3 Aquaculture and Coastal Space Management
97
Coastal aquaculture sites have also been suggested as having the potential to
disrupt the spawning of marine fish species if improperly placed, although little
evidence of this presently exists. Bjørn et al. (2005) found that wild coastal
Atlantic cod (Gadus morhua) avoided the smell of salmon farms in tank-based
olfactory experiments, which suggests they may also avoid areas with farms.
Atlantic cod are known to have high fidelity to specific spawning grounds
(Wright et al. 2006). If farms deter fish from accessing spawning areas or impede
migratory pathways to spawning areas, the success of spawning may diminish.
Detailed information on fish movements in space and time is required to determine if some fish species avoid farm areas. If so, farms may best be placed away
from known spawning areas.
3.5.2. Effects of Existing Fish Farms on Wild Fish
Once sea-cages have been deployed, they will attract wild fish to their immediate
surrounds, which in turn are likely to attract fishers. Deciding on the appropriate
level of interaction between aggregations of wild fish and commercial and recreational fisheries requires knowledge of the species and overall biomass of the wild
fish aggregations through time, the extent to which they will be targeted by fishers,
and importantly, the existing management regime of the fishery and the overall
status of the wild fish stock.
Coastal aquaculture farms have considerable demographic effects on wild fish by
aggregating large numbers in their immediate vicinity. Early studies by Carss
(1990) in Scotland and Bjordal and Skar (1992) in southern Norway around marine
salmon farms indicated that saithe (Pollachius virens) aggregated at farms in considerable numbers. Dempster et al. (2002, 2005) highlighted that Mediterranean
sea-cage fish farms attracted wild fish assemblages that had up to 30 different species and estimated that the aggregation biomasses ranged between 10 and 40 t at 5
of the 9 farms investigated (Dempster et al. 2004). Similarly large aggregations have
since been noted in Greece (Smith et al. 2003; Thetmeyer et al. 2003) and the
Canary Islands (Boyra et al. 2004; Tuya et al. 2005, Fig. 3.4). While mussel rafts in
the Mediterranean Sea (Brehmer et al. 2003) are also known to aggregate wild fish,
the majority of studies concerning demographic impacts of coastal aquaculture on
wild fish have focussed on aggregations around sea-cage farms.
3.5.3 Composition and Variability of Wild Fish Aggregations
Although zoogeographic differences in the species of fish that aggregate around
farms exists, pelagic planktivorous species dominate assemblages at most farms
and these fish opportunistically feed upon food pellets lost from cages. In warm
water areas, such as Mediterranean Spain and the Canary Islands, over 30 different
97
Coastal aquaculture sites have also been suggested as having the potential to
disrupt the spawning of marine fish species if improperly placed, although little
evidence of this presently exists. Bjørn et al. (2005) found that wild coastal
Atlantic cod (Gadus morhua) avoided the smell of salmon farms in tank-based
olfactory experiments, which suggests they may also avoid areas with farms.
Atlantic cod are known to have high fidelity to specific spawning grounds
(Wright et al. 2006). If farms deter fish from accessing spawning areas or impede
migratory pathways to spawning areas, the success of spawning may diminish.
Detailed information on fish movements in space and time is required to determine if some fish species avoid farm areas. If so, farms may best be placed away
from known spawning areas.
3.5.2. Effects of Existing Fish Farms on Wild Fish
Once sea-cages have been deployed, they will attract wild fish to their immediate
surrounds, which in turn are likely to attract fishers. Deciding on the appropriate
level of interaction between aggregations of wild fish and commercial and recreational fisheries requires knowledge of the species and overall biomass of the wild
fish aggregations through time, the extent to which they will be targeted by fishers,
and importantly, the existing management regime of the fishery and the overall
status of the wild fish stock.
Coastal aquaculture farms have considerable demographic effects on wild fish by
aggregating large numbers in their immediate vicinity. Early studies by Carss
(1990) in Scotland and Bjordal and Skar (1992) in southern Norway around marine
salmon farms indicated that saithe (Pollachius virens) aggregated at farms in considerable numbers. Dempster et al. (2002, 2005) highlighted that Mediterranean
sea-cage fish farms attracted wild fish assemblages that had up to 30 different species and estimated that the aggregation biomasses ranged between 10 and 40 t at 5
of the 9 farms investigated (Dempster et al. 2004). Similarly large aggregations have
since been noted in Greece (Smith et al. 2003; Thetmeyer et al. 2003) and the
Canary Islands (Boyra et al. 2004; Tuya et al. 2005, Fig. 3.4). While mussel rafts in
the Mediterranean Sea (Brehmer et al. 2003) are also known to aggregate wild fish,
the majority of studies concerning demographic impacts of coastal aquaculture on
wild fish have focussed on aggregations around sea-cage farms.
3.5.3 Composition and Variability of Wild Fish Aggregations
Although zoogeographic differences in the species of fish that aggregate around
farms exists, pelagic planktivorous species dominate assemblages at most farms
and these fish opportunistically feed upon food pellets lost from cages. In warm
water areas, such as Mediterranean Spain and the Canary Islands, over 30 different