Abstract
Narimatsu, Y., Ueda, Y., Okuda, T., Hattori, T., Fujiwara, K., and Ito, M. 2010. The effect of temporal changes in life-history traits on reproductive potential in an exploited population of Pacific cod, Gadus macrocephalus. – ICES Journal of Marine Science, 67: 1659–1666. The population size of Pacific cod (Gadus macrocephalus) in the northeastern Pacific has fluctuated at high levels during the past 10 years, despite heavy exploitation from the juvenile stage. Annual changes in growth, age, and standard length (SL) at maturity, potential fecundity (PF), and total egg production are evaluated in relation to the population fluctuations. Most 4-year-old females were mature, and the SL at which 50% of 3-year-old females matured fluctuated very little over the years. However, the proportion of mature 3-year-old females varied significantly among years. The values of PF-at-age also varied among years and were explained by a model containing SL, condition factor, and oocyte diameter. The population size was negatively correlated with the proportion of mature females and the PF of females 3 years old, so the range of total egg production was smaller than that of spawning-stock biomasses. Eggs were produced mainly by young adults (3 and 4 years of age). The age of adult females did not affect recruitment success. It is suggested that plasticity of life-history traits allowed for compensation of total egg production and that the compensation contributed to maintaining the abundance of a population consisting mainly of young fish.
Pacific cod (Gadus macrocephalus) as a paleothermometer: otolith oxygen isotope reconstruction