Do we need harvest regulations for European crayfish?

Summary Management of noble crayfish fisheries varies considerably between countries. Minimum legal harvest sizes range from 70 to 120 mm TL. National, regional and local crayfish harvesting regulations exist. The variations in regulations are strongly influenced by traditions for crayfish harvest and consumption. The current harvest of noble crayfish in Europe is approximately 220 tonnes; this is less than 10% of the pre-plague historic record. Improved fishery regulations may potentially increase the annual harvest. Because of allometric growth, noble crayfish increase by some 40–50% in weight by increasing in total length from 90 to 100 mm. Stock structure and stock characteristics vary between localities. Female noble crayfish mature at a size of 62–85 mm TL and the number of attached eggs is low, i.e. less than 200. Mean size of females in trap catches may be lower than mean size at maturity, indicating vulnerability to recruitment overfishing. There is a market for crayfish smaller than 90 mm TL, both for consumption and for stocking, and these often constitute more than 75% of trap catches. Regulations for catching crayfish are thus needed in order to prevent recruitment overfishing and to sustain high and stable yields. The authors therefore recommend a national minimum harvest size of 90–95 mm TL. The catching season should start after the first moult and after the brood have left their mother, and terminate when the mating period approaches in September. In localities with high exploitation a short harvest season (2–3 weeks) is recommended in the early August intermoult period. However, crayfish harvest regulations should also account for the variation that occurs between local stocks, and if necessary exemptions from the national regulations should be given where appropriate.