General: Thresher Sharks

1/14/2018

Slash!

I’m not talking about zorro here, but this shark does have a famous “sword” of its own. Meet the thresher sharks, probably one of the more recognised sharks thanks to their whip-like tail. Just as deadly as Zorro’s sword, they instead use the elongated upper lobe of their caudal (tail) fin to herd, stun, and ultimately kill their prey (which includes small fish, squids, octopi and sometimes seabirds).

Thresher sharks are large sharks in the Alopiidae family, with the species found in all temperate and tropical oceans. Rarely are they spotted in shallow waters, preferring the open ocean and can venture into deep waters. The thresher shark family currently has three species of active predators: Pelagic thresher (Alopias pelagicus), Thresher shark (Alopias vulpinus) and the Bigeye thresher shark (Alopias superciliosus). A fourth species (currently unrecognized) may exist, currently known from one specimen’s muscle samples. Thresher sharks, which are solitary creatures, are viviparous with yolk-sac with no distinct season for mating.

The threshers can be hard to tell apart (we’ll talk more about how they differ in their own individual blog posts) but a common way to do so is by their colouration. Bigeye threshers are often brown, common threshers are dark green and pelagic threshers are usually blue. These are of course generalisations and can vary by individuals; light and water quality can make colours seem different. All have a creamy underbelly, and their short snout and small mouth look even smaller in comparison to their big eyes. #Finfact: Thresher sharks can leap out of the water!

Did you know that thresher sharks are one of the few shark species that have the super power of endothermic capabilities? We’ve seen this in the great white shark and mako sharks (both the longfin mako and shortfin mako) – it’s a modified circulatory system that acts as a counter-current heat exchanger, allowing the retention of metabolic heat. IUCN assessments vary for these animals.

have you heard of this critter before?

glossary

Caudal fin: The tail fin.
Endothermic: Heat is absorbed.
Gestation: The period in which a fetus develops, beginning with fertilization and ends at birth.
IUCN: International Union for Conservation of Nature.
Temperate waters: The water between tropical seas and the Polar Regions (10-21° C, 50-69.8° F).
Viviparous with yolk-sac: Also known as aplacental viviparous and previously known as ovoviviparous/ovoviviparity; it is the production of eggs that are fertilised and hatch inside the female shark but the embryos lack a placental connection to the oviduct or uterus and so do not feed off the mother.