SMRU > Research > Population Modelling
Understanding how populations of marine mammals change through time and space is an important goal of marine mammal science that has a direct impact on conservation policy and practice. More often than not, however, the data that we can collect through surveys and studies of animals in the wild only gives a very restricted view of what the entire population might be doing. To make inferences from what we have observed to what might be going on for an entire marine mammal population often therefore requires some degree of statistical modelling.
Annual pup counts derived from aerial surveys enable us to estimate the total UK pup production for grey seals and harbour seals. To convert such numbers into estimates of the total population we need to be able to estimate several population parameters such as pup survival to maturity, age at first pup production, adult longevity and adult female fecundity. Information on likely values for these parameters, given certain caveats, can be obtained from long-term studies such as those at North Rona and the Isle of May. Statistical models can then be used to generate likely total population sizes.
For other species of marine mammals, especially cetaceans, the primary data on abundance may be the number of animals per unit area, as estimated through line transect surveys, or for relatively small or discrete populations, estimates from photo-ID studies. Additional information on calving intervals, longevity and mortality rates then need to be obtained or estimated to enable us to build statistical models of the population concerned, which can be used to explore the consequences of any observed change in, for example, mortality or calf production.
The UK seal populations are studied and reported on to the Special Committee on Seals every year. Population models for grey seals are being developed by John Harwood and Len Thomas to explore the likely limits to population growth and obtain the best estimates of current total population size. Jason Mathiopoulos is developing equivalent models to investigate he decline of harbour seals counts in the UK.
Phil Hammond and his students are examining how bottlenose dolphin populations may change through time, and at how bycatch may influence the abundance and conservation status of species such as the harbour porpoise.