Pinging shark populations

Climate change may be having an effect on the distribution of sharks on the Ningaloo coral reef off the Western Australian coast.

A group of researchers from Charles Darwin University, the Australian Institute of Marine Science, the University of Adelaide and CSIRO, have been tagging the sharks with electronic sensors to track their movements.

The reef sharks are being tracked by the Australian Acoustic Tagging and Monitoring System (AATAMS) which have set up permanent acoustic receivers at strategic points on the 280 km long reef. The receivers collect acoustic data or ‘pings’ from transmitters (pingers) either implanted in the sharks or attached as tags.

Conrad Speed, a PhD candidate from the School of Environmental Research at Charles Darwin University, said long term patterns of habitat use and dispersal will help manage the populations in areas where sharks are vulnerable to habitat degradation due to climate change.

Speed is investigating the movement patterns and feeding ecology of black tip (Carcharhinus melanopterus), white tip (Triaenodon obesus), grey reef (Carcharhinus amblyrhynchos), while at the same time monitoring juvenile lemon sharks (Negaprion acutidens) and nervous sharks (Carcharhinus cautius).

He said variations in oceanographic conditions will result from climate change. Shifting current patterns, rising sea levels and increasing temperatures could all affect the availability of prey and suitable habitat for shark populations. Tracking the sharks will provide a basis for predicting their adaptability over longer time scales.

“Their movement patterns are monitored using acoustic transmitters, also known as ‘pingers’, and a series of receivers along the Ningaloo Reef. Pingers can either be implanted internally or externally tag-mounted,” Speed said.

As well as the overall acoustic scanning of the shark populations, Speed observed fine-scale shark movement by actively tracking a number of tagged black tip reef sharks. This was to gather data to help answer the question of why reef sharks aggregate in inshore areas and how these sharks move and use their habitat.

Releasing shark

Releasing a shark back into the water after tagging it (Courtesy Conrad Speed)

He found that juvenile and adult black tip sharks visit the same inshore areas, where the reef is close to the WA coastline, but they travelled there at different times. Sharks have also been found to travel great distances, crossing the borders of marine parks.

“The distances the sharks travel have implications for management and protection of the reef sharks at Ningaloo,” he said. At least one tagged shark has caught by a recreational fisher outside the park border.

Grey reef shark

A grey reef shark, inshore, just after tagging and releasing (Courtesy Conrad Speed)

Ningaloo reef supports an abundance of marine life: 500 species of fish, 300 species of corals, 600 species of molluscs and many other marine invertebrates. The beaches are important breeding grounds for loggerhead, green and hawksbill turtles, and in winter, the reef is part of the migratory routes for dolphins, dugongs, manta rays and humpback whales.

The initial results of the reef shark tagging program were presented by Conrad Speed at GREENHOUSE 2009 environmental conference in Perth during March.

The next stage of Speed’s project will look at the feeding habits of reef sharks at Ningaloo Reef. “I will use fatty acid profiles and stable isotope ratios to examine the diet of reef sharks to establish the trophic role of these sharks within the reef community,” he said.

© Sue Cartledge

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