Changes in relative abundance of sharks and rays on Australian South East Fishery trawl grounds after twenty years of fishing

Upper continental slope trawling grounds (200-650 m depth) off New South Wales were surveyed with the same vessel and trawl gear and similar sampling protocols in 1976-77 (during the early years of commercial exploitation) and in 1996-97. The 1996-97 mean catch rate of sharks and rays, pooled for the main 15 species (or species groups), was similar to 20% of the 1976-77 mean. Individual catch rates were substantially lower in 1996-97 for 13 of the 15 species or species groups. The greatest decline was observed for dogsharks of the genus Centrophorus, which were most abundant in 1976-77 but rarely caught 20 years later. In contrast, 1996-97 catch rates of spiky dogshark (Squalus megalops) and, to a lesser extent, whitefin swell shark (Cephaloscyllaum sp. A) were similar to those in 1976-77. Trawling during 1979-81 provided data for nine species, albeit not corrected for larger gear size, and the pooled mean catch rate for sharks and rays in the depth range 300-525 m was similar to 28% of the mean for 1976-77. The results suggest that the biomass of most species of sharks and rays declined rapidly as the fishery developed and is now at very low levels.