• SharkieSophie

See a New Saw

Updated: Apr 26

With the incredible advancements of science and exploration, it may seem surprising that it is even possible to still discover new species of sharks. However, this year, not one, but two new species of sixgill sawshark (Order Pristiophoriformes) have been discovered off the coast of East Africa.


Newly discovered species of sawshark; Pliotrema kajae (Berggren & Temple, 2020)

Sawsharks are unique amongst sharks due to their impressive rostrum with “rostral teeth”, which exaggeratedly extends out from the front of the face. Unlike their doppelgängers, the sawfish (Order Rhinopristiformes, which are actually more closely related to rays than sharks), sawsharks have alternating large and small rostral teeth, which are consistently shed and replaced throughout their lives. Sawsharks have evolved this remarkable rostrum because it is vital during hunting; they use it to dig hidden animals out of sandy “substrate” and then to slash their prey into bite-size pieces. Sawsharks eat mainly small fish, squid crustaceans (such as shrimp and small crabs).



The two new species described have been named Pliotrema kajae and Pliotrema annae. Although they might look quite similar, the two have very different habitats; P. kajae live in insular slopes up to depths of 320 m, where P. annae live in shallow waters up to 35 m depth. P. kajae also has a longer snout than its cousin and has more numerous large rostral teeth. P. annae is medium to dark brown and has no dorsal colouration, where its relative is paler and has two yellow stripes on the dorsal side. These new species have different ranges, distribution and colouration than other sawsharks. Both differ from the previously known P. warreni, in the position of their sensory “barbels” and their constricted rostra (Weigmann et al, 2020).


Pliotrema kajae (Image credit: Oddgeir Berg Alvheim. Source: http://www.sci-news.com)

The new sawsharks were found by a research team studying small-scale fisheries in Madagascar and Zanzibar. Whilst the scientists were very excited by their discovery, the team were alarmed by the realisation that the new species they were describing may already be threatened with extinction!



Pliotrema annae (Image credit: Oddgeir Berg Alvheim. Source: http://www.sci-news.com)

There are at least half 150,000 fishing boats working off the east coast of Africa. Some fishers target large fish (including sharks and rays) specifically using long-lines, but many use driftnets or gillnets, which are preferable because they are cheap. From a conservation perspective these methods are considered detrimental, because they are not selective and catch any and all species which become entangled in them. These small-scale fisheries are not well documented and it is thought that there may be significant under-reporting of how many sharks and rays they land. Therefore, it is very possible that species may be going extinct before they have even been recognised by science (Berggren & Temple, 2020).



"Much is still unknown about biodiversity in coastal waters around the world, and how vulnerable it may be to poorly monitored and managed fisheries.”

- Berggren & Temple, 2020

As the waters off the coast of east Africa are a remarkable and unique hotspot for shark and ray biodiversity, it will be critical to assess the populations in the area and implement protective measures for any species under threat. These protective measures could have serious repercussions for local fishers and therefore it will be pivotal to involve the community and significant stakeholders in this process. The research team that described the new sawsharks stated that they could not have made the discovery without the assistance of local fishermen; highlighting how local knowledge and methods can be of enormous value to scientists (Berggren & Temple, 2020).


Small-scale fishers with their driftnets in Zanzibar (Berggren & Temple, 2020)

References

Berggren P & Temple AJ (2020). We’ve just discovered two new shark species–but they may already be threatened by fishing. The Conversation. Access online.


Weigmann S, Got O, Leeney RH, Barrowclift E, Berggren P, Jiddawi N & Temple AJ (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, 3:15, e0228791. Access online.


By Sophie A. Maycock for SharkSpeak.

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