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

The SEAwise project works to deliver a fully operational tool that will allow fishers, managers, and policy makers to easily apply Ecosystem Based Fisheries Management (EBFM) in their fisheries. This report demonstrates and quantifies the changes in productivity of exploited marine populations linked to the degradation in availability and suitability of their essential habitats. Specifically, this work link changes in exploited fish productivity to changes in habitat extent and quality using different models and data-analyses for specific case studies.

A generic stage-based life cycle model was used to simulate habitat scenarios of degradation/restoration for nursery-dependent species of fisheries interest at the stock management unit scale in the Eastern English Channel. Four species of high fisheries interest were accounted for this analysis: sole, plaice, whiting and seabass. Restoring the surface of juvenile habitat increased both maximum sustainable yield biomass but also the level of sustainable fishing mortality. The approach demonstrated the potential gains of restoring nursery areas. This approach was also partly applied to the sole in the Irish Sea with similar preliminary conclusions. Further analysis to estimate local levels of nursery habitat degradation, needed to simulate accurate scenarios, are still ongoing. The impact of basin scale hypoxia on population productivity for exploited species such as plaice, Atlantic cod and herring in the western Baltic Sea was investigated based on a simulation approach.

Field work within and around three German offshore windfarms was conducted by experimental angling fishing to analyse the effects of windfarms on cod. They demonstrated their large “artificial reef” effect, with huge increase in relative density at small scales around piles, however depending on the foundation and type of scour protection around the turbine.

Different anthropogenic pressures and their impacts on local fish species and habitats were investigated in the Eastern Ionian Sea. There was significant exposure to bottom trawling for European hake, deep water rose shrimp and red mullet and the regions with higher biomass of juveniles coincide with the areas of enhanced protection status. The invasive siganids are becoming the dominant herbivore, impacting native species with commercial value and also impacting canopy-forming algae. This has consequences on fish habitats and for exploited species. Marine litter act as an additional stressor on marine organisms that depend on the sea bottom for feeding, as the red mullet. The rose shrimp, which is less dependent on the sea bottom, appears less affected.

More information about the SEAwise project can be found at https://seawiseproject.org/