Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated

Numerical studies were conducted on the effects of trawl and longline catches on a cod stock and possible yields from it. Five year mean age composition of Pacific cod (Gadus macrocephalus) from the Bering Sea was used as initial age composition of the stock, which was normalized to 1 ton. Age speci...

Full description

Bibliographic Details
Main Authors: Bjordal, Åsmund, Laevastu, Taivo
Format: Report
Language:English
Published: ICES 1990
Subjects:
cod
Tac
Online Access:http://hdl.handle.net/11250/104771
id ftimr:oai:imr.brage.unit.no:11250/104771
record_format openpolar
spelling ftimr:oai:imr.brage.unit.no:11250/104771 2023-05-15T15:43:54+02:00 Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated Bjordal, Åsmund Laevastu, Taivo 1990 application/pdf http://hdl.handle.net/11250/104771 eng eng ICES ICES CM Documents;1990/G:32 This report is not to be cited without prior reference to the authors http://hdl.handle.net/11250/104771 31 s. cod torsk trawl trål long line line stock assessment bestandsberegning VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Catch: 925 VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452 Working paper 1990 ftimr 2021-09-23T20:16:01Z Numerical studies were conducted on the effects of trawl and longline catches on a cod stock and possible yields from it. Five year mean age composition of Pacific cod (Gadus macrocephalus) from the Bering Sea was used as initial age composition of the stock, which was normalized to 1 ton. Age specific Z (total mortality) was computed from this distribution and natural mortality was derived by subtracting fishing mortality from Z. Age compositions of catches were either prescribed from empirical data or created with fishing mortality coefficient (F), which was assumed constant with age after the age of full recruitment. The computations were done with different catch levels for six years assuming average constant recruitment. Essential results of this study are: a) The stock left in the sea decreases with increasing catch and reaches an equilibrium if recruitment and catches remain constant. With similar catch levels this equilibrium is reached earlier with longline and is higher than that of trawl. b) If a given level of stock in sea is desired,. higher annual catches can be taken with longlines than with trawl. c) By the same catch size longlines remove more older and more piscivorous fish which is beneficial to recruitment if the latter is largely controlled by predation. The above mentioned essential results indicate, among others that some longline fishing might be allowed to continue when TAC for trawlers has been reached. Report Bering Sea Institute for Marine Research: Brage IMR Bering Sea Pacific Tac ENVELOPE(-59.517,-59.517,-62.500,-62.500)
institution Open Polar
collection Institute for Marine Research: Brage IMR
op_collection_id ftimr
language English
topic cod
torsk
trawl
trål
long line
line
stock assessment
bestandsberegning
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Catch: 925
VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452
spellingShingle cod
torsk
trawl
trål
long line
line
stock assessment
bestandsberegning
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Catch: 925
VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452
Bjordal, Åsmund
Laevastu, Taivo
Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
topic_facet cod
torsk
trawl
trål
long line
line
stock assessment
bestandsberegning
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Catch: 925
VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452
description Numerical studies were conducted on the effects of trawl and longline catches on a cod stock and possible yields from it. Five year mean age composition of Pacific cod (Gadus macrocephalus) from the Bering Sea was used as initial age composition of the stock, which was normalized to 1 ton. Age specific Z (total mortality) was computed from this distribution and natural mortality was derived by subtracting fishing mortality from Z. Age compositions of catches were either prescribed from empirical data or created with fishing mortality coefficient (F), which was assumed constant with age after the age of full recruitment. The computations were done with different catch levels for six years assuming average constant recruitment. Essential results of this study are: a) The stock left in the sea decreases with increasing catch and reaches an equilibrium if recruitment and catches remain constant. With similar catch levels this equilibrium is reached earlier with longline and is higher than that of trawl. b) If a given level of stock in sea is desired,. higher annual catches can be taken with longlines than with trawl. c) By the same catch size longlines remove more older and more piscivorous fish which is beneficial to recruitment if the latter is largely controlled by predation. The above mentioned essential results indicate, among others that some longline fishing might be allowed to continue when TAC for trawlers has been reached.
format Report
author Bjordal, Åsmund
Laevastu, Taivo
author_facet Bjordal, Åsmund
Laevastu, Taivo
author_sort Bjordal, Åsmund
title Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
title_short Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
title_full Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
title_fullStr Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
title_full_unstemmed Effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
title_sort effects of trawling and longlining on the yield and biomass of cod stocks - numerically simulated
publisher ICES
publishDate 1990
url http://hdl.handle.net/11250/104771
long_lat ENVELOPE(-59.517,-59.517,-62.500,-62.500)
geographic Bering Sea
Pacific
Tac
geographic_facet Bering Sea
Pacific
Tac
genre Bering Sea
genre_facet Bering Sea
op_source 31 s.
op_relation ICES CM Documents;1990/G:32
This report is not to be cited without prior reference to the authors
http://hdl.handle.net/11250/104771
_version_ 1766378106594000896