Wednesday, February 1, 2012

Land of the rising Sunfish

New observations of Sunfish behaviour have revealed an intriguing symbiotic relationship with Laysan Albatross.

When Japanese researchers in the western North Pacific observed a school of Sunfish appearing to actively follow Laysan Albatrosses resting on the sea, they were soon to discover that this behaviour was mutually beneficial. The juvenile Sunfish, measuring about 40 cm across, were heavily infested with a parasitic worm-like copepod Pennella, a kind of crustacean, which held somewhat of an attraction for the birds. It soon became apparent that the albatrosses were feeding on the worms, as one was photographed doing just this.

The observers suggest that this cleaning behaviour may be frequent in the lifestyle of Sunfish, as the fish seem to actively seek out the birds, which then relieve them of their parasitic. the Sunfish school numbered about 57 individuals and were swimming right at the surface, exhibiting no defensive or evasive behaviour. The feeding actions of one Laysan Albatross soon attracted more, including a black-footed Albatross too. Some of the Sunfish appeared to present themselves by swimming sideways next to the birds, the better to show their parasites.

On a pelagic birding trip, Sunfish are often one of the major non-avian attractions a they swim on or near the surface, and it had been suggested that this behaviour might be due in some respect to their parasitic load. It would now appear that this might actually attract seabirds to remove the parasites. sunfish have also been noted to have associations with Sooty Shearwaters for possibly the same reason, and are attended by cleaner fish species.

Sunfish is the largest marine bony fish species, growing up to 2.7 m in length and weighing up to 2.3 tonnes. Laysan Albatross is a wide-ranging seabird in the North Pacific, with an estimated global population of over 1,180,000, though it is classed as Near Threatened by BirdLife International due to historical declines, but there are also signs that there has been a recent range expansion.

Abe, T, Sekiguchi, K, Onishi, H, Muramatsu, K and Kamito, T. 2012. Observations on a school of ocean sunfish and evidence for a symbiotic cleaning association with albatrosses. Marine Biology DOI 10.1007/s00227-011-1873-6

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