Naslov
Newly documented consequence of dolphin depredation: larynx strangulation with gillnet parts

Autori
Galov, Ana ; Đuras Gomerčić, Martina ; Gomerčić, Tomislav ; Lucić, Hrvoje ; Škrtić, Darinka ; Ćurković, Snježana ; Vuković, Snježana ; Gomerčić, Hrvoje

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Marine Mammals of the Holarctic. Collection of scientific papers after the Fifth international conference / Boltunov, A. N. - Odesa, 2008, 189-191

ISBN
978-966-190-025-6

Skup
Fifth international conference of Marine Mammals of the Holarctic

Mjesto i datum
Odesa, Ukrajina, 14.10.2008. - 18.10.2008

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
dobri dupin
(bottlenose dolphin)

Sažetak
Interactions of dolphins with fishing gear have been regularly reported and they occur because of the cetacean strategy to increase the rate of feeding while decreasing the energy expenditure associated with foraging (Fertl and Leatherwood 1997). The most frequently reported form of cetacean interactions with fishing gear involves entanglement in fishing nets. Limited records exist related to depredation resulting in fishing gear ingestion. Ingestion of fishing hook and lure were documented by Gorzelany (1998). However, there are no documented cases of fishing gear ingestion resulting in larynx strangulation. Here we present bottlenose dolphins {;Tursiops truncatus) from the Croatian part of the Adriatic Sea that have been affected with larynx strangulation with gillnet parts. The bottlenose dolphin is the only resident marine mammal species in Croatian part of the Adriatic Sea with the total number of individuals estimated at between 220 to 250 (Gomercic et al. 2002). It is endangered and legally protected species in Croatia. Croatia has a long tradition of small-scale coastal fishing, which exploits near-shore biological resources. Small-scale commercial and private fisheries use gillnets throughout the year. The level of exploitation is unknown because the catches of the coastal fishing gears are not recorded. However, the total amount of small-scale, artisanal fishers is estimated at around 18.000, of which only 8.500 are licensed (Dulcic et al. 2003). Fish entangled in gillnets present a source of concentrated prey all year round and are probably the only feeding source for animals with reduced hunting ability. The position of larynx in toothed whales makes it vulnerable to foreign bodies during deglutition. Their larynx is elongated into a tubular extension, the laryngeal spout, also commonly referred to as the "epiglottal beak" or "goose beak" (Gorzelany 1998) that transverses the digestive tract into the nasal cavity, where it remains in the erect position during deglutition. 120 bottlenose dolphins found dead throughout Croatian part of the Adriatic Sea were examined from 1990 till today. Age was estimated using annual growth layer groups (GLGs) from extracted teeth and based on modified methods described in Slooten (1991). Twelve bottlenose dolphins out of 120 examined (10%) had larynx strangulated with a gillnet part. In the majority of affected animals a fishing net part was hanging from the mouth and was the first indication of larynx strangulation. The gillnet part causing larynx strangulation was in form of a weaved cord encircling the dorsolateral wall of the laryngeal spout. Larynx strangulations most probably occur when dolphins feed on entangled fish from gillnets and accidentally tear off a part of the fishing net. The torn gillnet part might only partly pass into the esophagus during the swallowing of the prey and the rest of it hangs through the pharynx and the oral cavity out of the mouth. Partially swallowed gillnet part causes muscular actions of the pharynx advancing regurgitation. This muscular action brings the swallowed part of gillnet out of the esophagus and into the pharynx. If the swallowed part is directed into the opposite food channel of the food channel where the hanging part lies, it will encircle the laryngeal spout and larynx strangulation occurs. All animals affected by larynx strangulation were older than 7 years and the majority were older than 17 years, indicating that the animals acquired the feeding behavior of taking fish from gillnets from other conspecifics. The examined carcasses of other cetacean species did not show signs of larynx strangulation. Gillnet strangulations could impact the population dynamics of bottlenose dolphin population in the Adriatic Sea as much as 10% of examined bottlenose dolphin carcasses were affected. There are different measures proposed to reduce dolphin interactions with gillnets, e.g. reducing fishing seasons or regions (Murray et al. 2000), establishing marine protected areas free of gillnet fishing (Dawson and Slooten, 1993) and gear modifications (Dawson, 1991). The legislative regulation that would ensure avoiding spatio-temporal overlap of dolphin foraging and human gillnet fishing activities along the Eastern Adriatic Sea would not be feasible since the affected animals were found throughout the Croatian coast of the Adriatic Sea during all seasons. Additionally, both fishing ground closures and creation of MPAs can have deleterious social and economic effects on fishing- based communities (Mooney et al. 2007). Future investigations should focus on investigating pathological changes of larynxes affected by strangulation and their influence on the overall health of the individuals affected, since larynx strangulation seems to be a chronic condition. We also propose assessing further impact of larynx strangulations on the population dynamics of bottlenose dolphin in the Adriatic Sea and considering net alterations that would improve stiffness properties of the gillnets

Izvorni jezik
Engleski

Znanstvena područja
Biologija, Veterinarska medicina

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