The newly discovered Pliotrema kajae and Pliotrema annae six-gill saw sharks, were discovered during research investigating small-scale fisheries operating off the coasts of Madagascar and Zanzibar. The discovery of these two new sharks highlights how little we still know about life in the ocean and the impact we are having on it.
The study was led by Dr. Simon Weigmann of the Elasmobranch Research Laboratory in Germany, and involved a collaboration between several organisations and research institutions, one of those being the Natural History Museum in London which housed comparative specimens of known saw shark species. These findings have been recently published in the peer reviewed journal ‘PLOS One’.
The capture of sharks and rays by fisheries operating in the South West Indian Ocean often goes unreported, despite very little being known about saw sharks, what is known about the depth range they inhabit suggests, it is more than likely that they are being negatively impacted by existing fishery operations.
Saw Sharks (Pristiophoriformes) are found from the Indian Ocean to the Southern Pacific Ocean they can reach up to about 1.5 metres in length and are extremely distinct with their long saw like snout (rostrum) edged with sharp teeth which alternate in size (smaller teeth are inserted between larger teeth), which they wield around to both defend themselves against predators as well as to stun their prey such as fish crustaceans and squid.
Although their saw like rostrum is similar to those found in Saw Fish, the two are not to be confused, the latter belongs to the sharks close relatives, the ray family and can be separately identified thanks to some key physiological traits; (i) Saw fish are larger, (ii) they don’t have barbels (whisker like sensory organs used in prey detection), and (iii) their gills are located on the underside of their body as opposed to the saw sharks which are on the side of their heads as in all true shark species.
Both new species differ from existing ones in a number of characteristics including their known distribution range and colouration. Taxonomical differences include the location of barbels on the snout as well as overall length of the barbel, the size and shape of the snout, a greater number of large lateral rostral teeth and upper jaw tooth rows, jaw teeth with sharp basal folds, and colouration which is much paler brown and the presence of indistinct yellowish stripes when compared to species already described.
Link to the published paper: