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Incidence of Fish Hook Ingestion by Komodo dragons June 30, 2008

Posted by ekologi in Uncategorized.
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Incidence of Fish Hook Ingestion by Komodo dragons

Tim Jessop1, Jeri Imansyah2, Deni Purwandana2, Achmad Arifiandy2 and Devi S. Opat3

1Department of Wildlife Conservation and Research, Zoos Victoria, PO Box 74 Parkville VIC 3052, Australia

2 Komodo Dragon Species Survival Program Indonesia, Denpasar, Bali, Indonesia.

3 Taman National Komodo, Labuan Bajo, Flores, NTT, Indonesia.

Correspondence to Tim Jessop

(e-mail: tjessop@ zoo.org.au).

The Komodo dragon (Varanus Komodoensis), a large robust monitor lizard, persists on the 5 islands in Eastern Indonesia (Ciofi and deBoer 2004). The waters surrounding these islands are intensively utilized for marine resources and in particular line and net fishing are prolific. For other reptiles, particularly freshwater and marine turtles, incidental injury and mortality through ingestion of fishing hooks during routine foraging activities are not uncommon (Polovina et al. 2000). However, similar incidents of reptile by-catch in terrestrial species is poorly documented even though, many large lizards such as monitors, are semi-aquatic or cohabit and forage within coastal areas in which intense fishing activities persist. Here we report two incidents of ingestion of fishing gear by Komodo dragon during routine monitoring of island populations between 2002- 2006.

Annual mark recapture studies were conducted at 10 sites across 4 islands within Komodo National Park during both 2002 and 2005 and resulted in 827 dragons captures(> post-hatchling size). From this sample, 2 cases of fishhook ingestion were reported. The first case, comprised a small monitor (Animal ID: 00063A9978, 69.35 cm SVL, 7 kg) captured at Loh Buaya (8:39:21.7 S, 119:43:06.2 N) on Rinca Island and appeared to occurred recently as the line protruding from its mouth was still relatively long and the nylon in good condition. Based on the line weight it is suspected that the hook ingested by this lizard was relatively small. This lizard was recaptured in 2005, without any evidence of the protruding fishing line (however if the hook was remaining is unknown) and it had grown 8.75 cm in SVL and increased its mass by 1.45 kg. The second lizard, an adult male (Animal ID: 000643A7EC, 127.75 cm SVL, 41.8 kg) was captured on the 19th June 2004 also from Rinca Island at Loh Tongker (8:45:31.1 S, 119:42:57.3 E) a small coastal valley on the south east coast. In this incident the hook ingested was likely to have been considerably larger and typical of those used for capturing large pelagic species on long line. This hook was shackled with 2 strands of heavy trace wire (Fig 1). In this instance it is believed the hook was ingested several weeks to months earlier as indicated by the lesion induced by abrasion from the trace wire. In 2005, this adult male was recaptured, there was no evidence of the protruding trace, however it was not known if the hook still resided within the animal. The weight of this male had decreased by 8.8 kg from 2004 and 20 kg from its first capture in 2003 despite growing relatively little in length (4 cm in SVL).

Consumptions of fishing hooks by Komodo dragons, albeit rare, is a likely consequence of these lizard’s prodigious scavenging capacity coinciding with discarded fishing gear that finds it way into the intertidal areas exposed on the low tide. As yet we do not know what effects hook ingestion might incur for the specific individuals dragons, however, given that mortality occurs readily in other reptiles, it is possible that at least in the case of the second animal there may be negative consequences.

References

Ciofi, C. & de Boer, M.E. 2004. Distribution and conservation of the Komodo Monitor (Varanus komodoensis). Herpetological Journal 14: 99-107.

Polovina, J.J., Kobayashi, D.R., Ellis, D.M., Seki, M.P., & Balazs, G.H., 2000. Turtles on the edge: Movement of loggerhead turtles (Caretta caretta) along oceanic fronts in the central North Pacific, 1997-1998. Fisheries Oceanography 9(1):71-82.

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