17 DECEMBER 1997. AUSTRALIA: CLIMATE & SEABIRDS

"I have been following the ENSO updates regularly and with some interest. For the past six years I have been trying to investigate the relationship between seabirds at the Houtman Abrolhos, Western Australia (29 South, 114 East) and oceanographic conditions. Thought I might send some recent observations that may be related to the current event.

At the Houtman Abrolhos, Western Australia, offshore/pelagic-foraging species such as the Brown Noddy, Lesser Noddy and Sooty Tern have delayed laying considerably. All return to breeding sites by late August and had done so this year, laying usually commencing by early to mid October (Sooty Terns) or early Sept to late October ( noddies) and regularly on 17 November for Wedge-tailed Shearwaters. Although the two noddy species exhibit a fairly protracted laying period that appears to be regulated by the strength of the Leeuwin Current from year to year, the Sooty Tern and Wedge-tailed Shearwater always commence on or very close to the same date each year.

This year Lesser Noddies commenced laying on 12 November, the latest year since 1991(they commenced laying on 28 August in that season!); By 6 December there were less than 100 eggs in the 130 000 nest Brown Noddy colony and approximately 200-500 eggs in the 250 000 nest Sooty Tern colony. This year the first Sooty Terns layed between 12 and 27 November. Wedge-tailed Shearwaters may have commenced around 17 November, but only 4% of burrows contained eggs by early December, at a time in other years when approximately 40-60% of burrows would contain an egg.

Lisa reports that Wedge-tailed Shearwaters at the Lowendal Islands, off the coast of Dampier, Western Australia laid later this season and estimates of breeding attempts are 50% down on previously monitored seasons.

The Leeuwin Current was very weak this winter, it is a poleward flowing warm water current that flows strongest between march and august, resulting in some of the lowest sealevels on record. Low tides at the Houtman Abrolhos may also be responsible for large kills of reef fishes observed in late November. Interestingly, inshore foragers such as Roseate Terns, Crested Terns and Fairy Terns bred at their usual times, however the fish kill may affect Crested Terns fish catches since many of the prey recovered are favoured by this species.

It is certainly proving to be a very interesting season out here! We'll keep you posted."--Chris Surman and Lisa Nicholson <surman@possum.murdoch.edu.au>

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