The bigeye trevally Caranx sexfasciatus (also known as the Jacks) is famous among divers and snorkelers in Sipadan and it is commonly sighted at the entry point of Barracuda Point, Sipadan and at a very shallow depth of 1m.
The bigeye trevally is a fast-swimming predatory species of widespread large marine fish. It is an inshore fish and inhabits reef down to a depth of 100m but is commonly sighted in very shallow depths. This species can grow to a length of 100cm and can weigh 15kg.
The Jacks are a schooling species and they are widespread in the tropics and usually found in large slow moving schools during the day and the school of Jacks become active during feeding which takes place at night. The Jacks in Sipadan can form a school of more than 1000 fish! As a predatory fish, the bigeye trevally eats a variety of smaller fish, crustaceans and marine invertebrates.
The Jacks can also be found in another dive site of Sipadan called Drop Off and they usually hang out in the entrance of the Turtle Cave. The school here in Drop Off is smaller than the much larger school at Barracuda Point but the fish that makes up the school in Drop Off is visibly larger and lives deeper (around 20m).
The school of Jacks here will avoid getting too close to divers and snorkelers and are usually aware and alert towards approaching divers and snorkelers. But experienced scuba divers can easily get really close to them and even swim inside the circling school. The school of Jacks would usually swim calmly and slowly away from us but they can be frightened by noise caused by boat engines, surface splashes and bubbles exhaled by scuba divers. When frightened, the Jacks can swim together in blinding speed and the giant school of Jacks can be completely out of sight in a split second.
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