Opportunistic Survey Analyses Reveal a Recent Decline of Skate (Rajiformes) Biomass in Falkland Islands Waters

Abstract

Data were combined from surveys in 2013, 2018, 2019 and 2021 to examine biomass changes of the skate (Rajiformes) stock in waters around the Falkland Islands. The 2013 and 2019 surveys were research surveys for skate abundance and used 90 mm trawl mesh to capture species and size compositions. The 2018 survey was a mesh size trial, and the 2021 survey was a commercial exploration; both used 400 mm trawl mesh to target skates. All four surveys were compared for biomass by deselecting the proportions of skates per size interval caught in 90 mm mesh that would not have been caught in 400 mm mesh, calculated with the SELECT method. Estimated commercial-size skate biomass decreased for most species individually and approximately 61% overall. Estimated commercial-size skate biomass also decreased by as much south of 51° latitude, the area that was closed to skate target fishing since 1996, as north of 51° latitude, which has been maintained open to skate target fishing. The outcome is correlated with continuing skate bycatch in finfish trawls.

Keywords

• biomass estimation
• mesh size
• Falkland Islands
• skates
• species assemblage