ultimate ocean ranch, The

Sea Technology, Aug 1999 by Matsuda, Fujio, Szyper, James, Takahashi, Patrick, Vadus, Joseph R

Near-shore ocean ranching necessarily involves issues of proprietorship, tenure, and shared use of ocean areas. These issues have not been addressed for the case of mobile platforms in the open sea. But it would be intriguing to leap-frog existing terrestrial farming and ranching systems (which are energy intensive and add carbon dioxide to the atmosphere) with an OTEC-powered ocean ranch that is driven by natural energy, feeds itself, operates without cages, and can utilize acoustic techniques during the harvest.

Species selection and development for the fisheries products are critical for sufficient productivity as well as for consideration of impact on oceanic ecosystems. Upwelling is expected to produce "natural" changes in the species composition of the fertilized microbial communities.

With artificial upwelling providing nutrients, food-chain efficiency of the product would be greatest for a readily harvested primary producer, such as edible macroalgae. Seaweeds are not, however, a concentrated form of protein, and it is questionable that such a product could be competitive with present culture systems on and near land. Food-chain efficiency with an animal product will be greatest with a planktivorous herbivore or filter-feeder. Whale sharks, under study at the Sun Yat Sen University aquarium in Kaohsiung, or presently cultured herbivorous food fish such as rabbit fish, would be examined for feasible use in these systems. Their advantages include the ability to grow rapidly to desirable market sizes for food fishes and efficiency for protein production under limited nutrient conditions.

The fisheries productivity of the natural upwelling zones is derived from small planktivorous fishes (anchovies and sardines), some of which have been cultured. The depletion and decreasing reliability of the upwelling zones' capture fisheries, which produce fishmeal used by the terrestrial and aquatic animal feed industry, suggests a ready market for filter-feeding fishes as efficient products of upwelling mariculture systems.

Natural trophic position [nutrient level (see subparagraph below on "projection" for definitions of levels)] is by no means the sole determinant of a species' potential for efficient aquaculture production. Numerous species, which in nature are carnivorous or omnivorous, have been developed for practical culture in open-water systems using fish mealand fish oil-based feeds economically. However, they consume rather than enhance oceanic productivity of bulk foodstuffs, though they produce economic value. A smallfish production strategy could gain advantage from the facts that larvae and juveniles of most fish species are planktivorous, that some are likely faster growing and more amenable to culture than the upwelling zone planktivores, and that these species are of high value even at small food portion sizes. Open-water oceanic fishes (mahimahi, tunas) tend to grow rapidly as a natural adaptation against predation in an environment devoid of shelter, but unless feeds technology advances rapidly, natural carnivores may be unprofitable to culture.