Decadal trends in shark catches and effort from the New South Wales, Australia, Shark Meshing Program 1950 - 2010

Abstract

Abstract. The New South Wales (NSW) government has operated a program of netting beaches for the protection of swimmers and surfers against shark attack since 1937 in Sydney, and since 1949 in Newcastle and Wollongong. The scope and directives of the Shark Meshing Program have remained constant since its inception, with operational modifications in net specifications in 1972, changes in spatial deployment in 1972, 1987 and 1992, and the elimination of winter netting since 1989. This markedly increased meshing effort in 1972, and again in 1987. In the present study, we examine the trends in catch and effort for the period from 1950-1951 to 2009-2010 over this 200-km section of the NSW coast. Significant temporal trends in species, size and sex composition are described herein. Catches were consistently dominated by three shark taxa, hammerhead sharks (Sphyrna spp.), whaler sharks (Carcharhinus spp.) and Australian angel sharks (Squatina australis), although their relative contributions to catches varied over time. Catch per unit effort has significantly declined for five of the most abundant shark taxa over the study period, increasing only for a single taxon, the sevengill shark (Notorynchus cepedianus). Catches of larger, potentially dangerous white sharks (Carcharodon carcharias) and tiger sharks (Galeocerdo cuvier) saw fewer large animals being caught over time. This pattern was not observed across other taxa. Four different monthly trends were observed in landings of the most abundant eight taxa, reflecting differences in the biology of the catch species. The current study also provides useful information on catches and sizes of grey nurse (Carcharias taurus) and white sharks before and after their protection in NSW waters in 1984 and 1998, respectively.

Conservation challenges of sharks with continental scale migrations

“…Therefore, the results of this study, and more extensive tracking of mobile species, are crucial to development of effective conservation and management policy. Currently the largest threats to adult C. leucas in eastern Australia are fishing activities including recreational and commercial fisheries (Macbeth et al, 2009), bather protection programs (Reid et al, 2011;Taylor et al, 2011), and habitat degradation (e.g., loss of mangrove habitat).…”

“…Management arrangements for bull sharks vary between Queensland (QLD) and New South Wales (NSW), the two state jurisdictions of eastern Australia where bull sharks occur. The species is not protected in either jurisdiction, and both QLD and NSW target larger C. leucas in shark control programs at popular swimming beaches (Reid et al, 2011;Taylor et al, 2011). Catches in NSW commercial fisheries occur mostly in the Ocean Trap and Line Fishery where a longline fishery has targeted large sharks (Macbeth et al, 2009).…”

Intrapopulation variations in diet and habitat use in a marine apex predator, the broadnose sevengill shark Notorynchus cepedianus

“…This is probably again a result of differing movement patterns between sexes: females stay in the sampled coastal areas for longer periods of time, and this leads to measurable differences in muscle δ 13 C. Furthermore, evidence from electronic tagging suggests a seasonal northern migration by males to New South Wales (NSW) (Barnett et al 2011); 70% of Notorynchus cepedianus caught in the NSW shark control program are male and catches primarily occur in winter to spring (Reid et al 2011). In southeast Australia, fish predators (including sharks) north of the Tasman Front (~34°S) have lower δ 15 N than those found further south, probably as a result of differences in baseline δ 15 N (Revill et al 2009), as particulate organic matter δ 15 N is lower north of the Tasman Front than in waters further south (~6 vs. ~10 ‰) (Baird et al 2008).…”

The biology and ecology of the tiger shark (Galeocerdo cuvier) on the east coast of Australia

“…The QSCP drumlines are highly selective for G. cuvier (91% of catch) while only 9% are caught in nets (Holmes et al, 2012). In the net-only NSWSMP the overall catch of these species is considerably less than in Queensland, with 49 G. cuvier and 110 C. carcharias caught between 1990, and only 11 C. leucas caught between 1998(Reid et al, 2011.Despite these long-standing programs being in place on the Australian east coast, equivalent peer-reviewed publications on large shark biology, compared with the South African and Hawaiian research, have been less forthcoming (e.g. Paterson, 1990;Simpfendorfer, 1992a;Krogh, 1994;Sumpton et al, 2010;Noriega et al, 2011;Werry et al, 2012).…”

“…There was no evidence of multiple paternity, based on the litters of the four sharks examined using nine microsatellite loci, which may have implications for the genetic diversity of this population. Reid and Krogh, 1992;Simpfendorfer, 1992a;Krogh, 1994;Last and Stevens, 1994;Dudley, 1997;Green et al, 2009;Fisheries, 2006;Reid et al, 2011). …”