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T.F. Cross et al.
4.1 Introduction
As noted in earlier chapters, worldwide aquaculture production is increasing
rapidly and currently exceeds 45 million tonnes of marine and freshwater animals
and aquatic plants (FAO 2007). Since capture fisheries seem to have plateaued at
around 95 million tonnes and, as there is an ever-increasing demand for aquatic
food, the expansion of aquaculture is likely to continue. The western European
aquaculture industry produces a total of 1.6 million tonnes of fishery products a
year (FAO 2007). The European Union strongly endorses aquaculture, aiming to
reduce reliance on imported fish and shellfish products. Also, aquaculture plays a
significant role in creating employment opportunities in rural and coastal communities where job alternatives are often scarce.
New animal species are continuously being assessed in terms of their biological
and economic feasibility for culture, but there is a universal tendency to concentrate
development on relatively few optimal species (e.g., certain penaeid prawn, oyster,
cyprinid and salmonid fish species). The current chapter concentrates on marine
and anadromous animal species. The majority of production in this area is from
partial or whole life-cycle captive rearing for food, ornamental or medicinal
purposes (defined here as “farming”). Although, currently, a relatively smaller
proportion of total production comes from stocking/ranching programmes, this
source is predicted to increase rapidly in the future. Both of these types of
aquaculture can have detrimental genetic effects on wild populations, although, due
to the potential for increased interactions with wild animals, stocking or ranching
programmes may pose greater risks.
In finfish ranching, the juveniles are usually produced in hatcheries and then
released, whereas for most shellfish the seed (eggs or larvae) are initially collected from the wild. The latter may then either undergo a period of intensive
cultivation (e.g., scallop and lobster) before being released or are transferred
directly to the ongrowing area (e.g., mussels). If there is ownership of the transplanted stock, then according to FAO definitions the activity is categorised as
aquaculture (e.g., mussel farming in The Netherlands). However, if there is a
socio-economic reason for the activity then it would probably be classed as fisheries management/stock enhancement (e.g., lobster stocking in United Kingdom
and Norway). The source of the broodstock and the final destination of the juveniles are obviously important when considering potential genetic effects on conspecific indigenous populations.
Survival of ranched shellfish is relatively low and varies from 2% to 8% in
lobsters up to 30% in scallop. For this reason the cost of juveniles becomes a key
factor in deciding whether ranching or intensive culture is more economic. At the
moment, for example, mussel seed can be taken from the wild. This situation is
unlikely to continue and seed scarcity will force the industry to turn to hatcheries.
When this happens it will be more profitable to ongrow on longlines, where high
survival is guaranteed. However, such projections are somewhat academic regarding
the risk of contaminating wild populations with cultured genes. Bivalve molluscs
T.F. Cross et al.
4.1 Introduction
As noted in earlier chapters, worldwide aquaculture production is increasing
rapidly and currently exceeds 45 million tonnes of marine and freshwater animals
and aquatic plants (FAO 2007). Since capture fisheries seem to have plateaued at
around 95 million tonnes and, as there is an ever-increasing demand for aquatic
food, the expansion of aquaculture is likely to continue. The western European
aquaculture industry produces a total of 1.6 million tonnes of fishery products a
year (FAO 2007). The European Union strongly endorses aquaculture, aiming to
reduce reliance on imported fish and shellfish products. Also, aquaculture plays a
significant role in creating employment opportunities in rural and coastal communities where job alternatives are often scarce.
New animal species are continuously being assessed in terms of their biological
and economic feasibility for culture, but there is a universal tendency to concentrate
development on relatively few optimal species (e.g., certain penaeid prawn, oyster,
cyprinid and salmonid fish species). The current chapter concentrates on marine
and anadromous animal species. The majority of production in this area is from
partial or whole life-cycle captive rearing for food, ornamental or medicinal
purposes (defined here as “farming”). Although, currently, a relatively smaller
proportion of total production comes from stocking/ranching programmes, this
source is predicted to increase rapidly in the future. Both of these types of
aquaculture can have detrimental genetic effects on wild populations, although, due
to the potential for increased interactions with wild animals, stocking or ranching
programmes may pose greater risks.
In finfish ranching, the juveniles are usually produced in hatcheries and then
released, whereas for most shellfish the seed (eggs or larvae) are initially collected from the wild. The latter may then either undergo a period of intensive
cultivation (e.g., scallop and lobster) before being released or are transferred
directly to the ongrowing area (e.g., mussels). If there is ownership of the transplanted stock, then according to FAO definitions the activity is categorised as
aquaculture (e.g., mussel farming in The Netherlands). However, if there is a
socio-economic reason for the activity then it would probably be classed as fisheries management/stock enhancement (e.g., lobster stocking in United Kingdom
and Norway). The source of the broodstock and the final destination of the juveniles are obviously important when considering potential genetic effects on conspecific indigenous populations.
Survival of ranched shellfish is relatively low and varies from 2% to 8% in
lobsters up to 30% in scallop. For this reason the cost of juveniles becomes a key
factor in deciding whether ranching or intensive culture is more economic. At the
moment, for example, mussel seed can be taken from the wild. This situation is
unlikely to continue and seed scarcity will force the industry to turn to hatcheries.
When this happens it will be more profitable to ongrow on longlines, where high
survival is guaranteed. However, such projections are somewhat academic regarding
the risk of contaminating wild populations with cultured genes. Bivalve molluscs