Systematic bias in estimates of reproductive potential of a cod (Gadus morhua) stock: implications for stock-recruit theory and management

C Tara Marshall, Coby Needle, A. Thorsen, O. S. Kjesbu, N. A. Yaragina

Research output: Contribution to journalArticle

Abstract

Stock-recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs center dot g(-1) and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (1980-2001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.

Original languageEnglish
Pages (from-to)980-994
Number of pages14
JournalCanadian Journal of Fisheries and Aquatic Sciences
Volume63
DOIs
Publication statusPublished - 2006

Keywords

  • NORTHEAST ARCTIC COD
  • SEX-RATIO
  • POPULATION-DYNAMICS
  • EGG-PRODUCTION
  • FISH STOCKS
  • AGE
  • FECUNDITY
  • DEPENSATION
  • ABUNDANCE
  • INDEXES

Cite this

Systematic bias in estimates of reproductive potential of a cod (Gadus morhua) stock: implications for stock-recruit theory and management. / Marshall, C Tara; Needle, Coby; Thorsen, A.; Kjesbu, O. S.; Yaragina, N. A.

In: Canadian Journal of Fisheries and Aquatic Sciences, Vol. 63, 2006, p. 980-994.

Research output: Contribution to journalArticle

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abstract = "Stock-recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24{\%} and 68{\%}, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs center dot g(-1) and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (1980-2001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.",
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AU - Kjesbu, O. S.

AU - Yaragina, N. A.

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AB - Stock-recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs center dot g(-1) and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (1980-2001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.

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