SEAwise report on the bycatch mortality risk of potentially endangered and threatened species of fish, seabirds, reptiles and mammals
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 and bycatch of protected, endangered and threatened (PET) species is a major concern in EBFM implementation. This SEAwise report evaluates the effects of fishing on bycatch of PET species by applying a hierarchical framework that moves from qualitative to quantitative methodologies depending on species vulnerability to bycatch and data availability. By these means, this work identifies current areas of highest bycatch risk across the case studies and assesses the sustainability of bycatch levels on PET populations.
The first step of this report consisted of the application of the semi-quantitative Productivity-Susceptibility Analysis (PSA) to a wide range of sensitive species across European waters, including cetaceans, bony and cartilaginous fishes and a single seabird species. PSA measures the risk of a species to over-exploitation by a fishery based on two properties; productivity, defined by the life history characteristics determining the intrinsic rate of population increase, and susceptibility, based on the interactions between population and fishing dynamics. This analysis scores species’ productivity and susceptibility attributes from 1 (low risk) to 3 (high risk) for each fishery or gear of interest, allowing a rapid screening of the species most likely affected by bycatch.
Cetaceans were assessed in the Bay of Biscay and Irish waters, and in both cases, gillnets were identified as the gears with the highest bycatch risk, especially for common dolphin (Delphinus delphis) and harbour porpoise (Phocoena phocoena). Cartilaginous fishes were assessed in the Mediterranean Sea, including pelagic species such as the blue shark (Prionace glauca) and demersal species such as the longnose spurgod (Squalus blainville), the bull ray (Aetomylaeus bovinus) and the common smooth-hound (Mustelus mustelus). The blue shark, which is Critically Endangered in the Mediterranean, showed a high risk of being bycaught by pelagic longline, while demersal species were all highly threatened by bottom trawlers. A combination of elasmobranchs and teleost fishes was assessed along the North Sea, Bay of Biscay, and Celtic Seas, including common skate complex (Dipturus spp.), blonde ray (Raja brachyura), spurdog (Squalus acanthias), tope (Galeorhinus galeus), spotted ray (Raja montagui), undulate ray (Raja undulata), starry ray (Amblyraja radiata), John dory (Zeus faber), Atlantic wolffish (Anarhichas lupus) and Atlantic halibut (Hippoglossus hippoglossus). Highest bycatch risk was found for the common skate complex, spurdog and tope, showing highest bycatch risk for both beam- and otter trawls, as well as gillnets. The only seabird species analysed was the critically endangered Balearic shearwater (Puffinus mauretanicus), which showed a high risk to longlines in the Bay of Biscay.
Where quantitative data were available for populations size and bycatch in e.g, ICES reports, the impact of fisheries bycatch was estimated quantitively by estimating reference points and by comparing them to total bycatch mortalities. This quantitative assessment was completed for two cetaceans and two elasmobranch species that were also included in the previous step. Bycatch impact for the common dolphin in the Northeast Atlantic and for harbour porpoise in Irish waters was found to be unsustainable, as current bycatch mortalities are above the “allowable” capture limits in both cases. For spurdog and undulate ray in the Northeast Atlantic and English Channel, respectively, the fishing pressure on the stock was sustainable, as it is below the harvest rate of Maximum Sustainable Yield (MSY). Reference points for seabirds were also estimated, but no comparison with bycatch mortality could be done due to lack of data. Additionally, quantitative assessments were produced for grey seal in the North Sea and loggerhead turtle in the Mediterranean (despite not being included in the previous step), where current bycatch rates were evaluated to be sustainable.
Specific analyses were conducted for the Baltic Sea harbour porpoise with previously unused bycatch data from gillnets. Bycatch was modelled to estimate total bycatch mortality, addressing several objectives at once. On one hand, estimated total bycatch was compared with reference points, which showed that the current bycatch level was unsustainable for the population. Secondly, estimated total bycatch was compared with the results provided by previous simpler extrapolations, demonstrating that the later should not be applied when the fishery is heterogeneous due to the potential to provide biased estimates.
Overall, the qualitative approaches are commonly used as a tool to identify species that are minimally affected, so the more intensive analysed are limited to high-risk species. Here, most species analysed showed-medium-high risk and therefore, all of them should have been analysed in further steps. However, many of those species lack the necessary information to conduct a quantitative assessment, and as result, the impact of bycatch at population level could only be evaluated, as seen above, for a few of them. This highlights the need for more exhaustive data collection and further research that could answer to the requirements of the EBFM.
More information about the SEAwise project can be found at https://seawiseproject.org/
