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Ecology and Conservation

Marine Knowledge

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OnApril 12th, 2015, at four o’ clock in the afternoon when theshoreline was experiencing a high tide, a research team was conducting aresource survey of chondrichthyes in surrounding waters of Dongsha AtollNational Park. They captured a female Galeocerdo cuvier (nickname: SeaTiger) in 1.5-meter deep waters near the outline of the tetrapod at the 2ndbase of Dongsha Island. The total length of the Galeocerdo cuvier was 232cm,tail length was 171cm, and the fork length was 188cm. Based on the associatedfeatures of the fish, the research team could almost confirm that it is a newspecies in the records of this Park.

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"Scarface-tigershark"Cited from Wikimedia Commons
- http://commons.wikimedia.org/wiki/File:Scarface-tigershark.jpg

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Tiger shark (scientific name: Galeocerdo cuvieri) is the only member of the genus Galeocerdo in family Carcharhinidae in the world. It is also called “Tiger shark” because its body colors and markings resemble the markings on a tiger. On average, an adult Galeocerdo cuvier attains a length of 4 m and weighs around 400~635 kg.

Galeocerdo cuvieri is widely distributed over worldwide oceans between subtropical and temperate waters. Additionally, it is also seen in Southwest and Northeast waters in Taiwan. According to its habit, Galeocerdo cuvieri usually appears in the regions of river mouths, coral reefs and lagoons or the outlying waters of oceanic islands. Because of its vertical immigration habit, Galeocerdo cuvieri moves in deep waters during the daytime, and surfs to surface or shallow waters for predation during the nighttime. Sharks are omnivorous animals. Sometimes we can even find trash, metals and gunny bags in their stomachs. Galeocerdo cuvieri is ovoviviparous, it can deliver 10~82 pups each time, and the total length of the pup can attain to 60-104 cm at the time it is born. In addition, the consumption of shark fins and overexploitation make IUCN consider Galeocerdo cuvieri near threatened (NT) species.

Stabilization therapy for Galeocerdocuvieri (provided by the researchteam of NCKU Research and Development Foundation)
Stabilization therapy for Galeocerdo cuvieri (provided by the researchteam of NCKU Research and Development Foundation)

The Galeocerdo cuvieri captured by the research team this time is supposed to swim during the night in the deeper waters of the atoll. As to why it appeared around 4pm near North coast of Dongsha Island, Associate Professor Yu-Yun Chen from the research team indicated that according to the study results of seagrass bed in Australia and other associated studies, the distribution of Galeocerdo cuvieri is highly correlated to the distribution of prey (for example, stingrays, sharks, seabirds, manatees and sea turtles are all Galeocerdo cuvieri’s preys). However, there are not too many large seabirds, sea turtles or manatees in the waters surrounding Dongsha Island, so they speculated that maybe the breading seasons (between April and June) Negaprion acutidens pups were related to the distribution of skates. However, we are awaiting further examinationas as to the exact reasons. Hopefully we will have more descriptive charts for us to understand Galeocerdo cuvieri better in the future. (Written by the Chief of Dongsha Management Station Kuo-Yung Chen).

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