Investigating nursery areas for sharks on the Central GBR coast

Investigating nursery areas for sharks on the Central GBR coast

Coastal waters of northern Queensland are home to a variety of shark species, some of which use these waters as nursery habitat.

Scientists define shark nurseries as areas with a large number of young sharks that stay for a few months or more, and this is repeated across multiple years. These are valuable areas for shark populations so it is important to understand where they are and why they are suitable for young sharks.

NERP Tropical Ecosystems Hub Project 6.2 “Drivers of juvenile shark biodiversity and abundance in inshore ecosystems of the Great Barrier Reef” is doing exactly that on the central Great Barrier Reef coast.

The project team has been undertaking quarterly surveys of five bays between Cardwell and Mackay that initial surveys showed were potential nursery areas for sharks. A survey involves four days of fishing in each bay with both lines and nets to ensure a wide range of sharks is caught.

When sharks are caught they are tagged and released to help provide data on the movement of sharks within and between nursery areas and to estimate fishing and growth rates. A range of environmental parameters is also measured to examine their role in determining the species of sharks that may use each of the bays.

To date over 1,700 sharks from 19 species have been caught in the surveys. Blacktip sharks and Australian sharpnose sharks have been the most common species. Interestingly, the Australian sharpnose sharks are a very small species and occur in the bays as adults, unlike many of the other species that are mostly caught as juveniles.

The majority of the sharks caught have been less than one metre in length, supporting the assumption that smaller younger sharks occur in coastal bays. However, some sharks greater than three metres have been caught, most of them tiger and hammerhead sharks.

Differences in the composition of the shark communities between bays have also been observed. Rockingham Bay near Cardwell for example is home to more young scalloped hammerhead sharks than any of the other bays surveys. The team continues to explore whether differences in environmental parameters or habitats within bays are the drivers of these differences.

The results of this research will play an important role in the future management of the inshore regions of the Great Barrier Reef Marine Park, and the Queensland East Coast Inshore Finfish Fishery which take sharks in the region.

Professor Colin Simpfendorfer, JCU

For more information, contact Colin Simpfendorfer at: colin.simpfendorfer@jcu.edu.au

Proj 6.2: Drivers of juvenile shark biodiversity and abundance in inshore ecosystems of the Great Barrier Reef

 

 

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