Grey seal predation mortality on three depleted stocks in the West of Scotland: what are the implications for stock assessments?

Vanessa Trijoulet, Steven J. Holmes, Robin M. Cook

Research output: Contribution to journalArticle

Abstract

The decrease in groundfish stocks in the North Atlantic since the mid-1900s coupled with increases in grey seal populations is responsible for an enduring controversy between fishers and conservationists regarding the role seals have played in stock declines. We used a Bayesian state-space model to investigate stock trends in the presence of grey seals and associated MSY reference points in the West of Scotland. This study provides new estimates of seal predation mortality on haddock and whiting and updates the estimates for cod, which together form the traditional main components of the mixed demersal fishery in this area. Grey seal predation mortality is greatest on cod resulting in estimates of total natural mortality higher than those used in the current ICES assessments. Seal predation mortality is low for haddock and whiting. Considering seal predation in stock assessments changes the scale of biomass and fishing mortality estimates for the three stocks. The estimates of F0.1 and FMSY are sensitive to seal predation for cod and whiting but not for haddock. In all cases MSY decreases with increased seal predation.
LanguageEnglish
Number of pages41
JournalCanadian Journal of Fisheries and Aquatic Sciences
Early online date21 Jul 2017
DOIs
Publication statusE-pub ahead of print - 21 Jul 2017

Fingerprint

stock assessment
seals
Scotland
predation
mortality
whiting
haddock
cod (fish)
demersal fishery
fishing mortality
biomass
fisheries

Keywords

  • groundfish stocks
  • grey seals
  • West of Scotland
  • fisheries

Cite this

@article{8977c24c8e40414097cbc4c65ea39f9e,
title = "Grey seal predation mortality on three depleted stocks in the West of Scotland: what are the implications for stock assessments?",
abstract = "The decrease in groundfish stocks in the North Atlantic since the mid-1900s coupled with increases in grey seal populations is responsible for an enduring controversy between fishers and conservationists regarding the role seals have played in stock declines. We used a Bayesian state-space model to investigate stock trends in the presence of grey seals and associated MSY reference points in the West of Scotland. This study provides new estimates of seal predation mortality on haddock and whiting and updates the estimates for cod, which together form the traditional main components of the mixed demersal fishery in this area. Grey seal predation mortality is greatest on cod resulting in estimates of total natural mortality higher than those used in the current ICES assessments. Seal predation mortality is low for haddock and whiting. Considering seal predation in stock assessments changes the scale of biomass and fishing mortality estimates for the three stocks. The estimates of F0.1 and FMSY are sensitive to seal predation for cod and whiting but not for haddock. In all cases MSY decreases with increased seal predation.",
keywords = "groundfish stocks, grey seals, West of Scotland, fisheries",
author = "Vanessa Trijoulet and Holmes, {Steven J.} and Cook, {Robin M.}",
note = "(c) NRC Research Press.",
year = "2017",
month = "7",
day = "21",
doi = "10.1139/cjfas-2016-0521",
language = "English",
journal = "Canadian Journal of Fisheries and Aquatic Sciences",
issn = "1205-7533",

}

TY - JOUR

T1 - Grey seal predation mortality on three depleted stocks in the West of Scotland

T2 - Canadian Journal of Fisheries and Aquatic Sciences

AU - Trijoulet, Vanessa

AU - Holmes, Steven J.

AU - Cook, Robin M.

N1 - (c) NRC Research Press.

PY - 2017/7/21

Y1 - 2017/7/21

N2 - The decrease in groundfish stocks in the North Atlantic since the mid-1900s coupled with increases in grey seal populations is responsible for an enduring controversy between fishers and conservationists regarding the role seals have played in stock declines. We used a Bayesian state-space model to investigate stock trends in the presence of grey seals and associated MSY reference points in the West of Scotland. This study provides new estimates of seal predation mortality on haddock and whiting and updates the estimates for cod, which together form the traditional main components of the mixed demersal fishery in this area. Grey seal predation mortality is greatest on cod resulting in estimates of total natural mortality higher than those used in the current ICES assessments. Seal predation mortality is low for haddock and whiting. Considering seal predation in stock assessments changes the scale of biomass and fishing mortality estimates for the three stocks. The estimates of F0.1 and FMSY are sensitive to seal predation for cod and whiting but not for haddock. In all cases MSY decreases with increased seal predation.

AB - The decrease in groundfish stocks in the North Atlantic since the mid-1900s coupled with increases in grey seal populations is responsible for an enduring controversy between fishers and conservationists regarding the role seals have played in stock declines. We used a Bayesian state-space model to investigate stock trends in the presence of grey seals and associated MSY reference points in the West of Scotland. This study provides new estimates of seal predation mortality on haddock and whiting and updates the estimates for cod, which together form the traditional main components of the mixed demersal fishery in this area. Grey seal predation mortality is greatest on cod resulting in estimates of total natural mortality higher than those used in the current ICES assessments. Seal predation mortality is low for haddock and whiting. Considering seal predation in stock assessments changes the scale of biomass and fishing mortality estimates for the three stocks. The estimates of F0.1 and FMSY are sensitive to seal predation for cod and whiting but not for haddock. In all cases MSY decreases with increased seal predation.

KW - groundfish stocks

KW - grey seals

KW - West of Scotland

KW - fisheries

U2 - 10.1139/cjfas-2016-0521

DO - 10.1139/cjfas-2016-0521

M3 - Article

JO - Canadian Journal of Fisheries and Aquatic Sciences

JF - Canadian Journal of Fisheries and Aquatic Sciences

SN - 1205-7533

ER -