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23(4)_ Blue Water Spawning

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SINGLE PAPER

Volume 23, Issue 4 – 15 March 2018

Mandy T. Etpison and Patrick L. Colin: Blue Water Spawning by Moorish Idols and Orangespine Surgeonfish in Palau: Is it a “Suicide Mission”?, pp. 121-136

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SINGLE PAPER

Volume 23, Issue 4 – 15 March 2018

Mandy T. Etpison and Patrick L. Colin: Blue Water Spawning by Moorish Idols and Orangespine Surgeonfish in Palau: Is it a “Suicide Mission”?, pp. 121-136

Abstract

Spawning aggregations of the moorish idol (MI) and orangespine surgeonfish (OSS) were found on the western barrier reef of Palau. MI aggregated around the first quarter moon from Dec. to Mar., with largest groups in Jan. and Feb. Fish arrived near the sites in the morning, grouped together and moved up and down the reef face up in late morning attracting the attention of predators. At mid-day they ascend from the reef out into open water away from the reef. Gray reef sharks follow them and attack at the surface in a feeding frenzy. A high percentage of the ascending adults are eaten and few return safely to the reef. OSS aggregated in the same months, but on the last quarter moon with fewer observations being made. The observation of both fishes ascending high above and moving away from the reef to spawn is unusual and is termed “blue water spawning” with only a few similar examples known. Previously the importance of reef sharks in influencing reef fish spawning behavior has been reported as non-existent to “moderate” (a few spawning fish taken by sharks). This example of many individuals being taken by predators represents an extreme only reported previously for a grouper aggregation. The occurrence of sharks at the site during aggregation and spawning is indicative of a close relationship with reef fishes. The apparent high rate of predation on spawning MI and OSS may be specific to these study sites and it is likely individual fishes are generally iteropareous.