Garig Gunak Barlu National Park Green Sawfish (Pristis zijsron) aggregation surveys
This report details two surveys of Green Sawfish (Pristis zijsron) at two sites in Garig Gunak Barlu National Park in the Northern Territory. Weather conditions and limited water clarity restricting usable video footage from drones at one site (Lidarnardi) during survey 2. The use of Baited Remote Underwater Videos were unsuccessful. Drones recorded Green Sawfish on 88% of survey days and 30% of transect flights. Sawfish numbers ranged from 1–8 individuals per transect and density from 3.8–30.5 per hectare (the highest density of sawfish ever reported). Sawfish ranged from 57–167 cm total length (TL), with most 60–100 cm TL, suggesting a nursery area. The surveys confirmed the presence of juvenile Green Sawfish in intertidal waters of the national park, suggesting the park waters represents critical habitat, and provides the species some refuge from major threats. However, similar inshore intertidal habitat is not well represented in northern Australian protected areas.
Scientists have collected the first fine-scale maps and imagery of reefs and submarine canyons in the rarely visited Arafura Marine Park, revealing seafloor environments with surprisingly diverse coral and fish communities.
Exploring the status of Western Australia’s sea snakes
All sea snakes are listed marine species under the EPBC Act and three Australian endemic species are listed as Critically Endangered or Endangered, and as such are a national conservation priority. Recent findings of two Critically Endangered sea snake species (Aipysurus apraefrontalis and Aipysurus foliosquama) in locations outside of their previously defined ranges have highlighted the lack of information on species distributions along the North West coast of Australia. Data on sea snake sightings on previously collected baited remote underwater video surveys (BRUVS) and fisheries independent trawl surveys were used to assess the utility of these methodologies to accurately define relative abundance and distribution patterns of sea snakes in the North West Marine Region (NWMR), including within Commonwealth Marine Reserves (CMRs), to refine species’ status.
Presence/absence data from BRUVS were used to predict locations that are likely important habitats for sea snake populations within the NWMR, which included mid-shelf and oceanic shoals along the Kimberley and Pilbara coasts. Limited fisheries-independent trawl sampling data collected in Shark Bay and Exmouth Gulf highlighted patterns of interaction between sea snakes and trawl fishing, with survivorship curves indicating that most sea snake species encountered within these regions may be able to sustain low to moderate levels of trawl fishing. Trawl survey data also highlighted the need for additional fisheries interaction data to accurately assess the species-specific influence of fishing activities (e.g. trawl and trap fishing) on different life stages of sea snakes susceptible to incidental capture (bycatch). This project highlights the need for more data on sea snakes in regions lacking information (e.g. mid-shelf shoals of Kimberley coast, Pilbara coast and Rowley Shoals). In addition, further research is also required to assess the degree of connectivity between sea snake populations from offshore reefs that have seen recent declines, and those on adjacent mid-shelf and oceanic shoals.
Lainey James and Margot Delaporte have completed their first trip aboard the Australian Maritime College Research Vessel Bluefin. The Hub research team revisited reef systems in the Freycinet Commonwealth Marine Reserve.