Abstract
Marine mammals and fisheries often target the same resources, which can lead to operational interactions. Potential consequences of operational interaction include entanglements and damaged or reduced catches but also enhanced foraging opportunities, which can attract marine mammals to fishing vessels. Responsible fisheries management therefore requires detailed knowledge of the impact of these interactions. In northern Norway, killer whales Orcinus orca are frequently observed in association with large herring aggregations during the winter. We use a combination of biotelemetry and fisheries data to study if, to what extent and at what distances killer whales are attracted to fishing activity. Twenty-five satellite transmitters were deployed on killer whales at herring overwintering and spawning grounds, often near fishing vessels. Over 50% of the killer whale core areas of high usage overlapped with the fisheries core areas, and individual whales spent up to 34% of their time close to active fishing. We used a 3-state hidden Markov model to assess whether killer whale movements were biased towards fishing activities. Of the overall whale movements, 15% (CI = 11-21%) were biased towards fishing activities, with marked heterogeneity among individuals (0-57%). During periods of active fishing, whale movements were biased towards fishing events 44% (CI = 24-66%) of the time, with individual percentages ranging from 0 to 79%. Whales were more likely to be attracted when they were within 20 km. This information can be used in fishery management to consider potential consequences for fishers and whales.
Highlights
Commercial fisheries are present in all the world’s oceans and can affect marine wildlife and ecosystems in various ways (Botsford 1997)
The 11 killer whales instrumented during the first period accounted for 5465 hourly locations, and the 14 instrumented animals during the second period yielded 14 791 hourly locations
This study provided novel insight into fine-scale interactions between killer whales and herring fisheries in northern Norway
Summary
Commercial fisheries are present in all the world’s oceans and can affect marine wildlife and ecosystems in various ways (Botsford 1997) Marine top predators, such as marine mammals, seabirds, sharks and sea turtles, often inhabit the same regions and share resources with a variety of fisheries. Mar Ecol Prog Ser 652: 1–13, 2020 activities have caused increased operational interactions between fisheries and marine top predators (Read et al 2006, Read 2008, Northridge et al 2017) Consequences of these interactions can be neutral (no effect), positive or negative for either the animals, the fisheries or both. The foraging benefits near fishing activity can provide long-term effects for the killer whale population, such as increased calving rate (Tixier et al 2015) These effects can cascade through the ecosystem in which the killer whales are the top predator. Studying the interaction between fisheries and marine mammals requires finescale animal movement data, which can be used to detect changes in the movement that may be induced by the fisheries (Mathias et al 2012, Straley et al.2014, Towers et al 2019, Richard et al 2020)
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