Recapturing escaped fish from marine aquaculture is largely unsuccessful: alternatives to reduce the number of escapees in the wild

Abstract

Farmed fish that escape and mix with wild fish populations can have significant ecological and genetic consequences. To reduce the number of escaped fish in the wild, recapture is often attempted. Here, we review the behaviours of escapees post-escape, and how recapture success varies with escaped fish size, the size of the initial escape event and recapture methods. Success rates of fishing gears varied among species, with gill-nets and coastal barrier nets most effective for recapture of salmonids. Recapture success was strongly negatively correlated with both fish size and the number of fish escaped, regardless of species. Recapture success was universally low across all studied species (8%). Numerous tracking studies of escaped fish indicate that recapture efforts should be initiated within 24 h of an escape incident for highest recapture success. However, most large escape events are due to storms, which mean recapture efforts rarely start within this timeframe. Recapture of escaped fish is broadly ineffective in marine habitats, with rare exception. High bycatch rates during ineffective recapture attempts imply that large-scale recapture efforts should be weighed against the possibility of affecting wild fish populations negatively. We suggest three alternative approaches to reduce escapee numbers in wild habitats: (i) protect populations of predatory fish around sea-cage farms from fishing, as they prey upon smaller escapees; (ii) construct impact offset programmes to target recapture in habitats where escapees can be efficiently caught; and (iii) ensure technical standards are legislated so that fish farmers invest in preventative technologies to minimize escapes.

Climate change, biological invasions, and the shifting distribution of Mediterranean fishes: A large‐scale survey based on local ecological knowledge

“…and widespread mariculture and associated unintentional escapees (Dempster et al, 2018), which might act as inadvertent but continuous restocking of this species over large areas of the basin. and widespread mariculture and associated unintentional escapees (Dempster et al, 2018), which might act as inadvertent but continuous restocking of this species over large areas of the basin.…”

“…This was particularly clear for the Sicily strait, which was historically considered as an insurmountable barrier to the dispersion of Red Sea fishes and it is now colonized by species such as rabbitfishes (Siganus luridus) and cornetfish (F. commersonii). and widespread mariculture and associated unintentional escapees (Dempster et al, 2018), which might act as inadvertent but continuous restocking of this species over large areas of the basin.…”

Tracking escaped Atlantic cod (Gadus morhua L.) aggregated around Norwegian farms: Considerations for management strategies

“…Despite the relatively small sample size ( n = 20), most tagged individuals showed behaviour consistent with one another (high fidelity to the home farm rather than migration out of the fjord), so the findings of this study may be relevant for developing a strategy for recapturing escaped cod. Earlier studies indicate that immediately after a farm escape incident there is a low probability of recapture because escapees rapidly disperse from the farm (Dempster et al., ; Serra‐Llinares et al., ). Similarly, the long‐term recapture rate of escaped salmon has been low under commercial conditions, but studies on simulated salmon escapees indicate that a high recapture rate over time is also possible for escaped salmon (Chittenden et al., ; Uglem et al., ).…”

Marine Ranching Construction and Management in East China Sea: Programs for Sustainable Fishery and Aquaculture

“…Second, offshore marine ranching uses larger and stronger cages for high-value carnivorous fish cultivation. However, despite using ecosystem approaches, the debates on the cage aquaculture method still exist on the following two aspects: (1) cage aquaculture continues to be fed using large quantities of low-value (trash) fish from the wild, often comprising juveniles from potentially valuable species [61,62]; (2) some fish cultured in cages occasionally escape into the natural environment as a consequence of human error, net breakages, or natural causes such as predator or storm damage to cages [63,64]. Species like salmonids are likely to have considerable invasive and genetic impact on local ecosystems [17,[65][66][67][68][69].…”