Quantifying teleost discards in the shark fisheries of Western Australia

Quantifying discards is essential for assessing the impact of fisheries on non-target species and the ecosystems in which these fisheries operate. In Western Australia (WA), fishers are required only to report catches of retained species. For the currently operating shark fisheries of WA, the authors quantified catch time series of discarded teleosts using data from at-sea observers collected since 1993. Sixty-two teleost species were observed in the catch of which 20 were routinely discarded. The most commonly discarded teleosts were western buffalo bream/silver drummer, Kyphosus cornelii/K. sydneyanus, and dusky morwong, Dactylophora nigricans. Annual discards peaked in the 1990s; nonetheless, current discard levels, 36.9 ± 2.1 (S.E.) t year^-1 , are much lower than the overall annual retained catches (c. 1000 t year^-1 ). The catch time series reconstructed in this study are important inputs for assessing the ecosystem-based approach used for managing WA's shark fisheries.

Potential expansion in the spatial distribution of subtropical and temperate west Australian sharks

Fishery-dependent and -independent data collected since 1975 were examined to explore the spatial distribution of 30 shark and ray species in the west coast of Australia. Bigeye sixgill (Hexanchus nakamurai), tiger (Galeocerdo cuvier) and spinner (Carcarhinus brevipinna) sharks, and scalloped hammerhead (Sphyrna lewini) were observed >1000 and 300 km to the east of the edge of their reported distributions. Broadnose sevengill sharks (Notorhyncus cepedianus) and southern sawsharks (Pristiophorus nudipinnis) were observed >1000 km to the west of the edge of their reported distributions. Our study highlights the value of collecting and examining long time-series of data for understanding the spatial distribution of large marine predators.