Did population collapse influence individual fecundity of Northwest Atlantic cod?

Rideout, Rick M. and Stares, J. C. and Morgan, M. J. and Brattey, John (2007) Did population collapse influence individual fecundity of Northwest Atlantic cod? ICES Journal of Marine Science , 64 (7). pp. 1338-1347. ISSN 1095-9289

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Abstract

We examined the influence of population collapse on individual potential fecundity and total population egg production (TEP) of three northwest Atlantic cod (Gadus morhua) populations: northern cod (Divisions 2J3KL), southern Grand Bank cod (NAFO Divisions 3NO), and southern Newfoundland cod (Subdivision 3Ps). Fecundity at length increased in conjunction with population collapse for two (3NO, 3Ps) of the three populations. Subsequent moderate population recovery between the 1990s and 2000s in 3Ps was accompanied by a decrease in fecundity at length. A large decrease in fecundity at length for 3NO during the same time period, despite little or no population recovery, coupled with the fact that there was no obvious difference in fish condition between the two time periods, suggested that density-independent factors could be contributing to the changes in fecundity. Use of pre-collapse fecundity–length relationships to estimate TEP in the post-collapse period resulted in underestimation of TEP by as much as 30% in 3NO and 46% in 3Ps, whereas in 2J3KL, TEP was overestimated by as much as 18%. Although the results do not fully support the hypothesis of an inverse relationship between population size and fecundity, they do demonstrate the variable nature of cod fecundity which, if not accounted for, can lead to erroneous perceptions of stock reproductive potential.

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