Solutions for sustainable mariculture - Convention on Biological ...

<strong>Solutions</strong> <strong>for</strong> <strong>sustainable</strong> <strong>mariculture</strong> - avoiding the adverse effects of <strong>mariculture</strong> on biological diversity73. The production of sterile fish is often advancedas a mitigating technology. However, although sterilefish cannot establish wild populations or interbreedwith wild fish, they can still compete withwild fish <strong>for</strong> food, spread disease, and disturb wildnesting sites. Escaped or released fertile tetraploidsmay attempt to breed with wild fish and disruptoverall spawning success. Gene transfer (not yetused in commercial <strong>mariculture</strong>) may have ecologicaleffects if the introduced DNA causes majorchange in the ecological role of the transgenic fish(by, <strong>for</strong> example, increasing its size or its ability touse new food sources). Transgenic fish given a geneto speed growth, <strong>for</strong> example, could out-competewild fish <strong>for</strong> food or spawning sites, while fish engineered<strong>for</strong> cold-tolerance might intrude on theranges of more northerly species. Unanticipatedpleiotropic (multiple) effects may also appear.74. Most animals farmed on land are highlydomesticated, and without human protection theywould likely fail to survive in the wild. Organismsused in aquaculture on the other hand are still relativelywild, and may easily survive and reproduceoutside their natural ranges. 83 Because much of theworld’s aquaculture relies on species outside theirnative range, escapes are a constant biodiversityconcern. In the short term, escapes of hatcheryspecies may swamp wild populations through sheerweight of numbers. Skaala 84 stated that the numberof Atlantic salmon (Salmo salar) escaping fromfish farms in Norway exceeded the number of wildfish harvested in Norway. 85 A comparison of wildand farmed Atlantic salmon showed that farmedfish had higher growth rates and were more aggressivethan wild fish, thus posing a threat to nativepopulations that were already depleted by environmentalfactors. 8675. Many alien marine species resulting fromescaped cultured stocks have become firmly establishedfar from their native ranges and are culturallyaccepted as “just more biodiversity”. However,when self-sustaining populations of escapesbecome established, they could interact with nativecommunities in a number of ways, including predation,competition and even elimination of nativespecies. Japanese oyster and Manila clam, <strong>for</strong> example,are treasured by recreational fishermen on thePacific coast of North America as well as in Europe.The risk is probably greater with escape of speciesoccupying similar niches to local ones, because theyare more likely to interact with native populationsand affect their survival. The ability of natural populationsto recover from introgression of farmedgenes has been very little studied.83 Courtenay, W. R., Jr., and J. D. Williams. 1992. Dispersal of exotic species from aquaculture sources, with emphasis on freshwater fishes. Pages49-81 In A. Rosenfield, and R. Mann (eds.). Dispersal of living organisms into aquatic ecosystems. College Park, MD: Maryland Sea GrantCollege, University of Maryland. Cited in Goldburg.84 Skaala, O. 1995. Possible genetic and ecological effects of escaped salmonids in aquaculture. Pages 77-86 In Environmental impacts of aquaticbiotechnology. OECD, Paris. Cited in Penman 1999.85 Penman, D. J. 1999. Biotechnology and aquatic resources: genes and genetically modified organisms. Pages 23-33 In R. S. V. Pullin, D. M. Bartley,and J. Kooiman (eds.). Towards policies <strong>for</strong> conservation and <strong>sustainable</strong> use of aquatic genetic resources. ICLARM Conf. Proc. 59. 277 pp.86 Einum, S. and I. A. Fleming. 1997. Genetic divergence and intyeractions in the wild among native, farmed and hybrid Atlantuc salmon.Journal of Fish Biology 50:634-651. Cited in Smith 1999.25