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 diversityIn general, animals produced with such techniquescompete more efficiently <strong>for</strong> resources (food), disruptmating behaviour and success and may affectthe natural stocks. Research is required to elucidatethe potential impacts of such practices.38. Experiments are now under way to producetransgenic fish (genetically modified fish) in orderto enhance per<strong>for</strong>mance under growout condition. 31Special care must be taken to prevent broodstocksfrom mixing with wild populations.39. The common practice of transfer of broodstockand fry between different regions of the globecould have an effect on biodiversity through theintroduction of allochthonous species, diseases andother related impacts.40. Effluents from hatcheries are usually rich innutrients and chemical compounds. Recirculatingsystems control water quality and reduce diseaseintroduction. In flow-through systems, a generalpractice is to include a settling pond <strong>for</strong> the treatmentof wast-water be<strong>for</strong>e it is returned into theenvironment. Chemicals tend to persist in thewater column and are introduced into natural environments.Regular monitoring of inputs intoaquatic systems must be carried out.Growout41. For most of the major species of finfish, fertilizedeggs are incubated until hatching (a very shortprocess in tropical species, but several months insalmonids) and then conditioned to artificial feedin tanks be<strong>for</strong>e transfer to growout facilities (pens,cages, large tanks).42. Cage culture is divided into two main categories:inshore cages and offshore cages, and can beeither floating, fixed or submerged. Inshore cagesare located in protected and usually shallow areaswith generally less water circulation than offshorecages. On the other hand, offshore cages are locatedin deep water and open areas with less protectionfrom storms but with better water exchange.Cage-reared fish are fed supplemental or artificialdiets depending on the stocking density and thelevel of technology applied. 32 In inshore cages, possibleimpacts include water quality degradation,transfer of disease, alteration of the benthic communitybiodiversity, input of antibiotics, antifoulingand other chemicals as well as the risk ofescapes. These impacts can be minimized by theproper management, site selection and continuousmonitoring. In order to reduce potential impacts,clear monitoring parameters must be established.In offshore cages the highest risk results fromescapees. However, total nutrient inputs in the lattercould be similar or even greater than inshoresystems. For both types of cages, nets and mooringsystems provide additional substrate <strong>for</strong> colonization.43. Nets and fish pens are located in shallow, shelteredwaters, and their edges are anchored to thebottom/substrate. In the Philippines, milkfish pensgenerally have a nursery compartment within thegrow-out pen/enclosure. Fish in the nursery compartmentand are not generally given supplementalfeeding except <strong>for</strong> occasional rations of breadcrumbs, rice bran, broken ice cream cones, fishmeal, and ipil-ipil leaf mill. 33 Direct biodiversityimpacts of fish pens involve the disappearance ofbenthic communities over large areas. Strong alterationof hydrodynamics has also been observed.44. A typical fish pond system consists of the followingbasic components: pond compartmentsenclosed by dikes, canals <strong>for</strong> supply and drainage of31 FAO. 2000. The state of the world fisheries and aquaculture 2000. FAO, Rome. ISBN 92-5-104492-9.http://www.fao.org/DOCREP/003/X8002E/x8002e00.htm32 Baluyut, E. A. 1989. Aquaculture systems and practices: a selected review. UNEP/FAO, Rome. ADCP/REP/89/43.http://www.fao.org/docrep/T8598E/t8598e00.htm#Contents33 Ibid.17