SEAwise Report on changes in bycatch of fish, seabirds, reptiles and mammals in response to spatial management
Creators: name: Astarloa, Amaia
name: Bastardie, Francois
name: Batts, Luke
name: Binch, Logan
name: Bitetto, Isabella
name: Bluemel, Joanna K.
name: Carbonara, Pierluigi
name: Chatzispyrou, Archontia
name: Couce, Elena
name: Fotiadis, Nikolaos
name: García-Barón, Isabel
name: Kavadas, Stefanos
name: Lefkaditou, Evgenia
name: Louzao, Maite
name: Maina, Irida
name: Neglia, Cosmidano
name: Poos, J.J. (Jan Jaap)
name: Reid, David
name: Romagnonia, Giovanni
name: Spedicato, Maria-Teresa
name: van de Wolfshaar, Karen
name: Vassilopoulou, Celia
name: Zupa, Walter
name: Rindorf, Anna
Publisher: name: Technical University of Denmark
Year: 2025
Subjects: classificationCode: 410401
subject: Conservation and biodiversity
classificationCode: 410402
subject: Environmental assessment and monitoring
classificationCode: 410404
subject: Environmental management

description: 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. Bycatch of protected, endangered and threatened (PET) species is a key issue in the implementation of ecosystem-based fisheries management (EBFM). A suggested measure to reduce these is area and temporal closures, but the efficiency of these remains unclear, as spatial closures, rather than reducing total fishing effort, simply redistribute effort away from some areas/times while concentrating it in others. In this context, this SEAwise report evaluates the effects of applying different spatial management measures (i.e., fishing restrictions) on the bycatch of PET species. Restricting fishing activities can lead to bycatch reduction -if the area restricted hosts the species of interest-, to a bycatch increase -if the effort is redistributed to areas with high abundance of the species of interest- or produce no change. To answer that question, this report assesses the effect of this effort displacement by comparing the situation in relation to bycatch on the base scenario (current measures in place) with that on multiple scenarios hosting different fishing restrictions. By these means, this work aims to evaluate how effective are the multiple management measures tested here for reducing the bycatch of PET species. Management scenarios as well as fishing effort displacement were developed and modelled under task 5.5 (Bastardie et al. 2023), and used in this study to estimate potential changes in bycatch. These changes were mostly evaluated using the Productivity-Susceptibility Analysis (PSA), which is a semi-quantitative approach that evaluates bycatch in terms of risk using fishing effort and species distribution as the necessary data for performing more quantitative assessments were not available. Changes in bycatch risk using PSA were reported for 11 fish species, 4 cetaceans and 1 seabird. 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 bottlenose dolphin (Tursiops truncatus). In both case studies, gillnets were restricted from those MPAs hosting birds, cetaceans or pinnipeds listed in EU Directives. Across the Irish waters study region overall changes in risk were negligible between scenarios, although some localised effects were observed, while in the Bay of Biscay netters restriction produced an increase in the bycatch risk for common dolphin. Cartilaginous fishes were assessed in the Mediterranean Sea. In the South Adriatic, the implication of four different management scenarios on bycatch of longnose spurdog (Squalus Blainville) were tested. A reduction of bycatch risk was observed for otter trawls and longlines when applying the most restrictive scenario that combined multiple closures. In the Eastern Ionian Sea, the changes in the bycatch of bull ray (Aetomylaeus bovinus) were explored after restricting bottom trawls from MPAs. Here, the proposed bottom trawl ban was predicted to increase the fleet’s effort in an area where the species shows high preference, potentially increasing bull ray catches. 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.), spurdog (Squalus acanthias), tope (Galeorhinus galeus), spotted ray (Raja montagui), undulate ray (Raja undulata) and starry ray (Amblyraja radiata), John dory (Zeus faber), Atlantic wolffish (Anarhichas lupus) and Atlantic halibut (Hippoglossus hippoglossus). For these species, different fishing restrictions were tested on current species distribution but also on their potential distribution under RCP4.5 climate change scenario. Of the nine fish species and all gear types assessed, only spotted ray showed a change from medium to low risk after applying the fishing restrictions and the future species distribution, suggestion that a combination of climate change and spatial management impacts the final risk scores. The only seabird species analysed was the critically endangered Balearic shearwater (Puffinus mauretanicus), which showed no change in bycatch risk after applying the restrictions to netters and demersal trawlers in the Bay of Biscay. In the North Sea, the quantitative and dynamic approach OSMOSE was used to evaluate changes in bycatch. Although this analysis was developed under task 5.5, it was also included here to show how the effort redistribution and effort reduction of bottom trawlers affected to the bycatch of two PET species: spurdog (Squalus acanthias) and thornback ray (Raja clavata). Results seemed to indicate a positive impact of the measures on the two species assessed, especially when reducing fishing effort. The quantitative dynamic approaches provide more accurate decision support for effective management measure proposals than semi-quantitative risk assessment approaches. However, they are also very data demanding, which prevents from working with data poor species. In order to provide accurate estimates of the any potentially beneficial effects of closed areas, further data collection and research is needed.Read more about the SEAwise project at www.seawiseproject.org