Unlucky reef shark leads researchers to better understanding


17 April 2008

The fate of an unfortunate reef shark, caught and eaten 80 km from where it was tagged in a Sanctuary Zone in the Ningaloo Reef Marine Park off the Western Australian coast, is helping to unravel the mysterious life and movements of sharks.

An AIMS project to tag the common grey, black tip and white tip reef sharks and monitor their movements through the Marine Park is in its early stages and has already turned up useful information about shark movements, thanks to the shark that became a fisherman's dinner.

The black tip shark, a mature female about 1.4 m long, was caught by a fisherman who was standing on rocks at Gnaraloo, well south of the Sanctuary Zone. The recreational fisherman contacted AIMS when he saw the details on the attached tag. Gnaraloo is a popular fishing spot north of Carnarvon and the man was fishing legally.

"We are delighted that the fisherman made contact with us," AIMS fish biologist Dr Mark Meekan said. "He did exactly the right thing, and as a result we now know more than we did about how far from the protected area these animals can travel."

The shark was tagged and fitted with an acoustic transmitter last November by Charles Darwin University PhD student Mr Conrad Speed, who is tagging reef sharks as part of his studies, under Dr Meekan's supervision. The shark had been heavily pregnant at the time of tagging and it is likely to have given birth soon after.

It was last detected by an acoustic monitor on 5 January, still in the Sanctuary Zone, but on 3 February 2008 it was caught and eaten south of Ningaloo. Some time in that month, it travelled far away from the safe area.

Mr Speed tagged 10 sharks in Coral Bay last November, including the one that was caught.

Scientists have long surmised that reef sharks travel long distances, well outside those areas set aside for the protection of marine life. Little is known, however, about the impact of fishing and if this is great enough to put species at risk.

"The Sanctuary Zones, which cover about 30 per cent of the Ningaloo Reef Marine Park, are meant to protect sharks and other marine creatures, but it is difficult when very little is known about the migration patterns of top order predators and their prey," he said.

Dr Meekan hoped that other fisherman would make contact with AIMS if they caught a tagged shark. A distinctive bright yellow tag is clearly visible on the dorsal fin of those sharks in the study.

Reef sharks have a variety of behaviours that are currently mysterious, not just their propensity to cover long distances in unknown travel patterns. For example, large numbers of adults and juveniles congregate in knee-deep water at Coral Bay in the Ningaloo Marine Park, becoming something of a tourist attraction with visitors wading into the water with them.

Scientists speculate that pregnant females may be using the warm, shallow water as a kind of incubator to speed up the development of their embryonic young, while juveniles may gather there as protection from predators. The AIMS shark tagging and monitoring project is designed to better understand these creatures. Using permanent installations of acoustic "curtains", lines of reef-based receivers spanning the reef that pick up the "ping" from the transmitter attached to tagged sharks as they cross the receivers' field of detection, plus arrays of receivers closer to shore, scientists are hoping to learn much more about the movement of sharks around Ningaloo.

When a tagged creature swims across the detection field, the date and time are recorded electronically. At present, the data from the curtains and arrays is being downloaded every six months for analysis. This technology is moving ahead quickly and Dr Meekan hopes in a few years that real-time monitoring may be possible, enabling instant access to data.

At present, AIMS is monitoring the movements of around 20 Ningaloo reef sharks. Mr Speed's next tagging expedition is scheduled for October this year and it is hoped that a total of 100 sharks will be tagged and monitored in this project.

Media contacts:

Dr Mark Meekan, Fish biologist Phone: 08 8920 9240 E-mail: m.meekan@aims.gov.au

Wendy Ellery, AIMS Media Liaison Phone: 07 4753 4409 Mobil: 0418 729 265 eMail: w.ellery@aims.gov.au