Publication Abstract

Implications of fisheries-1 induced changes in stock structure and reproductive potential for stock recovery of a sex-dimorphic species, North Sea plaice

Implications of fisheries-1 induced changes in stock structure and reproductive potential for stock recovery of a sex-dimorphic species, North Sea plaice

A.D. Rijnsdorp, C.J.G. van Damme and P.R. Witthames*

A key assumption in stock assessment and stock forecasts often is that spawning stock biomass and egg production are proportional and independent of stock structure (agecomposition and sex ratio). We show that this can lead to a biased perception of the time trend in reproductive potential. A 60-year time series of total egg production of North Sea plaice is presented, which is based on (i) annual observations on maturity, growth and condition, (ii) a predictive model for inter-annual variations in fecundity caused by variations in body condition and by the probability of being a recruit spawner, and (iii) a cohort analysis of sex-specific landings-at-age since 1948. Following an increase in fishing mortality rate, total egg production declined from a peak in the 1970s to a minimum in 1999-2000 by a factor 7-8. Concurrent with this decrease, the contribution of recruit spawners, the age diversity of the spawning population, and the size difference between spawning males and females decreased. However, no effect on recruitment could be detected. The implications of phenotypic plasticity and fisheries-induced evolutionary changes in growth and maturation for the recovery potential of the stock are discussed.

Reference:

A.D. Rijnsdorp, C.J.G. van Damme and P.R. Witthames* (2010) Implications of fisheries-1 induced changes in stock structure and reproductive potential for stock recovery of a sex-dimorphic species, North Sea plaice. ICES Journal of Marine Science, 67: 1931–1938.

A.D. Rijnsdorp, C.J.G. van Damme and P.R. Witthames*

ICES Journal of Marine Science, 67: 1931–1938.