Harbour Seal Decline – vital rates and drivers.:Report to Scottish Government HSD2.
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 o...
| Main Authors: | , , , , , , , , , , |
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| Format: | Book |
| Language: | English |
| Published: |
Sea Mammal Research Unit
2017
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| Subjects: | |
| Online Access: | https://research-portal.st-andrews.ac.uk/en/publications/e63c0fbe-b5dd-44ef-b341-457c7bdda315 http://www.smru.st-andrews.ac.uk/files/2017/09/HSD-2-annual-rep-yr2_V5.pdf |
| Summary: | 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. Work has continued to build on the original Moray Firth study, re-coding a simplified version of the population model in JAGS language. A decision support tool (DST) has also been developed to include a biologically realistic simulation model and a model-fitting step that attempts to recover the parameters used in the simulation. A simple population model was successfully fitted to historical data for Scapa Flow (Orkney), with the Markov chain Monte Carlo (MCMC) converging and estimating reasonable-seeming parameter values. The DST was used to explore fitting limited data sets. The simulation/fitting approach showed that the fitting software was able to estimate parameters from the data even when the data set was ‘thinned’ (data not available for every year) and when no pup count data were available. Live capture-release studies were conducted in Orkney in April and May 2016 under the SMRU Animal (Scientific Procedures) Act, 1986, (Home Office Licence No. 192CBD9F). Adult and juvenile harbour seals ... |
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