15 - Puerto Rico

Atlantic surgeonfish aggregation site revisited after 34 years

In February 2011 an aggregation area for ocean surgeonfish Acanthurus bahianus and blue tang Acanthurus coeruleus on the south west shelf edge of Puerto Rico was re-surveyed. The original studies at this site took place between 1977 and 1979 and again in 1988, when the two surgeonfishes were seen to aggregate and spawn at a location on the shelf edge. The most recent survey was done to improve the spatial mapping of the original area (based on notes taken during the earlier research trips), and to resurvey the aggregation site for fish number and distribution.

Two dives were made on the original site and allowed mapping of areas and comparison of locations over time. On 21 February 2011 the dive started at 5.00 pm when fishes should have been aggregated and starting to spawn according to earlier data. Although there were no Acanthurus present at the original aggregation locations, spawning fishes were quickly located further east and towards the shelf edge break and within about 40-50 m of their previous aggregation centres. On 2nd February, a second 5.00 pm dive allowed the current aggregation areas to be delimited and mapped out by towing a GPS (Global Positioning System unit), while swimming on SCUBA. The 1977-79, mapped earlier, and 2011 distributions show minor differences.

It appears that there has been a major change in numbers of ocean surgeonfish aggregating at the site, with a smaller change in blue tang, over the 30+ year intervening period. In the original 1970s surveys an estimated 20,000 (very approximate given the difficulty in counting large numbers of fish) ocean surgeonfish were present at the site during peak aggregation periods. During the two visits to the site this year, only about 200 or so ocean surgeonfish on the first day (3 days after full moon) and approximately 300-400 during the second day (4 days after full moon) were present. The fish were spread out over an area that could not be seen from a single location, so overall fish numbers had to be estimated while swimming over the larger area. However, there is no doubt that there had been a large decrease in fish numbers (to only perhaps 5-10% of previous numbers) since 1988. For blue tang, the initial aggregation size was roughly 7,000 fish and on both days during 2011 only about 2,000 fish were estimated. The blue tang vastly outnumbered the ocean surgeonfish while the opposite had been the case previously. Both species are commercially exploited and neither is managed. For more details see Colin and Clavijo (1988, in press) and Colin (1996). The trip was partially funded by SCRFA.

Patrick L. Colin
Coral Reef Research Foundation 
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Reference

Colin, P.L (1996) Longevity of some coral reef fish spawning aggregations. Copeia 1996(1):189-192.

Colin P.L, Clavijo I.E (1988) Spawning activity of fishes producing pelagic eggs on a shelf edge coral reef, southwestern Puerto Rico. Bulletin of Marine Science 43(2):249-279.

Colin P.L, Clavijo I.E (in press) Case Study:Acanthurus bahianus (ocean surgeonfish) and Acanthurus coeruleus (blue tang) in Puerto Rico: in Sadovy de Mitcheson, Y and PL Colin (2012), Reef Fish Spawning Aggregations: Biology, Research and Management, Springer, Berlin.