Hermit crabs associated with catches from the eastern rock lobster (Sagmariasus verreauxi) fishery along the coast of NSW, Australia

Abstract

In New South Wales (NSW), Australia, the majority of the commercial catch of eastern rock lobster (Sagmariasus verreauxi) is captured from traps fished on the mid and outer continental shelf in depths 50 – 220 m (119.5 t in 2021–22: 66.5 % of landings). Hermit crabs are the greatest bycatch from this fishery. The Fishery Management Strategy (2007) for the NSW lobster fishery, recognised the need to quantify by-catch species associated with lobster catches with an emphasis on increasing knowledge of the populations of hermit crabs along the NSW coast. An observer-based survey during 2008 and 2009 quantified by-catch from the fishery including, for each hermit crab species identified: (i) spatial and temporal distribution; (ii) relative abundance (number per trap-lift), and (iii) size distribution (shield length, SL). A total of 5782 hermit crabs were collected from 70 offshore trips comprising 722 trap-lifts. No hermit crabs were collected from 73 inshore trips (< 50 m depth) comprising 3232 trap-lifts, due to the low number (seven) of hermit crabs observed. Five species of hermit crab were identified. Three species were captured in very low numbers: Dardanus crassimanus (n=2), Dardanus pedunculatus (n=2) and Dardanus australis (n=1). The striated hermit crab (Dardanus arrosor; Herbst, 1796; n = 1970) and the stridulating hermit crab (Strigopagurus strigimanus; White, 1847; n =3812) were common in all latitudinal zones (30° - 37°S) and offshore depths (50–220 m) sampled. Abundance of D. arrosor decreased southward in contrast to S. strigimanus that showed the opposite pattern. Both species were more abundant on the outer-shelf than the mid-shelf. Mean SL of males was greater than females for both species across all latitudes on both the mid- and outer-shelf. Annual catches by the commercial fishery, by latitude and depth, were estimated for each species. This research provides a baseline for monitoring and interpretation of any future changes in the distribution and abundance of hermit crab species along the NSW coast.