Using line acceleration to measure false killer whale (Pseudorca crassidens) click and whistle source levels during pelagic longline depredation

Abstract

False killer whales (Pseudorca crassidens) depredate pelagic longlines in offshore Hawaiian waters. On January 28, 2015 a depredation event was recorded 14 m from an integrated GoPro camera, hydrophone, and accelerometer, revealing that false killer whales depredate bait and generate clicks and whistles under good visibility conditions. The act of plucking bait off a hook generated a distinctive 15 Hz line vibration. Two similar line vibrations detected at earlier times permitted the animal's range and thus signal source levels to be estimated over a 25-min window. Peak power spectral density source levels for whistles (4-8 kHz) were estimated to be between 115 and 130 dB re 1 μPa/Hz @ 1 m. Echolocation click source levels over 17-32 kHz bandwidth reached 205 dB re 1 μPa @ 1 m pk-pk, or 190 dB re 1 μPa @ 1 m (root-mean-square). Predicted detection ranges of the most intense whistles are 10 to 25 km at respective sea states of 4 and 1, with click detection ranges being 5 times smaller than whistles. These detection range analyses provide insight into how passive acoustic monitoring might be used to both quantify and avoid depredation encounters.

When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence

“…Underwater cameras and, more recently, accelerometer devices, have been used as ways to detect cryptic depredation events but unlike acoustics, usually cover small proportions of gear and can hardly be used to fully quantify the conflict unless extensively deployed (IOTC, 2007;Lyle et al, 2016;Mathias, Thode, Straley, & Folkert, 2009;Richard et al, 2020;Thode et al, 2016). Underwater cameras can also help identify the depredating species.…”

“…Electronic monitoring cameras on‐board vessels, which have recently emerged to replace or supplement observers in fisheries (Bicknell, Godley, Sheehan, Votier, & Witt, 2016), can potentially improve the monitoring of depredation by recording partially depredated catches, damaged gear and/or by‐catch of depredating species in data poor fisheries. Acoustic recorders can be effective at detecting, and even quantifying, unseen depredation by odontocetes, as evidenced by studies on sperm whales (Mathias, Thode, Straley, & Andrews, 2013; Thode et al, 2015; Thode, Wild, Mathias, Straley, & Lunsford, 2014) and false killer whales (Hernandez‐Milian et al, 2008; McPherson et al, 2004) depredating on longline catches. Underwater cameras and, more recently, accelerometer devices, have been used as ways to detect cryptic depredation events but unlike acoustics, usually cover small proportions of gear and can hardly be used to fully quantify the conflict unless extensively deployed (IOTC, 2007; Lyle et al, 2016; Mathias, Thode, Straley, & Folkert, 2009; Richard et al, 2020; Thode et al, 2016).…”

“…Despite efforts to improve these methods, they remain likely to underestimate catch losses, because not accounting for undetected events (e.g. depredation occurring at great depths- Richard et al, 2020;Towers et al, 2019), nor hidden processes further reducing catches indirectly such as predators taking the bait (Thode et al, 2016) and/or scaring the catch by their presence around the gear (Moore, 2003;Nichols, Eldredge, & Cadrin, 2014;Wickens et al, 1992). (43% of all depredated fisheries) and was the most prevalent in the artisanal sector (54% of depredated artisanal fisheries), followed by the commercial (39%) and recreational (38%) sectors.…”

The Challenges of Managing Depredation and Bycatch of Toothed Whales in Pelagic Longline Fisheries: Two U.S. Case Studies

“…The relative rate of depredation of bait vs. catch is unknown and likely varies among fisheries, although small cetaceans are likely to engage in this behavior (Gilman et al, 2007a;Werner et al, 2015). Recent video and acoustic evidence confirmed that false killer whales depredate pelagic longline bait in the daytime using both visual and audio cues (Thode et al, 2016). Garrison (2007) also showed lower bycatch rates of Risso's dolphins in the U.S. East Coast pelagic longline fishery when fish bait was used in place of squid bait.…”

Killer whale (Orcinus orca) interactions with blue-eye trevalla (Hyperoglyphe antarctica) longline fisheries

“…Firstly, the issue often results in substantial financial losses to the fishers. The amount of fish or bait odontocetes removed from longlines imposes increased fishing time and displacements to achieve quotas and/or to implement strategies of avoidance ( Peterson et al, 2014 ; Thode et al, 2016 ). Secondly, the amount of depredated fish is often inaccurately assessed or unaccounted when setting catch limits, resulting in biased fish stock assessments ( Peterson et al, 2013 ; Peterson & Hanselman, 2017 ; Hanselman, Pyper & Peterson, 2018 ).…”