Monitoring and mitigating cetacean bycatch and entanglement in fishing gear, with a focus on humpback whales (Megaptera novaeangliae) in Iceland

• Main Author: Basran, Charla
• Other Authors: Marianne H. Rasmussen, Líf- og umhverfisvísindadeild (HÍ), Faculty of Life and Environmental Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Iceland, School of Engineering and Natural Sciences, Faculty of Life and Environmental Sciences 2021
• Subjects: Iðnaður; Hvalir; Hnúfubakur; Norður-heimskautið; Veiðarfæri; Sjávarlíffræði; Doktorsritgerðir; Arctic; New Zealand; Humpback Whale; Iceland; Megaptera novaeangliae
• Online Access: https://hdl.handle.net/20.500.11815/2655

As industries expand in sub-Arctic and Arctic waters there are increased conflicts between these industries and cetaceans. The aim of this work was to investigate the issue of cetacean bycatch/entanglement in Iceland, with a particular focus on the understudied issue of humpback whale entanglement. Bycatch/entanglement in fishing gear is a serious threat to cetaceans, as well as a detriment to fisheries, and mandatory bycatch reporting in logbooks could be of immense scientific value; however cetacean bycatch is considered greatly under-reported. I determined that cetacean bycatch was significantly under-reported in fisher logbooks in nearly all (7/8) trawl, net, and hook and line fisheries that could be examined in New Zealand, Iceland, and the USA when compared to observer data. The cod gillnets in Iceland had the biggest difference between fisher and observer catch per unit effort (with the observer estimate being 270 times greater). Large whale entanglements only accounted for an average of 12% of reported incidents, supporting the idea that these events are the most under-reported. Through scar-based analysis I determined that at least 25% of Icelandic humpback whales have been entangled and this is occurring at a rate of 2% annually. I tested acoustic alarms as an entanglement mitigation tool and through experimental exposure trials it was determined that humpback whales responded to the “whale pinger” by significantly increasing their speed and decreasing their surface feeding. These pingers were also fitted on a capelin purse seine net and I observed that humpback whales still entered the net from the bottom, but they were able to escape through a pinger-free opening. Using anonymous questionnaires and interviews, I gained further insight into entanglement from the fishers’ perspective. Humpback whales were the most commonly reported species that was witnessed entangled, and this occurred most often in capelin purse seines. Damage and losses due to whale collisions with gear was reported to cost fishers ...