CRC REEF RESEARCH CENTRE TECHNICAL REPORT No. 26

Fishes Of The Yongala Historic Shipwreck.

Hamish A. Malcolm, Queensland Department of Environment and Heritage
Alistair J. Cheal, Australian Institute of Marine Science
Angus A. Thompson , Australian Institute of Marine Science

FOREWORD

The wreck of the S.S. Yongala is a truly spectacular dive. Some claim it to be one of the top ten dives in the world. The Yongala's size, structural integrity and proximity to Townsville alone make it exceptional locally, but it is unique because of the fish community that makes the Yongala its home base. The sheer abundance, variety and large size of predators (especially snappers, cods and trevallies) is extraordinary on the Great Barrier Reef. Like the authors, I have seen nothing like it elsewhere.

This joint study by the Department of Environment and Heritage and the Australian Institute of Marine Science clearly measures the uniqueness of the Yongala fish community by comparison to "similar" shoals in the area. It also shows the attachment of fish to the wreck by documenting the stability of fish numbers and composition over a significant period. In doing so, the report confirms the value of the wreck and "no fish" Marine Park B zone for 500m around it as a significant fish refuge.

The relative stability of the Yongala fish community over the study period and the similarity of this community to that reported in 1981 suggests that the management of the site is effective for fish protection - despite thousands of diver days documented on the wreck each year. Observations of resident fish with obvious damage from fishermen suggest there is no cause for complacency, however.

This study provides a crucial baseline against which to monitor the Yongala fish community in the future. It addresses recommendations of a management planning study of the Yongala Historic Shipwreck (eg. research to assess human effects on the shipwreck and associated communities, interpretive and educational material to be produced to promote understanding of the value of the Yongala). In its completeness and clarity of presentation, the report stands as an excellent example of what can be done to promote understanding of the condition and value of other major dive sites on the Great Barrier Reef.

David Williams
Senior Principal Research Scientist
Associate Director (Research)
Australian Institute of Marine Science

EXECUTIVE SUMMARY

The Yongala shipwreck, located near Cape Bowling Green, south of Townsville, is an important historic and recreational site. It is currently protected under Marine Park zoning (Marine National Park B) and Historic Shipwreck legislation. The main users at this time are recreational divers who predominantly visit the wreck to view and swim amongst the abundant fish species. Little documented information exists on the fish community, from which effective protocols to manage an increasingly popular resource can be formulated.

This report represents the results of a collaborative project between the Queensland Department of Environment and Heritage, and the Australian Institute of Marine Science, undertaken to accurately describe the Yongala fish community and provide some assessment of it's uniqueness and temporal variability. This was to be achieved by addressing the following questions: 1) How many fish species inhabit the wreck? 2) How different is the Yongala fish community from nearby deepwater shoal communities? 3) How abundant are the various Yongala fish species and how does this abundance vary over time?

Visual censuses using a log5 counting technique were used to assess the numbers and species richness of fishes on the Yongala on five occasions over a 15-month period. For comparison, two deepwater shoals at comparable depth and in the region of the Yongala were similarly surveyed but only on one occasion.

The Yongala was found to support a uniquely structured fish community containing at least 122 different species. Nearby deepwater shoals (at comparable depths to the Yongala) held markedly different fish communities that more closely resembled those of shallower off-shore coral reefs. An unusually large number and diversity of schooling, commercially and recreationally significant, adult sea-perch species (Lutjanidae) visually dominated the Yongala community. Other large predators (Carangidae and Serranidae) were also prevalent. Herbivorous fishes and specialist benthic invertebrate feeders, abundant at the deepwater shoals, were generally conspicuous by their low abundance while planktivorous fishes were extremely abundant.

The Yongala fish community structure was remarkably stable through the 15 months of this study, suggesting a high degree of residency amongst its constituent species. The unusual trophic structure of the Yongala fish community is probably being maintained by a combination of the wreck's inshore location (in a high current regime within a vast expanse of relatively featureless lagoon habitat), topographic complexity and protected status.

Two major management issues arise from this study: 1) Given the unusually large number and variety of adult (and presumably highly fecund) commercially and recreationally significant species, and their apparent fidelity to the site, the continued protection of the wreck from fishing pressure is important. 2) Whilst diving trips to the wreck are a positive process in promoting the understanding and enjoyment of a protected marine environment, care should be taken to ensure that increasing numbers of divers do not have a detrimental effect on fish behaviour and residency.

THIS PUBLICATION IS CITED AS:
Malcolm, H.A., Cheal, A.J., & Thompson, A.A. (1999)
Fishes of the Yongala Historic Shipwreck
CRC Reef Research Centre Ltd
Technical Report No. 26
Townsville; CRC Reef Research Centre Ltd, 29 pp.

ISBN 1 876054 16 6

A full copy of this report may be obtained from the author(s), and through the following libraries: