Mapping the distribution and movement of gulper sharks, and developing a non-extractive monitoring technique, to mitigate the risk to the species within a multi-sector fishery region off southern and eastern Australia
There are some very clear needs arising both prior to and potentially following decisions about listing gulper sharks. These include:
1. The need to identify areas of remaining populations of gulper sharks, particularly on the east coast of Australia (Tasmania to northern NSW) and out onto the seamounts in the Tasman and Coral Seas. (Identifying these areas will help identify suitable areas for protection from further fishing, and to some extent will help determine whether current closures off Eastern Tasmania and Wollongong are appropriately located).
2. The need to determine movement rates and ranges occupied by gulper sharks, particularly into and out of closed areas. (This information would provide evidence to determine whether the current size and location of closures is appropriate).
3. The need to develop monitoring techniques that use non-lethal sampling to follow trends in abundance over time and between areas. Such techniques should be cost effective (ideally involving industry), provide sufficient resolution to detect change, and would form a key plank in a rebuilding strategy for gulper sharks should they be listed. The need for non-lethal sampling methods follows directly from concerns about the already highly depleted state of these species in key parts of their range.
Final report
This two year project provided the science to support the development of a management strategy for three gulper sharks species (genus Centrophorus) being assessed for threatened species listing. Their listing represented one of the most urgent environmental challenges to the South East Scalefish and Shark Fishery (SESSF), and had potential to threaten the fishery’s "licence to operate". The project successfully completed and communicated research results, and did so to the tight timelines dictated by the development of the management strategy, and the timetable of the listing process. Much of the science advice relied on an intensive and extensive field campaign, which was conducted very successfully, and which had strong support from the fishing industry.
Updated geographical and depth distributional ranges were established for the two gulper shark species of greatest interest, Harrisson’s Dogfish (C. harrissoni) and Southern Dogfish (C. zeehaani).
This project developed techniques to use acoustic telemetry technology in the deep ocean for the first time; this enabled movement data to be collected at spatial scales relevant to the sizes of fishery closures (10s of kilometres). Acoustic tagging in the GAB 60 mile closure showed 38% of sharks were detected near the margins of the acoustic receiver array at least once, but sharks were 5–14 times more likely to be detected near the middle section of the array, indicating that the closure is buffered for edge effects (sharks leaving the area and being caught by fishing). In this closure, mature breeding females were also concentrated near the centre of the closure. A strong diurnal pattern was evident with sharks moving inshore into shallower waters at night, and offshore into deeper waters during the day. Results indicate the appropriate size for gulper shark closures is likely to vary between latitudes, seasons and species, and depend on the precise management objective
The project evaluated and cross-referenced two methods with potential to provide quantitative, non-lethal, and cost effective data on gulper shark population status: capture by hook and line, and in situ photography. Observation of gulper sharks in three surveys confirmed the potential of both methods. Development of the new DeepBRUVS survey tool provides the potential to collect monitoring data on the status of gulper shark populations, but further work is required to establish whether photographic summaries of species abundance, size structure and sex ratio can be calibrated to the same metrics measured by hook-and-line catch data.
Timely delivery of results enabled 36 candidate areas for protecting gulper sharks across temperate Australia to be identified and short-listed. These areas were detailed as specific options for individual area closures, and as a closure network. All results were provided in discussion papers to stakeholders and the South East Management Advisory Committee (SEMAC), and underpinned the design of fishery closures for the Stage 2 implementation of AFMA’s Upper Slope Dogfish Management Strategy.
