Commercial pot selectivity for European lobster, Homarus gammarus, estimated through a novel v-notching mark-recapture approach

Abstract

Understanding gear selectivity can improve interpretation of population size data derived from commercial landings and support stock assessment models. The selectivity of gear over time often evolves, either due to industry modifications or as the result of implemented management regulations. Such gear modifications can be utilised to better target desired sizes of commercial species or to mitigate against bycatch issues. Most of the European lobster, Homarus gammarus, fishers use parlour pots and often utilise an escape gap to allow undersized animals and bycatch to exit. To quantify the gear selectivity of commercial parlour pots with and without escape gaps we utilise v-notching, as a novel approach to mark and recapture. Across both gear types, a total of 933 lobsters were notched (all sizes and both sexes) and 316 were recaught (34 %). A generalised linear model framework was applied to estimate selectivity which considered the interaction between size and sex of lobsters. Gear with escape gaps showed that males exhibit a dome-shaped selectivity curve, with the peak at 100–109 mm carapace length (CL) whereas females were less catchable for all size categories except for the smallest size class of 80–89 mm CL. Gear without escape gaps predominantly selected for small animals of both sexes (<90 mm) but, again, males exhibit a dome-shaped selectivity, with a peak at 80–89 mm (CL). This indicates that pots with escape gaps clearly select for legal-sized animals (>90 mm) for both sexes. This novel use of v-notching in mark-release-recapture surveys demonstrates the potential to quantify the efficacy of the gear used in the fleet and shows the scientific benefit of utilising current fishery management measures and fisher collaboration.