 was produced. The most frequently encountered prey was whitefish, sandeels and flatfish. However, an increase in the proportion of seals testing positive for salmonid DNA since the introduction of ADDs and net modifications may suggested that fewer ‘transient’ seals are now being shot with lethal control becoming more targeted to those consuming salmon.

Sea Mammal Research Unit (SMRU) personnel have continued to provide presentations on these studies and have provided support to river fisheries when requested. Where requests for support have been received this has led to the formation of a channel of communication between those working in river fisheries and SMRU that is beginning to form the basis for good collaborative work.

This project is continuing to produce encouraging results from the use of ADDs and net modifications at mitigating the effects of seals on these fisheries, and is maintaining positive and open relations with both net and river fisheries.

A copy of the report, entitled SSI_seals_and_salmon_VF1, is available to download.