The brown shrimp (Crangon crangon) fishery is of great socio-economic importance to coastal communities on the North Sea. The fishery is exploited by beam trawlers often using codends with very small mesh sizes, leading to concerns about catch rates of undersized shrimp. However, little information is available on codend size selection, making it difficult to provide scientifically based advice on alternative codend designs. Therefore, this study establishes a predictive framework for codend size selection of brown shrimp, based on a large selectivity dataset from 33 different codend designs tested during four experimental fishing cruises, during which more than 350,000 brown shrimp were length measured. Predictions by the framework confirm concerns about the exploitation pattern in the fishery, because the retention probability of undersized shrimp reaches 95% with the currently applied designs. The framework predictions allow the exploration of obtainable exploitation patterns depending on codend design. For example, increasing codend mesh size to 25–29 mm would reduce the retention rate of undersized shrimp to a maximum of 50%, depending on codend mesh type.

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We performed an ad libitum experiment over 30 d to generate otolith growth reflecting optimal fish growth for use in estimation of in situ food availability via otoliths in post-larval sprat (Sprattus sprattus L.). Between 16 and 22°C, no difference in length or wet mass growth was detected in contrast to a significant and direct increase from 5.5 to 7.9 µm d −1 in otolith and 8.7 to 10.5 mg d −1 in dry mass growth. The different responses in length/wet mass growth and otolith growth were likely caused by the onset of lipid storage, which we assume to be triggered ontogenetically. We estimated a 10-fold increase in food demand from metamorphosed sprat (30 mm length) to juveniles (50 mm length). According to a bioenergetic approach, juveniles needed a concentration of 3 and 5 individuals l −1 assuming ad libitum feeding on Acartia sp. at 16 and 22°C, respectively. We described increment width as a function of temperature (IW = −0.0326T 2 + 1.6472T − 12.506) and compared this reference with increment widths of Baltic Sea recruits at corresponding temperatures. On average, increments in 2007 were smaller than the laboratory reference, suggesting sub-optimal feeding conditions. In 2003, mean increments were larger, except for early born survivors which exhibited poorer growth. These early born sprat encountered high temperatures after metamorphosis, leading to a higher food demand. Our findings highlight the importance of food availability in near-shore nursery areas and the impact of the right seasonal timing of the juvenile stage on recruitment strength in Baltic sprat.

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