sharks-rays


The ecology of sharks and rays

As apex predators, the life history characteristics of sharks are typified by slow growth, late maturity and low rates of reproduction. These traits, which are shared by other elasmobranchs, make these animals particularly vulnerable to human exploitation. Anthropogenic threats have been an important driver of research and our work has pioneered the use of fishery independent, non-destructive techniques to assess species composition, distribution and abundance in tropical reef habitats. This has allowed sampling of habitats beyond the reach of traditional methods and has been used to quantify the effects of fishing (both legal and IUU) on abundance patterns. Recently, the work has broadened to encompass mark-recapture studies of pelagic and reef sharks to quantify movement patterns, stock boundaries and sustainable yields.

Concurrently, long term data bases of fish community structure are being interrogated to determine the ecosystem effects of the removal of these apex predators.

A central part of research effort focuses on the ecology of whale sharks at Ningaloo Reef. These animals form the basis of a major ecotourism industry, the future of which is threatened by fishing in South-East Asian waters to which animals migrate after residing at Ningaloo. Our research aims to: describe migration patterns of animals participating in the Ningaloo aggregation using a variety of tagging approaches; quantify patterns in the demography and composition of the population using both historical records and photo-identification libraries and; to describe the behaviour of whale sharks to determine why aggregations occur on a predictable basis.

Future directions

Migration and movement patterns of reef sharks and other elasmobranchs are a key focus for ongoing work. A successful application to the Integrated Marine Observing System (part of the National Collaborative Research Infrastructure Strategy) will allow deployment of cross-shelf curtains of sonar listening stations at Ningaloo Reef in 2008. These will be used to describe the residency and movement patterns of the major components of the elasmobranch assemblage (whale sharks, manta rays, stingrays, reef sharks etc) and some reef fishes. The project will estimate appropriate spatial scales for management strategies and in combination with genetic studies, investigate philopatry and sex-biased gene flow in populations. Because the larger components of the fauna (whale sharks and manta rays) are likely to migrate large distances (1000's km) tagging and photo-identification work will be extended to other locations in the Indian Ocean.

Related links:
Research indicates declining whale shark numbers

Science to support Northern Territory shark fishery

Illegal shark fishing devastates populations in northern Australia

Useful links:
Sharks and rays of the Great Barrier Reef

Shark research in the GBR and Coral Sea