4 Interactions of Wild and Reared Fish and Invertebrates
131
(Oystein Skaala, Institute of Marine Research, Bergen, Norway-personal
communication). Another important factor for recovery measures is that there is
rapid reporting of the escape incident, before the escapes disperse (Jorstad et al.
2006). It was previously assumed that a direct escape of cultured animals was the
only inadvertent way of influencing wild populations but recent results have
highlighted other ways. Cod (Jorstad et al. 2006) and sea bass (Youngson et al.
2001) can spawn in cages and their fertilised eggs subsequently drift into the wild
(as shown with genetically marked individuals (Jorstad et al. (2006) for cod).
Another possibility is that disease organisms can be transferred from cultured to
wild animals without physical contact between the host animals (e.g., furunculosis
in salmon in Norway) with subsequent detrimental effects to wild populations
either ecologically or at a molecular level (see below). In several diseases of
shellfish, transmission of pathogens has occurred when movements of shellfish
between culture sites have taken place, e.g., Bonamia ostreae in the flat oyster
Ostrea edulis and Haplosporidium nelsoni and Perkinsus marinus in the eastern
oyster Crassostrea virginica. With Perkinsus marinus and Bonamia ostreae, transmission of the parasite can occur from oyster to oyster, via the water column
(Andrews 1988; Culloty et al. 1999). Additionally, when Bonamia ostreae has been
introduced into an area, eradication of the disease has failed, as it appears that
Bonamia ostreae can be maintained in other benthic invertebrate species and later
infect relayed oysters, even after the area has been left fallow for a number of years
(Van Banning 1987).
4.3.2 Cultured Strains Deliberately Introduced to the Wild
(As in Stocking/Ranching)
Cultured strains are deliberately introduced to the wild in stocking/enhancement or
ranching exercises (referred to in Japan as “culture enhanced fisheries”). The
minimum requirement for reducing the risk of introducing foreign genetic material
to wild populations is to ensure that broodstock are from the same area as the
proposed release site. In Norway, the Institute of Marine Research (IMR) has been
releasing tagged juvenile lobsters (Homarus gammarus) around the islands of
Kvitsoy since 1990 (Agnalt et al. 1999, 2004), with returns of up to 8% at market
size (5–6 years after release). The juveniles in this case were obtained from wild
captured Kvitsoy “berried”-females, where the attached eggs were already
fertilised. The resulting larvae were hatchery reared through several moults before
being released into areas that had previously been identified as suitable nursery
sites. Some of these restocked lobsters are now sexually mature and IMR conducted
an experiment to investigate the performance of reared F 1 offspring against wild
lobster larvae from the same area (Jorstad et al. 2005). One of the main concerns
about interactions between wild populations and reared strains is that interbreeding
is likely to cause reduction in population fitness under natural conditions (as in
salmon, McGinnity et al. 2003). Alarmingly, the survival of the F 1 cultured lobster
131
(Oystein Skaala, Institute of Marine Research, Bergen, Norway-personal
communication). Another important factor for recovery measures is that there is
rapid reporting of the escape incident, before the escapes disperse (Jorstad et al.
2006). It was previously assumed that a direct escape of cultured animals was the
only inadvertent way of influencing wild populations but recent results have
highlighted other ways. Cod (Jorstad et al. 2006) and sea bass (Youngson et al.
2001) can spawn in cages and their fertilised eggs subsequently drift into the wild
(as shown with genetically marked individuals (Jorstad et al. (2006) for cod).
Another possibility is that disease organisms can be transferred from cultured to
wild animals without physical contact between the host animals (e.g., furunculosis
in salmon in Norway) with subsequent detrimental effects to wild populations
either ecologically or at a molecular level (see below). In several diseases of
shellfish, transmission of pathogens has occurred when movements of shellfish
between culture sites have taken place, e.g., Bonamia ostreae in the flat oyster
Ostrea edulis and Haplosporidium nelsoni and Perkinsus marinus in the eastern
oyster Crassostrea virginica. With Perkinsus marinus and Bonamia ostreae, transmission of the parasite can occur from oyster to oyster, via the water column
(Andrews 1988; Culloty et al. 1999). Additionally, when Bonamia ostreae has been
introduced into an area, eradication of the disease has failed, as it appears that
Bonamia ostreae can be maintained in other benthic invertebrate species and later
infect relayed oysters, even after the area has been left fallow for a number of years
(Van Banning 1987).
4.3.2 Cultured Strains Deliberately Introduced to the Wild
(As in Stocking/Ranching)
Cultured strains are deliberately introduced to the wild in stocking/enhancement or
ranching exercises (referred to in Japan as “culture enhanced fisheries”). The
minimum requirement for reducing the risk of introducing foreign genetic material
to wild populations is to ensure that broodstock are from the same area as the
proposed release site. In Norway, the Institute of Marine Research (IMR) has been
releasing tagged juvenile lobsters (Homarus gammarus) around the islands of
Kvitsoy since 1990 (Agnalt et al. 1999, 2004), with returns of up to 8% at market
size (5–6 years after release). The juveniles in this case were obtained from wild
captured Kvitsoy “berried”-females, where the attached eggs were already
fertilised. The resulting larvae were hatchery reared through several moults before
being released into areas that had previously been identified as suitable nursery
sites. Some of these restocked lobsters are now sexually mature and IMR conducted
an experiment to investigate the performance of reared F 1 offspring against wild
lobster larvae from the same area (Jorstad et al. 2005). One of the main concerns
about interactions between wild populations and reared strains is that interbreeding
is likely to cause reduction in population fitness under natural conditions (as in
salmon, McGinnity et al. 2003). Alarmingly, the survival of the F 1 cultured lobster