Heatwole, 1996:

"The populations of seabirds inhabiting the Swain Reefs, Great Barrier Reef, were censused at six-monthly intervals from 1982 to 1994.

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.

Reductions in available food, probably associated with elevated sea surface temperatures induced by El Nino, appears to be the most likely cause of the decline.

The islands of the Swain Reefs constitute one of six core seabird breeding areas identified in Queensland (King 1993).

Significant declines (p<0.05) in the numbers of brown booby nests occurred on four of the seven cays between 1983 and 1993. There is strong evidence that a major decline (p=0.002) in the combined numbers of nests counted in summer also occurred.

a. Sum of counts for all cays (except Bell Cay) of the number of Brown Booby nests recorded between 1980 and 1995.

 

Temporal trends in the numbers of adult brown boobies counted generally followed that of the number of nests. Significant declines in the numbers of adults counted in summer occurred on all cays except Bell and Thomas. The largest declines, in real terms, occurred on Gannet, Frigate and Price cays.

A highly significant decline in the total numbers of birds counted in summer was observed. This decline lagged behind the similar decline in nest numbers, by between two and three years. No significant trends in the much smaller winter numbers were detected.

b. Sum of counts for all cays (except Bell Cay) of the number of Brown Booby adults recorded between 1980 and 1995.

 

Silver gull numbers on the Swain Reefs showed a significant decline over the study period, similar to that of the brown booby. This decline can be largely attributable to the significant reductions in numbers on the un-vegetated cays.

In 1994, the population of silver gulls on all cays in the Swain Reefs was about 100 individuals. This number was a substantial reduction from the 150 birds counted in 1986."

c. Sum of counts for all cays (except Bell Cay) of the number of Silver Gull adults recorded between 1980 and 1995.

 

 

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Citation and/or URL

Heatwole, H., O’Neill, P., Jones, M. and Preker, M. (1996), ‘Long-term population trends of seabirds on the Swain Reefs, Great Barrier Reef’, in Technical Report No. 12, CRC Reef Research Centre Ltd, Townsville.

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Spatial Coverage

 Swain Reefs, Southern Great Barrier Reef

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Temporal Coverage

 1982 - 1994

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Update Frequency

 Not applicable 

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Other Information

 None