In ocean ranching, young fish are reared in captivity, released into the open ocean and later harvested as part of the “wild” fishery. Ranchers often release fry in staggering numbers. North American hatcheries, for example, release over five thousand million juvenile salmon each year (World Fisheries Trust 2002). Commonly used species include salmon as well as smelt, pike, abalones and flatfishes such as sole, flounder, and halibut. Ocean ranching is commonly practiced in China and Japan. Japan, for example, releases more than 70 species each year in its coastal waters, ten of which are ranched on a large scale (Arnason 2001). Ocean ranching requires a relatively moderate capital investment, is practised largely in rural or remote regions, and uses native species.
Ocean ranching can deplete wild fish through increased competition for food and habitat.
Ranch fish such as salmon, which return in large numbers for harvest, can attract predators such as fishes, birds and sea lions –
animals who can then fall prey to other predators or to fisheries operators who may kill or deter them. There are also concerns
over reduced genetic diversity, due to interbreeding.
The overall effect is a disruption of the food chain and, in some cases, a decline in genetic biodiversity and in endangered wild stocks. Methods for harvesting fish bring additional consequences. Bottom trawling or powerful vacuums disturb or damage the seabed, destroying critical marine habitats and nursery grounds. Trawling also stirs up seafloor sediments, which can clog fish and mollusc gills (Thorne-Miller 1999).
Toward best practices
Harmful environmental effects can be reduced by spreading the release of ranch fish over longer periods, establishing non-harvest conservation areas and exclusive harvest zones, and using fish such as salmon that exhibit homing instincts at specified times in their life history – a practice that can avoid harmful capture methods such as trawling or line capture which can net endangered species (FAO 1995). Capture methods that minimize physical disturbance to the environment should be strongly encouraged.