Unlike NSW and Queensland, grey nurse sharks have never been subjected to targeted fishing in WA. The only significant source of C. taurus mortality on the west coast has been from incidental capture by the demersal gillnet fishery that operates between Steep Point and the South Australia border. Relatively high quality grey nurse shark catch and catch rate data are available from this fishery. These data have been independently verified by estimating the fishery’s total catch from the CPUE recorded by scientific observers (McAuley and Simpfendorfer, draft report). However, these data are only available for the period July 1989 to December 1997, when the species was protected under the Endangered Species Protection Act and commercial reporting ceased. These data cover the eight year period immediately after the historical peak in demersal gillnet fishing effort and the period during which direct management adjustment reduced effort to 42% of its maximum level.
Catches of between 70-105 sharks per year (McAuley, unpublished data) indicate that grey nurse sharks were relatively abundant on the lower west coast of WA between 1989 and 1997 and CPUE of grey nurse sharks in the demersal gillnet fishery increased between 1989-1993 and then remained level until 1997, indicating that the population was stable.
WA Department of Fisheries (WA DOF) research records do not suggest that aggregation sites occur within the functional area of the WA demersal gillnet fishery. If such sites do occur within the fishery’s geographic boundaries, they are likely to be in areas of heavy reef, where gillnet vessels do not operate due to the risk of net entanglement. Additionally, there are several records of grey nurse shark occurrence in two significant regions outside of the fishery’s operational range, between Steep Point (26º 30’ S) and NW Cape (22º S), which has been closed to shark fishing since 1993 and, in deeper coastal waters (>100 m), where demersal gillnet vessels cannot operate due to their generally small size and the amount of expected damage to gear and catch caused by currents and predation. Both areas are likely to contain large amounts of suitable unfished habitat and are thought to offer significant refugia to this species in WA. However, there is also some concern regarding anecdotal reports that grey nurse sharks were more abundant in the 1960s and 1970s and that there may have been inshore aggregation sites that are no longer in existence.
Due to the limited reproductive capacity of C. taurus, the precarious status of the eastern subpopulation and the loss of an established index of abundance (commercial catch records), it is recognised that the western subpopulation still has the potential to become Vulnerable in the future. Therefore, developing a means to monitor the abundance of grey nurse sharks in Western Australia and further research into their ecology are necessary. Archival tagging of grey nurse sharks to provide data on distribution and migratory behaviour in Western Australia is expected to be undertaken in the next 12 months.
This species may well be reassessed over the coming year, as well as undergoing routine reassessments in the future.
No one has provided updates yet.