Two new shark species discovered

Two new species of sawshark have been found in the West Indian Ocean by an international team of marine scientists.

The newly discovered Pliotrema kajae and Pliotrema annae are species of rarely seen six-gilled sawsharks. 

The discovery came during an investigation of small-scale fisheries off the coast of Madagascar and Zanzibar.

The research team says the discovery of the two new sharks highlights how little remains known about life in the ocean and the impact humans are having on it..

The sharks, named affectionately by scientists as Kaja and Anna are characterised by their distinctive saw-like snout. Found mainly in the temperate waters of all three major oceans (with the centre of distribution in the western Pacific Ocean), the number of sawsharks has declined in the past couple of decades due to commercial fishing.

"The six-gill sawsharks are really quite extraordinary as most sawsharks have five gill slits per side.

"So it was really exciting to find a new six-gill sawshark species and to find two new species -- well that was simply astonishing”, said Lead researcher Dr Simon Weigmann.

The sawshark can reach up to 1.5 metres in length.

Another distinctive sign of a sawshark is its pair of barbels found in the centre of its snout. Barbels are whisker-like sensory organs that are located around the mouth of the shark and are there to help them seek-out prey.  This type of shark feeds on fish, crustaceans and squid.

The newly discovered species of saw shark, Pliotrema kajae and Pliotrema annae, differ from the only previously known species of six-gilled saw shark, Pliotrema warreni - due to the positioning of their barbels.

Kaja and Anna’s barbels sit about halfway from the tip of the snout, whereas for tPliotrema warreni, the barbels are about two thirds of the way down - much closer to the mouth. 

Sawsharks look similar to sawfish but the two are actually quite different, according to Simon Weigmann, who works at the Elasmobranch Research Laboratory in Hamburg, Germany.

Weighmann explains: “Sawfish actually belong to the ray family and are also much smaller than sawfish, which can grow up to 7 metres long.

“Sawsharks have gills on the side of their heads, whereas sawfish have them on the underside of their bodies.”

The researchers stress that fisheries of all sizes need to get better at reporting any sharks they find during their operations. Better reporting practices will help researchers monitor and protect more vulnerable species and help ensure the practice of sustainable fishing can be maintained. 

Reference: Weigmann S, Gon O, Leeney RH, Barrowclift E, Berggren P, Jiddawi N, et al. (2020) Revision of the sixgill sawsharks, genus Pliotrema (Chondrichthyes, Pristiophoriformes), with descriptions of two new species and a redescription of P. warreni Regan. PLoS ONE 15(3): e0228791. https://doi.org/10.1371/journal.pone.0228791