Vocal Behaviour of a Bottlenose Dolphin Pod during a Deadly Bycatch Event in the Gulf of Catania, Ionian Sea

Abstract

Cetacean bycatch is increasing worldwide and poses a threat to the conservation of several delphinids. The bottlenose dolphin (Tursiops truncatus) is frequently involved in bycatch incidents, due to its coastal distribution and opportunistic behaviour. The acoustic behaviour of cetaceans during death-related events is a largely unexplored topic. During an acoustic monitoring survey of the bottlenose dolphin population inhabiting the Gulf of Catania (Ionian Sea), we documented the entangling and subsequent death of a sub-adult male in a fishing net. Here, we provide a detailed analysis of the vocal behaviour of the pod of bottlenose dolphins during the event. We identified a total of 720 vocalisations in a timespan of 138 min, including 436 signature whistles, 51 non-signature whistles, and 233 burst pulses. We recorded high vocal activity, with a peak characterised by emission rates of 36 signature whistles per minute and 70 burst pulses per minute. Although future studies are required, our results show massive vocal activity during net entangling, characterised by a significant emission of signature whistles and burst pulses, including bray series of gulps and squeaks. Therefore, we suggest that developing tools for automatically detecting the peaks of these sound types could be helpful in recognising bycatch events, in order to better quantify the impact of professional fishing on small cetaceans.

Probable signature whistle production in Atlantic white‐sided (Lagenorhynchus acutus) and short‐beaked common (Delphinus delphis) dolphins near Cape Cod, Massachusetts

“…Leveraging that signature whistles often occur in bouts (Janik & Sayigh, 2013), SIGID defines signature whistle types as whistles of similar contour having 75% or more occurrences within 1–10 s. These criteria are conservative, and application of SIGID on T. truncatus (four captive and seven wild, all with known signature whistles) correctly identified 8 of 11 signature whistles (Janik et al, 2013) with no false positives. To date, multiple studies have applied the SIGID method on other bottlenose dolphin populations and other delphinid species (Fearey et al, 2019; Gridley et al, 2014; Longden et al, 2020; Luís et al, 2016; Matsushiro et al, 2022; Panova et al, 2021; Papale et al, 2015; Rio et al, 2022; Terranova et al, 2022).…”

Initial results on the variation of whistle characteristics of bottlenose dolphins from two neighbouring regions of the Mediterranean Sea: Northern Ionian and Southern Adriatic Sea

“…The vocal repertoires of dolphins are also known to vary significantly between populations at macro-and-micro geographic scales (Hawkins, 2010;Papale et al, 2013;La Manna et al, 2020). Within the Mediterranean Sea, acoustic studies on dolphins have mostly been assessed by categorisation of whistle type characteristics (Dı ́az Lo ́pez, 2011; La Manna et al, 2017;La Manna et al, 2020;Corrias et al, 2021;Terranova et al, 2021;La Manna et al, 2022;Terranova et al, 2022;Pace et al, 2022). These studies have mainly focused on the identification of species presence, geographical variation in vocalisation types, the impact of boat traffic, dolphinfishery interactions, and whistle characteristics with bottlenose dolphins, being by far the most frequently studied species (Connor and Smolker, 1996;Boisseau, 2005; Dı ́az Lo ́pez and Shirai, 2010; La Manna et al, 2017).…”