Factors Influencing the Rate of Sexual Maturity and the Effect on Spawning Stock for Georges Bank and Gulf of Maine Atlantic Cod Gadus morhua Stocks
Stocks of Atlantic cod, Gadus morhua, off the coast of New England have been heavily exploited by distant water fleets in the 1960s and 1970s and by domestic fisheries in recent years and abundance has declined. Maturation data collected by Northeast Fisheries Science Center research bottom trawl su...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.580.5674 http://journal.nafo.int/J25/OBrien.pdf |
| Summary: | Stocks of Atlantic cod, Gadus morhua, off the coast of New England have been heavily exploited by distant water fleets in the 1960s and 1970s and by domestic fisheries in recent years and abundance has declined. Maturation data collected by Northeast Fisheries Science Center research bottom trawl surveys from 1970–98 were examined to determine if the rate of sexual maturation of Atlantic cod varied in response to fluctuations in stock density, growth, or ambient temperature. Median age and length at maturity by sex for the 1970– 96 year-classes was estimated by using logistic regression. Both age and length at maturity have significantly declined during the past 25 years. Mean length at age did not show significant trends for the time series. Stepwise logistic regression with interaction was used to determine if such factors as cod stock biomass and bottom temperature explain variation in maturation rates. Regressions were performed by aggregating all year-classes for each sex. Both stock biomass and temperature explained a significant amount of the variation (P<0.05) in sexual maturation. The influence of stock biomass was similar for both stocks, but bottom temperature had a slightly greater and opposite influence on maturation for Gulf of Maine cod than for Georges Bank cod. The sensitivity analysis of biological reference points to regime shifts in maturation and partial recruitment illustrated more variation in spawning stock numbers per recruit and F20 % than in spawning stock biomass per recruit. |
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