Quantifying teleost discards in the shark fisheries of Western Australia

Abstract

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 À1 , are much lower than the overall annual retained catches (c. 1000 t year À1 ).The catch time series reconstructed in this study are important inputs for assessing the ecosystem-based approach used for managing WA's shark fisheries.

The age estimation of an extremely old Silver Drummer Kyphosus sydneyanus (Günther 1886) from southern Western Australia

“…Although not retained, K. sydneyanus and Kyphosus cornelii, referred to collectively as K. cornelii, historically constituted the largest component, by weight, of the scalefish catch in the Temperate Demersal and Gillnet and Demersal Long-line Fishery (TDGDLF) off south-western Australia (McAuley and Simpfendorfer 2003). More recently, total annual catch from the TDGDLF has declined due to management decisions and the consequent declining effort (Watt et al 2021), with K. sydneyanus and K. cornelii now estimated to constitute a negligible proportion of the catch in comparison to retained scalefish and elasmobranchs (Braccini et al 2022).…”

“…While K. sydneyanus is not targeted by commercial or recreational fishers and the numbers of individuals caught as bycatch in the commercial gillnet fishery off southern Western Australia is now considered to be negligible (Braccini et al 2022), they have historically been taken in large quantities in this fishery (McAuley and Simpfendorfer 2003). Attributes such as schooling behaviour and high site fidelity of kyphosids (Ferguson et al 2013;Pillans et al 2017) lend these species, when caught, to be caught in large numbers, as is demonstrated by the very high catches of G. tricuspidata in New South Wales (Gray et al 2010).…”