Conference Paper

Evidence of hearing loss due to dynamite fishing in two species of odontocetes

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Abstract

Blast fishing is an illegal and unsustainable practice that is often reported in Southeast Asia and Africa. Its impact on fish and reef-building corals is well documented, yet there is limited information on the effects on other larger species and near-shore predators. In recent years, several marine mammal strandings in the Philippines have coincided with underwater explosions associated with blast fishing. The goal of this study was to measure the hearing of stranded dolphins, including two spinner dolphins (Stenella longirostris) and two rough-toothed dolphins (Steno bredanensis), that were rehabilitated in Subic Bay at Ocean Adventure in cooperation with the Philippines Marine Mammal Stranding Network and Wildlife in Need. Hearing measurements were conducted using noninvasive auditory brain stem responses (ABRs). Test stimuli consisted of tone pips ranging from 8 to 128 kHz. The results indicated elevated thresholds and limited hearing range, including three individuals with no hearing response beyond 22.5 kHz. These results may indicate evidence of hearing loss associated with blast and related impulsive sound exposure.

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... No ototoxic drugs were administered. An audiogram of this individual was previous published, indicating it had sensitive hearing from 16 to 90 kHz with possible indications of some degree of high frequency hearing loss, which may have been due to acoustic trauma from an anthropogenic sound source such as dynamite fishing (Pacini et al., 2016). ...
... Given the arrangement of the pen complex, it was possible that signals generated from the rough-toothed dolphins in an adjacent pen (see Fig. 2) on the opposite side of the array could be recorded with the same incident angle as the spinner dolphin's signals. However, the three rough-toothed dolphins held in that pen exhibited acute hearing loss (Pacini et al., 2016) and were considered mute as no acoustic signals had been heard or recorded with these animals. Therefore, all signals that originated from a location perpendicular to the plane of the array hydrophones could be attributed to the study subject. ...
... 2010). A previously published audiogram of this spinner dolphin indicates sensitive hearing up to approximately 90 kHz, but also suggests some degree of high frequency hearing loss possibly due to the effects of dynamite fishing (Pacini et al., 2016). If the spinner dolphin were to primarily produce clicks with centroid frequencies found in wild individuals (70-90 kHz), a large fraction of the spectral energy in the outgoing clicks and returning echoes would fall within the supra-audal range of the animal's hearing. ...
Article
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Toothed whales possess a sophisticated biosonar system by which ultrasonic clicks are projected in a highly directional transmission beam. Beam directivity is an important biosonar characteristic that reduces acoustic clutter and increases the acoustic detection range. This study measured click characteristics and the transmission beam pattern from a small odontocete, the spinner dolphin (Stenella longirostis). A formerly stranded individual was rehabilitated and trained to station underwater in front of a 16-element hydrophone array. On-axis clicks showed a mean duration of 20.1 μs, with mean peak and centroid frequencies of 58 and 64 kHz [standard deviation (s.d.) ±30 and ±12 kHz], respectively. Clicks were projected in an oval, vertically compressed beam, with mean vertical and horizontal beamwidths of 14.5° (s.d. ± 3.9) and 16.3° (s.d. ± 4.6), respectively. Directivity indices ranged from 14.9 to 27.4 dB, with a mean of 21.7 dB, although this likely represents a broader beam than what is normally produced by wild individuals. A click subset with characteristics more similar to those described for wild individuals exhibited a mean directivity index of 23.3 dB. Although one of the broadest transmission beams described for a dolphin, it is similar to other small bodied odontocetes.
... Auditory Brainstem Responses (ABRs) have been increasingly used to investigate many aspects of the odontocete auditory system, including directional hearing (e.g., Popov and Supin 1988Popov et al. 1992Popov et al. , 2006, hearing pathways (e.g., Møhl et al. 1999;Mooney et al. 2008Mooney et al. , 2014Mooney et al. , 2015Popov et al. 2016), audiograms (e.g., Nachtigall et al. 2005Nachtigall et al. , 2007Yuen et al. 2005;Cook et al. 2006;Finneran et al. 2009), binaural hearing cues (Popov and Supin 1991), and temporal resolution (Supin and Popov 1995a, b;Dolphin et al. 1995;Mooney et al. 2006). Use of ABR methodology is advantageous by allowing research with subjects that have little behavioral training and has proven valuable for measuring auditory characteristics of previously unstudied odontocete species from the wild that have stranded or been rehabilitated (Nachtigall et al. , 2007Cook et al. 2006;Finneran et al. 2009;Mann et al. 2010;Pacini et al. 2010Pacini et al. , 2011Pacini et al. , 2016Schlundt et al. 2011;Montie et al. 2011;Greenhow et al. 2014). ...
... No ototoxic drugs were administered to the animal. An audiogram of this individual was previously published by Pacini et al. (2016). Auditory temporal resolution measurements were collected on October 8, 2015. ...
Article
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Odontocete marine mammals explore the environment by rapidly producing echolocation signals and receiving the corresponding echoes, which likewise return at very rapid rates. Thus, it is important that the auditory system has a high temporal resolution to effectively process and extract relevant information from click echoes. This study used auditory evoked potential methods to investigate auditory temporal resolution of individuals from four different odontocete species, including a spinner dolphin (Stenella longirostris), pygmy killer whale (Feresa attenuata), long-finned pilot whale (Globicephala melas), and Blainville’s beaked whale (Mesoplodon densirostris). Each individual had previously stranded and was undergoing rehabilitation. Auditory Brainstem Responses (ABRs) were elicited via acoustic stimuli consisting of a train of broadband tone pulses presented at rates between 300 and 2000 Hz. Similar to other studied species, modulation rate transfer functions (MRTFs) of the studied individuals followed the shape of a low-pass filter, with the ability to process acoustic stimuli at presentation rates up to and exceeding 1250 Hz. Auditory integration times estimated from the bandwidths of the MRTFs ranged between 250 and 333 µs. The results support the hypothesis that high temporal resolution is conserved throughout the diverse range of odontocete species.
... One of the ways to confirm acoustic trauma is through histological observations of the inner ears [56]. Acoustic trauma was suggested as the cause of some previously reported cetacean stranding events in the Philippines, possibly due to blast fishing activities near the stranding sites [23,57]. There is a growing concern on marine environment being compromised by human activities (e.g. ...
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The relatively high frequency of marine mammal stranding events in the Philippines provide many research opportunities. A select set of stranders (n = 21) from 2017 to 2018 were sampled for bacteriology and histopathology. Pertinent tissues and bacteria were collected from individuals representing eight cetacean species (i.e. Feresa attenuata, Kogia breviceps, Globicephala macrorhynchus, Grampus griseus, Lagenodelphis hosei, Peponocephala electra, Stenella attenuata and Stenella longirostris) and were subjected to histopathological examination and antibiotic resistance screening, respectively. The antibiotic resistance profiles of 24 bacteria (belonging to genera Escherichia, Enterobacter, Klebsiella, Proteus, and Shigella) that were isolated from four cetaceans were determined using 18 antibiotics. All 24 isolates were resistant to at least one antibiotic class, and 79.17% were classified as multiple antibiotic resistant (MAR). The MAR index values of isolates ranged from 0.06 to 0.39 with all the isolates resistant to erythromycin (100%; n = 24) and susceptible to imipenem, doripenem, ciprofloxacin, chloramphenicol, and gentamicin (100%; n = 24). The resistance profiles of these bacteria show the extent of antimicrobial resistance in the marine environment, and may inform medical management decisions during rehabilitation of stranded cetaceans. Due to inadequate gross descriptions and limited data gathered by the responders during the stranding events, the significance of histopathological lesions in association with disease diagnosis in each cetacean stranding or mortality remained inconclusive; however, these histopathological findings may be indicative or contributory to the resulting debility and stress during their strandings. The findings of the study demonstrate the challenges faced by cetacean species in the wild, such as but not limited to, biological pollution through land-sea movement of effluents, fisheries interactions, and anthropogenic activities.
... A significant limitation to odontocete auditory research is the small number of species and individuals with which such research can be conducted. Both auditory study methods currently require the involvement of either subjects trained via operant conditioning, 3,4 subjects that have stranded, [5][6][7] or subjects from the wild that are temporarily restrained for opportunistic study. [8][9][10][11] Thus, hearing data are published for only 20 of the approximately 76 extant odontocete species 12 and often from only a few individuals. ...
Article
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Empirical measurements of odontocete hearing are limited to captive individuals, constituting a fraction of species across the suborder. Data from more species could be available if such measurements were collected from unrestrained animals in the wild. This study investigated whether electrophysiological hearing data could be recorded from a trained harbor porpoise (Phocoena phocoena) using a non-invasive, animal-attached tag. The results demonstrate that auditory brainstem responses to external and self-generated stimuli can be measured from a stationary odontocete using an animal-attached recorder. With additional development, tag-based electrophysiological platforms may facilitate the collection of hearing data from freely swimming odontocetes in the wild.
... But seePacini et al. (2016) for a report of stranded odontocetes that may have been exposed to dynamite fishing. After stranding, auditory evoked potential measurements revealed elevated thresholds and a limited range of hearing for several individuals.2 ...
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... 1995). Pacini et al. (2016) found that fish bombing activities had caused hearing loss in two species of cetaceans that had stranded in the Philippines due to the said destructive fishing method. In Tanzania, where blast fishing was recently discovered to be widespread along the country's coastline, scientists expressed that the impacts are highly likely to be substantial for its populations of endangered coastal cetaceans (Braulik et al. 2015). ...
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... But seePacini et al. (2016) for a report of stranded odontocetes that may have been exposed to dynamite fishing. After stranding, auditory evoked potential measurements revealed elevated thresholds and a limited range of hearing for several individuals.2 ...
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Behavioral and auditory evoked potential (AEP) audiograms of a false killer whale were measured using the same subject and experimental conditions. The objective was to compare and assess the correspondence of auditory thresholds collected by behavioral and electrophysiological techniques. Behavioral audiograms used 3-s pure-tone stimuli from 4 to 45 kHz, and were conducted with a go/no-go modified staircase procedure. AEP audiograms used 20-ms sinusoidally amplitude-modulated tone bursts from 4 to 45 kHz, and the electrophysiological responses were received through gold disc electrodes in rubber suction cups. The behavioral data were reliable and repeatable, with the region of best sensitivity between 16 and 24 kHz and peak sensitivity at 20 kHz. The AEP audiograms produced thresholds that were also consistent over time, with range of best sensitivity from 16 to 22.5 kHz and peak sensitivity at 22.5 kHz. Behavioral thresholds were always lower than AEP thresholds. However, AEP audiograms were completed in a shorter amount of time with minimum participation from the animal. These data indicated that behavioral and AEP techniques can be used successfully and interchangeably to measure cetacean hearing sensitivity.
Historical whaling in the Philippines: origins of 'indigenous subsistence whaling', mapping whaling grounds and comparison with current known distribution" HMPA Asisa Project Paper Murdoch University working paper no 151 National Library of Australia
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Green, S., White, A., Flores, J., Careon, M. and Sia, A., (2003). "Philippines fisheries in crisis: A framework for management." Coastal resource management project of the department of environment and natural resources, Cebu City, Philippines www.oneocean.org/download/db_files/Philippine_fisheries_in_crisis.pdf