Shrinking shrimp - Investigating the weight loss of northern shrimp Pandalus borealis following boiling

Reported landings from commercial fisheries are a main source of information on the removed biomass of a species and/or stock from the sea. In many fisheries, however, on-board processing to meet market demand causes a discrepancy between the landed weight and original live weight, necessitating the use of correction factors during data preparation for stock assessment and advice. One such fishery is for northern shrimp ( Pandalus borealis) in the Skagerrak, Kattegat and northern North Sea. In this fishery, large, often female shrimp are boiled in salt water while on-board to maximise sale prices and scientists currently use a correction factor of 1.13 to account for the weight loss of shrimp from boiling. Here, we investigated this correction factor by conducting a weight loss experiment on-board the Swedish shrimp fishery between 2022 and 2024. We estimate that shrimps lose 10.26 % of their weight during boiling which corresponds to a correction factor of 1.11. Further, we find that weight loss likely varies on a seasonal basis, with more weight being lost during Q2 and Q3 compared to Q1 and Q4, potentially due to changes in the biology of the species as well as environmental conditions. Our findings suggest that the current correction factor used in the assessment of the stock should be reduced for the Swedish fishery and should preferably vary based on when the shrimp are caught. The experimental methodology used here could also be used to estimate weight loss in other shrimp fisheries. • Large shrimp are often boiled on-board to meet market demand. • Shrimp lose weight during boiling causing discrepancies in landed weights. • Correction factors ensure that landed weight represents original live weight. • Current correction factor is likely too high for the Swedish shrimp fishery. • Findings relevant for stock assessment of an overexploited and important stock.