European Sea Bass

Dicentrachus labrax

Escapes and Introductions

Escapees from aquaculture facilities can potentially impact on habitats and species in the receiving water bodies. Problems could occur due to competition, potential disease transfer, establishment of non-native species, interbreeding with wild populations, and impacts on sensitive habitats.

With any open water containment system there is the potential for stock to escape. Whilst establishing contingency plans in case of sea bass escapes is essential1, prevention is the key to mitigating escapes. Escapes from farms occur both through repeated low-number incidents and through large-scale events. Technical and operational failures can lead to escapes: cages can be breached in storms; holes can appear through wear and tear; predator interaction and operational accidents can occur, and so on. Losses due to escapes represent a considerable financial loss to a farm, so it is in its interest to prevent them.

Increased production has led to an increase in escape incidents from Mediterranean farms2, and there is evidence of interbreeding of escaped sea bass with wild stocks, potentially weakening their genetics3. Advances in sea bass genetic research and the enhancement of farmed strains via breeding programmes has been on a lesser scale than in other farmed fish (such as salmon); consequentially farmed sea bass are not too distinct genetically from wild populations. However, as more attention is focused on breeding to improve productivity the issue of sea bass escapes may well become of increasing concern.

It may be possible that technologies become available to produce sterile populations of sea bass that are unable to reproduce if they escape. However, in the absence of this technology broodstock should ideally originate from local endemic or naturalised sea bass populations to minimise the potential impacts of cross breeding.

Recapturing fish after escape (at or close to the point of escape) is a logical management option, however evidence suggests that fish tend to disperse rapidly from the point of release and recapture efforts are often delayed after large-scale escape events, which typically occur during storms. These two factors mean that few attempts to recapture sea bass after large-scale escape incidents have been successful4.

Improved netting materials, enhanced engineering standards and equipment build quality, better staff training around vessel handling and use, and efforts to deter predators all reduce escape incidents, whilst the biosecurity of land-based sea bass RAS facilities means that escape risks are minimal within these systems.

References

  1. Arechavala-Lopez, P et al, 2018. Recapturing fish escapes from coastal farms in the western Mediterranean Sea: Insights for potential contingency plans. Ocean and Coastal Management 151, 2018 p69–76
  2. The Fish Site
  3. FAO
  4. Dempster, T. et al, 2016. Recapturing escaped fish from marine aquaculture is largely unsuccessful: Alternatives to reduce the number of escapees in the wild. Reviews in Aquaculture, 2016