The corals look good, but where are the Fish?

February 4, 2013

Our partners at the The Khaled bin Sultan Living Oceans Foundation continue their Global Reef Expedition, a worldwide survey of coral reefs, reporting their findings to the world as they go. In the Acteon Group of French Polynesia, they found excellent coral cover, but a surprising lack of fish. The question is, why?  ~ Ed.

During our surveys in the Acteon group we saw very few fish.  There were few sharks or other large predators and even large herbivorous fish such as surgeonfishes and parrotfishes were noticeably low in number. The fish community was dominated by small-bodied species such as damselfishes, wrasses, and butterflyfishes.

So why are the fish communities in such a pristine and isolated coral reef in such poor condition? Several factors may be at play. The Acteon group of islands is relatively isolated. The closest major land mass to the group is Mangareva, more than 220 km away. Due to its isolation the Acteon group is difficult to patrol and may be vulnerable to poaching. Both local and foreign fishing vessels may target tuna, jacks, groupers and snappers, and also sharks for the fin trade.

Also due to the large distances between the Acteon islands the other major island groups, it is possible that recruitment of fish larvae and immigration of adult fish into the islands is limited. This means that if the fish stocks were depleted by fisheries, recovery would largely depend on Acteon’s own remaining stocks.

Despite the very high cover of live corals, the physical complexity of the reef was rather poor, with very little suitable habitat and shelter for large fish. The amount of large predatory reef fish has been associated with the availability of suitable shelter, and the physical complexity of the reef.

But all is not lost. Improved efforts to patrol the area may help prevent possible poaching of fish. And together with the very good condition of the coral reef, which has been relatively buffered from stressors which cause tremendous damage to reefs elsewhere, the abundance and variety of the large predatory species of fish may increase at the Acteon in time.

Written by Badi Samaniego

Originally posted at The Khaled bin Sultan Living Oceans Foundation website.