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Laryngeal Snaring by Ingested Fishing Net in a CommonBottlenose Dolphin (Tursiops truncatus) Off the IsraeliShorelineAuthors: Alon M. Levy, Ori Brenner, Aviad Scheinin, Dan Morick, ElianaRatner, et. al.Source: Journal of Wildlife Diseases, 45(3) : 834-838Published By: Wildlife Disease AssociationURL: https://doi.org/10.7589/0090-3558-45.3.834

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Journal of Wildlife Diseases, 45(3), 2009, pp. 834–838# Wildlife Disease Association 2009

Laryngeal Snaring by Ingested Fishing Net in a Common Bottlenose

Dolphin (Tursiops truncatus) Off the Israeli Shoreline

Alon M. Levy,1,2,4 Ori Brenner,1 Aviad Scheinin,2,3 Dan Morick,2 Eliana Ratner,2,3 Oz Goffman,2,3 andDan Kerem2,3 1 Weizmann Institute of Science, PO Box 12, Rehovot 76100, Israel; 2 Israeli MarineMammal Research & Assistance Center (IMMRAC), Michmoret 40297, Israel; 3 Recanati Institute for MaritimeStudies and Department of Maritime Civilizations, University of Haifa, Mount Carmel, Haifa 31905, Israel;4 Corresponding author (email: alon.levy@weizmann.ac.il)

ABSTRACT: We report an unusual snaring ofthe larynx in an adult, female common bot-tlenose dolphin (Tursiops truncatus). Thedolphin was observed swimming and diving inHaifa Port, Israel, but was found dead the nextday, 60 km south, on the coast. Postmortemexamination revealed stranded-cordage, nylonfilaments wrapped around the larynx, cuttingthrough the soft tissue, and extending downinto the forestomach, where a large mass ofnetting was found. The cachectic state of thedolphin and the subacute to chronic, hyper-plastic response of soft tissue surrounding thefilaments lodged around the larynx, suggest aprolonged period of starvation, which led to thefinal weakness and wasting of the dolphin.

Key words: Cetacea, gillnet, marine pol-lution, Tursiops truncatus.

The effect of plastic debris on marinemammals is a major environmental con-cern worldwide. Although entanglementin derelict fishing gear poses a majorthreat (Donohue et al., 2001), cetaceansoften suffer from blockage of the alimen-tary tract due to ingested items (Laist,1987, 1997; Derraik, 2002). We report anunusual, but possibly not uncommon,outcome of fishing net ingestion by abottlenose dolphin off the Israeli coast.

On 2 February 2007, at 9 AM, a dolphinentered the Port of Haifa (32u499390N,34u599430E), Israel, and swam between thebreakwater and the passenger docks. Themature common bottlenose dolphin (Tur-siops truncates) was very thin and wasobserved swimming normally and actively,performing up to 2-min-long dives andapparently foraging. It was last reportedinside the port at 3:30 PM. In late afternoonof the next day, the very fresh body of a

dolphin (intact glossy skin with fresh abra-sions, clear corneas, fading rigor mortis) wasreported floating in the breakers of PolegBeach, 60 km south of the port of Haifa.Strong southwesterly winds were blowingthroughout the day. It was identified as amature, female common bottlenose dolphinand was transported that evening to a facility25 km away, where it remained at ambienttemperature (16 C) awaiting necropsy; thenecropsy was performed early next morning.Comparison of external scars and dorsal finnotching pattern to photographs taken ofthe swimming dolphin (Fig. 1), confirmedthat it was the same individual sighted insideHaifa Port on the previous day.

The dolphin measured 303 cm, thelongest female ever documented by theIsraeli Marine Mammal Research & As-sistance Center (IMMRAC). Skin pigmen-tation, especially neck markings, wasuncharacteristic of the Israeli coastalpopulation. The dolphin was cachectic,showed epaxial muscle wasting and weigh-ing only 180 kg, less than half the weightexpected using an exponential equationderived from length-weight data of localbeached specimens (IMMRAC, unpubl.).Later on, age determination (performedby P. Goldin, Vernadsky Taurida NationalUniversity, Simferopol, Ukraine) indicatedthat the dolphin was 16 yr old.

On gross necropsy, the midlateral (inline with the anterior edge of the dorsalfin) blubber thickness was 15 mm, slightlyless than the mean of 18 mm observed inapparently healthy individuals bycaughtalong the Israeli Mediterranean coast.

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There were no external lacerations, netmarks, or subcutaneous hemorrhages. Thedolphin was neither gravid nor lactating.Kidneys, liver, and heart were grosslyunremarkable. Yellowish frothy liquidfilled the airways.

There were two round, approximately1.3-cm-diameter ulcers, on the tongue.When cut, the ulcer was found to consistof well-demarcated necrotic tissue, whichextended approximately 1 cm deep. Themain abnormal finding was the presence ofstranded-cord, nylon, gillnet filamentswrapped around the larynx (Fig. 2A), justcaudal to the ary-epiglottic tube (goose-neck). The filaments cut into the soft tissueand were located within a deep grooveflanked by exuberant and irregular softtissue proliferation. The epiglottis and plicaary-epiglottica were rounded and appearedswollen. The netting material extendeddown into the esophageal lumen and wasattached to a 15-cm-diameter, solid mass

inside the forestomach (Fig. 2B). The masswas composed of netting, parasitic nema-todes (Anisakis spp.), and brown, tar-likecement with four embedded, 2-cm-longfishhooks, each with an attached length of2–5 cm monofilament fishing line. Thehooks were neither pitted nor corroded. Asingle cephalopod beak was the only preyitem found. The fundic and pyloric (secondand third) gastric chambers and the intes-tines were empty and contained slimy,yellowish-green mucus.

When partially unraveled, the mass wasfound to be composed of sections of ninedifferent types of gillnet with mesh sizes,ranging from 1.531.5 cm to 434 cm. Thematerial of seven of the gillnet types wasdouble/multiple-stranded, cotton chord;the other two were made of nylonmonofilament line. Dominating the masswas the extension of the laryngeal snare,with an estimated size of 5 m2. Uponinspection, local fishermen claimed that

FIGURE 1. Matched scars and dorsal fin profile in swimming and autopsied common bottlenose dolphin(Tursiops truncatus). A. Scar marks on carcass. B. Scar marks on the swimming dolphin. C. Profile of theposterior edge of the dorsal fin—carcass. D. Profile of the posterior edge of the dorsal fin in theswimming dolphin.

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most of the net types were not being usedby Israeli artisan fishermen.

Histologically, a sample from the caudo-ventral aspect of the larynx demonstrated adeep groove, flanked by marked submuco-sal fibrosis and mucosal hyperplasia(Fig. 2C). The deeper aspect of the groovewas ulcerated with superficial necrosis;mild, mixed, inflammatory infiltration; andbacteria. The relatively mature fibroustissue, covered with hyperplastic mucosa,indicated a subacute to chronic course. Thelesions in the tongue (Fig. 3A, B) were well-demarcated areas of locally extensive,

coagulative necrosis and ulceration, sepa-rated from the surrounding normal tissueby neutrophilic infiltration, accumulation ofnecrotic cellular debris, and hemorrhage(Fig. 3C). The ulcerated surface was cov-ered by innumerable, Gram-negative, fila-mentous bacteria admixed with Gram-positive cocci and coccobacilli. Multiplecolonies of Gram-negative, filamentousbacteria were also present in the deeptissue (not shown). The pathologic featuresof the lesions in the tongue are typical oforal necrobacillosis, caused by Fusobacteri-um necrophorum, a Gram-negative, fila-

FIGURE 2. Main pathology. A. Macroscopic view of the larynx and the nylon filaments tightly woundaround it and within the soft tissue. B. Macroscopic view of the mass of netting in the forestomach. C. Low-power view of the groove (asterisk) flanked by fibrous tissue covered with hyperplastic mucosa. H&Estain. 13.

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mentous anaerobe (Brown et al., 2007).There were no significant findings in theremaining organs examined.

The cetacean larynx protrudes into theglottis up to the soft palate, where it isinserted into the lower (bony) naris andheld in place by the palatopharyngealsphincter (Reidenberg and Laitman,1987). This arrangement completely sep-arates the respiratory and alimentarytracts from each other, allowing simulta-neous swallowing and breathing/vocalizing

without risk of aspiration. Ingestion ofhooked fish with attached nylon monofil-aments or lures, which get tied around thelarynx, is not uncommonly found incommon bottlenose dolphins residing inan area with extensive angling and/or long-line fishing activity (Gorzelany, 1988).

The circumstances under which thenetting material was ingested by thisdolphin are obscure. The wide assortmentof net types, and the snagged hooks couldeither point to a mass of debris that was

FIGURE 3. Tongue ulcer pathology. A. A close-up view of the macroscopic appearance of the superficialaspect of the lesion in the tongue. There is a well-demarcated focus of necrosis and ulceration. B. The cutsurface of the lesion shown in A. In the center, there is a focus of coagulative necrosis (pale) surrounded by adarker band of hemorrhage. C. Low-power view of a histologic section of the lesion shown in B. The centralarea is pale because of coagulative necrosis. It is separated from the surrounding normal tissue by neutrophilicinfiltration, cellular debris, and hemorrhage. H&E stain. 0.53.

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balled-up before being ingested (i.e.,Secchi and Zarzur, 1999) or, as suggestedby the condition of the hooks, that thedolphin was in the habit of wresting preyitems from active fishing gear and accu-mulated the mass over time. Puncturewounds from the fishing hooks may wellhave been the source of the observedtongue ulcers, as can happen in domesticanimals. In cattle and sheep, oral ulcersoften result from puncture wounds ofthorny fiber or metal, which disrupt theintegrity of the oral mucosa (Langworth,1977; Yeruham and Elad, 2004).

It is likely that feeding and swallowingwas impaired in this animal because everycontraction of the stomach pulled on thefilaments, causing them to cut deeper intothe larynx. Judging by its final weight, itmust have been severely starved anddehydrated, although its surprising mobil-ity during its last day makes the directcause of death uncertain.

LITERATURE CITED

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DERRAIK, J. G. 2002. The pollution of the marineenvironment by plastic debris: A review. MarinePollution Bulletin 44: 842–852.

DONOHUE, M. J., R. C. BOLAND, C. M. SRAMEK, AND

G. A. ANTONELIS. 2001. Derelict fishing gear inthe northwestern Hawaiian Islands: Divingsurveys and debris removal in 1999 confirmthreat to coral reef ecosystems. Marine PollutionBulletin 42: 1301–1312.

GORZELANY, J. F. 1988. Unusual deaths of two free-ranging Atlantic bottlenose dolphins (Tursiopstruncatus) related to ingestion of recreationalfishing gear. Marine Mammal Science 14:614–617.

LAIST, D. W. 1987. Overview of the biological effectsof lost and discarded plastic debris in the marineenvironment. Marine Pollution Bulletin 18:319–326.

———. 1997. Impacts of marine debris: entangle-ment of marine life in marine debris including acomprehensive list of species with entanglementand ingestion records. In Marine debris: Sourc-es, impacts, and solutions, J. M. Coe and D. B.Rogers (eds.). Springer Ltd., New York, NewYork, pp. 99–139.

LANGWORTH, B. F. 1977. Fusobacterium necro-phorum: Its characteristics and role as an animalpathogen. Bacteriological Reviews 41: 373–390.

REIDENBERG, J. S., AND J. T. LAITMAN. 1987. Positionof the larynx in Odontoceti (toothed whales).Anatomical Record 218: 98–106.

SECCHI, E. R., AND S. ZARZUR. 1999. Plastic debrisingested by a Blainville’s beaked whale, Meso-plodon densirostris, washed ashore in Brazil.Aquatic Mammals 25: 21–24.

YERUHAM, I., AND ELAD, D. 2004. Necrotizingstomatitis associated with Fusobacterium necro-phorum in two goats. Journal of VeterinaryMedicine B 51: 46–47.

Received for publication 1 April 2008.

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