Movements and dive behaviour of a toothfish-depredating killer and sperm whale

Abstract

Depredation of demersal longlines by killer and sperm whales is a widespread behaviour that impacts fisheries and whale populations. To better understand how depredating whales behave in response to fishing activity, we deployed satellite-linked location and dive-profile tags on a sperm and killer whale that were depredating Patagonian toothfish from commercial longlines off South Georgia. The sperm and killer whale followed one fishing vessel for >180 km and >300 km and repeatedly depredated when longlines were being retrieved over periods of 6 and 7 d, respectively. Their behaviours were also sometimes correlated with the depths and locations of deployed gear. They both dove significantly deeper and faster when depredating compared with when foraging naturally. The killer whale dove >750 m on five occasions while depredating (maximum: 1087 m), but these deep dives were always followed by long periods (3.9–4.6 h) of shallow (<100 m) diving. We hypothesize that energetically and physiologically costly dive behaviour while depredating is driven by intra- and inter-specific competition due to the limited availability of this abundant resource.

Fear of Killer Whales Drives Extreme Synchrony in Deep Diving Beaked Whales

“…Although they can take fish from fishing lines up to 1000 m depth 42 , biologging data suggest that they spend most of their time at <20 m depth 41 . Further, the protracted and intense pack hunting effort required for killer whales to subdue cetaceans 21 , and their restricted ~10 min dive duration 41 strongly suggest that they can only hunt mammals at or near the sea-surface.…”

Killer whales are attracted to herring fishing vessels

“…The start of fishing activity triggered a change of behaviour, and killer whale movements were biased towards herring purse seiners, suggesting that killer whales were sometimes attracted to fishing activity. Killer whales are attracted to fisheries around the world (Luque et al 2006, Peterson et al 2013, Escalle et al 2015, Söffker et al 2015, Towers et al 2019, because fishing activities offer beneficial foraging opportunities (Tixier et al 2015, Esteban et al 2016. The fishing events in our study aggregated large quantities of herring at the surface in purse seine nets.…”

“…Top predators may benefit from fisheries, as fishing activity may provide good foraging opportunities by immobilizing or aggregating prey or by relocating prey to the surface. Predators can either take fish that have been captured by the fishers (depredation) or target discarded or escaped fish or fish that aggregate around a fishing net (Söffker et al 2015, Tixier et al 2019. As a result, some species are attracted to fishing activity.…”

“…However, operational interactions can also have adverse consequences. Fisheries may lose revenue due to depredation or competition, lost or damaged fishing gear or in creased operation time (Kock et al 2006, Güçlüsoy 2008, Tixier et al 2019. A wide range of seabirds, sea turtles, sharks and marine mammals die in various fishing gears around the world as a result of operational interactions (Moore et al 2009, Abdul qader et al 2017, Northridge et al 2017, Carretta et al 2019.…”

“…Little is known about the mechanisms behind the interaction between fisheries and marine mammals and how animal behaviour is influenced by the presence of fishery activity (Richard et al 2020). 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.…”