The Bigeye Thresher Shark weights up to 300kg and reaches lengths of 3 to 4 meters. It is named for its large eyes (1). The upper section of the tail fin is very long and almost equal to the length of the rest of the shark (2). It is purplish grey in colour, fading to cream on the under belly (2). It has 19-24 teeth on the upper jaw while the lower jaw usually has between 20-24 teeth.
Little is known of the behaviour of Bigeye Thresher sharks (4). They are strong swimmers, and it is known that they use their long tails to stun their prey (3).
Bigeye thresher sharks have a lifespan of up to 20 years and reach sexual maturity between 10 to 12 years old (4), however, there is little else known about the lifecycle of this species. The species is ovoviviparous, with the eggs developed in uterus and the embryos nourished by yolk stored in the yolk sacs (1). When young are born they measure approximately 1 meter and there are usually 2 per litter (4). There does not appear to be a distinct breeding season, as birth occurs throughout the year (1).
The Bigeye Thresher shark is found in oceanic and coastal waters down to 150m (1). Although they have been sighted in inshore shallow waters, they are found more often in oceanic waters (4).
Found nearly worldwide (1) in tropical and temperate regions (4).
There is limited knowledge concerning the migration patterns of Bigeye Thresher sharks. Acoustic telemetry has been used to study short term migration patterns, but long term patterns are still a mystery. The species appears to migrate extensively on a diurnal basis, coming closer to the surface at night (5).
Feeds on fish including herring, mackerel and hake, along with cephalopods by stunning prey with its long tail (2).
Not Listed under the IUCN Redlist (6).
Description written by Jo Pollett (2009)
(1) Jensen, C., 2009. Florida Museum of Natural History: Ichthyology Department. Biological Profiles – Bigeye Thresher. [Online] Available at: http://www.flmnh.ufl.edu/fish/gallery/descript/bigeye/bigeye.html [Accessed 19 August 2009].
(2) Compagno, L.J.V. 1998. Alopiidae. Thresher sharks. p. 1269-1273. In: K.E. Carpenter and V.H. Niem (eds.) FAO identification guide for fishery purposes. The Living Marine Resources of the Western Central Pacific. Rome: FAO.
(3) Compagno, L.J.V. 1984 FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1 – Hexanchiformes to Lamniformes. FAO Fish. Synop. 125(4/1):1-249.
(4) Compagno, L.J.V. 2001 Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. 269p.
(5) Nakano, H., Matsunaga, H., Okamoto, H. & Okazaki, M., 2003. Acoustic Tracking of Bigeye Thresher Shark Alopias superciliosus in the Eastern Pacific Ocean. Marine Ecology Progress Series, 265, pp.255-61.
(6) IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. <www.iucnredlist.org>. Downloaded on 19 August 2009.