ArticlePublisher preview available

Boat disturbance affects the acoustic behaviour of dolphins engaged in a rare foraging cooperation with fishers

Animal Conservation

January 2021
24(4)

DOI:10.1111/acv.12667

Authors:

Andrea Yanina Pellegrini

Universidade Federal de Santa Catarina

Bianca Romeu

Universidade Federal de Santa Catarina

Fábio Gonçalves Daura-Jorge

Universidade Federal de Santa Catarina

Acoustic behaviour is a key component of specialized foraging tactics for many aquatic species, especially cetaceans. However, in recent decades the natural environment has been increasingly exposed to a variety of anthropogenic noise sources, with the potential to impact natural foraging specializations dependent on acoustic communication. Here we evaluated whether boat noise has the potential to impact a rare foraging tactic used by individuals from a small population of the vulnerable Lahille’s bottlenose dolphin (Tursiops truncatus gephyreus) specialized in cooperation with artisanal fishers in southern Brazil. We tested whether the presence of boats changed the acoustic behaviour of dolphins when engaged in this cooperative foraging. We found that whistles and echolocation click rates were lower when boats were present, suggesting that cooperative foraging may potentially be reduced or interrupted by the presence of boats. Whistle parameters changed in response to the number, type and speed of boats, indicating a behavioural change and acoustic masking. Locally, our results reinforce the need for boat traffic regulations to minimize their impacts on these endangered dolphins and their rare cooperative tactic. From a broad perspective, we demonstrate how nonlethal impacts such as vessel disturbance can manifest subtle changes in animals’ natural behaviour and, in this case, present an insidious threat to a unique foraging specialization.

(a) Map of the study area with the main fishing sites where the dolphin–fisher interaction routinely occurs (yellow circles). In red is the home range of the dolphins that tend to forage independent of fishers; in blue, the home range of dolphins that tend to forage with fishers. (b) Inset showing in the Praia da Tesoura, the main cooperative site, the fixed point where the hydrophone was positioned and data were sampled (yellow circle) and the limits of the cooperative zone and the influence zone. (c) Inset showing the limits of the cooperative zone, the fishers’ line, the hydrophone position and a dolphin in interaction. [Colour figure can be viewed at zslpublications.onlinelibrary.wiley.com.]

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Mean and standard deviation of dolphin whistles (a) and clicks rates (b) in the absence (No boat) and presence of boats (Boat). Rates were measures as the absolute amount of sounds per individual per minute (n° of sounds ind⁻¹ min⁻¹).

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Predictions of the selected models, (a)–(i), indicating the effect of the explanatory variables with significant influence on the acoustic parameters of whistles. The values predicted by the model are represented in lines or points. Bars and shaded areas represent the 95% confidence intervals of predicted values. In (g) to (i), red are the predictions and the confidence intervals for boat absence, while blue for boat presence. The number of boats was categorized as either one (One) or more than one (>1). The types of boats were fishing (F), jet‐ski (JS), speedboat (S). The velocity categories considered were slow (S), medium (M) and fast (F). [Colour figure can be viewed at zslpublications.onlinelibrary.wiley.com.]

…

Predictions of selected models, (a)–(d), indicating the effect of explanatory variables with influence on the emission rates of whistles and echolocation clicks in the presence of boats. The values predicted by the model are represented in lines or points. Bars and shaded areas represent the 95% confidence interval of predicted values. In (d), red represents the predictions and the confidence interval for boat absence, while blue represents for boat presence. Boat number was only categorized as one (One) or more than one (>1). The types of boats were fishing (F), jet‐ski (JS), motorboat (M). The velocity categories considered were (S) slow, (M) medium and (F) fast. Rates were measures as the absolute amount of sounds per individual per minute (n° of sounds ind⁻¹ min⁻¹). [Colour figure can be viewed at zslpublications.onlinelibrary.wiley.com.]

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Boat disturbance affects the acoustic behaviour of

dolphins engaged in a rare foraging cooperation with

ﬁshers

A. Y. Pellegrini

, B. Romeu

, S. N. Ingram

& F. G. Daura-Jorge

1 Programa de P

os-graduac

ao em Ecologia, Departamento de Ecologia e Zoologia, Universidade Federal de Santa Catarina. Campus

Universit

ario, Florian

opolis, SC, Brazil

2 School of Biological and Marine Sciences, University of Plymouth, Plymouth, United Kingdom

Keywords

acoustic behaviour; anthropogenic noise;

dolphin–ﬁshers interaction; Tursiops

truncatus gephyreus; vessel disturbance.

Correspondence

F

abio G. Daura-Jorge, Programa de P

os-

graduac

ao em Ecologia, Departamento de

Ecologia e Zoologia, Universidade Federal de

Santa Catarina. Campus Universit

ario, Caixa

Postal 5102, 88040-970 Florian

opolis, SC,

Brazil.

Email: daura.jorge@ufsc.br

Editor: Sadie Ryan

Associate Editor: Elissa Cameron

Received 17 February 2020; accepted 08

December 2020

doi:10.1111/acv.12667

Abstract

Acoustic behaviour is a key component of specialized foraging tactics for many

aquatic species, especially cetaceans. However, in recent decades the natural envi-

ronment has been increasingly exposed to a variety of anthropogenic noise sources,

with the potential to impact natural foraging specializations dependent on acoustic

communication. Here we evaluated whether boat noise has the potential to impact

a rare foraging tactic used by individuals from a small population of the vulnerable

Lahille’s bottlenose dolphin (Tursiops truncatus gephyreus) specialized in coopera-

tion with artisanal ﬁshers in southern Brazil. We tested whether the presence of

boats changed the acoustic behaviour of dolphins when engaged in this cooperative

foraging. We found that whistles and echolocation click rates were lower when

boats were present, suggesting that cooperative foraging may potentially be reduced

or interrupted by the presence of boats. Whistle parameters changed in response to

the number, type and speed of boats, indicating a behavioural change and acoustic

masking. Locally, our results reinforce the need for boat trafﬁc regulations to mini-

mize their impacts on these endangered dolphins and their rare cooperative tactic.

From a broad perspective, we demonstrate how nonlethal impacts such as vessel

disturbance can manifest subtle changes in animals’natural behaviour and, in this

case, present an insidious threat to a unique foraging specialization.

Introduction

The expansion of human activities in coastal waters in recent

decades has increased the exposure of coastal ecosystems

and cetacean populations to a variety of anthropogenic dis-

turbances (Kelly, Glegg & Speedie, 2004; Sini et al., 2005;

Neumann et al., 2015). Among them, the increase in boat

trafﬁc represents one of the main threats, interfering with

vital animal activities such as foraging, reproduction and

socialization (Reeves et al., 2003; La Manna et al., 2010).

For instance, nonlethal boat disturbance has been shown to

cause behavioural response in cetaceans, such as changes in

ranging patterns and habitat use (Nowacek, Wells & Solow,

2001), in respiratory intervals (Nowacek, Wells & Solow,

2001), in group composition and cohesion (Do Valle &

Melo, 2006) and in foraging activities (Christiansen, Ras-

mussen & Lusseau, 2013; Pirotta et al., 2015).

Motorized boats are likely one of the main sources of

noise in coastal waters (Buckstaff, 2004). They introduce

noise into the environment through cavitation, where air bub-

bles are generated and explode at the edge of the propeller

when rotating rapidly (Hatch & Wright, 2007). Cavitation

noise occupies a wide spectrum of frequencies, overlapping

with the frequency of most cetacean sounds, masking com-

munication (Jensen et al., 2009), interfering with group coor-

dination, mother–calf cohesion and the detection of predators

and prey in the environment (Lemon et al., 2006; Weilgart,

2007). Typically, dolphins use two types of sounds: whistles,

narrow-band and frequency-modulated signals used for com-

munication, individual recognition and group cohesion (Her-

man & Tavolga, 1980; Janik & Slater, 1998); and pulsed

sounds, including echolocation clicks, used mainly during

navigation, socializing and foraging (Au, 1993; Ridgway

et al., 2015). In order to compensate for noise and to main-

tain group communication, individuals may change the

amplitude, duration, repetition rate or frequency of their

sounds (May-Collado & Wartzok, 2008; Holt et al., 2009;

Papale et al., 2015). As expected, stronger reactions (includ-

ing surface and acoustic behavioural change) are reported in

response to boats travelling at higher speeds and with fre-

quent course changes (Sini et al., 2005; Lusseau, 2006; Jen-

sen et al., 2009; La Manna et al., 2013).

Animal Conservation 24 (2021) 613–625 ª2021 The Zoological Society of London 613

Animal Conservation. Print ISSN 1367-9430

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Nov 2018

Recent years have seen an increasing interest in individual behavioral variation. However, the implications of such variation for population dynamics are often unknown. We studied the dynamics of a bottlenose dolphin (Tursiops truncatus gephyreus) population from southern Brazil, where some individuals forage cooperatively with artisanal fishermen. We fitted mark‐recapture models to 10 yr of photo‐identification data to investigate the influence of this foraging specialization on dolphins’ population parameters, controlling for sex and ranging behavior. We estimated adult survival to be high (0.949 ± 0.015 SE), weakly influenced by home range size, sex or the frequency of interaction with fishermen. The slightly higher survival probability for individuals with smaller home ranges could stem from the benefits of reduced spatial requirements implied by the specialized foraging. Foraging also influenced the probability of resighting individuals, and there was no temporary or permanent emigration. Abundance fluctuated slightly over the years from 54 (95% CI = 49–59) to 60 (95% CI = 52–69) individuals, with no evident population trend. Despite such apparent population stability, we confirm this population remains small and geographically isolated which may threaten its viability and the viability of its unusual, localized foraging specialization. Our study also illustrates how accounting for individual variation can portray animal population dynamics more realistically.

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