Conserving the GBR’s predators - Michelle Heupel

Sharks, giant trevally, coral trout and other large reef predators present a challenge to reef managers. Their mobility complicates estimates of population status, which makes assessment of man-made and natural changes hard to define. In addition, mobility makes the effectiveness of some management practices, including marine protected areas, hard to evaluate.

Dr Michelle Heupel is tackling questions of large predator mobility in collaboration with other researchers from AIMS and James Cook University, within NERP TE Hub Project 6.1. Individual sharks and fish have been fitted with acoustic transmitters that are detected by an array of acoustic monitoring stations which record the presence and movement of fish between the coast and the reef, and between reefs. These data are used to define the amount of time individuals spend within marine park zone regions and determine how much protection individuals and populations receive from these zones. To date more than 460 tags have been fitted to reef predators from thirteen different species in the Townsville reefs region and the Capricorn Bunker Group.

The team have found a number of patterns in the Townsville reefs data. For example, grey reef sharks don’t move much from home reefs which means that their protection would depend on marine zoning. Bull sharks, on the other hand, move much more within the reef network; into near-shore regions such as Orpheus Island and Cleveland Bay, and alongshore to Moreton Bay; so the time spent in protected zones varies much more. In contrast, blacktip reef sharks have been recorded moving from inshore to Townsville reefs suggesting connectivity between inshore and offshore components of this population.

The work continues but early indications are that reef-based marine park zonation will not provide a single management solution for protecting all these highly mobile predators. Instead it is likely that a combination of management measures will be needed to effectively manage and conserve mobile predator species.

Photos:
A tagged blacktip reef shark fitted with an acoustic transmitter. Credit: AIMS.
Acoustic monitoring station picking up signals from tagged sharks and fish. Credit: AIMS.

For further information contact: m.heupel@aims.gov.au

Project: 6.1 Maximising the benefits of mobile predators to Great Barrier Reef ecosystems: the importance of movement, habitat and environment