Article

Behavioral Responses of Bottlenose Dolphins, Tursiops truncatus, to Gillnets and Acoustic Alarms

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Along the east coast of the United States, by-catches of bottlenose dolphins, Tursiops truncatus, in gillnet fisheries exceed removal levels set under the US Marine Mammal Protection Act. One measure proposed to reduce this mortality is the use of acoustic alarms, or pingers, which have proven effective in reducing by-catches of other small cetaceans, but have not been tested with bottlenose dolphins. We examined the responses of bottlenose dolphins to a commercial gillnet equipped with functional (active) and non-functional (control) Dukane NetMark® 1000 alarms near Fort Macon, NC. Between 5 April and 10 May 2001 we used a theodolite to track 59 groups of dolphins around the net. Choice of treatment was random each day and the two shore-based observers were unaware of whether alarms were active (13 days) or controls (9 days). There were no significant differences in the number of groups observed (P=0.315; 1−β=0.835) or in the closest observed approach to the net (P=0.307; 1−β=0.828) between treatments. However, dolphins entered a circular buffer approximately 100 m around the net more frequently with control than active alarms (P=0.015). We conclude that some dolphins responded to the alarms by avoiding the net, but caution that the potential efficacy of alarms is confounded by dolphin behavior. Most dolphins were aware of the net, regardless of the status of alarms, and some dolphins fed on fish in the net or discarded by the fishing vessel. We believe that it would be unwise to use pingers in these fisheries because of the limited behavioral responses we observed in our experiment. Furthermore, the responses we observed are likely to diminish or change over time as dolphins habituate or sensitize to these alarms. Further research is required to understand the behavior responsible for entanglement.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... However, there is limited information based on in situ observations of dolphin behaviour associated with trawling operations (Broadhurst 1998;Jaiteh et al. 2013Jaiteh et al. , 2014Wakefield et al. 2014Wakefield et al. , 2017. Most studies rely on surface observations near fishing vessels (Chilvers et al. 2003;Cox et al. 2004;Gonzalvo et al. 2008) or on reports of gear and catch damage that is attributed to dolphins (Fertl and Leatherwood 1997;Gazo et al. 2008;Goetz et al. 2014). ...
... Mitigation strategies to reduce dolphin interactions with fishing gear include the relocation of fishing effort (e.g., time and (or) area closures, depth limits; Fernández-Contreras et al. 2010;Goetz et al. 2014), gear modifications (e.g., bycatch reduction devices, herein BRDs; Cox et al. 2007;Wakefield et al. 2017), and the use of acoustic deterrents (herein pingers; Cox et al. 2004;Dawson et al. 2013;Hamer et al. 2012;Kraus et al. 1997). Pingers are active sound emitters used to alert individuals of the presence of fishing gear to avoid entanglement (e.g., cetacean interactions with gillnets; Dawson et al. 2013) and (or) to reduce cetacean echolocation capabilities in close proximity to fishing operations (e.g., depredation in longlines; Mooney et al. 2009). ...
... Pingers are active sound emitters used to alert individuals of the presence of fishing gear to avoid entanglement (e.g., cetacean interactions with gillnets; Dawson et al. 2013) and (or) to reduce cetacean echolocation capabilities in close proximity to fishing operations (e.g., depredation in longlines; Mooney et al. 2009). The effectiveness of pingers to mitigate cetacean depredation and bycatch has mostly been assessed for passive fishing methods like gillnets and longlines (Carretta and Barlow 2011;Cox et al. 2004;Dawson et al. 2013;Hamer et al. 2012;Waples et al. 2013). A number of experimental studies have found that pingers can be an effective measure to reduce depredation, gear damage, and cetacean bycatch in these fisheries (Barlow and Cameron 2003;Brotons et al. 2008;Cox et al. 2004;Gazo et al. 2008;Kraus et al. 1997;Waples et al. 2013). ...
Article
An improved understanding of interaction dynamics between dolphins and trawlers is essential for improving bycatch mitigation strategies. In-situ observations using video at increasing distances from the net opening during 50 commercial fish trawls, recorded 5908 common bottlenose dolphin (Tursiops truncatus (Montagu, 1821)) interactions and provided details on their duration, depredation rates, and behaviours. Dolphin interactions with trawls were very common (98% of day-trawls, 118 ± 16 interactions per trawl), with durations and prey consumption positively correlated with the distances ventured into the net. Acoustic deterrents (pingers) had no effect on interaction numbers or durations. Based on in-situ observations, the factors that contribute toward dolphin bycatch in demersal fish trawls were likely associated with (i) risky dolphin behaviour (i.e., entering net during hauling, residing deep within trawl for extended periods or social aggression) and (or) (ii) instability of fishing gear resulting in entrapment. Given the high level of dolphin attendance during most day-trawls, mitigation strategies that focus on improving and monitoring the stability of trawl gear would be more effective than current acoustic deterrent devices aimed at modifying dolphin behaviour.
... Similarly, studies on different dolphin, porpoise, and beaked whale species have reported optimistic results of bycatch reduction by pingers (Carretta et al., 2008;Gearin et al., 2000;Mangel et al., 2013;Palka et al., 2008). However, for the common bottlenose dolphin (Tursiops truncatus), a species with a wide behavioral diversity, the success of the pingers as deterrents is controversial (Buscaino et al., 2009;Cox et al., 2003). ...
... It has been suggested that the reduced click train detections in the vicinity of an active pinger were caused by a reduction in vocalizations rather than the dolphins leaving the area (Cox et al., 2003;Kyhn et al., 2015;Leeney et al., 2007). On the other hand, the sound of a pinger may stimulate a dolphin to start echolocation or echolocate at a higher rate (Koschinski et al., 2006). ...
... Bottlenose dolphins, however, are known to be much bolder than franciscanas and are even involved in depredation (e.g., Buscaino et al., 2009). The Netmark 1000 pinger used in the experiment by Cox et al. (2003) transmitted 10 kHz pings with fixed 4 s intervals, whereas the experimental Banana Pinger in our study produced several slightly varying multiharmonic, frequency modulated sounds with semirandomized 4-12 s intervals (Omeyer et al., 2020), a strategy believed to reduce possible habituation effects. On the other hand, Amano et al. (2017) observed possible habituation in finless porpoises (Neophocoena asiaorientalis) to an AQUAmark100 pinger (Aquatec Subsea Ltd., Basingstoke, UK), that also transmits different multiharmonic, frequency modulated sounds with 5-30 s semirandom intervals, after 4-5 months from the start of the experiment. ...
Article
The franciscana (Pontoporia blainvillei) is the most endangered dolphin in the western South Atlantic Ocean due to bycatch. Our goal was to test the efficiency of a likely "seal safe" pinger (Banana Pinger, Fishtek Marine Ltd.) to ward off fran-ciscanas, as well as investigating possible side effects of habit-uation and habitat exclusion. We deployed the pinger within a grid of click detectors (C-POD, Chelonia Ltd.) in Babitonga Bay, southern Brazil, and the narrow band high frequency sonar click trains were used as a proxy for presence of the franciscanas and response to the pinger. The presence of franciscanas next to the pinger and at 100 m away decreased by 19.4% and 15.4%, respectively, when the pinger was switched on, indicating that the franciscanas avoided the area of the pinger. This avoidance response could not be seen at 400 m away. No habituation effect was noted at any distance. There was a slight gradual decrease in detections over the course of the study at all distances, which is probably related to seasonal variation in the population's habitat use, but this requires attention in future studies. The likely "seal safe" pinger sounds effectively warded off franciscanas and thus has the potential to reduce bycatch.
... However, as mentioned by , experimental conditions were in most cases difficult to control and conclusions drawn from some of the studies might be viewed as being rather limited. 8 In the course of the San Francisco-Oakland Bay Bridge Project, a variety of external and internal injuries, including reddening of the liver, rupture of the swim bladder, or internal bleedings were observed in one of the investigations (Caltrans 2001). In another study, no physical injuries were observed in caged sea trout within a radius of 400 m from the piling (estimated SL = 194 dB re 1 µPa peak to peak) in the harbour of Southampton during construction of the Red Funnel Terminal (Nedwell et al. 2003b). ...
... There is considerable variation in the frequency ranges used by commercial modems. For example, the AQUAModem produced by Aquatec produces a relatively low frequency (8)(9)(10)(11)(12) acoustic signal compared to the Hydroacoustic Modem S2C M 48/78 produced by EvoLogics GmbH . However, most encompass a range of around 18-40 kHz. ...
... It is also important to note that different cetacean species may respond differently to pingers. For instance, wild bottlenose dolphins did not show strong avoidance responses to a simulated gillnet equipped with Dukane NetMark 1000 pingers (8). A captive study on a single harbour porpoise (Phocoena phocoena) and a striped dolphin (Stenella coeruleoalba) demonstrated differential responses to pinger-type signals with the dolphin showing much weaker aversive responses than the porpoise (25). ...
... Similarly, studies on different dolphin, porpoise and beaked whale species have reported optimistic results of bycatch reduction by pingers (Carretta et al., 2008;Gearin et al., 2000;Mangel et al., 2013;. However, for the bottlenose dolphin, a species with a wide behavioral diversity, the success of the pingers as deterrents is controversial (Buscaino et al., 2009;Cox et al., 2003). ...
... It has been suggested that the reduced click train detections in the vicinity of an active pinger were caused by a reduction in vocalizations rather than the dolphins leaving the area (Cox et al., 2003;Kyhn et al., 2015;Leeney et al., 2007). On the other hand, the sound of a pinger may stimulate a dolphin to start echolocation or echolocate at a higher rate (Koschinski et al., 2006). ...
... Habituation was neither observed for P. phocoena during eight months of experiments with the same pinger . In contrast, Cox et al. (2003) using a theodolite to record bottlenose dolphin surfacing in the vicinity of a Netmark 1000 pinger (Dukane Corporation's Seacom Division, Illinois, USA), observed no significant deterrent effect after only 11 days of study, strongly suggesting that habituation occurred. Bottlenose dolphins, however, are known to be much bolder than franciscanas and are even involved in depredation (e.g., Buscaino et al., 2009). ...
Thesis
The franciscana dolphin (Pontoporia blainvillei) is a small cetacean critically endangered in Brazil, mainly due to the high number of incidental captures in fishing nets (bycatch). In Babitonga Bay, Santa Catarina, there is a resident population which is threatened by habitat degradation. The general objective of the study was to analyze the bioacoustics, behavior, distribution, habitat use and evaluate the effectiveness of an acoustic deterrent device ("pinger") for franciscanas, at different spatial and temporal scales, by means of a passive acoustic monitoring (PAM) device called C-POD (Chelonia Ltd., UK). The acoustic behavior of franciscana was analyzed comparatively in two habitats: estuary (Babitonga Bay: BB) and open sea (Itapirubá Beach: IB). The acoustic parameters of the click trains were analyzed and the minimum inter-click interval criterion <10ms was used as a proxy for foraging/feeding behavior. The main acoustic difference observed between habitats was related to the frequency spectrum, with a bandwidth of 17kHz in BB and 10kHz in IB. Also, the click repetition rate was almost 20% higher in the estuary. Both habitats studied presented a high feeding rate (BB = 68%; IB = 58%), higher in BB (p<0.001) and at night (p<0.001), for both habitats. To analyze the habitat use and distribution of franciscanas in Babitonga Bay, sixty C-PODs stations were implemented between June and December 2018. The generalized additive model selected to describe the relationship between the occurrence of franciscanas and several environmental variables incorporated 51% of the data variation. There is a diel pattern, where franciscanas remain in the areas of high occurrence mainly in the morning. The rest of the day, the population dispersed to other areas with different seasonal patterns. Franciscana avoid areas in periods when the presence of Guiana dolphins (Sotalia guianensis) is very intense and prefer areas with a flat bottom and sandy substrate, but during the evening and dawn they goes into areas of muddy bottom predominantly for feeding. The distribution was predominant in the innermost region of the estuary, without significant use of the bay's inlet channel. The distribution was wider in winter than in spring. The entire central region of the islands, between the north and south margins of the bay, represents an important feeding area. To test the deterrent effect of Banana pinger (Fishtek Marine Ltd, UK), as well as side effects of habituation and habitat exclusion, an exposure-controlled experiment was carried out with 5 C-PODs positioned at different distances from the pinger. The data indicate that the pinger effectively withdraw the franciscanas up to 100m, but not 400m, and therefore has the potential to reduce bycatch. No habituation effects were observed at any distance. There was a gradual decrease in the presence of franciscanas over the days, probably due seasonal variations in the population's habitat use but requires attention in future studies. C-PODs were used in an unprecedented way for the study of franciscanas and showed great potential to monitor the occurrence, behavior, distribution, and habitat use of the species. The results representing an important subsidy for management of the Babitonga Bay population and for the implementation of bycatch mitigation measures for the species in general. Available at: https://repositorio.ufsc.br/handle/123456789/227086?show=full
... However, as mentioned by , experimental conditions were in most cases difficult to control and conclusions drawn from some of the studies might be viewed as being rather limited. 8 In the course of the San Francisco-Oakland Bay Bridge Project, a variety of external and internal injuries, including reddening of the liver, rupture of the swim bladder, or internal bleedings were observed in one of the investigations (Caltrans 2001). In another study, no physical injuries were observed in caged sea trout within a radius of 400 m from the piling (estimated SL = 194 dB re 1 µPa peak to peak) in the harbour of Southampton during construction of the Red Funnel Terminal (Nedwell et al. 2003b). ...
... There is considerable variation in the frequency ranges used by commercial modems. For example, the AQUAModem produced by Aquatec produces a relatively low frequency (8)(9)(10)(11)(12) acoustic signal compared to the Hydroacoustic Modem S2C M 48/78 produced by EvoLogics GmbH . However, most encompass a range of around 18-40 kHz. ...
... It is also important to note that different cetacean species may respond differently to pingers. For instance, wild bottlenose dolphins did not show strong avoidance responses to a simulated gillnet equipped with Dukane NetMark 1000 pingers (8). A captive study on a single harbour porpoise (Phocoena phocoena) and a striped dolphin (Stenella coeruleoalba) demonstrated differential responses to pinger-type signals with the dolphin showing much weaker aversive responses than the porpoise (25). ...
... The reasons why marine mammals become entangled is not clear (Goodson A.D. 1996, Cox T.M. et al. 2003. Much of the research into bycatch mitigation has been focused on gear modification rather than understanding marine mammal fishing gear interactions underwater (Goodson A.D. 1996). ...
... Hence our understanding of why the bycatch events actually occur remains limited. It is clear however that marinemammals forage around or interact with nets regularly and only occasionally become fatally entangled in them (Cox T.M. et al. 2003). It may be that marine mammals are taking advantage of the availability of food in the fishing gear or in close proximity (Cox T.M. et al. 2003, Zollett E.A. & Rosenberg A.A. 2005 foraging either on the target or associated species. ...
... It is clear however that marinemammals forage around or interact with nets regularly and only occasionally become fatally entangled in them (Cox T.M. et al. 2003). It may be that marine mammals are taking advantage of the availability of food in the fishing gear or in close proximity (Cox T.M. et al. 2003, Zollett E.A. & Rosenberg A.A. 2005 foraging either on the target or associated species. It may be that juvenile animals are more susceptible to bycatch through curiosity or inexperience around fishing gear (Zollett E.A. & Rosenberg A.A. 2005). ...
... Acoustic deterrent devices or pingers, actively emit mid to high frequency signals (2.5 to 10 kHz) at a low intensity (< 150 dB, 1 µPa at 1 m) that "deter" marine mammals from approaching fishing gear. Pingers have been shown to reduce the bycatch of bottlenose dolphins (Cox et al., 2004), harbor porpoises (Phocaena phocaeana) and Franciscana (Pontoporia blainvillei) (Dawson et al., 2013;Mangel et al., 2013;Chladek et al., 2020) in gillnet fisheries. Pingers have also proven successful in reducing pinniped interactions with aquaculture operations and have reduced the bycatch of some (but not all) species of cetaceans in gillnets (Clay et al., 2019). ...
... For instance, pingers successfully reduced Franciscana bycatch in bottom-set gillnet fisheries, and common dolphins and beaked whale bycatch in drift gillnet operations. However, Cox et al. (2004) concluded that after the initial success in bottlenose dolphin bycatch reduction, these devices were unlikely to further reduce their bycatch rates in gillnets. ...
Article
Full-text available
Marine mammal interactions with fisheries, such as bycatch and depredation, are a common occurrence across commercial and small-scale fisheries. We conducted a systematic review to assess the management responses to marine mammal interactions with fisheries. We analyzed literature between 1995 and 2021 to measure research trends in studies on direct and indirect interactions for: (i) high and low to middle-income countries, (ii) fishery operations (commercial and small-scale), and (iii) taxonomic groups. Management responses were categorized using the framework described previously in peer-reviewed studies. Marine mammal bycatch remains a major conservation concern, followed by marine mammal depredation of fishing gear. A high proportion of studies concentrated on commercial fisheries in high-income countries, with an increase in small-scale fisheries in low to middle-income countries between 1999 and 2020. The insufficient understanding of the social dimensions of interactions and the inevitable uncertainties concerning animal and human behaviors are major challenges to effective management. Despite the key role of human behavior and socioeconomics, we found only eight articles that incorporate human dimensions in the management context. Integrating social dimensions of marine mammal interactions with fisheries could help in setting pragmatic conservation priorities based on enhanced understanding of critical knowledge gaps. An area-specific adaptive management framework could be an effective tool in reducing the risk to marine mammals from fisheries by coupling technical solutions with socio-economic and political interventions. We conclude that despite the vast body of literature on this subject, a “silver bullet” management solution to marine mammal interactions with fisheries does not yet exist.
... Una diversa categoria è quella degli acoustic deterrent devices (dispositivi acustici deterrenti), noti anche come pingers, utilizzati principalmente per ridurre le catture accidentali nelle reti (Kraus et al. 1997, Dawson et al. 2013. Questi dispositivi contribuiscono (almeno per un certo tempo) a ridurre le catture accidentali di piccoli cetacei nelle reti da posta, ma è noto che possono anche attrarre varie specie di mammiferi marini funzionando come "campane che annunciano la cena" (dinner bells; Cox et al. 2003, Carretta e Barlow 2011. ...
... Sfortunatamente, le ricerche tendono a interrompersi prima che i delfini (dopo una fase iniziale di spavento o cautela) si abituino a questi rumori, o addirittura imparino a riconoscerli e a interpretarli come segnali della presenza di una rete da depredare. Per quanto l'uso di dissuasori acustici possa contribuire a ridurre la depredazione nel periodo iniziale di utilizzo, in molti casi non sembra un modo efficace per impedire la depredazione sul medio e lungo termine (Cox et al. 2003, Santana-Garcon et al. 2018. Nei casi peggiori, i dissuasori possono trasformarsi in "attrattori" che contribuiscono a esacerbare il problema (con l'aggravante dell'investimento fatto dal pescatore per acquistare i dispositivi e installarli sulla rete). ...
Technical Report
Full-text available
Bearzi G., Bonizzoni S. 2018. Interazioni fra delfini e pesca in Adriatico settentrionale. Resoconto tecnico. Consulenza e supporto tecnico-logistico per Università degli Studi di Padova. 26 pp.
... Dolphins were described as notably intelligent animals by the fishers, able to distinguish between different engine sounds, sometimes following a specific vessel from the moment it leaves the port, a behaviour that has been described in the literature (Reeves et al. 2001). Fishers (< 5%) who had used pingers in the past as a means of mitigating conflicts stated that pingers were not effective after some (Cox et al. 2003, Kastelein et al. 2006, Brotons et al. 2008, Gazo et al. 2008, and in the long run, issues of habituation and the 'dinner-bell' effect do arise (Kraus 1999, Reeves et al. 2001, Cox et al. 2003. A small portion of fishers (7.2%) regarded themselves as 'intruders' into the animals' environment. ...
... Dolphins were described as notably intelligent animals by the fishers, able to distinguish between different engine sounds, sometimes following a specific vessel from the moment it leaves the port, a behaviour that has been described in the literature (Reeves et al. 2001). Fishers (< 5%) who had used pingers in the past as a means of mitigating conflicts stated that pingers were not effective after some (Cox et al. 2003, Kastelein et al. 2006, Brotons et al. 2008, Gazo et al. 2008, and in the long run, issues of habituation and the 'dinner-bell' effect do arise (Kraus 1999, Reeves et al. 2001, Cox et al. 2003. A small portion of fishers (7.2%) regarded themselves as 'intruders' into the animals' environment. ...
Article
Full-text available
Anecdotal information provided by local fishers is an invaluable tool in the study of marine mammal−fisheries interactions. This paper summarizes empirical and anecdotal information voluntarily provided by fishers during a survey monitoring the damage to coastal fisheries caused by dolphins. We visited 23 fishing harbours along the northern Aegean Sea coastline and monitored the fishing gear of 113 coastal fishers in order to identify the damage caused by dolphins. While we were monitoring the damage, the fishers voluntarily shared their general views on marine mammals and fisheries interactions, which were recorded and are presented here. The majority of fishers indicated that fishing gear, mesh size, depth and target species were important factors that determine depredation frequency and gear damage, whereas soaking time, time of day and season were not considered crucial. These findings provide useful insight in the study of dolphin−fishery interactions, especially for data-poor areas such as the northeastern Mediterranean Sea. The empirical knowledge of the fishers and their views is also important from an ethical perspective because, historically, dolphins in the Mediterranean had been culled and hunted for bounties for many years; even today, occasional deliberate dolphin killings are still recorded. Such information is required in the design of any management strategy that aims to minimize the conflicts with dolphins, thus preserving the fishers’ livelihood.
... A number of studies have shown that pingers reduced harbour porpoise (Phocoena phocoena) bycatch (Dawson et al. 2013;Kraus et al. 1997;Larsen and Eigaard 2014;Larsen et al. 2013;Palka et al. 2008;Reeves et al. 2013). However, results for bottlenose dolphins have been less clear with some research reporting significantly reduced interactions (Crosby et al. 2013;Gazo et al. 2008;Leeney et al. 2007;Mangel et al. 2013), while others showed no deterrent effect (Cox et al. 2003;Erbe et al. 2016). Pingers have been ineffective, or the results have been inconclusive, in deterring Hector's dolphin (Cephalorhynchus hectori), tucuxi (Sotalia fluviatilis), and other small coastal species such as the Australian snubfin (Orcaella heinsohni) and humpback dolphin (Sousa chinensis) (Berg Soto et al. 2013;Dawson and Lusseau 2005;Dawson and Slooten 2005). ...
... Developing 'responsive pingers' for gillnets, which only emit sounds in response to cetacean echolocations, may reduce the likelihood of pinger habituation for some species (Leeney et al. 2007;Waples et al. 2013). Bottlenose dolphins may become more sensitised to pingers, which could increase the mitigation effect on this species over time (Cox et al. 2003). With respect to trawl gear, some captive pinniped species became habituated to pingers on a simulated net and continued to depredate netted fish, while some dolphin species charged the netting despite pinger presence (Bowles and Anderson 2012). ...
Article
Full-text available
Fisheries bycatch is one of the biggest threats to marine mammal populations. A literature review was undertaken to provide a comprehensive assessment and synopsis of gear modifications and technical devices to reduce marine mammal bycatch in commercial trawl, purse seine, longline, gillnet and pot/trap fisheries. Successfully implemented mitigation measures include acoustic deterrent devices (pingers) which reduced the bycatch of some small cetacean species in gillnets, appropriately designed exclusion devices which reduced pinniped bycatch in some trawl fisheries, and various pot/trap guard designs that reduced marine mammal entrapment. However, substantial development and research of mitigation options is required to address the bycatch of a range of species in many fisheries. No reliably effective technical solutions to reduce small cetacean bycatch in trawl nets are available, although loud pingers have shown potential. There are currently no technical options that effectively reduce marine mammal interactions in longline fisheries, although development of catch and hook protection devices is promising. Solutions are also needed for species, particularly pinnipeds and small cetaceans, that are not deterred by pingers and continue to be caught in static gillnets. Large whale entanglements in static gear, particularly buoy lines for pots/traps, needs urgent attention although there is encouraging research on rope-less pot/trap systems and identification of rope colours that are more detectable to whale species. Future mitigation development and deployment requires rigorous scientific testing to determine if significant bycatch reduction has been achieved, as well as consideration of potentially conflicting mitigation outcomes if multiple species are impacted by a fishery.
... In one swim-with-dolphins programs (SWDP) without trainers' control on the animals, the presence of humans in the pool caused a decrease in play (Kyngdon, Minot, & Stafford, 2003) but this study was only conducted on three adult females. The non-significant decrease in play in our dolphins' group could be explained by the fact that the animals are habituated to these events that are frequent and thus do not impact their behavior (Connor & Smolker, 1985;Cox, Read, Swanner, Urian, & Waples, 2004) and/or by the fact that the free divers were the animals' familiar trainers, contrary to swimwith-dolphins programs where unfamiliar people enter the dolphins' habitat. ...
... The absence of modulations of the dolphins' social play could be due to their habituation to this frequent event and thus do not impact their behavior (Connor & Smolker, 1985;Cox et al., 2004). During our observation, California sea lions stimulated exploratory and agonistic behavior in dolphins but they did not seem to enhance dolphins' ...
Article
Social play varies among species and individuals and changes in frequency and duration during ontogeny. This type of play is modulated by environmental changes (e.g., resource availability). In captivity, cetaceans and their environment are managed by humans, and training sessions and/or public presentations punctuate the day as well as other frequent or occasional events. There is a lack of research on the effects of environmental events that occur in captivity and might affect dolphins' behavior. We studied the context in which nine bottlenose dolphins (Tursiops truncatus) played socially and the events that could potentially impact this social interaction. The dolphins' social play behavior was significantly more frequent and lasted longer in the morning than in the afternoon and was present before and after interactions with their trainers with a non-significant tendency to be more frequent before and after a training session than a public presentation. In an experimental paradigm using familiar environmental enrichment, our results demonstrated that environmental enrichment tended to increase social play duration whereas temporary noisy construction work around the pool and display of agonistic behaviors by members of the group significantly decreased it. These results contribute to better understand the social play distribution in captive bottlenose dolphins and the impact of different events within their daily lives. Since play decreases or disappears when animals are facing unfavorable conditions, the evaluation of social play may relate to the animals' current well-being. We suggest that social play has potential to become an indicator of bottlenose dolphins' current welfare state.
... Sound acoustic devices will be avoided by dolphin species, as well as bottlenose species. Bottlenose dolphins will avoid gillnet when acoustic devices emit sound [5], [6]. ...
... However, most of the target strength measurement of the intensity value is always referred as peak square [31]. The TS of the marine animals like fish, squids and shrimps can be represented by (5). ...
Article
Full-text available
Fisherman accidentally caught sea turtles in their fishnet. It could be dangerous for its population. This study measures the turtle target strength (TS) using modified echosounder. The result could be used to improve the efficiency of turtle repellent device. The experiment conducted in a hatchery fiber tank contained saline water. The Green were 1, 3, 12 and 18 years old. The study used three species of fish to ensure there are no overlapped value between fish and sea turtle. TS of the animals were calculated incorporating reference targets (sphere). The echo power of the turtle was compared with the solid steel sphere which is confirmed good agreements with the theoretical values. The echo power reference by applying Fast Fourier Transform (FFT) analysis has been used in calculating TS of the animal. From the echo evaluation in time domain at different angles, it is obviously shown that echo signal structure is different between the parts of turtle body. This study reveals that high echo strength is acquired from the carapace and the plastron parts. The finding also showed that there are significant differences between 3, 12, 18 years old turtles and fish in every angle measurement.
... However, ADDs do not always provide the expected results (Pirotta et al., 2016). Moreover, the fact that in some cases the pingers actually seemed to attract bottlenose dolphin (Aydi et al., 2013) suggests an adaptation to their sound, which may in fact alert groups of dolphins to the presence of fishing gear ("dinner-bell" effect) (Richardson et al., 1995;Cox et al., 2004;Carretta & Barlow, 2011). The phenomenon is likely related to the highly adaptive foraging behaviour of the species (Cox et al., 2004;Brotons et al., 2008b), which makes it hard to predict how a population will react to the device (Leeney et al., 2007;Gazo et al., 2008). ...
... Moreover, the fact that in some cases the pingers actually seemed to attract bottlenose dolphin (Aydi et al., 2013) suggests an adaptation to their sound, which may in fact alert groups of dolphins to the presence of fishing gear ("dinner-bell" effect) (Richardson et al., 1995;Cox et al., 2004;Carretta & Barlow, 2011). The phenomenon is likely related to the highly adaptive foraging behaviour of the species (Cox et al., 2004;Brotons et al., 2008b), which makes it hard to predict how a population will react to the device (Leeney et al., 2007;Gazo et al., 2008). The severe threat against fishers' livelihoods therefore calls for additional/alternative mitigation tools suitable to the socio-economic context of each affected area. ...
Article
Full-text available
In a test-control study conducted in the Aeolian Archipelago (Southern Italy), acoustic deterrent devices (pingers) were applied to four gear types typical of local artisanal fisheries to assess their effectiveness in mitigating dolphin-fishery interactions. In this area ecosystem degradation and overfishing have been increasing bottlenose dolphin (Tursiops truncatus) and striped dolphin (Stenella coeruleoalba) conflict with fishers. Banana Pingers were applied to Spicara maena gillnets, trammel nets, “lampara” nets and hand-operated squid jig lines (“totanara”) in trials conducted from April to September 2017. Dolphin depredation events were greatly reduced in the gillnet (100%) and the “lampara” net (86%), resulting in a strong increase in catch weight (kg) and revenue (€). In the squid hand-jig line trials, severe depredation events (60%) markedly reduced catch and revenue. In the trammel net, catch weight and revenues were not significantly different in the test and control nets. Despite the absence of dolphin damage, the fish species that are part of the dolphin diet were more abundant in the test net. Our findings suggest that pinger effectiveness may be influenced by a variety of factors including dolphin species, season, habitat and fish species distribution. Notably, the discards of trammel nets account for nearly 50% of the catch and include potentially valuable bycatch species, like Sparisoma cretense, which however commands a low price on the local market. We suggest that together pingers and the local sale of non-target species could mitigate the economic loss due to dolphin damage, although this requires appropriate planning.
... The use of acoustic deterrent devices (ADDs), also known as pingers or simple acoustic alarms, is a non-lethal method that produces sounds within the hearing range of the target species. Their aim is to deter depredating species from approaching and damaging fishing gear (Findlay et al., 2018), to prevent loss of catch (Gazo, Gonzalvo & Aguilar, 2008;Buscaino et al., 2009;Waples et al., 2013), and to avoid bycatch of the depredating species themselves (Cox et al., 2004). Most ADDs emit sounds in the range 2-40 kHz, with source levels <150 dB re 1 μPa @ 1 m (Dawson et al., 2013). ...
... Behavioural observations of bottlenose dolphins around nets with pingers show that while interaction rates (measured as closest approach distance or time in the area around the net) may be reduced, interactions are not fully eliminated for this species (Cox et al., 2004;Waples et al., 2013). ...
Preprint
Full-text available
1. Dolphins interact with many types of fishing gear, causing damage to fishing activities and in some cases facing harm and becoming entangled as bycatch. 2. In this study, the behaviour of bottlenose dolphins during their interaction with set nets, equipped with and without interactive pingers, was investigated. Acoustic monitoring of the nets was conducted for a total of 56 hauls and 814.9 hours of recordings, from the 16th of October to 13th of November 2015, along the coast of Lampedusa Island (Sicilian Channel, Italy, Mediterranean Sea). 3. The level of interaction between dolphins and the nets was evaluated considering the number of dolphin clicks grouped over time (single acoustic incursion on each net), the duration of every acoustic incursion, and the number of dolphin clicks per incursion. Moreover, the catch rate as the number of fish per hour for each net was measured. 4. Based on the recording time of dolphin clicks, the spatio-temporal development of the interaction with the nets located in different bays of the island was assessed. 5. The duration of the interaction between dolphins and nets significantly increased over the study period, with a concomitant reduction in catch rate. The interactive pinger showed efficacy in protecting the nets from dolphin depredation during the first period of 36 hauls and 11 fishing days (higher catch rates and lower incursion durations), whereas in the second period (20 hauls and 6 fishing days), no differences were found in any interaction parameters between pinger and control nets. 6. Interactive pingers may be an effective, short-term (2-3 weeks) tool in deterring depredation by bottlenose dolphins in small-scale artisanal fisheries. Other mitigation approaches, such as gear modification, lessons learned through outreach, and passive acoustic monitoring of the nets could improve the management of the interactions between fisheries and bottlenose dolphins.
... The variable nature of cetacean-fisheries interactions requires species-and fishery-specific approaches to bycatch mitigation (Cox et al. 2004(Cox et al. , 2007. Without any prior cetacean research having been conducted in the Pilbara region, the dolphin species interacting with the PTF was previously undetermined, but assumed to be the common bottlenose dolphin (Tursiops truncatus), based on a limited number of length measurements and photographs. ...
Article
The identification of species and population boundaries are important in both evolutionary biology and conservation. In recent years, new population genetic and computational methods for estimating population parameters and testing hypotheses in a quantitative manner have emerged. Using a Bayesian framework and a quantitative model-testing approach, we evaluated the species affiliations and genetic connectivity of bottlenose dolphin (Tursiops spp.) populations off remote north-western Australia, with a focus on pelagic 'offshore' dolphins subject to incidental capture in a trawl fishery. We analysed 71 dolphin samples from three sites beyond the 50 m depth contour (the inshore boundary of the fishery) and up to 170 km offshore, including incidentally caught and free-ranging individuals associating with trawl vessels; and 273 dolphins sampled at 12 coastal sites within 10 km of the coast. Results from 19 nuclear microsatellite markers showed significant population structure between dolphins from within the fishery and coastal sites, but also among dolphins from coastal sites, identifying three coastal populations. Moreover, we found no current or historic gene flow into the offshore population in the region of the fishery, indicating a complete lack of recruitment from coastal sites. Mitochondrial DNA corroborated our findings of reproductive isolation between dolphins from the offshore population and coastal sites. Most offshore individuals formed a monophyletic clade with common bottlenose dolphins (T. truncatus), while all 273 individuals sampled coastally formed a well-supported clade of Indo-Pacific bottlenose dolphins (T. aduncus). By including a quantitative modelling approach, our study explicitly took evolutionary processes into account for informing the conservation and management of protected species. As such, it may serve as a template for other, similarly inaccessible study populations. This article is protected by copyright. All rights reserved.
... The extremely variable nature of cetacean-fisheries interactions requires a necessarily cetacean species-, fishery type-and sometimes even local condition-specific approach to bycatch mitigation efforts (Bache 2003;Cox et al. 2004Cox et al. , 2007. Numerous delphinid species suffer fisheries-related mortality throughout Southeast Asian and Australian waters Hamer et al. 2008;Yousuf et al. 2008;Jaaman et al. 2009). ...
Technical Report
Full-text available
Non-Technical Summary: The incidental capture of cetaceans (whales, dolphins and porpoises) in fishing gear is a serious threat to populations and species worldwide. In Australia, several dolphin populations are being impacted by mortalities through interaction with fisheries, in particular, gillnetting, purse-seining, long-lining and trawling fisheries. The capture of dolphins has been a conservation issue in the Pilbara Fish Trawl Interim Managed Fishery (PFTIMF) that was first assessed in 2002 by the Department of Fisheries Western Australia (DoFWA). At that time, an estimated 50 to 100 dolphins were being caught each year. A number of bycatch mitigation techniques were trialed between 2004 and 2007, including pingers (acoustic deterrents) and different exclusion grids, meeting with varying degrees of success (FRDC 2004/068). Due to ongoing dolphin bycatch, successive Ministers for Fisheries have not been prepared to move the fishery beyond ‘Interim Managed’ status. In late 2007, Murdoch University was asked to provide expertise on cetacean behaviour and fisheries interactions in the Pilbara trawl fishery. Two companies were active in the fishery in 2007, completing between 5-6,000 trawls per year, at a fishing effort equivalent to 4.3 full-time vessels. In that year, bycatch levels reported by independent observers remained as high as ~40 dolphins per year. Since the commencement of this project in May 2008, our aims were to: coordinate a directed program of research that maintained communication and collaboration between industry, resource managers and research; assess factors affecting dolphin bycatch using skipper logbook and observer data from late 2003 onward; trial modified exclusion grids and escape hatches in an attempt to further reduce dolphin bycatch; assess the extent and nature of interactions between dolphins and trawl nets; and assess the efficacy of different exclusion grids in allowing dolphins and other megafauna to escape from the trawl nets. Spatial and temporal extent of dolphin-fishery interactions: Data from both skipper logbooks and independent observers indicate that dolphins are caught throughout the fishery and that dolphin bycatch rates: (a) Varied between the four vessels that conduct most fishing activity; (b) Did not vary spatially (management area and water depth) or seasonally (wet vs dry), but were significantly lower during the early morning period (00:00 to 05:59) than other times of day; (c) Decreased significantly (by ~50%) when exclusion grids and bottom-opening escape hatches were built into trawl nets; and (d) May have been further reduced when the grids and escape hatches were moved forward to the beginning of the net extension in June 2008. These data, however, include information only on those dolphins that are landed on the decks of the trawl vessels. We do not know how many dolphins are caught and then fall from the bottom-opening escape hatch prior to being landed on deck. Further work using video deployments is needed to determine whether the declines in dolphin catches observed by skippers and observers equates to less dolphins being injured and killed during all trawling operations. Grid designs and subsurface dolphin behaviour: Using the nets with the grid placed forward, dolphin behaviour was studied by reviewing video footage collected from within actively fishing trawl nets as part of an Honours thesis by Ms. Vanessa Jaiteh (with co-supervision at Murdoch University and the University of Western Australia). Analyses of the footage collected from 36 trawls revealed high interaction rates: (a) Dolphins were recorded inside trawl nets during 29 trawls and for up to 98% of the total trawl duration, and outside trawl nets in 34 trawls for up to 99% of the trawl time; (b) The behaviours displayed by dolphins inside and outside the net differed, with dolphins inside the net engaging predominantly in foraging activity, while those outside the net exhibited mostly travelling behaviours. Some socialising also took place both inside and outside the nets. These results indicate that dolphins are motivated by numerous factors to interact with trawl nets; (c) Furthermore, despite this subset of 36 trawls being taken across a broad extent of the fishery, only 29 dolphins were individually identified foraging inside the nets. Since these individuals were seen repeatedly both within and between trawls and fishing trips, it is likely that they represent a small community of dolphins within the population in the fishery that are behaviourally specialising in foraging inside trawl nets. This has implications for the level of impact that bycatch has on the dolphin community or population as a whole, since there may be just a small proportion of the population subject to unnatural mortality through bycatch. A further net design modification was made to two nets (one per fishing company) in March 2009. These nets were fitted with top-opening escape hatches. However, observers have not collected data on the use of these nets, except for one trip in which fish catch rate was higher than average and no dolphins were caught. Adequate observer coverage and net-mounted underwater video camera deployment (perhaps up to 2000 trawls; which would take around six months of fishing) will be required to monitor nets with top-opening escape hatches in the future. Analysis of wildlife interactions with exclusion grids: The efficacy of two different grid designs (both placed at the forward-end of the extension) in allowing wildlife to escape was assessed by reviewing footage of 22 trawls with a larger, older grid in place, as well as 22 trawls with a new grid installed in a more upright position. Overall, this indicated that the diversity and abundance of bycatch is high in the PFTIMF, and that the two grids differed in their function: (a) The 44 trawls resulted in the incidental capture of at least 86 individuals from 19 species including dolphins, sharks, rays, turtles, sea snakes and pipefish; (b) Three dolphins interacted with the grids, resulting in the apparent death of all three. Two of these three fell out of the bottom-opening escape hatch prior to the net being hauled up and, as a consequence, were not reported by the skippers or observers, i.e. only one dolphin catch was recorded in the logbooks and observer reports. Dolphin and other bycaught species are therefore under-reported whilst the current net designs remain in use; (c) Results from the analysis of 22 trawls each with an old and new grid design showed that 50% and 24% of captured wildlife escaped or fell from the hatches, respectively. Large sharks and rays typically escaped or fell from the bottom-opening hatch and the older grid model was more effective at excluding bycatch than the newer grid model. This seems likely to have been due to a combination of 1) the lower angle at which the old grid was placed in the net, which meant that bycatch was guided toward the escape hatch, and 2) the older grid featured a horizontal bar across the middle section, which prevented large animals from swimming through gaps between the vertical bars into the codend. Further instances of dolphins, sea snakes, sharks and a turtle swimming upward upon interacting with the grid were observed, indicating that a top-opening escape hatch would be the logical next step in reducing the bycatch of megafauna. Since bycaught wildlife remains in the cod-end for the duration of the trawl, then spends time on deck before being expelled overboard where scavenging sharks and dolphins occur, post-capture and post-discard mortality of bycaught wildlife is high. This highlights the need for further improvements in the design and positioning of exclusion grids and escape hatches. We recommend that trials be carried out with an exclusion grid featuring a top-opening escape hatch. This is likely to require a trial period of six months with observer coverage and video camera deployments to confirm the fishing efficiency and non-target wildlife excluding efficiency of these nets. Independent observer coverage: Independent observer coverage has yielded dolphin capture rates that are typically 1.6 to 3.7 times higher than those reported in skippers’ logbooks. The DoFWA established that observer coverage at a minimum of 22% of total fishing effort was required in order to provide robust estimates of dolphin and other bycatch levels from 2006-2007 onward. This level has never been attained and has subsequently fallen each financial year (17% in 2006-2007, 13% in 2007-2008, 13% in 2008-2009 and 8% to the present). This low coverage, combined with the relatively infrequent incidence of dolphin capture, means that the comparisons of dolphin catch rates between the different net designs have low power. Identification of the dolphins: We used small biopsy samples from dolphins caught in trawls and samples taken from free-ranging dolphins over an east-west distance of 160 nm to assess the species identity and the genetic diversity of dolphins interacting with the fishery. The results of this research showed that: (a) Most dolphins interacting with the fishery are common bottlenose dolphins (Tursiops truncatus); (b) One bycaught individual shared a closer genetic affinity to the Indo-Pacific bottlenose dolphin (T. aduncus); (c) Four individuals appear more closely related to the Fraser’s dolphins (Lagenodelphis hosei); and, (d) Population genetic diversity appears comparable to other dolphin populations, with 16 haplotypes identified across 43 sampled individuals. Further research is needed to assess the size of the dolphin population(s) that are impacted and the levels of gene flow and connectivity between the impacted population(s) and those in adjacent regions. Recommendations: This research indicates that bycatch in the PFTIMF still includes protected dolphins (at 20 to 50 dolphins per year based on logbook and observer figures, respectively, from 2008-2009), sharks and rays, critically endangered sawfish and various other wildlife species. It also demonstrates that the current exclusion grid and escape hatch design leads to the under-reporting of injury and mortality of bycatch by both skippers and observers. 1. Further investigation into the efficacy of exclusion grids with top-opening escape hatches is needed to inform management action in the PFTIMF. Research based on footage obtained with trawl net-mounted video cameras will allow more accurate estimates of actual (i.e. landed and non-landed) dolphin and other species bycatch to be made; 2. Differences between logbook and observer reported bycatch levels indicate that greater observer coverage is needed. A period of intensive observer coverage and video camera deployments (i.e. 6 months or approx. 2000 shots) will be necessary to evaluate top-opening escape hatches; 3. The spatial and temporal extent of interactions between dolphins and the fishery make it difficult for fishery management measures to reduce the level of interaction without reducing fishing effort across the fishery. Results suggest that catch rates are higher in one vessel and lower in the early morning, but do not vary spatially or seasonally; 4. In order to quantify the level of threat that ongoing bycatch poses, a population study (including assessment of abundance and gene flow) of the dolphins inhabiting the fishing grounds and adjacent regions is required. Knowledge of a maximum allowable mortality rate will provide direction for future bycatch mitigation efforts and allow the fishery to better demonstrate the outcomes of such efforts; 5. A more detailed study quantifying the composition and biomass of landed bycatch would also provide direction for bycatch mitigation efforts. An electronic observer system could be trialled in addition to an intensive period of observer coverage; 6. Dolphin mortality events currently lead to immediate discarding of carcasses. This is a waste of invaluable sources of information and dolphins that are landed dead in future should be accurately measured and have various samples taken by observers.
... Dünyanın bir çok bölgesinde, yunusların avcılık operasyonu sırasında istenmeden ağa takılmalarını (bycatch), ağa yakalanan balıkları çalmalarını (depredasyon) ve ağlara zarar vermelerini önlemek amacıyla, ağlara akustik kaçırıcılar takılarak yunusların ağlardan uzak tutulması konusunda değişik araştırmalar yapılmıştır [9][10][11][12][13][14][15][16][17][18][19][20]. Karadeniz'de özellikle istemeden yapılan yunus avcılığı (bycatch) konusunda bazı çalışmalar gerçekleştirilmiş [1,2,4,21,22,23], fakat bu çalışmalarda akustik caydırıcılar denenmemiştir. ...
Article
Full-text available
Bu çalışma, Sinop yarımadası civarında 18 Aralık 2005 ve 21 Ocak 2006 tarihleri arasında 34mm ve 44mm dip uzatma solungaç ağlarında yunusların balıkları çalmaları üzerine akustik pingerlerin etkisini belirlemek amacıyla yürütülmüştür. Araştırmada, ağ göz açıklığı 34mm ve 44mm olan monofilament tora sahip sade dip uzatma ağları ve 4 adet AQUAmark 200, akustik cihaz kullanılmıştır. Akustik cihazlar 34mm ve 44mm ağ göz açıklığındaki ağların mantar yakasının uç kısımlarından, 50 kulaçlık mesafeye bağlanarak (cihazlı ağlar) denize bırakılmıştır. 34mm ağ gözü açıklığına sahip aktif ve kontrol ağlarla sırasıyla, toplam 76kg, 1115 adet ve 25,0kg, 292 adet, 44mm ağ gözü açıklığına sahip aktif ve kontrol ağlarıyla ise sırasıyla, toplam 90,5kg, 749 adet ve 18,5kg, 230 adet balık yakalanmıştır. Yine, 34mm ağ gözü açıklığına sahip aktif ağlarla kontrol ağlara göre ağırlık ve sayı olarak sırasıyla, 3,0 kat ve 3,8 kat, 44mm ağ gözü açıklığına sahip aktif ağlarla ise ağırlık ve sayı olarak sırasıyla, 4,9 kat ve 3,3 kat daha fazla balık yakalandığı belirlenmiştir (p<0,05). Ayrıca, ağların toplanması ve ürün alınması sırasında, bazı balıkların ısırılarak ağdan alındığı ve balığın özellikle baş vb. bölgelerinin ağda kaldığı, yunuslar tarafından parçalanmış olan ağ gözü iplerinde de filizlenme şeklindeki karakteristik yıpranmalar tespit edilmiştir. Sonuç olarak, monofilament dip uzatma ağlarına akustik pingerler takılarak avcılık yapıldığında yunusların ağdan uzak tutulması, ağa zarar vermesi ve yakalanan balıkları çalmasını önlemenin mümkün olabileceği görülmüştür. Yunusların üzerine akustik pingerlerin etkisinin kapsamlı olarak belirlenmesini geliştirmek için, gelecekte yunus populasyonu habitatları, alışkanlıkları, göçleri ve dağılımlarını da dikkate alan daha kapsamlı çalışmaların yapılmasına ihtiyaç vardır. Abstract: This study was carried out to determine the effects of acoustic pingers on dolphins depredation in the monofilament bottom gillnets of 34 and 44mm mesh sizes around the Sinop Peninsula between 18 December 2005 and 21 January 2006. The monofilament bottom gillnet of 34 and 44mm mesh sizes and 4 acoustic device (AQUAmark 200) were used. Acoustic devices were placed on the edge of float line with 50 fathom interval (active) then left to the sea. A total of 76kg and 1115 fish and 25kg and 292 fish were caught by active of 34mm mesh size and control, respectively, while 90.5kg and 749 fish and 18.5kg and 230 fish were caught by active of 44mm mesh size and control, respectively. 3.0-4.9 and 3.3-3.8 folds more products as weight and numerical, respectively, were obtained by active of 34 and 44mm mesh size (with acoustic device) than by control net (without acoustic device) (p<0.05). In addition to these results, during the collection of the nets and the harvesting of the fish it was observed that some of the fish were taken by biting from the net and especially the head of the fish were left in the net and characteristic sprout like frays were presented in the thread of mesh which severed by dolphins. As a result, when fishing were performed by using acoustic pingers on the monofilament gill net, these were possible being able to kept away of dolphins from net, damaging on the net by dolphins, preventing of stealing of the fish by dolphins. In order to improve the determination of the effect acoustic pingers on dolphins, more comprehensive studies are needed by taking into accound of habitats, habituate, migration and distribution of dolphins.
... The failure of the Airmar pinger to mitigate dolphin entanglement was a failure of the Airmar pinger type with Indo- Pacific bottlenose dolphin only but noted in a fishery context at least. Cox, Read, Swanner, Urian & Waples (2003) observed that entanglement was a rare event compared to the number of interactions between dolphins and gillnets irrespective of whether Dukane 10 kHz pingers were present or not. Read, Waples, Urian & Swanner (2003) concluded that dolphins become entangled when they are unaware of the net, or are distracted by other stimuli in its vicinity. ...
Article
Full-text available
Interactions between cetaceans/sirenians and commercial fishing gear in Australian waters generate biodiversity concerns with by-catch interactions and depredation product loss interactions impacting on the viability of many fisheries. Despite acoustic capabilities to detect gillnets, continued bycatch mortalities resulted in the development of acoustic alarms/pingers from the late 1980's to alert inattentive/resting animals to the presence of nets during hours of darkness or in turbid water conditions. New depredation mitigation pingers have demonstrated significant reductions in longline depredation and fish trawl entrapment of relevance to Australian fisheries. Developments with early acoustic detection of depredation behaviour will permit fishery operators to take steps to minimise depredation interaction exposure periods and pinger exposure time. Fisheries adapt to benefits demonstrating economic and biologically relevant advantages faster than directed research projects. Where interactions with marine mammals occur, fisheries are encouraged to conduct their own monitoring activities with organisations that share common positive objectives for their fishery.
... While the deployment of acoustic deterrents (pingers) in certain fisheries has been effective in reducing cetacean bycatch and possibly depredation rates (Bordino et al., 2002;Carlstrom et al., 2002;Cox et al., 2001;Cox et al., 2003) there is uncertainty about the long-term efficacy of acoustic deterrents and the possibility that they cause displacement of cetaceans away from key feeding habitat. These types of 'technical fixes' are also fairly expensive and difficult to monitor making their application to small-scale fisheries in developing nations generally infeasible. ...
Technical Report
Full-text available
Marine cetaceans live within a vast aquatic environment that covers over 71% of the Earth’s surface. Their habitats are foreign to humans, comprising extensive submerged landscapes of mountain ranges, plains, volcanoes and deep trenches; often eclipsing the size or majesty of many of their terrestrial counterparts. Driven by massive and layered currents and counter-currents, channels and columns of water, the ocean mass is a complex three dimensional environment. Within this complex environment are the migratory pathways and habitats of marine species - the living threads that weave throughout currents, channels, columns and basins; living conduits between separated ecosystems and habitats. 2. River cetaceans live in dynamic running water systems that emphasize terrestrial and upstream downstream connectivity. Their habitat is generally more familiar to humans compared with cetacean habitat in marine environments; together the Ganges and Yangtze River basins, in addition to supporting endangered cetaceans, sustain roughly 25 percent of the people living on Earth today. The habitat of these animals undergoes dramatic changes seasonally, expanding during high-water periods into small tributaries, appended lakes and sometimes flooded forests. The sensitivity of riverine environments to altered flow regimes caused by engineering structures and a changing climate pose particular challenges for protecting priority habitat, where the animals find refuge from downstream and tidal currents, and movement corridors along the main river course that connect these patchily distributed areas. 3. This review examines the progress and intent of CMS and its agreements to date and offers advice on how the CMS Family can be more effective through strong collaboration with other relevant Multi-lateral Environmental Agreements (MEAs) such as the International Maritime Organization (IMO), the International Whaling Commission (IWC) and its Scientific Committee (IWC SC) and Conservation Committee (IWC CC), the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR), the United Nations Informal Consultation on Protection of the Oceans and the Law of the Sea (UNICPOLOS), the Cartagena Convention, European Union Habitats and Species Directive, the Bern Convention and the United Nations Environment Programme (UNEP) Regional Seas Programme.
... The effectiveness of acoustic pingers to mitigate bycatch of several cetacean species has been documented previously (e.g. harbor porpoises Phocoena phocoena, Kraus et al. 1997, Palka et al. 2008, Larsen & Eigaard 2014; common dolphins Delphinus delphis and beaked whales, Barlow & Cameron 2003, Carretta et al. 2008, Carretta & Barlow 2011; franciscanas Pontoporia blainvillei, Bordino et al. 2002), however, this effectiveness is not evident for bottlenose dolphins Tursiops truncatus (Cox et al. 2004, McPherson et al. 2004. Although no evidence of habituation has been reported for large-scale applications of pingers in gillnet fisheries (Palka et al. 2008, Carretta & Barlow 2011, other experimental studies have suggested the occurrence of habituation to pinger alarms (Kraus 1999, Cox et al. 2001, Carlström et al. 2009), and Dawson et al. (2013) stated that habituation might occur for inshore and resident populations. ...
Article
Full-text available
Finless porpoises Neophocaena spp. are under pressure from various anthropogenic impacts due to their coastal habitat. Net fishery bycatch is considered a major risk for the populations around Japan, and mitigation measures are required. We carried out a long-term study to assess the efficiency of acoustic pingers in reducing the encounter rates of narrow-ridged finless porpoises with fishing nets. We used a passive ultrasonic event recorder (A-tag) to obtain acoustic encounter rates of echolocating finless porpoises and compared results for the presence and absence of pinger transmissions in Omura Bay, Japan, over two 8-mo periods (2011 and 2012). Encounter rates were significantly lower during periods when pingers were in operation, but the effect of pingers decreased with time. By the eighth month of the study in each study year, the number of encounters during the ensonified period was greater than that during periods without pingers, suggesting habituation. When pingers were reactivated at the study site after 4 mo of silence, the encounters with the active pingers returned to the lower level observed at the beginning of the experiment. These results reveal that the pingers effectively induce avoidance in porpoises, but that this effectiveness only lasts for a few months, which is likely due to habituation which could be mitigated by alternating periods of several months of silence between periods of active pinger use.
... In previous studies harbour porpoises have been shown to respond to sounds at a relatively low RL at frequencies between 8 and 80 kHz (Johnston, 2002;Kastelein et al., 2005;Brandt et al., 2013). Since harbour porpoises did not respond to our playbacks, we feel confident that results would be similar with other odontocete species, such as bottlenose dolphins Tursiops truncatus or long-finned pilot whales Globicephala melas, which have a broadly similar hearing sensitivity to harbour porpoises but generally seem to tolerate noise much better (Cox et al., 2004;Antunes et al., 2014). We also observed European otters near the fish farm. ...
Article
Full-text available
Carnivore depredation on human livestock is a worldwide problem with few viable solutions. Non-lethal management tools such as acoustic devices show highly varying success and often pose a conservation risk due to noise pollution and habitat degradation. We tested the long-term effectiveness of a deterrence system which harnesses an autonomous reflex (startle) to selectively inflict avoidance responses in a target species (phocid seals) by emitting band-limited noise pulses with sharp onset times. Seal predation was monitored at a marine salmon farm (test site) over a full production cycle (19 month) with a multi-transducer deterrent system deployed for the final year. Predation was also monitored for several months at two control sites and additional short-term tests were carried out at sites which suffered higher predation rates. Generalized linear (mixed) models revealed that sound exposure caused a 91% reduction in lost fish when comparing predation levels within the test site and 97% when comparing the test site against both control sites. Similarly, sound exposure led to a 93% reduction in the number of fish lost due to seal damage at a short-term test site. Visual monitoring of marine mammals around the long-term test site showed that the number of seal surfacings within 100 m from the loudspeakers was only slightly lower during sound exposure. Harbour porpoise and otter distribution around the farm was not affected by sound exposure. By adjusting the frequency composition of startle stimuli, our method has the potential to provide solutions for managing human-wildlife conflicts in terrestrial and marine habitats by selectively deterring target species.
... Habituation to pinger noise is currently not included in the IBM as field studies thus far (including our own experiment at Jammerland Bay as described above) have not provided evidence that porpoises habituate to the broadband randomized signals emitted by the AQUAmark100 (Kindt-Larsen 2015), although habituation may occur with signals emitted by other pinger types (Cox et al. 2004. ...
Article
Full-text available
Unintentional mortality of higher trophic-level species in commercial fisheries (bycatch) represents a major conservation concern as it may influence the long-term persistence of populations. An increasingly common strategy to mitigate bycatch of harbor porpoises (Phocoena phocoena), a small and protected marine top predator, involves the use of pingers (acoustic alarms that emit underwater noise) and time-area fishing closures. Although these mitigation measures can reduce harbor porpoise bycatch in gillnet fisheries considerably, inference about the long-term population-level consequences is currently lacking. We developed a spatially explicit individual-based simulation model (IBM) with the aim to evaluate the effectiveness of these two bycatch mitigation measures. We quantified both the direct positive effects (i.e., reduced bycatch) and any indirect negative effects (i.e., reduced foraging efficiency) on the population size using the inner Danish waters as a biological system. The model incorporated empirical data on gillnet fishing effort and noise avoidance behavior by free-ranging harbor porpoises exposed to randomized high-frequency (20- to 160-kHz) pinger signals. The IBM simulations revealed a synergistic relationship between the implementation of time-area fishing closures and pinger deployment. Time-area fishing closures reduced bycatch rates substantially but not completely. In contrast, widespread pinger deployment resulted in total mitigation of bycatch but frequent and recurrent noise avoidance behavior in high-quality foraging habitat negatively affected individual survival and the total population size. When both bycatch mitigation measures were implemented simultaneously, the negative impact of pinger noise-induced sub-lethal behavioral effects on the population was largely eliminated with a positive effect on the population size that was larger than when the mitigation measures were used independently. Our study highlights that conservationists and policy makers need to consider and balance both the direct and indirect effects of harbor porpoise bycatch mitigation measures before enforcing their widespread implementation. Individual-based simulation models, such as the one presented here, offer an efficient and dynamic framework to evaluate the impact of human activities on the long-term survival of marine populations and can serve as a basis to design adaptive management strategies that satisfy both ecological and socioeconomic demands on marine ecosystems.
... Habituation to pinger noise is currently not included in the IBM as field studies thus far (including our own experiment at Jammerland Bay as described above) have not provided evidence that porpoises habituate to the broadband randomized signals emitted by the AQUAmark100 (Kindt-Larsen 2015), although habituation may occur with signals emitted by other pinger types (Cox et al. 2004. ...
... Behavioral responses are wide ranging and might include subtle changes in respiration, brief changes in orientation, fluke slapping, changes in phonation patterns or levels, mother calf separations, changes in dive behavior, and abandonment of foraging or breeding. Indeed, site avoidance responses have been exploited in fisheries management; pingers and acoustic deterrents on gillnets are designed to cause avoidance responses by dolphins (Burke, 2004;Cox, Read, Swanner, Urian, & Waples, 2004;Tyack, 2008;Wartzok, Popper, Gordon, & Merrill, 2003), although responses can be variable and some dolphin populations habituate rapidly to the deterrent, putting them at risk of the nets. ...
Thesis
Full-text available
Sound is the primary sensory modality for dolphins, yet policies mitigating anthropogenic sound exposure are limited in wild populations and even fewer noise policies or guidelines have been developed for governing dolphin welfare under human care. Concerns have been raised that dolphins under human care live in facilities that are too noisy, or are too acoustically sterile. However, these claims have not been evaluated to characterize facility soundscapes, and further, how they compare to wild soundscapes. The soundscape of a wild dolphin habitat off the coast of Quintana, Roo, Mexico was characterized based on Passive Acoustic Monitoring (PAM) recordings over one year. Snapping shrimp were persistent and broadband, following a diel pattern. Fish sound production was pulsed and prominent in low frequencies (100 - 1000 Hz), and abiotic surface wave action contributed to noise in higher frequencies (15 - 28 kHz). Boat motors were the main anthropogenic sound source. While sporadic, boat motors were responsible for large spikes in the noise, sometimes exceeding the ambient noise (in the absence of a boat) by 20 dB root-mean-squared sound pressure level, and potentially higher at closer distances. Boat motor sounds can potentially mask cues and communication sounds of dolphins. The soundscapes of four acoustically distinct outdoor dolphin facilities in Quintana Roo, Mexico were also characterized based on PAM, and findings compared with one another and with the measurements from the wild dolphin habitat. Recordings were made for at least 24 hours to encompass the range of daily activities. The four facilities differed in non-dolphin species present (biological sounds), bathymetry complexity, and method of water circulation. It was hypothesized that the greater the biological and physical differences of a pool from the ocean habitat, the greater the acoustic differences would be from the natural environment. Spectral analysis and audio playback revealed that the site most biologically and physically distinct from the ocean habitat also differed greatly from the other sites acoustically, with the most common and high amplitude sound being pump noise versus biological sounds at the other sites. Overall the dolphin facilities were neither clearly noisier nor more sterile than the wild site, but rather differed in particular characteristics. The findings are encouraging for dolphin welfare for several reasons. Sound levels measured were unlikely to cause threshold shifts in hearing. At three of four facilities, prominent biological sounds in the wild site - snapping shrimp and fish sounds - were present, meaning that the dolphins at these facilities are experiencing biotic features of the soundscape they would experience in the wild. Additionally, the main anthropogenic sounds experienced at the facilities (construction and cleaning sounds) did not reach the levels of the anthropogenic sounds experienced at the wild site (boat motor sounds), and the highest noise levels for anthropogenic sounds fall outside the dolphins' most sensitive range of hearing. However, there are anthropogenic contributors to the soundscape that are of particular interest and possible concern that should be investigated further, particularly pump noise and periodic or intermittent construction noise. These factors need to be considered on a facility-by-facility basis and appropriate mitigation procedures incorporated in animal handling to mitigate potential responses to planned or anticipated sound producing events, e.g. animal relocation or buffering sound producing activities. The central role of bioacoustics for dolphins means that PAM is a basic life support requirement along with water and food testing. Periodic noise is of highest concern, and PAM is needed to inform mitigation of noise from periodic sources. Priority actions are more widespread and long-term standardized monitoring, further research on habituation, preference, coupling and pool acoustics, implementation of acoustics training, standardization of measurements, and improved information access.
... Furthermore, the diet of many cetaceans overlap with other marine mammal, seabird, and fish species, and therefore individuals may eavesdrop on acoustic signals produced by other species to inform foraging opportunities (Evans 1982, Clua and Grosvalet 2001, Davoren et al. 2010, Thiebot and Weimerskirch 2013. Likewise, cetaceans may use acoustic signals from anthropogenic noise sources as foraging opportunity cues, such as ship propeller cavitation (Thode et al. 2007) and acoustic pingers (Cox et al. 2004). Acoustic signals from conspecifics and other sources is hypothesized to inform dolphins at micro, fine, and low end meso scales in the scaleof-senses schematic (Fig. 1), and to inform baleen whale foraging at scales between micro and large, but most significantly at the meso scale (Fig. 2). ...
Article
Full-text available
Research on cetacean foraging ecology is central to our understanding of their spatial and behavioral ecology. Yet, functional mechanisms by which cetaceans detect prey across different scales remain unclear. Here, I postulate that cetaceans utilize a scale-dependent, multimodal sensory system to assess and increase prey encounters. I review the literature on cetacean sensory systems related to foraging ecology, and hypothesize the effective scales of each sensory modality to inform foraging opportunities. Next, I build two “scale-of-senses” schematics for the general groups of dolphins and baleen whales. These schematics illustrate the hypothetical interchange of sensory modalities used to locate and discriminate prey at spatial scales ranging from 0 m to 1,000 km: (1) vision, (2) audition (sound production and sound reception), (3) chemoreception, (4) magnetoreception, and somatosensory perception of (5) prey, or (6) oceanographic stimuli. The schematics illustrate how a cetacean may integrate sensory modalities to form an adaptive foraging landscape as a function of distance to prey. The scale-of-senses schematic is flexible, allowing for case-specific application and enhancement with improved cetacean sensory data. The framework serves to improve our understanding of functional cetacean foraging ecology, and to develop new hypotheses, methods, and results regarding how cetaceans forage at multiple scales.
... Understanding turtles' behaviour, particularly their physiology (auditory, chemosensory, and visual abilities, Southwood et al., 2008;Jordan et al., 2013), is crucial to minimize fisheries interactions. Anatomical, physiological, and behavioural studies of their reactions to acoustic stimuli (Southwood et al., 2008;Fritsches and Warrant, 2013) suggest that acoustic deterrents such as the pingers used to protect dolphins (Nestler et al., 1992;Dawson et al., 1998;Cox et al., 2004) are not effective, because the sound intensity required to exert the desired effect is so high that it may also affect the behaviour of other species. Sea turtles rely extensively on visual cues, particularly when foraging (Swimmer et al., 2005), due to their well-developed visual system provided with a wide spectral range (Mäthger et al., 2007;Southwood et al., 2008). ...
Article
Sea turtles suffer from the cumulative and synergistic effects of natural phenomena and human activities. Among the latter, incidental interaction with commercial fisheries is considered as the main threat to their conservation. Fixed nets are common gears traditionally used in Mediterranean small scale fisheries (SSF). The loggerhead turtle bycatch of fixed nets is estimated to be high and similar to that of trawl nets and longlines, but seems to be associated with higher mortality rates. Devices aiming at reducing sea turtle bycatch through gear modifications have largely been developed for large-scale commercial fisheries, i.e. longlines and trawls, but not for set nets. In the present study ultraviolet LED lamps, which have already proved to be effective visual deterrents along the Northern and Southern Pacific coasts, were mounted on fixed nets and assessed for their ability to reduce the loggerhead turtle bycatch in the Mediterranean set net fishery. No turtles were caught in the illuminated net, whereas 16 individuals were captured by the traditional net (mortality rate, 30%). There were no significant differences in the catch rates of target species. This is the first test of a BRD designed to reduce sea turtle bycatch in a Mediterranean set net fishery. A broad diffusion of these bycatch reducer devices (BRDs) would provide a significant contribution to the conservation of loggerhead turtles while enabling large-scale production and cost reduction. However, until this happens the cost of adopting this BRD cannot be afforded by the fishermen operating SSF.
... However, they do not elicit consistent responses in all small cetacean species, nor do they have the same effects across all types of fisheries. For example: gill nets equipped with active pingers induced only subtle behavioural changes, rather than an avoidance response, in bottlenose dolphins (Cox et al. 2003); a more recent study found fewer bottlenose dolphins approaching within 100 m of pinger-equipped gill nets, suggesting that pingers reduce the frequency of, but do not eliminate, interactions ; and Berg Soto et al. (2013) found that pingers elicited only subtle behavioural responses in Australian snubfin and humpback dolphins, suggesting they may not be effective in reducing bycatch of these species in gill nets or anti-shark meshing for bather protection and that alternative mitigation measures should be explored. ...
... A distância de detecção pode ser afectada pelo ângulo de aproximação do animal à rede, pelos níveis de ruído no meio marinho, pelo nível de concentração dos animais ou pela distracção decorrente do investimento na procura de presas. Para além das dificuldades em detectar as redes, podem ocorrer falhas de detecção por diversas razões(Au & Jones, 1991, Bordino et al. 2002, Cox et al. 2003. Por exemplo, os indivíduos não estão sempre a ecolocar pelo que ...
... Kraus et al. (1997), it is essential that a proper evaluation of the efficacy of this approach be undertaken for Amakusa Indo-Pacific bottlenose dolphins in this region before widespread use can be recommended and a number of issues must be considered in such an evaluation. Depredation is already reported by many gillnetters and although evasive behaviour of the dolphins might be seen at first (Leeney et al., 2007), they may later learn to associate the pingers with the presence of a gillnet that contains fish (Cox et al., 2003). The habitat use patterns of the dolphins are also important. ...
Article
Full-text available
A year-round resident population of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) inhabits the waters off Amakusa-Shimoshima Island (32°25'N, 130°05'E), in Japan. The effect of bycatch in gillnet fisheries on the Amakusa population was examined. Population size in 2007 and 2008 was estimated at 230 individuals (CV = 2.5%) and 216 individuals (CV = 2.1%), respectively, based on a mark-recapture technique. The magnitude of bycatch was evaluated by analysing interview surveys (263 gillnetters) during these two years. Minimum numbers of dolphin bycatch were 12 individuals in 2007 and 14 individuals in 2008. Most of the dolphins, which were captured by bottom-set gillnets, were considered to be Indo-Pacific bottlenose dolphins for the following reasons: (1) two individuals were identified based on DNA analysis; (2) only Tursiops sp. and finless porpoises were found in the sighting survey by ferry boats, and fishermen can distinguish between the two; and (3) the seasonal and spatial distribution of bycatch corresponded well to habitat use patterns of the Amakusa population. If the US potential biological removal (PBR) approach is used it estimates two individuals per year, which is much lower than the minimum bycatch numbers of 12-14 individuals per year (5.2-6.5% of abundance estimates). Reducing bycatch mortality caused by bottom-set gillnets is essential for the effective conservation of Indo-Pacific bottlenose dolphins in Amakusa, Japan.
... In other words, the response to -203 -dolphin-watching operations can be seen as an additional element to the convoluted mechanism determining dolphins' movement. This finding demonstrates that the appropriate use of robust measurement tools with high precision is crucial to accurately measure fine-scale behavioural response (Cox et al., 2004;Ribeiro et al., 2007). The findings in Chapter 5 are the first of its kind to demonstrate humpback dolphin behavioural response to a specific anthropogenic impact, with a component quantifying the specific response to natural and anthropogenic variables. ...
Thesis
Full-text available
The world's largest population of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary is exposed to some of the world's greatest concentration of anthropogenic threats, much of it due to the region's rapid urbanisation and industrialisation in recent decades. By assessing behavioural responses of humpback dolphins to long-term and large-scale environmental change in Hong Kong, and short-term but frequent behavioural disturbance due to unregulated dolphin-watch tourism, this study investigates humpback dolphins as a model system of a coastal delphinid in the coastal seas of the Anthropocene. Field surveys were conducted between 2011 and 2014 to identify humpback dolphins’ distribution pattern. Resource selection function was applied to model the dolphin's habitat selection process and quantify their long-term habitat preference. The results indicate that humpback dolphins display a heterogeneous pattern in habitat selectivity that is conditional to distinctive sets of key factors at different spatial scales. By using Landsat data and historic archives, and by quantifying a cumulative habitat loss over the past 40 years, this study reveals that during that time the natural shoreline providing critical ecological functions to humpback dolphins in Hong Kong has been drastically reduced. Occurrence probabilities reconstructed for the time-periods prior to major habitat alterations, and occurrence probabilities projected into future years (when all currently planned projects are to be completed) indicate a major drop of habitat use by the dolphins in areas neighbouring reclamation sites. All current Marine Protected Areas (MPAs) for humpback dolphin conservation are already affected by the ongoing environmental change and this will intensify in the future. Shore-based scan-sampling surveys were conducted between 2013 and 2014 to identify a distribution pattern of the dolphins at one of their main feeding areas in Hong Kong. With year-round sightings, the dolphins used this area selectively at different seasons and time of day. Only a small portion of the area was used as feeding location, within a narrow range of distances from shore, demonstrating a clear pattern of spatio-temporal fine-scale habitat selection that has not been accounted for in all current conservation actions in Hong Kong. Behavioural responses of humpback dolphins to small-scale dolphin-watch operations were investigated by tracking the dolphins' movement and recording fine-scale changes in the movement parameters. Analyses show that movement patterns of the dolphins, distinctive between behavioural states, were significantly altered by the presence of dolphin-watch boats. Multivariate models reveal that the disturbance by dolphin-watch operations can be seen as an external factor affecting the dolphins’ spatial decisions. Consequently, an appropriate regulatory mechanism is needed to manage the dolphin-watch tourism and minimise its impact on the target species. In summary, this study quantifies humpback dolphins’ response to large long-term and short-term chronic anthropogenic impacts, and indicates that various human activities affect the dolphins' daily behaviour and habitat selection. The conservation actions that are currently in place are ineffective in protecting humpback dolphins from man-made threats and will not be effective in preserving their habitat in the long-term. This implies serious ecological consequences and an urgent need for science-based and habitat-oriented conservation strategy.
... In other words, the response to -203 -dolphin-watching operations can be seen as an additional element to the convoluted mechanism determining dolphins' movement. This finding demonstrates that the appropriate use of robust measurement tools with high precision is crucial to accurately measure fine-scale behavioural response (Cox et al., 2004;Ribeiro et al., 2007). The findings in Chapter 5 are the first of its kind to demonstrate humpback dolphin behavioural response to a specific anthropogenic impact, with a component quantifying the specific response to natural and anthropogenic variables. ...
... There have been many attempts to mitigate depredation events in the Mediterranean basin, from modifications to nets to keep animals away, to several acoustic deterrents (e.g., pingers [12]). Nevertheless, these solutions alone have proved ineffective, with dolphins habituating to acoustic deterrents after only a few exposures [13]. Furthermore, several studies have reported cetaceans using pingers as cues to locate fisher nets [14]. ...
Article
Full-text available
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.
... Noise from acoustic devices may impair dolphin communication and cause hearing harm (Dawson et al., 2013;Waples et al., 2013), while also having unintended negative impacts on marine organisms and fish behaviour, with potential effects on fishing yields (Kastelein et al., 2007). These negative impacts may end up exceeding any real or supposed conservation benefit in terms of lower dolphin bycatch, also considering that: 1) incidental mortality rates in Adriatic midwater trawls appear to be low (Fortuna et al., 2010;De Carlo et al., 2012;Sala et al., 2018); 2) mortality rates in Adriatic otter trawls remain unknown; 3) compelling evidence on the long-term effectiveness of acoustic devices as a way of reducing bottlenose dolphin bycatch in trawl gear is lacking; 4) acoustic devices might function as 'dinner bells' once bottlenose dolphin have become accustomed to their noise (Cox et al., 2003;Carretta & Barlow, 2011); and 5) several studies strongly suggest that acoustic devices may not bring the intended benefits in terms of reducing conflict between bottlenose dolphins and trawlers (Stephenson & Wells, 2008;Allen et al., 2014;Goetz et al., 2014;Santana-Garcon et al., 2018). ...
Article
• Many species and populations of odontocetes have modified their behaviour to take advantage of feeding opportunities provided by fishing activities, with depredation of fishing gear being the most common type of adaptation. • The northern Adriatic Sea has been identified as an important marine mammal area because of a regular occurrence of common bottlenose dolphins. Boat surveys were conducted within a 3,000 km² sector of the Adriatic Sea off the coast of Veneto, Italy, between April and October 2018–2019. Based on 76 days at sea, 10,711 km of navigation, and 81 h 26 min of dolphin tracking, this study contributes novel quantitative information on dolphin spatial distribution, and on their occurrence in the wake of beam trawlers, otter trawlers, and midwater pair trawlers. • A combined generalized additive model and generalized estimation equation framework indicated that trawling—along with other physiographic, biological and anthropogenic variables—influenced dolphin distribution. In days of trawling, the chance of encountering dolphins increased by ~4.5 times (95% confidence interval 1.8–11.0) near active beam trawlers, by ~16.0 times (7.1–36.0) near otter trawlers, and by ~28.9 times (12.0–69.6) near midwater pair trawlers. • Spatial modelling was used to create maps of predicted distribution, suggesting differences in habitat use between trawling and no‐trawling days. Spatial modelling for all days identified a dolphin distribution hotspot of 832 km², situated off the Po river delta. • Evidence contributed by this study can be used to inform management action within one of the world's areas most heavily impacted by fishing and other human encroachment. Such management action would help enforce the European Union's Habitats Directive and Marine Strategy Framework Directive, while also informing EU's Maritime Spatial Planning.
... Acoustic deterrence, attempted through a large range of ADDs marketed by private companies under various names (e.g. Pingers, Acoustic Alarms, Seal Scarer, Dolphin Interactive Deterrent, Orcasaver, etc.) and characterized by high amplitude sounds (130-200 dB re 1 mPa 1 m from the source), often generated responses from odontocetes and pinnipeds in early trials but were not effective at minimizing depredation on the long-term(Buscaino et al., 2009;Cox, Read, Swanner, Urian, & Waples, 2004;Götz & Janik, 2013;Maccarrone et al., 2014;Santana-Garcon et al., 2018;Sepúlveda et al., 2007;Snape et al., 2018;. Among the six fisheries reporting effective ADDs, ...
Article
The sustainable mitigation of human–wildlife conflicts has become a major societal and environmental challenge globally. Among these conflicts, large marine predators feeding on fisheries catches, a behaviour termed “depredation,” has emerged concomitantly with the expansion of the world’s fisheries. Depredation poses threats to both the socio‐economic viability of fisheries and species conservation, stressing the need for mitigation. This review synthesizes the extent and socio‐ecological impacts of depredation by sharks and marine mammals across the world, and the various approaches used to minimize it. Depredation was reported in 214 fisheries between 1979 and 2019 (70% post‐2000) and affected fleets from 44 countries, in all sectors (commercial, artisanal and recreational), and in all major fishing techniques (nets, traps and hook‐and‐lines). A total of 68 predator species were involved in depredation (20 odontocetes, 21 pinnipeds and 27 sharks), and most (73%) were subject to either by‐catch and/or retaliatory killing from fishers when interacting with gear. Impacts on fishers were primarily associated with catch losses and gear damage but often lacked assessments. Deterrence was a major mitigation approach but also the least effective. Gear modifications or behavioural adaptation by fishers were more promising. This review highlights the need for improved monitoring, and interdisciplinary and integrated research to quantify the determinants and impacts of depredation in the socio‐ecological dimension. More importantly, as the conflict is likely to escalate, efforts directed towards changing perceptions and integrating knowledge through adaptive co‐management are raised as key directions towards coexistence between fisheries and large marine predators.
... Plusieurs études ont été effectuées sur l'efficacité des bouées acoustiques, communément appelées « pingers », comme moyen d'éloignement des filets maillants pour les marsouins communs et les dauphins (Cox et al., 2004;McPherson, 2011;Bordino et al., 2013;Barlow et Cameron, 2003;Jefferson et Curry, 1996;Carretta et al., 2008;Dawson et Northridge, 2013;Gearin et al., 2000;Larsen et Eigaard, 2014a). Certains chercheurs ont souligné leurs inquiétudes concernant la possibilité d'accoutumance des mammifères marins aux alarmes acoustiques réduisant la fiabilité de cette mesure (Dawson et Northridge, 2013;Berg Soto et al., 2013). ...
... GPS distance to the coast, dimensions of known fishing gear, nearby boats and coastal landmarks) (Morteo & Hernández-Candelario, 2007;Morteo et al., 2012Morteo et al., , 2014Morales-Rincon, 2016;Rechimont et al., 2018). However, these were also calibrated regularly during the fixed point observations by means of the theodolite as described earlier (Cox et al., 2003). ...
Article
Behavioural plasticity in animals is tested whenever competitive interactions for space and/or food resources occur between wildlife and human activities. This study uses the concepts of operational and non-operational interactions between bottlenose dolphins ( Tursiops truncatus ) and artisanal fisheries in Alvarado, to search for differences in behaviour, age structure and group size. We conducted 20 surveys between 2015 and 2016, and recorded 64 groups by means of scan sampling from either a research boat or a fixed vantage point. Average dolphin group size was small ( ${\bar{\rm x}}$ = 3.2, SD = 2.2 individuals) and fewer individuals were commonly present when interaction with fisheries occurred. Operational interactions were defined within the first 30 m and occurred mainly with lone individuals (54% recorded from the lighthouse and 82% during surveys); this benchmark also accounted for higher frequencies in locomotion and feeding (χ ² = 83.10; df = 7; P < 0.001). We found a higher rate of new behavioural events for dolphin groups furthest from human activities, as well as a decrease in behaviours that imply greater body exposure as dolphins approach the fishing spots. Age structure and dolphin group size were not different during and in the absence of interaction with fisheries, but most interactions involved male dolphins. Behavioural variations in the dolphins' repertoire are likely a strategy to reduce the risk of injuries or death when interacting with human activities; these dolphins seem to have habituated to or at least tolerate fishing activities within the study area, possibly constituting a sex-biased pressure.
... Several decades of study have indicated that the efficacy of pingers is largely case-or species-specific, often linked to the experimental protocol or operational characteristics of the fishery, as well as the behaviour of species studied (reviewed in Dawson et al. 2013). For example, while pingers elicit aversive behaviours in harbour porpoises which are largely consistent across studies (Cox et al. 2001, Culik et al. 2001, Carlström et al. 2009, but see ICES 2018), results have been mixed for other species such as Hector's Cephalorhynchus hectori and bottlenose dolphins Tursiops truncatus (Stone et al. 1997, Cox et al. 2004, Leeney et al. 2007, Snape et al. 2018). In addition, while experimental studies allow researchers to control for potentially confounding operational or environmental factors (Northridge et al. 2017), results may not always be scaled up to real fishery situations, in part due to logistical, political or economic factors, such as a lack of compliance or inappropriate use of gear (Cox et al. 2007, Carretta & Barlow 2011, Dawson et al. 2013, Read 2013 or high levels of ambient noise (Hardy et al. 2012). ...
... For example, tucuxi (Sotalia fluviatilis) and captive striped dolphins (Stenella coeruleoalba) showed no reaction to acoustic alarms, while harbor porpoises produced strong behavioral responses in the same conditions (Monteiro-Neto et al., 2004;Kastelein et al., 2006a). Cox et al. (2003) found no differences in the behavior of bottlenose dolphins around acoustic alarm-equipped gillnet regardless of whether the devices were active or inactive. Brotons et al. (2008) suggested that acoustic alarms in the artisanal fisheries of the Balearic Islands reduced the rate of net interaction, but the details of behavioral responses were not given. ...
Article
Full-text available
At present, the fundamental frequencies of signals of most commercially available acoustic alarms to deter small cetaceans are below 20 kHz, but it is not well ascertained whether higher frequencies have a deterrent effect on bottlenose dolphins (Tursiops truncatus). Two captive bottlenose dolphins housed in a floating pen were subjected to a continuous pure tone at 50 kHz with a source level of 160 6 2 dB (re 1 lPa, rms). The behavioral responses of dolphins were judged by comparing surfacing distance relative to the sound source, number of surfacings, and number of echolocation clicks produced, during forty 15 min baseline periods with forty 15 min test periods (four sessions per day, 40 sessions in total). On all 10 study days, surfacing distance and the number of surfacings increased while click production decreased during broadcasts of test sound. The avoidance threshold sound pressure level for a continuous 50 kHz tone for the bottlenose dolphins, in the context of this study, was estimated to be 144 6 2 dB (re 1 lPa, rms). The results indicated that a continuous 50 kHz tonal signal can deter bottlenose dolphins from an area.
... De todos as artes de pesca, as redes de emalhar são uma das principais ameaças para as populações de pequenos cetáceos (Perrin et al., 1994;Read et al., 2006;Dawson et al., 2013). O roaz está mencionado como uma das espécies que frequentemente interage com este tipo de pescaria, raramente ficando preso nas artes (Cox et al., 2003;Buscaino et al., 2009) no entanto é, muitas vezes, responsável por redes danificadas e depredação (Lauriano et al., 2004(Lauriano et al., , 2009López et al., 2004;Brotons et al., 2008;Buscaino et al., 2009;Rocklin et al., 2009;Goetz et al., 2014). Neste trabalho, o uso de dispositivos acústicos mostrou não ter o efeito pretendido na redução da interação de golfinhos com as redes de pesca tanto ao nível da presença de animais nas proximidades da arte, danos nas redes e diminuição de depredação. ...
Thesis
Full-text available
Bycatch in fishing gear is one of the main causes that leads to the mortality of cetaceans. It is therefore important in each coastal area to have knowledge of the main affected species and fisheries involved to study the application of appropriate solutions in each case. This work had two objectives: 1. Describe the species of cetaceans stranded dead along the Algarve coast in 34 years (1983-2016), analyzing their spatial and seasonal distribution and main cause of death; 2. Analysis of the results of pilot tests with acoustic devices carried out on gillnets. For the Algarve coast for the analyzed period, there were 801 strandings with the presence of 13 Odontoceti and 3 species of Mysticeti. With the implementation of a local stranding network in 2010 it was possible to obtain more and better data, namely the cause of death. Anthropogenic causes, mainly incidental capture or bycatch were the main cause of dead, affecting about 50% of the stranded cetaceans. The common dolphin and bottlenose dolphin are two of the species that show more evidences on bycatch. In the pilot test with acoustic devices the only species to interact with the gillnet was the bottlenose dolphin. These devices have not shown to have an effect on the reduction of interaction, damage to the nets and depredation, however, the CPUE values of fish have been shown to be higher with the use of pingers. The results obtained highlight the importance of having in permanent operation a stranding network for collection of data at different levels to acquire scientific knowledge that allows application of conservation measures for these species. The interaction and bycatch of cetaceans in fishing gear proves to be an extremely complex process requiring a careful analysis of spatial, oceanographic and socioeconomic parameters so that effective solutions can be found for the preservation of these endangered species and the reduction of economic losses for the fishermen.
... Dünyanın bir çok bölgesinde, yunusların avcılık operasyonu sırasında istenmeden ağa takılmalarını (bycatch), ağa yakalanan balıkları çalmalarını (depredasyon) ve ağlara zarar vermelerini önlemek amacıyla, ağlara akustik kaçırıcılar takılarak yunusların ağlardan uzak tutulması konusunda değişik araştırmalar yapılmıştır [9][10][11][12][13][14][15][16][17][18][19][20]. Karadeniz'de özellikle istemeden yapılan yunus avcılığı (bycatch) konusunda bazı çalışmalar gerçekleştirilmiş [1,2,4,21,22,23], fakat bu çalışmalarda akustik caydırıcılar denenmemiştir. ...
Article
Full-text available
zet: Bu çalışma, Sinop yarımadası civarında 18 Aralık 2005 ve 21 Ocak 2006 tarihleri arasında 34mm ve 44mm dip uzatma solungaç ağlarında yunusların balıkları çalmaları üzerine akustik pingerlerin etkisini belirlemek amacıyla yürütülmüştür. Araştırmada, ağ göz açıklığı 34mm ve 44mm olan monofilament tora sahip sade dip uzatma ağları ve 4 adet AQUAmark 200, akustik cihaz kullanılmıştır. Akustik cihazlar 34mm ve 44mm ağ göz açıklığındaki ağların mantar yakasının uç kısımlarından, 50 kulaçlık mesafeye bağlanarak (cihazlı ağlar) denize bırakılmıştır. 34mm ağ gözü açıklığına sahip aktif ve kontrol ağlarla sırasıyla, toplam 76kg, 1115 adet ve 25,0kg, 292 adet, 44mm ağ gözü açıklığına sahip aktif ve kontrol ağlarıyla ise sırasıyla, toplam 90,5kg, 749 adet ve 18,5kg, 230 adet balık yakalanmıştır. Yine, 34mm ağ gözü açıklığına sahip aktif ağlarla kontrol ağlara göre ağırlık ve sayı olarak sırasıyla, 3,0 kat ve 3,8 kat, 44mm ağ gözü açıklığına sahip aktif ağlarla ise ağırlık ve sayı olarak sırasıyla, 4,9 kat ve 3,3 kat daha fazla balık yakalandığı belirlenmiştir (p<0,05). Ayrıca, ağların toplanması ve ürün alınması sırasında, bazı balıkların ısırılarak ağdan alındığı ve balığın özellikle baş vb. bölgelerinin ağda kaldığı, yunuslar tarafından parçalanmış olan ağ gözü iplerinde de filizlenme şeklindeki karakteristik yıpranmalar tespit edilmiştir. Sonuç olarak, monofilament dip uzatma ağlarına akustik pingerler takılarak avcılık yapıldığında yunusların ağdan uzak tutulması, ağa zarar vermesi ve yakalanan balıkları çalmasını önlemenin mümkün olabileceği görülmüştür. Yunusların üzerine akustik pingerlerin etkisinin kapsamlı olarak belirlenmesini geliştirmek için, gelecekte yunus populasyonu habitatları, alışkanlıkları, göçleri ve dağılımlarını da dikkate alan daha kapsamlı çalışmaların yapılmasına ihtiyaç vardır. Abstract: This study was carried out to determine the effects of acoustic pingers on dolphins depredation in the monofilament bottom gillnets of 34 and 44mm mesh sizes around the Sinop Peninsula between 18 December 2005 and 21 January 2006. The monofilament bottom gillnet of 34 and 44mm mesh sizes and 4 acoustic device (AQUAmark 200) were used. Acoustic devices were placed on the edge of float line with 50 fathom interval (active) then left to the sea. A total of 76kg and 1115 fish and 25kg and 292 fish were caught by active of 34mm mesh size and control, respectively, while 90.5kg and 749 fish and 18.5kg and 230 fish were caught by active of 44mm mesh size and control, respectively. 3.0-4.9 and 3.3-3.8 folds more products as weight and numerical, respectively, were obtained by active of 34 and 44mm mesh size (with acoustic device) than by control net (without acoustic device) (p<0.05). In addition to these results, during the collection of the nets and the harvesting of the fish it was observed that some of the fish were taken by biting from the net and especially the head of the fish were left in the net and characteristic sprout like frays were presented in the thread of mesh which severed by dolphins. As a result, when fishing were performed by using acoustic pingers on the monofilament gill net, these were possible being able to kept away of dolphins from net, damaging on the net by dolphins, preventing of stealing of the fish by dolphins. In order to improve the determination of the effect acoustic pingers on dolphins, more comprehensive studies are needed by taking into accound of habitats, habituate, migration and distribution of dolphins.
... Similar findings were reported by Pardalou and Tsikliras (2018). The behaviour of dolphins to relate acoustic signals from the vessel engines and acoustic deterrent devices to the presence of prey is clear evidence of the 'dinner-bell' effect (e.g., Visser, 2000;Cox et al., 2004;Carretta and Barlow, 2011;Wargo Rub and Sandford, 2020). ...
Article
Full-text available
Depredation by cetaceans on fisheries is a major issue globally, both in terms of conservation and fisheries economics. The present study conducted in Cyprus, Eastern Mediterranean Sea, aimed to understand the extent, level, and type of cetacean depredation on the albacore tuna pelagic longline fishery, and in particular to quantify and evaluate the economic consequences of depredation and identify potential dolphin-longline conflict areas and mitigation practices for management. The data were obtained from fisher's logbooks, interviews and onboard observations between June and August 2018. A novel and simple approach was applied to estimate the depredation rate and economic loss by using simple calculations including the number and weight of depredated fish, landings and fishing effort. The results revealed that there is an estimated economic loss per fishing trip of 313.07± 486.19 EUR and an estimated annual economic loss for the entire fleet of 259,272 EUR from depredation caused by cetaceans. The study also estimated that 16,639 albacore tunas were depredated in 2018 and the depredation rate ranged between 0% to 100% with a mean depredation rate of 17% per fishing trip. Depredation by the common bottlenose dolphin and striped dolphin was reported in more than 50% of their fishing trips. Other species that were found to be involved in depredation were the neon flying squid, the shortfin mako shark and the Risso's dolphin. This is the first official record worldwide of depredation from the common bottlenose dolphin, the striped dolphin and the neon flying squid on the pelagic longline albacore tuna fishery. A total bycatch of 62 individuals of common bottlenose dolphins and one individual of stripped dolphin were reported in interviews as a result of depredation on bait and catch. The study also identified depredation hotspots and possible depredation mitigation measures. Such information could support the development of management action plans and measures to minimise interactions between cetaceans and pelagic longlines.
Chapter
Full-text available
Some mammalian species that have not succumbed to pervasive human impacts and encroachments have managed to adapt to certain types of human activities. Several odontocetes have modified their behavior to persist, and in some cases even prosper, in human-altered riverine, coastal, and oceanic habitat. Examples include cooperation with fishers to catch fish, depredation on fishing gear, scavenging, and other kinds of opportunistic foraging (e.g., behind trawlers, around fish farms, or near built structures such as dams and offshore platforms). Some populations have adapted to life in human-made channels and waterways. We review information on the variety of odontocete adaptations to human encroachment, highlight some of the risks and benefits, and try to single out factors that may trigger or contribute to adaptation. Adaptation often brings wildlife into close contact with humans, which leads to conflict. We discuss the challenges of coexistence and contend that we humans, too, need to adjust our behavior and change how we perceive and value wildlife for coexistence to be possible. In addition to good management and conservation action, tolerance on our part will be key for allowing wildlife—odontocetes included—to persist. We advocate cultural and even spiritual shifts that can foster tolerance, nurture the social change that leads to appreciation for wildlife, and create more opportunities to preserve nature.
Poster
Full-text available
Trial of acoustics deterrents for prevention of bottlenose dolphin depredation on gillnets
Data
Full-text available
El Mar Argentino cuenta con una importante diversidad de mamíferos marinos que totalizan aproximadamente 50 especies. Si bien en nuestro país no existe en la actualidad captura intencional de mamíferos marinos, se han identificado otras amenazas que pueden afectar su estado de conservación, entre las cuales se destacan la captura incidental por las artes de pesca. El 3 de diciembre de 2015 el Consejo Federal Pesquero aprobó mediante Resolución CFP Nº 11/2015 el “Plan de Acción Nacional para Reducir la Interacción de Mamíferos Marinos con Pesquerías en la República Argentina (PAN Mamíferos Marinos)”, cuyo objetivo principal es contribuir al manejo ecosistémico de las pesquerías del Mar Argentino, evaluando las interacciones entre éstas y los mamíferos marinos a fin de disminuir los impactos negativos sobre ambos. Dicho PAN fue elaborado en forma conjunta por la Subsecretaría de Pesca y Acuicultura de la Nación y esta Secretaría, con la participación de organismos provinciales, instituciones científicas y académicas y ONGs. La preparación final de este PAN fue realizada por María Laura Tombesi y Débora Winter (Secretaría de Ambiente y Desarrollo Sustentable). El capítulo “Pesquerías en Argentina” fue elaborado por Ramiro P. Sánchez, Gabriela Navarro, Mariano Monsalvo y Gustavo Martínez Puljak (Subsecretaría de Pesca y Acuicultura de la Nación) y contó con la colaboración de Laura Prosdocimi. El capítulo “Introducción a la captura incidental y los impactos de las interacciones operacionales y específicas” fue elaborado por Enrique Alberto Crespo, Silvana Laura Dans, Susana Noemí Pedraza, Néstor Aníbal García (Centro Nacional Patagónico y Universidad Nacional de la Patagonia) y Mariano Koen Alonso (Department of Fisheries and Oceans, Saint John’s, Newfoundland, Canada). El capítulo “Captura incidental de franciscana” fue elaborado por Luis Cappozzo (Museo de Ciencias Naturales Bernardino Rivadavia) y el capítulo “Mitigación de la captura incidental de mamíferos marinos” por Pablo Bordino (Fundación Aquamarina).
Article
Bottlenose dolphins, Tursiops truncatus, co-exist with artisanal fisheries in Kerkennah Island (Southern part of Tunisia) and are blamed for damage to some fisheries. The resulting catch loss engenders hostility from fishers, and interactions between dolphins and nets can result in bycatch mortality. One potential mitigation measure is the placement of marine mammal acoustic deterrent devices, or pingers, on the nets. With the support of local fishermen, Aquamark 210 pingers were deployed on trammel net set for cuttlefish (Sepia officinalis) during the spring season (March 2010 to May 2010), when there is more interaction with dolphin. Throughout the period of experimentation, we have used trammel nets equipped with pingers (pinger net) and trammel nets that have played the role of control (control net). During the trial, data on fishing operations were recorded by onboard observers. We analysed two response variables, the presence or absence of evidence that dolphins had interacted with the net and catch per unit effort. The pingers attracted the bottlenose dolphins (T. truncatus) to trammels nets. Overall, pinger nets were more attacked than control nets. Tested pingers also appeared to have affected on fishery target species. The catch per unit effort decreased by 22%. Our results suggest that Aquamark 210 pingers in the artisanal fisheries of Kerkennah islands increase the rate of net interaction, but it was recommended to investigate how bottlenose dolphin (T. truncatus) may interact with other acoustic devices.
Article
This study was conducted at the Unye-Ordu coasts of the South-eastern Black Sea, from May 2015 and February 2017, to investigate the frequency of dolphins-bottom gillnet fisheries interactions, the role of using acoustic deterrent in reducing the damage inflicted by the dolphins to the gillnets and to the fish caught in the gillnets. For this purpose, two gillnet sets with similar technical and equipment characteristics were prepared. While one of the groups had acoustic deterrent (active group), the other did not have acoustic deterrent (control group). In the study were used Future Oceans (70 kHz) deterrent. During the study, in only 3 of the 65 fishing trials have determined the interaction of dolphins with gillnets. It was determined that the number of holes in the gillnets caused by the dolphins was 36.3% less in the nets with acoustic deterrent than the control nets. On the other hand, the CPUE value of the whiting was estimated as 2.01 ± 0.23 kg km-1 s-1 in the gillnets with acoustic deterrent and 1.97 ± 0.24 kg km-1 s-1 in the control nets. These results showed that the use of acoustic deterrent does not have a negative effect on the catch of whiting caught in the gillnets.
Thesis
Full-text available
The conflict between fisheries and cetaceans exists in many areas around the world, and the Bulgarian territorial waters of the Black Sea are no exception. In Bulgaria, almost missing studies on the conflict’s nature and extent, and the government and local authorities do not have appropriate policies for conflict management. Studies of the different fishing gears in the Bulgarian Black Sea waters and the interactions that cetaceans have with them are presented in current thesis. Various methods have been used in the dissertation aiming to identify the different sides of the interaction between Bulgarian fisheries and cetaceans.
Chapter
The main threat of franciscana dolphins (Pontoporia blainvillei) is the incidental bycatch in artisanal fishing gillnets. Several studies were implemented during the past two decades along with the local fishing communities in Brazil, Uruguay, and Argentina in order to address this conservation issue. Acoustic deterrent devices, commonly known as “pingers”, were shown to be one of the most effective bycatch mitigation method. Bottom longlines were tested as alternative fishing gear and resulted in reduced bycatch but fishermen found them difficult to implement. Gillnets modified to be acoustically reflective and have greater stiffness were ineffictive for reducing bycatch. The conclusions from this body of research is important for informing effective strategies for mitigating franciscana bycatch.
Article
Full-text available
Small cetaceans are susceptible to incidental mortality in the various forms of gillnet fisheries throughout their range. Research conducted since 1994 has shown that acoustic alarms (pingers) emitting high-frequency pulsed sounds effectively reduce the number of harbor porpoise Phocoena phocoena casualties in sink gillnets. However, the mechanisms behind the effects of pingers were still not understood. Until now, advantages and risks associated with their widespread use could not be evaluated. Here we present the results of 2 field experiments: (1) theodolite-tracking of harbor porpoises exposed to a single PICE-pinger in Clayoquot Sound, Vancouver Island, Canada and (2) herring Clupea harengus capture rates in surface gillnets equipped with and without acoustic alarms (Dukane Netmark 1000, Lien, PICE) in the Baltic Sea herring fishery at Rugen Island, Germany. Our results show that harbor porpoises do not seem to react to an experimental net in their foraging area (n = 172 groups, median group size = 2 porpoises). Porpoise distance from the mid-point of the net was distributed around a median of only 150 m (range 4 to 987 m). A net equipped with an acoustic alarm, however, was avoided (n = 44 groups) within audible range (distance distribution median = 530 m, range 130 to 1140 m). The porpoises were thus effectively excluded from the ensonified area. Herring, one of the main prey species of harbor porpoises, were not affected by the acoustic alarms tested (n = 25 407 fish captured). The advantages and risks of using acoustic alarms to mitigate by-catch are discussed.
Article
Full-text available
1Some effects of fisheries on the associated biological systems are reviewed and management options and their inherent risks are considered.2In addition to the effects on target species, other sensitive groups impacted by fishing are considered including marine mammals, turtles, sea birds, elasmobranchs and some invertebrates with low reproductive rates.3Other impacts discussed include the destruction of benthic habitat, the provision of unnatural sources of food and the generation of debris.4Management options are considered including the designation of marine protected areas, risk aversion, and the burden of proof.5A balanced consideration of the risks and consequences of ‚Type 1’ and ‚Type II’ errors is advocated.
Article
Full-text available
Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz ever y4sa t al evel of 133-145 dB re 1 μPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were presumed to be clearly audible to harbour porpoises at ranges of 0.1- 0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.
Article
Full-text available
Field tests were conducted on the effectiveness of acoustic alarms (pingers) in reducing the incidental catch of harbour porpoise (Phocoena phocoena) in a salmon gillnet fishery in northern Washington in July and August of 1995-1997. The alarms produced a broadband signal with peaks at 3 and 20kHz, with mean source levels between 121.7-124.7dB re 1 mu Pa at 1m. For 1995 and 1996 combined, 47 harbour porpoise were taken in control nets and only two were taken in alarmed nets. The alarms significantly reduced the bycatch of harbour porpoise for both seasons (1995: chi super(2) = 5.28, df = 1, p = 0.02; 1996: chi super(2) = 11.2, df = 1, p = 0.001). In 1997, all nets were alarmed and 12 porpoise were taken; however, the expected catch without alarms would have been 79. There were no significant differences in catch rates of chinook salmon (Oncorhynchus tshawytscha) ( chi super(2) = 0.31. df = 1, p = 0.58), or sturgeon (Acipenser sp.) ( chi super(2) = 1.44, df = 1, p = 0.23) in control or alarmed nets. There were also no significant differences in the bycatch of harbour seals (Phoca vitulina) ( chi super(2) = 0.09, df = 1, p = 0.76) or depredation of salmon by seals in nets with and without alarms ( chi super(2) = 0.07, df = 1, p = 0.79). The results of these studies indicate that acoustic alarms significantly reduce the probability of harbour porpoise entanglement in bottom-set gillnets in the fishery without reducing the catch of target fish species.
Article
Full-text available
It has been suggested that most teleost fishes cannot detect sounds higher than 2 or 3 kHz (ref. 1). However, we report here that at least one species of clupeid fish (herrings and shads), the American shad (Alosa sapidissima), can detect sounds up to 180 kHz. We speculate that clupeids are able to detect the ultrasonic clicks of one of their major predators, echolocating cetaceans.
Article
Full-text available
Records show that the common skate, Raia batis, has declined in abundance in the Irish Sea since the early years of the twentieth century, and is now very rare. As I report here, it is possible to calculate the highest mortality which the species will withstand without collapsing. It is likely that the mortality due to fishing has exceeded this level for some time and that the species will not recover while fishing continues. This represents the first clear case of a fish brought to the brink of extinction by commercial fishing.
Article
Full-text available
1.Entanglement in gillnets constitutes the greatest known threat to populations of small cetaceans. In 1988, in response to data on the distribution and abundance, incidental catch, reproduction and population biology of Hector's dolphins, and after an extended period of public consultation, New Zealand's Department of Conservation created a 1170 km2 Marine Mammal Sanctuary. Within this area, gillnetting on a commercial scale is illegal and amateur fishers may only set gillnets in specific times and places.2.This paper summarizes the salient points of research that led to the creation of the sanctuary, briefly describes the process by which the sanctuary was established, and offers some comments on the information required for conservation management of small cetaceans.
Article
Full-text available
Despite the vaquita being commonly cited as one of the most endangered marine mammals in the world, there is still disagreement over which factors put the species at greatest risk of extinction. This lack of agreement hinders management decisions needed to reduce the risk to the species. To expedite decision-making we consider four major risk factors. Habitat alteration from reduced flow of the Colorado River does not currently appear to be a risk factor because productivity remains high in vaquita habitat. Pollutant loads are low and pose low to no risk. Reduced fitness from inbreeding depression and loss of genetic variability are unlikely to pose high risk currently, though risk will increase if vaquitas remain at low abundance over long periods of time. Mortality resulting from fisheries bycatch poses high risk. Thus, short term management should not be hindered by uncertainty in estimating the risk of these factors, and primary conservation efforts should be directed to wards immediate elimination of incidental fishery mortality.
Article
Full-text available
Large bycatches of harbour porpoises (Phocoena phocoena) occur in gillnet fisheries throughout the Northern Hemisphere. Several mitigation measures, including acoustic deterrent devices or 'pingers', have been used in efforts to reduce this bycatch. The potential exists for harbour porpoises to habituate to pingers, thus reducing their effectiveness over time. A field experiment was conducted to test the hypothesis that porpoises habituate to the sound produced by pingers. Porpoise echolocation and movements were monitored around a mooring equipped with a pinger (Dukane NetMark™ 1000) for three months in summer 1998 in the Bay of Fundy. Using a mean-shift model it was estimated that porpoises were initially displaced 208m from the pinger (p = 0.019), but this displacement diminished by 50% within four days (p = 0.019). Using a probability model it was demonstrated that the probability of porpoises within 125m of the pinger initially decreased when the pinger was turned on, but then increased to equal the control in 10-11 days. Echolocation rate (p < 0.001) and occurrence (p < 0.001) were significantly reduced in the vicinity of the pinger. These results indicate that porpoises habituated to the Dukane NetMark™ 1000 pinger and are not alerted to echolocate in the presence of nets by pingers.
Article
Full-text available
A global review of mortality of porpoises in gillnet fisheries indicates that individuals of all six species become entangled and die in gillnets. Harbor porpoises Phocoena phocoena are taken throughout their range and several populations are in decline, at least partly as a result of gillnet entanglement. The vaquita P. sinus is the most endangered cetacean species, and gillnet fisheries in the northern Gulf of California, Mexico, threaten the single population with extinction. Burmeister's porpoises P. spinipinnis are taken in several gillnet fisheries in South America; populations in Peru appear to be most severely affected. In southern South America, spectacled porpoises Australophocaena dioptrica are known to be caught in gillnets, but the effects of these takes are unknown. Primarily in the western North Pacific, Dall's porpoises Phocoenoides dalli are entangled in driftnet fisheries in large numbers, but so far major impacts have not been apparent. Although taken in gillnets in many areas throughout the Indo-Pacific region, only those finless porpoise Neophocaena phocaenoides populations in China are considered to be threatened by gillnet catches. In most circumstances, existing information is insufficient to evaluate the effects of gillnets on porpoise v to be severe. Gillnets represent the single most important threat to porpoises as a group, and this may be an example of a ‘no technical solution problem’. We conclude that better documentation of catches and new approaches to dealing with porpoise/gillnet interaction problems are needed in order to prevent the loss of several species and populations.
Article
Full-text available
Incidental mortality in gillnets is probably the most serious global threat to dolphin and porpoise populations. In 1994, a well-designed study demonstrated a 92% reduction in bycatch of harbour porpoises in sink gillnets equipped with acoustic pingers. This result has not yet been fully replicated; in the New Hampshire area where the experiment was conducted or elsewhere. Statistical power analyses indicate that such studies are feasible only in areas of high entanglement rate. Currently unanswered research questions include whether the 1994 results can be replicated, whether habituation might decrease effectiveness over time, and what the mechanism of deterrence is. Practical constraints include the size, cost and battery life of current pingers, and whether their use could be monitored cost-effectively. From a management perspective, even if the effectiveness of pingers is confirmed, widespread incorporation of them into gillnets may not alone be sufficient to meet the requirements of the US Marine Mammal Protection Act. For this reason scientists, managers and fishers must continue to explore other options, including time/area closures and encouragement of more selective fishing methods.
Article
Many marine mammals communicate by emitting sounds that pass through water. Such sounds can be received across great distances and can influence the behavior of these undersea creatures. In the past few decades, the oceans have become increasingly noisy, as underwater sounds from propellers, sonars, and other human activities make it difficult for marine mammals to communicate. This book discusses, among many other topics, just how well marine mammals hear, how noisy the oceans have become, and what effects these new sounds have on marine mammals. The baseline of ambient noise, the sounds produced by machines and mammals, the sensitivity of marine mammal hearing, and the reactions of marine mammals are also examined. An essential addition to any marine biologists library, Marine Mammals and Noise will be especially appealing to marine mammalogists, researchers, policy makers and regulators, and marine biologists and oceanographers using sound in their research.
Article
Georges Bank, a shallow submarine plateau located off the New England coast, has supported valuable commercial fisheries for several centuries. The region is characterized by high levels of primary productivity and, historically, high levels of fish production, Within the last four decades Georges Bank has been subjected to major perturbations that have profoundly altered levels of catch, abundance, and species composition. The arrival of distant water Beets during the early 1960s resulted in dramatic increases in effective fishing effort and the subsequent commercial collapse of several fish populations. Total fish biomass is estimated to have declined by >50% on Georges Bank during the period of operation of the distant water Beets, The implementation of extended jurisdiction (the 200-mile [370.4-km] limit) in 1977 was followed by modernization and increased capacity of the domestic Beet, resulting in a second perturbation to the system that resulted in further declines in groundfish populations to historically low levels, A subsequent increase in the abundance of species of low commercial value was documented, with an apparent replacement of gadid and Bounder species by small elasmobranchs (including dogfish sharks and skates), Examination of feeding guild structure suggests that this switch in species dominance may have been Linked to a competitive release, The small elasmobranchs, notably dogfish sharks, also prey on species of commercial importance (primarily small pelagics, including herring and mackerel), The cumulative impacts on the groundfish populations as a result of intense exploitation and predation pressure may have been further exacerbated by effects of fishing gear on the physical structure of the habitat. Implications for the development of an ecosystem-based management approach are described.
Article
A broad-based public consensus has emerged that bycatch should be minimized to levels approaching insignificance. This view, as reflected in U.S. and worldwide legislation and agreements, demonstrates the widely held belief that discarded portions of fishery catches (including economic resources, protected species, and unobserved mortalities of animals not caught) represent an unacceptable waste of natural resources. Bycatches in their various forms can have significant consequences for populations, food webs, and ecosystems. The economic effects of bycatches can influence not only the levels of yields to individual fisheries, but also may have major effects on allocations among competing fisheries. The lack of comprehensive monitoring programs in most areas to assess bycatches and integrate them into population and multispecies models seriously impedes a full understanding of bycatch consequences and the efficacy of measures for their amelioration. Nevertheless, where evidence for significant bycatches exists, a risk-averse and perhaps adaptive management philosophy is clearly warranted. Establishing the benefits and costs associated with bycatch management is a priority as managers attempt to define the practicality of bycatches approaching zero given the institutional, scientific, and industry resources necessary to accomplish the job.
Article
Past statistical power analyses show that abundance estimation techniques usually have high β, the probability of not rejecting a null hypothesis when it should have been, and that only large effects are detectable. I review relationships among β, power, detectable effect size, sample size, and sampling variability. I show how statistical power analysis can help interpret past results and improve designs of future experiments, impact assessments, and management regulations. I make recommendations for researchers and decision makers, including routine application of power analysis, more cautious management, and reversal of the burden of proof to put it on industry, not management agencies. -from Author
Article
During a 21-month study, 53 individual bottle-nosed porpoises were recognized by photographs of their dorsal fins. They traveled in small subgroups (mean size = 15) composed of a stable core of five animals plus other individuals that varied greatly from sighting to sighting.
Article
The three sections of this book are devoted to (1) a discussion of the general concepts of drive, directiveness and purpose and instinct, (2) six chapters on general features of the learning process, including habituation, associative learning, latent learning and insight, together with a discussion of physiological mechanisms in learning, and (3) eight chapters devoted to a systematic review of the learning abilities of the main animal groups. In the latter section the European literature of recent years is extensively reviewed. Bibliography and three indices: scientific names of animals, authors cited, and general topical index. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
AbstractA controlled experiment was carried out in 1996–1997 to determine whether acoustic deterrent devices (pingers) reduce marine mammal bycatch in the California drift gill net fishery for swordfish and sharks. Using Fisher's exact test, bycatch rates with pingers were significantly less for all cetacean species combined (P < 0.001) and for all pinniped species combined (P= 0.003). For species tested separately with this test, bycatch reduction was statistically significant for short-beaked common dolphins (P= 0.001) and California sea lions (P= 0.02). Bycatch reduction is not statistically significant for the other species tested separately, but sample sizes and statistical power were low, and bycatch rates were lower in pingered nets for six of the eight other cetacean and pinniped species. A log-linear model relating the mean rate of entanglement to the number of pingers deployed was fit to the data for three groups: short-beaked common dolphins, other cetaceans, and pinnipeds. For a net with 40 pingers, the models predict approximately a 12-fold decrease in entanglement for short-beaked common dolphins, a 4-fold decrease for other cetaceans, and a 3-fold decrease for pinnipeds. No other variables were found that could explain this effect. The pinger experiment ended when regulations were enacted to make pingers mandatory in this fishery.
Article
In an attempt to test the effectiveness of sounds in deterring harbor porpoises from nets and reducing porpoise bycatch in gill net fisheries, two harbor porpoises, kept in a large floating pen at Neeltje Jans, The Netherlands, were subjected to 3 different underwater sounds. The effect of each sound was judged by comparing the animals' behavior during a 15-min test period with that during a 15-min baseline period immediately before the test and a 15-min recovery period immediately after the test. The effects of the alarms were quantified as the distance between the porpoises' surfacings and the alarm and the animals' respiration rates. Each alarm was tested in two positions in the pen. The behavior observed was related to the sound-pressure-level distribution in the pen. All three alarms: the standard Dukane alarm (a commercially available alarm with a regular pulse interval of 4.3 sec used to deter dolphins from fishing nets), the random Dukane alarm (the same alarm with random pulse interval of between 2 and 30 sec), and the “bird alarm” (a sound from a generator) resulted in increases in both the distance of the animals' surfacings from the alarms and their respiration rates. The standard Dukane alarm and the bird alarm were more effective than the random Dukane alarm in inducing the animals to swim away from the sound source.
Article
The most serious danger to dolphins and porpoises around the world is the threat from various forms of gill-net fishing. One potential way to reduce the number of deaths of marine mammals is the use of active acoustic alarms to warn animals about the presence of nets1. Until now, acoustic alarms have not been tested in field experiments with sufficient statistical power2. Here we describe a field experiment showing that acoustic alarms are effective at reducing the number of deaths of harbour porpoises (Phocoena phocoena) in sink gill-nets.
Article
Are extinctions of marine vertebrates as rare and unlikely as current data indicate? Long-term research surveys on the continental shelf between the Grand Banks of Newfoundland and southern New England reveal that one of the largest skates in the northwest Atlantic, the barndoor skate (Raja laevis), is close to extinction. Forty-five years ago, research surveys on St. Pierre Bank (off southern Newfoundland) recorded barndoor skates in 10% of their tows; in the last 20 years, none has been caught, and this pattern of decline is similar throughout the range of the species.
Article
Many odontocetes die annually in gillnet fisheries. Why they become entangled is not yet clear. Maybe some species detect the nets too late to avoid collision. Therefore, the target strength of 11 types of bottom-set gillnets was measured under 0 and 45 degrees angles of incidence. From these target strengths and from knowledge on the echolocation abilities of two odontocete species (harbour porpoises, bottlenose dolphins), the detection ranges of the nets by these small cetaceans could be estimated. The 90% detection range by echolocating harbour porpoises, approaching the nets at right (perpendicular) angles under low noise level conditions, varied between 3 and 6 m depending on the net type. For bottlenose dolphins, under high noise conditions, the 90% detection range varied between 25 and 55 m. At other angles of approach, the estimated detection ranges are shorter. The study suggests that echolocating bottlenose dolphins can detect nets in time to avoid collision, whereas echolocating harbour porpoises cannot in most cases. Suggestions for future research to reduce small cetacean bycatch by improving the nets' detectability by echolocation are given.
Status and aspects of the ecology and behavior of the Baiji, Lipotes vexillifer, in the Lower Yangtze River
  • Z Kaiya
  • L W F Yuemin
  • R L Perrin
  • Jr Brownell
  • Z Kaiya
  • L Jiankang
Kaiya, Z., Yuemin, L., 1989. Status and aspects of the ecology and behavior of the Baiji, Lipotes vexillifer, in the Lower Yangtze River. In: W.F. Perrin, R.L. Brownell, Jr., Z. Kaiya, L. Jiankang (Eds.), Biology and Conservation of the River Dolphins: Proceedings of the Workshop on Biology and Conservation of the Platanistoid Dol-phins held at Wuhan, People’s Republic of China, 28–30 October 1986. IUCN Species Survival Commission
Interac-tions between Harbour Porpoises and Fishing Nets: Laboratory Studies to Reduce By-catch. De Spil Bycatch estimates of coastal bot-tlenose dolphin (Tursiops truncatus) in U.S. Mid-Atlantic gillnet fisheries for
  • P E Nachtigall
  • W Au
  • J Lien
  • A J Read
  • D L Palka
  • M C Rossman
Nachtigall, P.E., Au, W., Lien, J., Read, A.J. (Eds.), 1995. Interac-tions between Harbour Porpoises and Fishing Nets: Laboratory Studies to Reduce By-catch. De Spil, Woerden, Holland. Palka, D.L., Rossman, M.C., 2001. Bycatch estimates of coastal bot-tlenose dolphin (Tursiops truncatus) in U.S. Mid-Atlantic gillnet fisheries for 1996 to 2000. Northeast Fisheries Science Center Reference Document 01-15. Available from Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543.
Status and aspects of the ecology and behavior of the Baiji, Lipotes vexillifer, in the Lower Yangtze River
  • Z Kaiya
  • L Yuemin
Kaiya, Z., Yuemin, L., 1989. Status and aspects of the ecology and behavior of the Baiji, Lipotes vexillifer, in the Lower Yangtze River.
Environmental effects of fishing. Aquatic Conservation: Marine and Freshwater Ecosystems
  • P K Dayton
  • S F Thrush
  • M T Agardy
  • R J Hofman
Dayton, P.K., Thrush, S.F., Agardy, M.T., Hofman, R.J., 1995. Environmental effects of fishing. Aquatic Conservation: Marine and Freshwater Ecosystems 5, 1-28.
Marine Mammals and Noise Risk factors affecting the vaquita (Phocoena sinus)
  • W J Richardson
  • Greene Jr
  • C G Malme
  • C I Thomson
Richardson, W.J., Greene Jr., C.G., Malme, C.I., Thomson, D.H., 1995. Marine Mammals and Noise. Academic Press, San Diego. Rojas-Bracho, L., Taylor, B.L., 1999. Risk factors affecting the vaquita (Phocoena sinus). Marine Mammal Science 15, 974–989.
A Global Assessment of Fisheries Bycatch and Discards. FAO (UN Food and Agriculture Organization). FAO Fisheries Technical Paper 339
  • D L Alverson
  • M H Freeburg
  • S A Murawski
  • J G Pope
Alverson, D.L., Freeburg, M.H., Murawski, S.A., Pope, J.G., 1994. A Global Assessment of Fisheries Bycatch and Discards. FAO (UN Food and Agriculture Organization). FAO Fisheries Technical Paper 339.
Atlantic and Gulf of Mexico Marine Mammal Stock Assessments-2001
  • G T Waring
  • J M Quintal
  • S L Swartz
Waring, G.T., Quintal, J.M., Swartz, S.L. 2001. U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments-2001. NOAA Technical Memorandum NMFS-NE-168.
Report of the workshop on bycatch mitigation measures in static fisheries
International Whaling Commission, 2001. Report of the workshop on bycatch mitigation measures in static fisheries. Journal of Cetacean Management and Research 3 (Supplement), 292-296.
Taking of marine mammals incidental to commercial fishing operations; harbour porpoise take reduction plan regulations. Department of Commerce; National Oceanic and Atmospheric Administration 50CFR Part 229
Federal Register, 1998. Taking of marine mammals incidental to commercial fishing operations; harbour porpoise take reduction plan regulations. Department of Commerce; National Oceanic and Atmospheric Administration 50CFR Part 229. Federal Register 63 (231), 66464-66490.
Interactions between Harbour Porpoises and Fishing Nets: Laboratory Studies to Reduce By-catch
  • P E Nachtigall
  • W Au
  • J Lien
Nachtigall, P.E., Au, W., Lien, J., Read, A.J. (Eds.), 1995. Interactions between Harbour Porpoises and Fishing Nets: Laboratory Studies to Reduce By-catch. De Spil, Woerden, Holland.
Bycatch estimates of coastal bottlenose dolphin (Tursiops truncatus) in U.S. Mid-Atlantic gillnet fisheries for 1996 to 2000. Northeast Fisheries Science Center Reference Document 01-15
  • D L Palka
  • M C Rossman
Palka, D.L., Rossman, M.C., 2001. Bycatch estimates of coastal bottlenose dolphin (Tursiops truncatus) in U.S. Mid-Atlantic gillnet fisheries for 1996 to 2000. Northeast Fisheries Science Center Reference Document 01-15. Available from Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543.
Gillnets and Cetaceans. Reports of the International Whaling Commission
  • W F Perrin
  • G P Donovan
  • J Barlow
Perrin, W.F., Donovan, G.P., Barlow, J. (Eds.), 1994. Gillnets and Cetaceans. Reports of the International Whaling Commission, Special Issue 15.
Depredation by Bottlenose Dolphins on Gill Nets in Dare County
  • S C Hagedorn
Hagedorn, S.C., 2002. Depredation by Bottlenose Dolphins on Gill Nets in Dare County, North Carolina. Masters Project, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC. International Whaling Commission, 2000. Report of the sub-committee on small cetaceans. Journal of Cetacean Management and Research 2 (Supplement), 235-263.
Conservation of Hector's dolphins
  • Dawson
Large-scale disturbance and the structure of marine systems
  • Fogarty
A global review of porpoise (Cetacea
  • Jefferson