Investigating trends in the growth of five demersal fish species from the Firth of Clyde and the wider western shelf of Scotland

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Abstract

Demersal fish landings from the Firth of Clyde peaked in 1973, then declined rapidly until the targeted demersal fishery ceased in 2005. The abundance of large fish decreased during this period, and their numbers have not recovered since 2005. We aim to determine whether changing growth rates have con- tributed to the decline in the abundance of large fish. Bottom trawl survey data from 1980–2012 was used to calculate the annual mean length-at-age and time series of von Bertalanffy growth parameters of five demersal species; cod, haddock, whiting, Norway pout and saithe. Two regions were considered: the Firth of Clyde and the neighbouring seas west of Scotland (the western shelf). There have been substantial decreases in the lengths of most age groups of Clyde haddock and whiting due to declines in both asymptotic length and von Bertalanffy growth rate. Lengths-at-age have also declined in western shelf populations, but at markedly slower rates than within the Clyde. Trends in temperature and year class strength tended to contribute little to changes in the growth parameters, so declines in length-at-age have been largely due to other factors. Fishing intensity is greater in the Clyde than western shelf, and the size selectivity of the fisheries differ as more Clyde vessels use Nephrops trawling gear. Since trends in growth were also more extreme in the Clyde, it appears as though size-selective fishing may have caused reductions in the lengths of these fish. If the changes in growth are partially due to fishing induced evolution then it may take many generations for the changes to reverse.
LanguageEnglish
Pages71-81
Number of pages11
JournalFisheries Research
Volume177
Early online date1 Feb 2016
DOIs
Publication statusPublished - 1 May 2016

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demersal fish
Fish
Scotland
fishing
whiting
haddock
Fisheries
fish
demersal fishery
bottom trawling
trawling
fisheries
Nephrops
Pollachius virens
vessel
fishery
Survey Data
cod (fish)
time series
Selectivity

Keywords

  • Firth of Clyde
  • growth rate
  • demersal fish

Cite this

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title = "Investigating trends in the growth of five demersal fish species from the Firth of Clyde and the wider western shelf of Scotland",
abstract = "Demersal fish landings from the Firth of Clyde peaked in 1973, then declined rapidly until the targeted demersal fishery ceased in 2005. The abundance of large fish decreased during this period, and their numbers have not recovered since 2005. We aim to determine whether changing growth rates have con- tributed to the decline in the abundance of large fish. Bottom trawl survey data from 1980–2012 was used to calculate the annual mean length-at-age and time series of von Bertalanffy growth parameters of five demersal species; cod, haddock, whiting, Norway pout and saithe. Two regions were considered: the Firth of Clyde and the neighbouring seas west of Scotland (the western shelf). There have been substantial decreases in the lengths of most age groups of Clyde haddock and whiting due to declines in both asymptotic length and von Bertalanffy growth rate. Lengths-at-age have also declined in western shelf populations, but at markedly slower rates than within the Clyde. Trends in temperature and year class strength tended to contribute little to changes in the growth parameters, so declines in length-at-age have been largely due to other factors. Fishing intensity is greater in the Clyde than western shelf, and the size selectivity of the fisheries differ as more Clyde vessels use Nephrops trawling gear. Since trends in growth were also more extreme in the Clyde, it appears as though size-selective fishing may have caused reductions in the lengths of these fish. If the changes in growth are partially due to fishing induced evolution then it may take many generations for the changes to reverse.",
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author = "Aidan Hunter and Speirs, {Douglas C.} and Heath, {Michael R.}",
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AU - Hunter, Aidan

AU - Speirs, Douglas C.

AU - Heath, Michael R.

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N2 - Demersal fish landings from the Firth of Clyde peaked in 1973, then declined rapidly until the targeted demersal fishery ceased in 2005. The abundance of large fish decreased during this period, and their numbers have not recovered since 2005. We aim to determine whether changing growth rates have con- tributed to the decline in the abundance of large fish. Bottom trawl survey data from 1980–2012 was used to calculate the annual mean length-at-age and time series of von Bertalanffy growth parameters of five demersal species; cod, haddock, whiting, Norway pout and saithe. Two regions were considered: the Firth of Clyde and the neighbouring seas west of Scotland (the western shelf). There have been substantial decreases in the lengths of most age groups of Clyde haddock and whiting due to declines in both asymptotic length and von Bertalanffy growth rate. Lengths-at-age have also declined in western shelf populations, but at markedly slower rates than within the Clyde. Trends in temperature and year class strength tended to contribute little to changes in the growth parameters, so declines in length-at-age have been largely due to other factors. Fishing intensity is greater in the Clyde than western shelf, and the size selectivity of the fisheries differ as more Clyde vessels use Nephrops trawling gear. Since trends in growth were also more extreme in the Clyde, it appears as though size-selective fishing may have caused reductions in the lengths of these fish. If the changes in growth are partially due to fishing induced evolution then it may take many generations for the changes to reverse.

AB - Demersal fish landings from the Firth of Clyde peaked in 1973, then declined rapidly until the targeted demersal fishery ceased in 2005. The abundance of large fish decreased during this period, and their numbers have not recovered since 2005. We aim to determine whether changing growth rates have con- tributed to the decline in the abundance of large fish. Bottom trawl survey data from 1980–2012 was used to calculate the annual mean length-at-age and time series of von Bertalanffy growth parameters of five demersal species; cod, haddock, whiting, Norway pout and saithe. Two regions were considered: the Firth of Clyde and the neighbouring seas west of Scotland (the western shelf). There have been substantial decreases in the lengths of most age groups of Clyde haddock and whiting due to declines in both asymptotic length and von Bertalanffy growth rate. Lengths-at-age have also declined in western shelf populations, but at markedly slower rates than within the Clyde. Trends in temperature and year class strength tended to contribute little to changes in the growth parameters, so declines in length-at-age have been largely due to other factors. Fishing intensity is greater in the Clyde than western shelf, and the size selectivity of the fisheries differ as more Clyde vessels use Nephrops trawling gear. Since trends in growth were also more extreme in the Clyde, it appears as though size-selective fishing may have caused reductions in the lengths of these fish. If the changes in growth are partially due to fishing induced evolution then it may take many generations for the changes to reverse.

KW - Firth of Clyde

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