Report on the effect of changes in habitat on productivity, species and habitats

SEAwise research

The crucial conclusion of our researchers was that restoring essential habitats and protecting these through EBFM may have an even greater impact on the sustainability of fish stocks than regulating fishing pressure. To reach this, the researchers explored a range of scenarios in fisheries across the four SEAwise Case Study regions, considering not just loss of habitat and degradation in habitat quality, but also improvements in habitat quality and extent. By region, they found that:

• Eastern English Channel (North Sea): Restoring nursery areas for sole, plaice, whiting, and seabass would increase catches and levels of biomass, benefiting both the ecosystem and fisheries. For example, fishers could sustainably take an extra >20% of sole per year, if key sole habitat was restored. Wind farms further east in the North Sea may also offer protection to cod attracted to them.
• Irish Sea (Western Waters): Restoring nursery habitats for sole in estuarine environments (estuaries being the tidal mouths of rivers as they meet the sea) would – similar to the Eastern Channel case – ultimately increase the amount of sole which fishers could sustainably catch. In comparison, restoring coastal habitats showed less effect, based on modelling.
• Baltic Sea: This region is heavily affected by “hypoxia” (a shortage of oxygen), which has a knock-on negative effect on the reproduction and growth of commercial stocks. Restoration of spawning and nursery habitats could buffer the effects of hypoxia, and modelling different scenarios revealed that such habitat restoration could markedly increase productivity for plaice, cod, and herring, especially through increased spawning success. 
• Eastern Ionian Sea (Mediterranean): In areas where an enhanced protection status has been applied to the seabed, reducing or preventing the use of bottom trawling, biomass is higher for juveniles of three key commercial species: European hake, deep water rose shrimp, and red mullet.

Taken together, these findings make a clear case that the loss and degradation of habitat in coastal ecosystems has a significant negative impact on the productivity of commercial fish species – and that restoring and protecting these habitats should play a key role in sustainable management of fish stocks.