Assessing the susceptibility to fishing of populations of rare trawl bycatch: sea snakes caught by Australia’s Northern Prawn Fishery

Abstract

The susceptibility to fishing of the populations of 13 sea snake species caught as bycatch by trawlers in Australia’s Northern Prawn (shrimp) Fishery (NPF) was examined to identify species at potential risk that should become priority for research and management. Each species was assessed according to two groups of criteria — (1) their relative vulnerability to capture by prawn trawling and (2) the relative capacity of their populations to sustain increased mortality due to fishing. Within each group, each species was ranked (1–3) on individual criteria reflecting distribution, catch rates, habitat selection, activity patterns, reproductive biology and survival. These criteria were then weighted according to their relative importance. The mean weighted ranks of each species for the two groups of criteria were plotted and zones of relative priority were identified. Only one species, Hydrophis pacificus, fell into the high-priority category, being both highly vulnerable to trawling and having a poor capacity to sustain fishing mortality. However, this species has been very rare in prawn trawl catches for at least 10 years, making it difficult to assess any temporal or spatial changes in catch. Among the species of moderate priority, two large, bulky species — Aipysurus laevis and Astrotia stokesii — had the poorest capacity to sustain fishing mortality of any of the species examined and would become a research and management priority if the percentage of the population vulnerable to capture increased. New fisheries management changes to (1) reduce effective fishing effort and (2) reduce bycatch by inclusion of Turtle Excluder Devices that take effect in 2000 are both expected to reduce the susceptibility of sea snakes to trawling in the NPF. Further studies to better estimate the sizes of sea snake populations and model natural and fishery processes will help clarify if populations of the most susceptible species are indeed at risk.