Grey seal predation impairs recovery of an overexploited fish stock
1. Grey seal predation has been blamed by fishers for the decline of Atlantic cod stocks andhas led to calls for seal culls. In the West of Scotland, estimates of cod consumption by sealshave exceeded reported catches and spawning biomass, focussing attention on the interactionbetween fishers and se...
| Published in: | Journal of Applied Ecology |
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| Main Authors: | , , |
| Language: | English |
| Published: |
WILEY-BLACKWELL
2015
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| Subjects: | |
| Online Access: | https://publications.jrc.ec.europa.eu/repository/handle/JRC93528 http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.12439/abstract https://doi.org/10.1111/1365-2664.12439 |
| Summary: | 1. Grey seal predation has been blamed by fishers for the decline of Atlantic cod stocks andhas led to calls for seal culls. In the West of Scotland, estimates of cod consumption by sealshave exceeded reported catches and spawning biomass, focussing attention on the interactionbetween fishers and seals.2. Bayesian models making different assumptions about seal predation were used to estimatethe size of the West of Scotland cod stock between 1985 and 2005 and the mortalities due tofishing and seal foraging. A simple population model was used to identify the likely directionof cod population change at recent mortality rates.3. All model configurations suggest that the total mortality of cod has remained fairly stableand high for many years regardless of the assumptions on seal predation. The high mortalityexplains the long-term decline of the stock.4. The best-fitting model suggests that mortality due to fishing reduced substantially in thedecade up to 2005, but has been replaced by increased seal predation mortality on a smallercod stock. Given total mortality estimates, the stock is unlikely to recover even at presentreduced levels of fishing.5. Synthesis and applications. Our model offers a method of estimating seal predation mortalityas part of routine stock assessments that inform fishery management. The analysis showsthat predation by seals can be an important component of the total stock mortality. It alsoshows that assuming invariant natural mortality, as adopted in many standard fish stockassessments, may lead to incorrect perceptions of fishing mortality, over-estimating the benefitsof reducing fishing mortality when there is density-dependent predation. It is essential toconsider predation by top predators when formulating appropriate advice for managing thefishery. JRC.G.3 - Maritime affairs |
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