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AQWA FOUNDATION - FINAL UPDATE
june 2005
In October 2003 the AQWA Foundation team, comprising members of the CSIRO and AQWA, achieved a fantastic result in tagging five great white sharks in the south of Western Australia.
Tagging was conducted just south of Tooregullup Beach in Doubtful Island Bay - half an hour by boat from Bremer Bay, in Western Australia’s Great Southern Region. Tooregullup Beach was the location in which nine adult sperm whales beached themselves. Although this was an unfortunate event, the whale’s bodies attracted great whites to this area creating a fantastic opportunity. More than twelve great whites were seen over the three days of the expedition which is incredible as no great whites were found during the previous tagging trip.
A variety of tags were used including PAT (pop-off archival transponding) tags, standard ID tags and satellite tags.
Unfortunately, no information was received from the satellite tags. There are two possible reasons for this including:
- The tagged sharks did not come to the surface frequently enough or at the right times for the tag transmissions to be detected by satellites.
- Alternatively, the lithium batteries within the tags failed to deliver sufficient current for the tags to transmit properly. Lithium batteries can be temperamental, particularly if they are in tag units for a while.
However, despite the current lack of information from the satellite tags, one of the PAT tags that detached from a tagged 3m female shark has provided some very exciting data on the shark’s movements.
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The tag started transmitting from the northern area of Shark Bay. The shark swam up the western WA coast at the time of year observations have pointed to a seasonal movement of sharks in the area. Another shark tagged with a PAT tag in South Australia at the same time also appeared in Shark Bay. This suggests a link between the sharks seen in southern Australia and the sharks along the southern and western WA coast – something we have previously not been able to establish.
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The actual track of the shark is fairly hard to decipher as the tag estimates longitude (east-west) more accurately than latitude (north-south). The best estimate is that the shark tagged off Doubtful Island Bay on 4 October remained in the vicinity of Bremer Bay for a few days (2-4) after tagging. The shark then headed west to near Cape Leeuwin (about 500 km west of Bremer) by approximately 10-12 October. This suggests that the shark moved consistently for these days (given that the average swimming speed of white sharks is approximately 3 km per hour when travelling). The longitude data then placed the shark on the west coast from at least the 29 October onwards and the positions cluster broadly around the Shark Bay region from 6 November onwards.
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The swim depth data (although limited to 8 days across the track) suggests the shark mainly swam in depths of 0-10 m with the deepest depths being 50 – 75m.
In summary, it appears that the shark stayed within the vicinity of Bremer Bay for only a couple of days after tagging (despite the continued attraction provided by the dead whales); moved steadily west to the Cape Leeuwin region by mid October where it may then have continued briefly offshore before returning to the coast and moving north past Perth in late October, reaching the Shark Bay region by early November.
These time frames would suggest that the shark travelled steadily throughout its move from Bremer to Shark Bay – a distance of approximately 1700km!
The AQWA Foundation