Determining the value of near-shore habitats to fish	FN 0539
Jeremy Hindell, Marine and Freshwater Resources Institute January, 2003

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Scientists from the Marine and Freshwater Resources Institute (MAFRI), Griffith University (GU), and Edith Cowan University (ECU) are undertaking a joint project to assess the importance of different near-shore habitats to marine fish in sub-tropical and temperate waters across Western Australia, South Australia, Victoria and Queensland.

The study will focus on fish species targeted by recreational and commercial fishers in all States. The study aims to increase our understanding of fish–habitat links by determining why different species of fish and different life-stages of a species are using a particular habitat. This information is crucial in identifying and protecting important fish habitats and thus maintaining sustainable fisheries.

To do this, scientists from MAFRI, GU and ECU are using standardised methods to survey the fish found in a range of habitats in Victoria. The University of Queensland in another FRDC project is conducting a parallel survey of Queensland’s near shore habitats.. As well, the scientists will use chemical signatures to track the transfer of primary production through food chains in South Australia, Western Australia, Victoria and Queensland.

The Victorian aspect of this work is focussing on Western Port Bay and Corner Inlet, where the factors that link fish to rubbly reef–algae, saltmarsh, mangrove, seagrass and unvegetated habitats are being investigated. To date, MAFRI scientists have surveyed two near-shore habitats about which very little is known—mangroves and intertidal unvegetated sand.

The survey, the first year of which has been completed (summer, autumn, winter and spring) has shown that mangroves are commonly used by late-juvenile and adult fishes. Many of the fish species found within the mangroves are of importance to commercial and recreational fishers. The density and abundance of fishes within mangroves was found to be higher than that on intertidal unvegetated sediments. Mangroves harbour small fish and invertebrates, many of which are preyed on by the larger fish. For example, small mullet found in the mangrove forests were prey for larger estuary perch.

The study also suggests that the position of mangroves with relation to the main water body may influence the numbers of fish that use this habitat. Mangroves which are located near water channels may be more accessible to fish than mangroves located further away, most commonly across vast areas of unvegetated sand.

Fisheries Victoria and the Fisheries Research and Development Corporation funded the project.

For more information about this project, contact Dr Jeremy Hindell at MAFRI on 5258 0231.

Newly-settled baby snapper feed on microscopic bottom dwelling crustaceans. As the snapper grow, their food preferences broaden to include a wider variety of larger benthic organisms. Within Port Phillip Bay as the juvenile snapper grow they become more mobile and utilise a range of habitats including reefs.

The numbers of baby snapper found in each bay and inlet varied from year to year. The Gippsland Lakes had the most consistent recruitment of baby snapper to nursery habitat, while Port Phillip Bay exhibited the largest variation, with 10-fold differences in recruitment from year to year. The strong recruitment of baby snapper to nursery habitat in Port Phillip Bay in summer 2001 is responsible for the large numbers of undersized snapper currently in the Bay and along the west Victorian coast.

Recent research by MAFRI scientists has included a new method of tracking snapper by using natural chemical tags in their earbones (otoliths). Using this method it is possible to determine where the snapper go once they migrate from the nursery areas, and, therefore, which nursery areas contribute most to large juvenile and adult snapper stocks. This research has demonstrated that a large proportion of the juvenile snapper (15-25 cm in length) inhabiting the waters of Port Phillip Bay and the west Victorian coast are derived from the Port Phillip Bay nursery area. This has highlighted the importance of the Port Phillip Bay nursery area to the maintenance of snapper stocks in western Victoria.

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