Assessment of catches from Protective Shark meshing off NSW beaches between 1950 and 1990

Abstract

Mesh netting of beaches along the more populous sections of the NSW coast for the protection of swimmers and surfers against shark attack has been carried out since 1937 in Sydney and since 1949 in Newcastle and Wollongong. Data for the catches of sharks by taxonomic groups are presented for the period from 1950 to 1990. Although there were large year-to-year fluctuations, neither catch nor catch per unit effort showed any discernible trend for the period up to 1972. In 1973, the catches of all taxonomic groups increased substantially following changes to the specifications of nets and their deployment. Since 1974, there has been a continuing decline in both the numbers of sharks caught and the catch per unit effort. Although Carcharhinus spp. (whalers) and Carcharodon carcharias (white pointer sharks) have shown an almost unbroken decline since the commencement of meshing, Sphyrna spp. (hammerheads) and Squatina australis (angel sharks) have shown large fluctuations over the entire study period, particularly in the period following the upgrading of netting effectiveness (post-1973). Substantial changes have occurred in the size compositions of a number of the taxonomic groups between the first and second 20-year periods of the meshing programme. High proportions of S. Australis and Carcharias taurus (grey nurse sharks) were females. There were major differences in the species compositions of catches between the three major meshing areas and between the pre- and post- 1973 periods. Data on the catches of nontarget species for the Newcastle region for the period from 1965-66 to 1980-81 indicated significant increases in the catches of rays and jewfish in the post-1973 period. Post-1973 changes in the catches of dolphins, turtles and tunas were not statistically significant.