Management Implications of Sexual Differences in Maturation and Spawning Mortality of Northeast Arctic Cod

• Main Authors: Tore Jakobsen, Adnan Ajiad
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Key words; Arctic; cod; maturation; mortality; Northeast Atlantic; spawning; Lofoten; Arctic cod; Gadus morhua; Northeast Arctic cod
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.457.9587; http://journal.nafo.int/J25/jakobsen.pdf

There is evidence of earlier maturation in males than in females and indications of higher mortality among mature males than mature females in the Northeast Arctic cod (Gadus morhua L.) stock. Both factors affect the composition of the spawning stock by sex and age. One possibility is that spawning mortality is involved. Spawning mortality may occur in both sexes, but observations indicate that it might be higher in males. The possibility of a spawning mortality is investigated by adding spawning mortality in calculations of the history of a year-class to see if this improves the fit with observed sex ratios in commercial landings from the Lofoten spawning fishery. The best fit was obtained for a spawning mortality of about 0.05 on the males. However, the results are not conclusive. Splitting the spawning stock into males and females shows that the earlier maturation in males has a larger impact on the sex ratio in the spawning stock than the spawning mortality rates. Increasing the fishing mortality rates will increase the surplus of male spawners. The results have implications for estimation of biological reference points and the way spawning stock biomass is used in management considerations. Estimation of the female SSB is necessary if maternal effects are to be taken into account.