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T.F. Cross et al.
of sexually-mature individually-tagged wild and farm salmon in large freshwater
arenas with suitable spawning substrates. Such experiments are required with other
species and although it is recognised that they may be more difficult to set up, these
are being attempted with cod in Iceland (Gudrun Martinsdottir, Marine Research
Institute, Iceland- personal communication).
The presence of reared animals in nature also increases the propensity of
interspecific hybridisation with congenerics, certainly for reared Atlantic salmon
and wild brown trout, Salmo trutta (Youngson et al. 1993; Hindar and Balstad
1994). Whether this is the case with other European aquaculture species has not
been established but since inter-specific hybrids are rarely fully fertile, this could
result in another potential problem for wild populations when reared aquaculture
species enter the wild.
4.4.2 Indirect Genetic Interactions
Certain bivalve diseases have had major ecological consequences for native populations, for example, the overall European aquaculture production of flat oysters
Ostrea edulis fell from 29,595 t in 1961 to 5,921 t in 2000 due to epizootics caused
by Bonamia ostreae and a second protistan Marteilia refringens. Also, in the early
1970s, the Portuguese oyster (Crassostrea angulata) was dramatically depleted
within Europe by an iridovirus (Marteil 1976). It has been speculated that the
uncontrolled transfer of Crassostrea gigas introduced this iridovirus to Crassostrea
angulata, which was highly susceptible (Boudry et al. 1998).
Despite this evidence of ecological effects, there are relatively few examples
of indirect genetic interactions between cultured strains and wild populations,
primarily because this aspect has not been investigated in detail in species other
than Atlantic salmon. However, conditions undoubtedly exist where such
interactions are possible. For Atlantic salmon “common-garden” experiments
in Ireland (McGinnity et al. 2003), the farmed strain involved grew significantly faster in freshwater than the wild population (presumably since the
farmed strain had been subject to several generations of selection for fast
growth). As substantially more of the wild population migrated downstream out
of the experimental stretch, competitive displacement of wild fish by farmed
was considered likely. Several other authors have cited examples of ecological
interactions in salmonids, e.g.,
●
farmed salmon feeding on natural prey (Hislop and Webb 1992)
●
potential for feeding competition at sea (Jonsson and Jonsson 2006)
●
competition for mates (Fleming et al. 2000)
●
competitive displacement of juveniles (McGinnity et al. 1997, 2003; in press)
●
predator avoidance (Einum and Fleming 1997; Fleming and Einum 1997)
GM individuals for growth hormone, providing they survive, could act as super
competitors/predators, though it has been suggested that these individuals will have
T.F. Cross et al.
of sexually-mature individually-tagged wild and farm salmon in large freshwater
arenas with suitable spawning substrates. Such experiments are required with other
species and although it is recognised that they may be more difficult to set up, these
are being attempted with cod in Iceland (Gudrun Martinsdottir, Marine Research
Institute, Iceland- personal communication).
The presence of reared animals in nature also increases the propensity of
interspecific hybridisation with congenerics, certainly for reared Atlantic salmon
and wild brown trout, Salmo trutta (Youngson et al. 1993; Hindar and Balstad
1994). Whether this is the case with other European aquaculture species has not
been established but since inter-specific hybrids are rarely fully fertile, this could
result in another potential problem for wild populations when reared aquaculture
species enter the wild.
4.4.2 Indirect Genetic Interactions
Certain bivalve diseases have had major ecological consequences for native populations, for example, the overall European aquaculture production of flat oysters
Ostrea edulis fell from 29,595 t in 1961 to 5,921 t in 2000 due to epizootics caused
by Bonamia ostreae and a second protistan Marteilia refringens. Also, in the early
1970s, the Portuguese oyster (Crassostrea angulata) was dramatically depleted
within Europe by an iridovirus (Marteil 1976). It has been speculated that the
uncontrolled transfer of Crassostrea gigas introduced this iridovirus to Crassostrea
angulata, which was highly susceptible (Boudry et al. 1998).
Despite this evidence of ecological effects, there are relatively few examples
of indirect genetic interactions between cultured strains and wild populations,
primarily because this aspect has not been investigated in detail in species other
than Atlantic salmon. However, conditions undoubtedly exist where such
interactions are possible. For Atlantic salmon “common-garden” experiments
in Ireland (McGinnity et al. 2003), the farmed strain involved grew significantly faster in freshwater than the wild population (presumably since the
farmed strain had been subject to several generations of selection for fast
growth). As substantially more of the wild population migrated downstream out
of the experimental stretch, competitive displacement of wild fish by farmed
was considered likely. Several other authors have cited examples of ecological
interactions in salmonids, e.g.,
●
farmed salmon feeding on natural prey (Hislop and Webb 1992)
●
potential for feeding competition at sea (Jonsson and Jonsson 2006)
●
competition for mates (Fleming et al. 2000)
●
competitive displacement of juveniles (McGinnity et al. 1997, 2003; in press)
●
predator avoidance (Einum and Fleming 1997; Fleming and Einum 1997)
GM individuals for growth hormone, providing they survive, could act as super
competitors/predators, though it has been suggested that these individuals will have