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Sustainable Resource Management Program

Offshore Aquaculture

Aquaculture has been a method of food production for thousands of years, and is a viable method of supplementing wild caught fish in order to feed an ever-growing global population. Recently, studies have indicated that many fish stocks around the world will be extinct within the next fifty years if overfishing continues at its current level, increasing the focus on aquaculture. Traditional inshore aquaculture systems are associated with many negative environmental impacts including eutrophication, disease transmission, and habitat destruction. Advances in aquaculture pen technology, however, have allowed the movement of aquaculture operations into environments previously deemed unusable. The strong currents and wave action associated with the offshore environment actually reduce the overall environmental impact of aquaculture operations making them more sustainable by diluting and dissipating fish wastes.

Cobia (Rachycentron canadum) is an ideal candidate for offshore aquaculture. Its excellent growth rates (500 g/month) and high food conversion ratio (1 kg of body mass for every 1.3 kg of feed) make it a commercially viable aquaculture species, and its firm white flesh and rich taste has made it a popular restaurant food with a market price of approximately $10 per kilogram.

In October 2004, 14,000 cobia fingerlings were stocked in the Cape Eleuthera Institute’s 3000m² offshore aquaculture cage. Over the course of the fish grow-out, the environment impacts of the aquaculture cage were monitored by surveying the wild fish community structure, nutrient levels, and algal growth at the cage location. There was no significant difference in these variables as a function of distance from the cage or relative to upstream or downstream direction. The project enjoyed over a year of problem free operation with exceptional growth rates, but unfortunately ended prematurely due to sharks. Sharks targeted dead fish resting against the net and created large holes in the cage allowing 75% of the cobia to escape.

Recently, the second phase in our offshore aquaculture project has commenced. We have begun to raise a brood stock of cobia. The long-term goal of phase two is to raise cobia eggs spawned by our brood stock through to market size fish. In order to realize this goal a novel solution to the shark problem has been developed. An internal ‘ecosystem’ will be maintained within the aquaculture cage; sick or dead fish will be consumed by large piscivorous grouper before they can attract sharks, herbivorous species will be stocked to consume algae on the net, and crustaceans will consume excess food and other detritus. A lower stocking density of cobia is also planned to reduce overall mortalities.

The offshore aquaculture project is proud to work in collaboration with the University of Miami Rosenstiel School of Marine and Atmospheric Science Aquaculture Program.