Optimising fisheries monitoring for rare and protected species: A south-eastern Australian case study shows low levels of interaction with a critically endangered species

Abstract

Scientific observer programs are often the only means to estimate the total number and circumstances of interactions (including the life status at the time of the interaction) between commercial fisheries and threatened, endangered and protected species (TEPS). However, without estimating the precision of predefined sampling fractions, the accuracy of estimates are often poorly understood. We present a methodology to estimate appropriate sampling fractions using historical observer data from the New South Wales (Australia) ocean trap and line fishery, and implement an on-board monitoring program to estimate contemporary rates of interactions with TEPS in the fishery to evaluate the effectiveness of management measures implemented to reduce interactions. A total of 327 fishing trips (~61,150 hook deployments) were sampled over 31 months with a single observed interaction each with the critically endangered grey nurse shark (Carcharius taurus) and scalloped hammerhead (Sphyrna lewini) recorded along with the capture of six seabirds. Observed catches included 97 species (70 finfish, 23 elasmobranchs, 1 invertebrate and 3 birds), of which 74 and 57 species were retained and discarded, respectively. Current fishing practices, combined with declines is reported effort targeting ‘large sharks’ following management reform, spatial protection measures, and gear regulations, were found to be minimising interactions between the main fishing method and TEPS. However, regular monitoring and research may be required to continually assess the effectiveness of mitigation strategies. The logic and methodology for determining appropriate sample fractions using existing data before implementing on-board sampling is relevant to the monitoring of other commercial fisheries.