Bycatch of marine mammals and seabirds: Occurrence and mitigation
Gillnet fisheries are generally considered environment-friendly, causing limited bottom-impact and generating high-quality fish. Nevertheless, gillnets are also associated with high risks of bycatch of non-target animals, including seabirds and marine mammals. To fulfil Denmark’s obligations with re...
| Main Authors: | , , , |
|---|---|
| Format: | Book |
| Language: | English |
| Published: |
DTU Aqua
2021
|
| Subjects: | |
| Online Access: | https://orbit.dtu.dk/en/publications/9992bda6-1f64-4e53-9985-710ec26d46ef https://backend.orbit.dtu.dk/ws/files/261340293/389_2021_Bycatch_of_marine_mammals_and_seabirds.pdf https://www.aqua.dtu.dk/-/media/institutter/aqua/publikationer/rapporter-352-400/389-2021-bycatch-of-marine-mammals-and-seabirds.pdf |
| Summary: | Gillnet fisheries are generally considered environment-friendly, causing limited bottom-impact and generating high-quality fish. Nevertheless, gillnets are also associated with high risks of bycatch of non-target animals, including seabirds and marine mammals. To fulfil Denmark’s obligations with regards to European legislations and other international agreements, the present report assesses for the first time the magnitude and the spatiotemporal distribution of marine mammal and seabird bycatch in Danish gillnet fisheries and proposes solutions to mitigate this bycatch. Bycatch of seabirds and marine mammals in gillnets was estimated using electronic monitoring (EM) with videos on a sample of the Danish commercial gillnet fleet (Section 2). EM systems combined video data and fine-scale tracking data, allowing to record and analyse a census of the fishing activity of 16 vessels, including bycatches of vulnerable species, between 2010 and 2016, in the North Sea, Skagerrak, Kattegat, Belt Seas and Western Baltic Sea. Monitoring focused on seabirds, harbour porpoise and seals for which it was possible to document the temporal and spatial distribution of bycatches in gillnets in areas where data had been collected and to estimate mean quarterly bycatch rates in areas where enough EM data were available, i.e. the North Sea, the Skagerrak, the Øresund and the Belt Sea. Based on these estimates, bycatch mortality at fleet-level was calculated as the product of the estimated bycatch rates and the total fleet effort, for each area and per quarter. This work revealed important seasonal variations in bycatch rates within and between fishing areas for all the considered species. Notably, more than half of all seabird bycatches occurred in quarters 1 and 4 in the Western Baltic Sea, with a mean yearly estimate of 3,249 bycatches (95% CI: 1,439-5,759). Harbour porpoises and seals were generally more impacted by gillnet fishing in quarter 3, totalling on average 2,722 porpoise bycatches per year (95% CI: 1,323-4,518) and 890 ... |
|---|