Bayesian occupancy models for populations of crawfish, Palinurus elephas.
Abstract
This study used the Sparta occupancy model with records from the Seasearch programme from coastal waters of Britain and Ireland during the period 2000-2020, to determine the stock status of three species of Crustacea (Cancer pagurus, Homarus gammarus and Palinurus elephas). Populations of P. elephas decreased in the 1970s but now appear to be re-establishing in South-west England. The Sparta model showed that the recovery that was more robust than anecdotal reports or simple counts of records. Estimates of occupancy were made at different spatial scales and compared among species and areas. Trends in occupancy were compared qualitatively with patterns in fisheries landings data. Occupancy by P. elephas has significantly increased since 2014, a pattern not seen in the other two species. For each species, occupancy varied among areas and in some areas, patterns in estimates of occupancy were similar to trends in landings from fisheries. Citizen science records are increasingly recognized to have value which has not yet been fully exploited. Greater use should be made of the Seasearch dataset in order to provide population trends for benthic marine taxa. Such analyses will broaden our understanding of and taxonomic coverage of changes in biodiversity.