The Scalloped Hammerhead Shark, Sphyrna lewini. Image: CSIRO
Many species of sharks and rays are slow-growing, long-lived, and have low rates of reproduction.
These characteristics make them vulnerable to the impacts of human activities, and populations can take decades to recover once they have declined. Nine species of sharks and rays are protected in Australia under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), and the population status of more than 10 further species offers cause for concern.
Marine spatial planning for sharks and rays is challenging because many species traverse inshore areas managed by different states, offshore waters managed by the Commonwealth, and spatial closures covering both. Cost-effective, integrated spatial management requires identifying areas in which several species co-occur. Importantly, proposed management measures for individual species need to be jointly evaluated as they could help one species while harming another.
Approach
This project improved species mapping, identified areas shared between species, and measured the overlap with existing marine spatial planning areas, with a focus on temperate waters off south-eastern Australia.
Species maps from the Atlas of Living Australia were improved using updated seafloor bathymetry overlaid with fishery catch data (where available). The maps were refined in workshops attended by 23 specialists who also helped to group species according to movement patterns.
Shared areas were mapped by overlaying species maps in each group. This simple, biogeographic approach avoids some of the (time and spatial) scale issues with alternative approaches. For example, while geomorphology has been used as a proxy for critical habitat, shark breeding and foraging ranges occur at finer scales than the available mapping.
IMAGE: The Eagle Ray, Myliobatus tenuicaudatus. Image: CSIRO.
Eagle ray distribution in south-eastern Australia.
IMAGE: Eagle Ray distribution in south-eastern Australia. Green: adult core range; orange: adult minor range. Image: Ross Daley.
Key findings
Common corridors, feeding patches and breeding patches were identified around temperate Australia. Several feeding patches were within CMRs, and most breeding areas were in state waters. Corridors stretched for hundreds of kilometres and these are only partially protected by marine spatial planning.
The landscape approach was found to have higher utility for benthic sharks, skates and rays, which often are overlooked in conservation activities such as recovery planning. It was not as useful for highly migratory species such as white sharks.
New knowledge and opportunities
Many species of sharks and rays share similar breeding grounds, feeding grounds and corridors. It is possible to gain better management outcomes by integrating existing areas identified for marine spatial planning with areas used by many species. This would improve the general conservation of sharks and rays while limiting reductions in resource access. Marine spatial planning alone is not a full solution, however, and corridors will be difficult to manage.
Outputs and outcomes
This project generated improved species maps and maps of common corridors, feeding patches and breeding patches, identifying areas used by many species that will assist future fisheries and biodiversity management.
contract
Ross Daley
ross.daley@csiro.au
(03) 6232 5352