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

• Published in: ICES Journal of Marine Science
• Main Authors: Rijnsdorp, A.D., van Damme, C.J.G., Witthames, P.R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2010
• Subjects: age; annual egg-production; atlantic cod; broadcast spawner; cod gadus-morhua; fecundity; growth; maturation reaction norms; pleuronectes-platessa l; size; Gadus morhua
• Online Access: https://research.wur.nl/en/publications/implications-of-fisheries-induced-changes-in-stock-structure-and-; https://doi.org/10.1093/icesjms/fsq049

A key assumption in stock assessment and stock forecasts often is that spawning-stock biomass (SSB) and egg production are proportional and that the reproductive potential is independent of stock structure (age composition and sex ratio). Based on a 60-year time-series of total egg production (TEP) of North Sea plaice, we demonstrate that this assumption could result in a biased perception of the temporal trend in reproductive potential. The time-series incorporates: (i) annual observations on maturity, growth, and condition, (ii) a predictive model for interannual 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, TEP declined by a factor of 7–8 from a peak in the 1970s to a minimum in 1999–2000. Concurrent with this decline, the contribution of recruit spawners and the size difference between spawning males and females decreased. The implications of phenotypic plasticity and fisheries-induced evolutionary changes in growth and maturation for the recovery potential of the plaice stock are discussed.