SMRU > Research > Dive Behaviour
Marine mammals must balance the need to feed underwater, often at considerable depth, with the need to breath. Dive duration capability is determined by the amount of oxygen it can store and the rate at which it uses it. Furthermore, the percentage of time spent diving over longer periods is also influenced by the rate of gas exchange during surface intervals. Within these physiological capabilities marine mammal may choose to dive for shorter periods.
Dive behaviour is studied in two ways at SMRU. Fist, we study the behaviour of animals under controlled conditions in our seal holding facility. The aim is to present seals with a habitat that includes all the important aspects of their usual habitat, e.g. they are free to dive at will, but they can be made to swim up to 160m underwater to their feeding site, covering the range of dive depths that we know they perform in the wild. We can monitor their breathing rates and oxygen consumption. The pool is fitted with a special feeding station that allows us to vary the amount and type of food available to them and vary the amount of swimming effort required to ‘catch’ prey. This allows us to observe the behavioural responses to changes in prey distributions and simultaneously measure both the energetic costs and benefits of the decisions they make.
The second approach is to fit free-ranging animals with telemetry tags. Whilst this approach does not permit experimental manipulation, it does shows how animals behave in the wild. Most of the tags deployed are developed by SMRU’s Instrumentation Group.
Dave Thompson, Carol Sparling and others have used the pool facility to estimate the metabolic rates of seals while they swim and forage out at sea. This is important because the metabolic rate determines how much food marine mammals need to survive, grow and reproduce. This in turn is needed to allow us to estimate how much food they consume. We use this experimental set-up to test different indicators of metabolic rate - such as heart rate, breathing rate and water turnover against an accurate continuous measurement of oxygen consumption. We use the data from these studies to develop models that also incorporate animal weight and activity patterns, to estimate the metabolic rates of different activities at sea.
Bernie McConnell and others use telemetry data to extract dive capability from at-sea dive behaviour. In 2004 a rehabilitated Mediterranean Monk Seal (Monachus monachus) pup was fitted with a SMRU satellite tag. In conjunction with Kimberley Bennett a cohort of grey seal pups of known condition were fitted with SMRU satellite tags at the Isle of May. The idea here was to identify how weaning and departure condition affected dive development. In both studies we used quantile statistics to detect how upper 95th percentile dive performance varied through time.
Martin Biuw, Mike Fedak and others have estimated changes in buoyancy (and thus the body condition) of southern elephant seals using the rate of drift in drift dives. They have also related the dive behaviour to oceanographic features using SMRU satellite tags that also relay conductivity and temperature profiles.