Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?

Anna Gårdmark, Örjan Östman, Anders Nielsen, Karl Lundström, Olle Karlsson, Jukka Pönni, Teija Aho

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973–2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change
Original languageEnglish
JournalICES Journal of Marine Science
Volume69
Issue number8
Pages (from-to)1448-1456
ISSN1054-3139
DOIs
Publication statusPublished - 2012

Keywords

  • assessment models
  • fishery management
  • maximum sustainable yield
  • population dynamics
  • species interactions
  • stock assessment
  • top-predators
  • marine mammals

Cite this

Gårdmark, Anna ; Östman, Örjan ; Nielsen, Anders ; Lundström, Karl ; Karlsson, Olle ; Pönni, Jukka ; Aho, Teija. / Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?. In: ICES Journal of Marine Science. 2012 ; Vol. 69, No. 8. pp. 1448-1456.
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title = "Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?",
abstract = "Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973–2009. Accounting for predation increased the herring SSB 16{\%} (maximum 19{\%}), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change",
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author = "Anna G{\aa}rdmark and {\"O}rjan {\"O}stman and Anders Nielsen and Karl Lundstr{\"o}m and Olle Karlsson and Jukka P{\"o}nni and Teija Aho",
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Gårdmark, A, Östman, Ö, Nielsen, A, Lundström, K, Karlsson, O, Pönni, J & Aho, T 2012, 'Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?', ICES Journal of Marine Science, vol. 69, no. 8, pp. 1448-1456. https://doi.org/10.1093/icesjms/fss099

Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates? / Gårdmark, Anna; Östman, Örjan; Nielsen, Anders; Lundström, Karl; Karlsson, Olle; Pönni, Jukka; Aho, Teija.

In: ICES Journal of Marine Science, Vol. 69, No. 8, 2012, p. 1448-1456.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?

AU - Gårdmark, Anna

AU - Östman, Örjan

AU - Nielsen, Anders

AU - Lundström, Karl

AU - Karlsson, Olle

AU - Pönni, Jukka

AU - Aho, Teija

PY - 2012

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N2 - Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973–2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change

AB - Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973–2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change

KW - assessment models

KW - fishery management

KW - maximum sustainable yield

KW - population dynamics

KW - species interactions

KW - stock assessment

KW - top-predators

KW - marine mammals

U2 - 10.1093/icesjms/fss099

DO - 10.1093/icesjms/fss099

M3 - Journal article

VL - 69

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EP - 1456

JO - I C E S Journal of Marine Science

JF - I C E S Journal of Marine Science

SN - 1054-3139

IS - 8

ER -