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Behavioral Responses of Bottlenose Dolphins, Tursiops truncatus, to Gillnets and Acoustic Alarms
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.
... 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. ...
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.
... 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). ...
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). ...
... 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). ...
... 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). ...
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.
... Guzmán, 2015). Otros estudios han analizado comportamientos relacionados con interacciones con embarcaciones (Mattson et al., 2005;Dans et al., 2008) y con la pesca (Simões-Lopes et al., 1998;Bearzi, 2002;Cox, et al., 2003;Gonzalvo et al., 2008;Morteo et al., 2012;Stolen et al., 2012;Jaiteh et al., 2013), los cuales son descritos en las secciones 2.5 y 2.6 de este documento. ...
... no operacional) o capturando las presas desde los artes de pesca (interacción operacional)(Simões-Lopes et al., 1998;Bearzi, 2002;Cox et al., 2003;Morteo y Hernández, 2007;Brotons et al., 2008;Morteo et al., 2012;Jaiteh et al., 2013;Nadeau, 2013).La pesca de subsistencia también denominada pesca artesanal, es una actividad de bajo nivel tecnológico, que generalmente involucra embarcaciones menores (<10 m de eslora), con motores pequeños (< 80 hp), cuyas actividades se desarrollan cerca de la costa (< 20 km mar adentro). Asimismo, se emplean diversas artes de pesca como la línea de mano, el palangre, redes agalleras, atarraya, el chinchorro y el trasmallo(Fig. ...
relationship of organisms with their environment influences their behavioral plasticity, modifying their behavior in response to stimuli or pressures, and consequently affecting the ecological relations of species. The expansion of human activities leads to conflicts between humans and wildlife, and these are mainly associated with interactions during competition for space and / or food availability. These conflicting interactions have been reported on the shores of the Gulf of Mexico, where the artisanal fishermen denounce the looting and damage of their equipment by tursiones (Tursiops truncatus), which are sometimes injured or killed. The objective of this work was to study the behavior of bottlenose dolphins in their interaction with artisanal fishery in the coastal waters of Alvarado, establishing: 1) the first etogram for the case, 2) the behavioral differences associated with fishing, and 3) the variations in relation to the age and group size of the dolphins interacting with this activity. Between 2015 and 2016, 64 groups have been observed by sampling scanning from boats and fixed points. We obtained 4,898 records that used body patterns and other characteristics associated with the behavioral deployment form. The events were organized in the states: food, locomotion, social, socio-sexual, play and rubbing with objects. There were significant differences in the frequency (X2 = 55.93, gl = 5, p <0.001) and the local rate of behavior in the presence and absence of fishing activity (X2 = 25.16, gl = 5; However, their intensity was lower than in the absence of fishing (5.3 min-1 vs 7.0 min-1) and in relation to the other behaviors, that in general had low frequencies. During the fishing activity, the dolphins that interacted most were adults, however, no significant group differences were found in the proportion of individuals by age in relation to the fishery ( X2 = 1429, gl = 2, p <0.4894). The average group size comprised two individuals in both conditions (without = 42% and con = 54% interaction), so no differences were observed (X2 = 1.56, gl = 15, p <0.001); however, the direct operational interaction to the net was performed by 51% individually, and mostly (84%) in the first 30 m. The behavioral differences partially support the hypotheses and evidence the influence of human activities on the behavioral display of the T. truncatus dolphins in Alvarado. The lack of evidence on differences in age and group size suggest the need for a larger sample size, as well as the habituation of some dolphins to the fishery interaction, possibly being these experienced dolphins that will pass; these dolphins would have to be photo-identified to determine their contribution in the effects on the behavior of the population, derived from their interaction with the artisanal fishery.
... Several studies have addressed mitigating measures to reduce the impact of dolphins on trammel net fisheries. The most widely applied measure is to use pingers (Brotons et al., 2008b;Buscaino et al., 2009;Carretta and Barlow, 2011;Carretta et al., 2008;Cox et al., 2004;Dawson et al., 2013;Gazo et al., 2008;Kraus, 1999;Maccarrone et al., 2014;Schakner and Blumstein, 2013;Snape et al., 2018). However, the results do not clearly support the use of pingers. ...
... However, the results do not clearly support the use of pingers. While their short-term use may have some effect on reducing the number of interactions and damage, in the mid-to long-term, dolphins get adapted (Cox et al., 2004). Furthermore, in the long term, pingers may elicit a dinner-bell effect (Carretta and Barlow, 2011;Gazo et al., 2008;Richardson et al., 2013;Schakner and Blumstein, 2013). ...
... Other non-echolocating mammals, such as dugongs (Dugong dugon), exhibited no behavioural change when close to 4 or 10 kHz pingers (Hodgson et al. 2007), highlighting that bycatch technologies should not be implemented in fisheries before thorough testing on bycatch species. Cox et al. (2004) reported no avoidance response from common bottlenose dolphins (Tursiops truncatus) around gillnets equipped with pingers, except reduced entry into a 100 m buffer around nets when the alarms were active. The results from Kastelein et al. (2006) and Cox et al. (2004) provided evidence that not all odontocetes avoid pingers, perhaps explained by behavioural flexibility in these species . ...
... Cox et al. (2004) reported no avoidance response from common bottlenose dolphins (Tursiops truncatus) around gillnets equipped with pingers, except reduced entry into a 100 m buffer around nets when the alarms were active. The results from Kastelein et al. (2006) and Cox et al. (2004) provided evidence that not all odontocetes avoid pingers, perhaps explained by behavioural flexibility in these species . In contrast, Barlow and Cameron (2003) conducted a study on gillnets on the USA Pacific coast, where there were significant reductions in bycatch of odontocetes and pinnipeds (pooled across species-eight odontocetes and two pinnipeds), which were led by significant bycatch reductions of 85.1% and 68.9% in common dolphin and California sea lion respectively. ...
Marine megafauna are critical for marine ecosystem health and their removal can cause food webs to collapse. Methods to reduce marine megafauna mortality can result in conflict between scientists, conservationists, fishers and fisheries management due to real or perceived effects on target catch, income and food security. Sensory deterrents have been used in attempts to mitigate bycatch and retain target catch quantity and quality. Here, we completed a systematic review of 116 papers, plus 25 literature reviews published between 1991 and 2022, to investigate potential for sensory deterrents to mitigate bycatch across four marine megafauna taxonomic groups (marine mammals, sea turtles, seabirds and elasmobranchs). Lights on gillnets are the only technology so far to result in significant bycatch reductions across all four taxonomic groups. It is difficult to make generalisations about the efficacy of sensory deterrents and their ability to deliver consistent bycatch reductions. The efficacy of each method is context dependent, varying with species, fishery and environmental characteristics. Further research is recommended for field studies assessing bycatch mitigation in all sensory deterrents, including combinations of deterrents, to assess effects on target and non-target species. The associated issues of habituation, habitat exclusion and foraging around fishing gear are important, although reducing mortality of vulnerable species should remain the highest priority for conservation and preserving ecosystems that fishers depend on. Multiple complementary measures will be required to achieve consistent bycatch reduction targets in many fisheries, of which sensory deterrents could play some part if implemented appropriately.
... 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. ...
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.
... 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. ...
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). ...
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.
... 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). ...
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.
... 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). ...
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.
... 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). ...
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.
... 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. ...
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.
... The latter have been extensively tested in several fisheries of the Mediterranean and Black Seas (FAO, 2021) but, despite citizen science campaigns, their uptake by fishers is limited, while their effectiveness is controversial, with positive results in some areas e.g. (Monaco et al., 2020;Ceciarini et al., 2023) and less in others e.g (Cox et al., 2004;Buscaino et al., 2021). Some authors suggest that pingers may not be successful bycatch mitigation devices for all cetacean and pinniped species (Dawson et al., 2013). ...
Mortality resulting from interactions with fishing gears represent an important threat to sensitive species globally. In this study, we address this issue by defining five species groups of marine megafauna (marine mammals, seabirds, demersal and pelagic elasmobranchs, and sea turtles), and conducting a productivity-susceptibility analysis (PSA) within the context of data-limited fisheries in the Mediterranean and Black Sea. Although there are significant differences among species within each group, this approach has been considered much more direct and functional for management purposes. The productivity (P) of each species group was determined by evaluating a set of attributes averaged across representative species within each group. Species groups’ susceptibility (S) to bycatch was assessed through a comprehensive review of existing literature and expert judgment, considering a series of semi-quantitative attributes. Our analysis identified areas and fishing gears posing potential risks to the species groups assessed, highlighting that sea turtles and elasmobranchs face the potential risk of incidental captures from various fishing gears operating in both neritic (bottom trawls, set nets and bottom longlines) and pelagic (drifting longlines) environments. Marine mammals exhibit moderate risk across most fishing gears, with particular concern for the harbour porpoise Phocoena phocoena relicta in the Black Sea, primarily due to the interaction with set nets, which can severely impact entire population even capturing few specimens due the species low productivity. Seabirds face reduced impact with fishing activities, irrespective of the type of gear examined or the specific area under investigation. Overall, our study highlights the specific basins and fishing gears requiring focused management measures, mitigation strategies, and enhanced monitoring activities to mitigate the impacts of bycatch on vulnerable marine megafauna.
... In the last decades, deterrent devices, mainly acoustic alarms known as "pinger", have raised interest by both fishers and environmentalists, as they are non-lethal methods to deter depredation on fishing gear and dolphin entanglement. However, after years of experimentations and use, their long-term efficiency is still controversial (Hamilton and Baker, 2019) In fact, depredating dolphins have shown to quickly habituate to the acoustic signals emitted by the deterrent devices, even being attracted to the net after a time lag (Cox et al., 2003). The economic compensation, which is the most favored management options for fishers, was less appreciated by the other stakeholder groups. ...
Finding solutions for a sustainable coexistence between wildlife and humans is considered among the most challenging environmental management issues for scientists, conservationists, managers, and stockholders worldwide. Depredation by the common bottlenose dolphin (Tursiops truncatus) on small scale fisheries has increased in the recent years, leading to a growing conflict in many areas of the Mediterranean Sea and pressing for urgent management solutions. This study aims at developing a management framework for a sustainable coexistence between fishers and dolphins in Sardinia (Mediterranean Sea). Relying on the combination of different approaches (field study, literature review and Multi Criteria Decision Analysis), the scientific evidence necessary for understanding dolphin depredation were updated and improved, the related economic damage was calculated, and different management options were identified and evaluated by several stakeholder groups to support the decision-making process. Averaging for all investigated net types (gillnet and trammel net), a depredation frequency of 53% was found, the highest values ever found in both Sardinia and many other Mediterranean sites. Depredation probability was influenced by different factors, such as net type, fishing operation duration, depth of the fishing site and period. The estimated economic damage due to depredation ranges on average between 6492 and 11,925 euro per year and depends on the type of fishing net. The results from the field study, the literature review and the stakeholder involvement allowed us to define the most plausible and shared management options, identifying a framework for assessing and managing the conflict between fishers and dolphins for the creation of a more sustainable vision for the future.
... Different types of pingers were widely used, and formal results as well as fishers' opinions, have been assessed for each type 61,62 . Though several studies have proven dolphin net damages and catch depredation reduction using ADD 54,59 , some experiments have shown that the constant sound emitted by the pinger generates dolphin habituation [63][64][65] . In these circumstances, pingers go from being deterrents to attractants, acting as a kind of "dinner bell" for dolphins. ...
Dolphin–fishery interaction is a worldwide issue affecting dolphins through bycatch and fishers through catch or gear damages. Concerning the Mediterranean Sea, problematic interactions mainly occur between common bottlenose dolphin and small-scale fisheries. Acoustic Deterrent Devices such as pingers, are one of the most widespread measures used in attempts to face this issue. Therefore, the efficiency of interactive pingers (DiD01) in protecting the trammel nets from dolphin interactions was assessed in the Northern Tyrrhenian Sea. From March to October 2021, a total of 139 fishing trials using nets with pingers (TEST) and without pingers (CTRL), respectively n = 97 and n = 42, were carried out. Non-parametric statistic of the Catch per Unit Effort, comparing control and test nets, was not significantly different (p > 0.05) using catches weights (CPUEW) while it was significant (p < 0.01) considering the number of individuals (CPUEN). Moreover, richness and relative abundance of species resulted statistically higher in test nets (p < 0.05). This finding suggests that the absence of dolphin in the neighbourhood of fishing areas thanks to the use of pingers increases the diversity of target species. Catch damages caused by dolphins were statistically higher in nets without pinger than in nets with pinger (p < 0.05). No dolphin bycatch was recorded during fishing operations.
... Field studies with acoustic pingers on set gillnets have shown reductions in bycatch of harbour porpoise (Phocoena phocoena) in a sink gillnet fishery (Kraus et al., 1997;Trippel et al., 1999) and of common dolphins (Delphinus delphis) in a drift net fishery (Barlow and Cameron, 2003). There have also been a number of studies of the effectiveness of acoustic alarms using simulations at sea (Carlström et al., 2009;Cox et al., 2003;Culik et al., 2001) and studies of their effects on captive animals (e.g. Kastelein et al., 2000) and in the wild (Culik et al., 2001). ...
In Europe, problems with the use of pingers on larger fishing vessels have raised the question as to whether pingers would be practical on smaller vessels, which are a large proportion of the European static net fishing fleet. In this study, four netting vessels less than 10m long used AQUAmark pingers on part of their nets off the southwest coast of Britain over a 12 month period. Boat skippers recorded ease of use. Acoustic click detectors were deployed on test and control nets to assess the response of cetaceans to the pingers. No significant practical problems, apart from premature failure of pingers, were encountered. During the study, only one harbour porpoise was bycaught, in an unpingered net. In 650 days of acoustic data from pingered and non-pingered nets, matched by location, date and boat, there was a highly significant reduction in the number of porpoise clicks recorded at nets with pingers to 48% of the number predicted from the number recorded at control nets (range 35–51%). To assess habituation, single, modified pingers that were active for alternate seven hour periods were moored below a click detector at two sites, one of which has strong tides and high levels of associated ambient noise. This study showed a stronger pinger effect at the quiet site and a much reduced effect at the noisy site. There was evidence of a period of exclusion of porpoises following pinger use that could exceed seven hours, and no evidence of habituation. Results suggest that pingers are practical on small vessels, that they reduce harbour porpoise activity around nets and are therefore likely to reduce bycatch. Easier means of detecting pinger failure are needed. Pingers should be considered as a bycatch mitigation method in small vessel fisheries using bottom set nets.
... This underlines that, potentially, these devices can still be tested, either by fishers themselves or through research and dissemination projects in several coastal areas to verify their efficacy. However, the different perceptions and attitudes of those fishers having used (or using) the pingers during their normal fishing activities well reflect the divergent results obtained in scientific studies (promising outcomes; e.g., [49]; ineffective; e.g., [50]). Some evidences have suggested that they can be effective only in the short term to deter depredation by bottlenose dolphins [51], while in the long term they can have a null if not opposite effect (e.g., acting as a "dinner bell", as hypothesized by [52] in the "Volante" Adriatic fishery). ...
Interactions between fishing and dolphins can be detrimental, since on one hand dolphins can be lethally entangled by nets and trawls, and on the other dolphins can predate fish caught by nets. For dolphins, this interaction can be dangerous as they can be wounded or accidentally killed; for fishers, the predation of their catch results in economic losses due to reduced quantity and/or quality of catches and damage to fishing gear. During July and November 2020, we surveyed the “dolphin–fisheries conflict” through compiling 209 fisher interviews from nine locations in Italy and Croatia. Fishers mentioned the common bottlenose dolphin (Tursiops truncatus) as the species primarily interacting with fishing, with the major issue being catch damage by predation. The interaction probability varied among gears and seasons, with some fishing activities (e.g., passive nets) more affected than others (e.g., bottom trawls), especially in terms of economic loss (1000–10,000 €/year on average). More than 70% of the fishers claimed that dolphin populations have increased over the last 10 years, in different degrees and based on different areas. Dolphin bycatch rates are generally low; however, 34.6% of respondents reported having captured at least one dolphin during their career. The fishers’ attitude towards acoustic deterrents (“pingers”) as a mitigation measure revealed that few of them were aware of these devices or were using them.
... Although it was not always observed [9,19], some repellent pingers can induce aversive behaviour in marine mammals [17,101] or even a stressful escape behaviour, which was notably observed on a group of common dolphins with the STM DDD03L repellent pinger [51], which has been mandatory since 2019 for French pair trawlers in the Bay of Biscay. In contrast, using the bio-inspired prototype, visual surface observations showed attentive behaviours of dolphins, which kept a distance of a few metres to a few tens metres away from the emission source before calmly leaving without showing any signs of "fear" reactions, which corresponds to estimated net detection distances of (bottlenose) dolphins [38]. ...
By-catch is the most direct threat to marine mammals globally. Acoustic repellent devices (pingers) have been developed to reduce dolphin by-catch. However, mixed results regarding their efficiency have been reported. Here, we present a new bio-inspired acoustic beacon, emitting returning echoes from the echolocation clicks of a common dolphin ‘Delphinus delphis’ from a fishing net, to inform dolphins of its presence. Using surface visual observations and the automatic detection of echolocation clicks, buzzes, burst-pulses and whistles, we assessed wild dolphins’ behavioural responses during sequential experiments (i.e., before, during and after the beacon’s emission), with or without setting a net. When the device was activated, the mean number of echolocation clicks and whistling time of dolphins significantly increased by a factor of 2.46 and 3.38, respectively (p < 0.01). Visual surface observations showed attentive behaviours of dolphins, which kept a distance of several metres away from the emission source before calmly leaving. No differences were observed among sequences for buzzes/burst-pulses. Our results highlight that this prototype led common dolphins to echolocate more and communicate differently, and it would favour net detection. Complementary tests of the device during the fishing activities of professional fishermen should further contribute to assessment of its efficiency.
... 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). ...
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.
... 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]. ...
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). ...
• 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, ...
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.
... 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). ...
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 ( = 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.
... 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. ...
... 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. ...
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. ...
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. ...
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.
... 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). ...
... 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. ...
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.
... 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. ...
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.
... 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. ...
... 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). ...
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.
... 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). ...
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.
... 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. ...
... 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. ...
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.
The behavioral plasticity among and within cetacean species can be driven by their prey sources, local adaptations to environmental features, and/or interactions with human activities. One of the tactics displayed by cetaceans is the barrier feeding, in which individuals or groups herd fish schools against natural and non‐natural barriers to restrict movements of their prey. Coastal odontocetes, for example, are known for using shorelines and underwater slopes to trap their prey. Here, we documented two distinct populations of Guiana dolphin using the mangrove margins as a natural barrier to herd and capture fish. The observations took place in the Cananéia estuary, São Paulo State, southeastern Brazil, and in the Paranaguá estuary, Paraná State, southern Brazil. A total of 63 dolphins over eight encounters were observed performing six different events using mangroves as a natural barrier, summing both study areas. These findings not only expand our understanding of the behavior plasticity of the species but also call attention to the importance of the mangrove ecosystem directly to Guiana dolphins and indirectly to the components of their food web.
Interactions between bottlenose dolphin and recreational rod and reel fisheries are a complex issue for resource managers in the United States, which may impact anglers' catch and lead to dangerous situations for scavenging or depredating dolphins. To examine this issue, we analyzed data collected by observers on for‐hire fishing vessels off the eastern U.S. Gulf Coast from 2009 to 2020. A generalized additive model indicated number of anglers, number of discarded fish, proximity to shore, prior scavenging events, type of released fish, and area fished were all significant predictors of scavenging by dolphins. The Florida panhandle had the highest odds of scavenging, while scavenging in the Big Bend and Tampa Bay has increased through time. The Florida panhandle is a well‐known area for illegal feeding of dolphins, suggesting human behavior may be influencing fisheries interactions. Model outputs indicate that dolphins are primarily cuing on fishing activity rather than number of discards, but are more likely to scavenge discards from the family Lutjanidae (snappers), which comprised 40% of observed discards but 80% of scavenging events. This study highlights factors influencing the frequency of dolphin scavenging events, guiding managers and scientists on additional studies and mitigation measures needed to address this issue.
Bycatch of common dolphin (Delphinus delphis) in commercial trawl fisheries in the Bay of Biscay (NE Atlantic) is of concern and its mitigation a priority. Active acoustic deterrent devices (pingers) attached to fishing gear seem to be promising for bycatch mitigation, as they have demonstrated to effectively reduce cetacean bycatch in some set-net fisheries. However, the low occurrence of common dolphin bycatch in many trawl fisheries, coupled with the extensive amount of time needed to monitor them, makes it difficult to prove the effectiveness of pingers. Remote electronic monitoring (REM) systems in fisheries can substantially increase onboard observation, providing access to extensive databases to comprehensively address bycatch mitigation studies. In this study, the effectiveness of DDD®03H Dolphin Dissuasive Device (hereinafter DDD pingers) to reduce common dolphin bycatch was evaluated in a demersal pair trawler in FAO Division 27.8.c. In 195 fishing days, one of the vessels in the pair operated with a set of DDD pingers whereas the other operated without them, and the bycatch of common dolphin was monitored through the REM system. In total, 660 fishing hauls were conducted of which 223 hauls had the DDDs attached. The results showed that the DDDs reduced common dolphin bycatch by more than 90%, with both bycatch frequency and the number of individuals bycaught per haul being significantly lower. The results also showed that common dolphin bycatch in this fishery is related to factors such as the fishing zone and depth, whereas the type of net deployed, time of day and haul duration were found to not significantly affect the bycatch of this species.
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.
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.
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.
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.
ABSTRACT: The study was performed in Sinop between September 2015-January 2017 to investigate whether it is a profitable
application to attach pinger devices to bottom-gillnets used in coastal fisheries. Gear specifications of both fishermen group were
same as follows; mesh size: 34 mm, length: app. 1,1km. The frequency range of the pinger device is 1–500 kHz and effective up to
200m. The most important distinctive feature of those devices is having a built-in rechargeable 1,6 Ah NiMH battery pack but
limited up to 2-2,5 months (1000-1500h) total lifetime. In experimental group; average fish catch in the first periods (SeptemberDecember 2015) was 15,34±1,22 kg and it decreased by 56% to 6,83±0,31 kg between January 2016–2017. According to results
obtained from both control and experimental group, Catch Per Unit Effort (CPUE) was calculated as 0,63±0,02 kgkms-1 and
0,67±0,02 kgkms-1, respectively. Total incomes from the sale of fish were 20880,90 TL and 22259,65 TL for control and
experimental groups. The fishermen in control group spent 4000 TL to repair nets damaged due to dolphin presence while other
fishermen spent 3400 TL to repair nets. Considering the device expenses for the experimental group (2x1500 TL), total cost was
calculated as 6400 TL for experimental group and 4000 TL for control group. Therefore, net income was calculated as 16879,90
TL in control group while it decreased to 15859,65 TL in experimental group, representing 6% decline
Trial of acoustics deterrents for prevention of bottlenose dolphin depredation on gillnets
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.
Some effects of fisheries on the associated biological systems are reviewed and management options and their inherent risks are considered.
In 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.
Other impacts discussed include the destruction of benthic habitat, the provision of unnatural sources of food and the generation of debris.
Management options are considered including the designation of marine protected areas, risk aversion, and the burden of proof.
A balanced consideration of the risks and consequences of ‚Type 1’︁ and ‚Type II’︁ errors is advocated.
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.
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.
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.
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.
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 km ² 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.
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.
A bstract
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.
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.
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.
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.
In 1994, the United States National Marine Fisheries Service (NMFS) implemented a series of time/area closures for the Gulf of Maine sink gillnet fishery to reduce the bycatch of harbour porpoises (Phocoena phocoena). The present study evaluates the effectiveness of the Mid-Coast closure area, implemented during November 1994. Rates of porpoise bycatches are analysed prior to, during and after the closure. In addition, individual vessels are tracked and the spatial distribution of fishing effort examined to determine how fishermen responded to the closure. The highest bycatch rate occurred in September in the Mid-Coast region, well before the closure. During November, fishermen concentrated much of their effort adjacent to the closed area in unrestricted waters, where bycatch occurred. The Mid-Coast closure was not in place for a long enough period, nor was it large enough, to be effective in reducing bycatch rates of harbour porpoises. The failure of the Mid-Coast closure is attributed to temporal and spatial variation in patterns of bycatch rates, and to the displacement of fishing effort and porpoise bycatch outside the closed area.
A bstract
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.
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.
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.
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.
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
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.
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)
A bstract
A 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.
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.
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.
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
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(231), 66464-66490.
Interactions between Harbour Porpoises and Fishing Nets: Laboratory Studies to Reduce By-catch
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