TECHNICAL REPORT NO. 12:

Long-Term Population Trends Of Seabirds On The Swain Reefs, Great Barrier Reef

EXECUTIVE SUMMARY

The populations of seabirds inhabiting the Swain Reefs, Great Barrier Reef, were censused at six-monthly intervals from 1982 to 1994. Some cays are more important for seabird breeding than others, and an appropriate management strategy is outlined. Difficulties with censusing some species did not allow a reliable assessment of population trends, and these are reported in general terms only.

Data for three species, the masked booby (Sula dactylatra), the brown booby (Sula leucogaster) and the silver gull (Larus novaehollandiae) were analysed for trends in numbers of adults and numbers of nests counted. Significant declines in the numbers of adults and nests of the brown booby, and in the number of adult silver gulls, were detected during the period of the study.

Minimal human disturbance has occurred on the Swain Reefs cays compared with many other seabird breeding islands on the Great Barrier Reef. A range of natural and human factors were investigated for possible causes of the observed seabird declines, and human factors do not appear to have been influential. Reductions in available food, probably associated with elevated sea surface temperatures induced by El Ni-o, appears to be the most likely cause of the declines.

Trends in seabird populations observed in the Swain Reefs are useful baselines with which to compare populations from more disturbed areas. Such comparisons are necessary to separate impacts on seabird populations caused by human factors from those that occur naturally.

by H. Heatwole (1), P. O'Neill (2), M. Jones (3) and M. Preker (4)
(1) Department of Zoology, North Carolina State University, Raleigh, NC, 27695-7617, USA.
(2) Queensland Department of Environment, PO Box 3130, Rockhampton Shopping Fair, Qld. 4701, Australia.
(3) Department of Zoology, University of Tasmania, Hobart, Tas. 7005, Australia.
(4) 321 Pullenvale Road, Pullenvale, Qld. 4069, Australia.

THIS PUBLICATION IS CITED AS:
Heatwole, H., O'Neill, P., Jones, M., & Preker, M. (1996)
Long-term population trends of seabirds on the Swain Reefs, Great Barrier Reef
Technical Report No. 12
Townsville; CRC Reef Research Centre Ltd, 50 pp.

ISBN 1 876054 11 5.

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