Cohorts from winter-reared eggs of common brown shrimp Crangon crangon surpass the growth of summer-hatched cohorts under equal conditions

The common brown shrimp Crangon crangon is a key species in the Wadden Sea ecosystem and a valuable resource for commercial fisheries in the southern North Sea region. Despite its importance, assessment and management of the common brown shrimp fishery remains challenging, as evidenced by steadily declining landings per unit effort since 2018. A central tool in the current assessment strategy is a yield-per-recruit model that is parametrized with lab-observed growth rates. However, growth observations for C. crangon vary widely across studies. Following preliminary indications from an earlier study, the present work investigates to what extent the seasonal origin of shrimp influences growth potential. By measuring individual growth rates of shrimp collected throughout the season under standardized laboratory conditions, we found that shrimp originating from winter eggs exhibit consistently higher growth rates than summer-egg recruits, suggesting a cohort-specific advantage. Additionally, the findings highlight that faster-growing individuals optimize both their moult intervals and increments. The findings suggest that targeted management measures, such as seasonal fishing restrictions to protect winter egg-bearing females, could improve stock productivity and long-term fishery yields.