"The phrase 'non-destructive fishing methods' often used by those in the aquarium trade may actually be highly misleading with respect to the conservation status of reef fish," say Niclas Kolm and Anders Berglund of Uppsala University in Sweden in the June issue of Conservation Biology.
Coral reefs have the greatest diversity of fish worldwide and many species are unique to particular reefs. Prized for their bright colors, coral reef fish are harvested by the hundreds of thousands each year. While non-destructive fishing methods are clearly an improvement over cyanide and dynamite, they are not necessarily benign and little is known about their effects on fish populations.
Kolm and Berglund studied the effects of a non-destructive fishing method on the Banggai cardinalfish, which is about two inches long and is silver with black stripes. Popular in North America, Japan and Europe, the fish has been found only in the Banggai archipelago off the east coast of Sulawesi, Indonesia, and is fished throughout its range. Banggai cardinalfish live in groups near long-spined sea urchins and seek shelter in the urchins when threatened. Fishermen take advantage of this behavior by pushing urchins into a cage with a stick, which tricks the fish into swimming right in after them. The researchers monitored the Banggai cardinalfish at eight sites in the archipelago and interviewed local fishermen to assess the fishing intensity, which ranged from low (never or rarely fished) to high (frequently fished).
Kolm and Berglund found that fishing cut the size of Banggai cardinalfish groups by half. Specifically, while the average number of fish per group was 11.5 at low-intensity fishing sites, it was only 5.7 at high-intensity fishing sites. This is troubling because at the time of the study, the species had been commercially fished for only six years and the industry is still expanding. "Our data suggest that the popular Banggai cardinalfish is under threat from the aquarium trade industry," say the researchers.
The fishery could threaten the Banggai cardinalfish in two ways. First, fishermen move to new sites after depleting the old ones, and depleted populations are unlikely to be replenished because young Banggai cardinalfish apparently do not disperse far. Second, pushing the sea urchins with a stick often damages them, and the researchers found that the size of a given Banggai cardinalfish population depends on the size of the associated urchin population.
There is, however, an easy way to turn this into a win-win situation for both the fish and the fishermen. Banggai cardinalfish can be raised reliably and cheaply in aquariums, and the researchers are currently encouraging local people to do so. "A fruitful industry could be developed with little or no negative impact on the Banggai cardinalfish," say Kolm and Berglund.
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