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The Rhino-Saws

Sharks and rays are so closely related to each other, that they are often discussed together as "Chondrichthyans" (meaning cartilaginous fishes) or "Elasmobrachs" (meaning sharks and rays). Several million years ago, these animals all shared a "common ancestor", but over that time, evolution has changed and adapted them into very different animals. Now there is a huge diversity in body forms - in a wonderful spectrum from the flattened skates, to the elongated and enormous body of the whale shark, with a plethora of different species in between. Allow me to introduce you to an especially interesting little group of shark relatives known as the "Rhinopristiformes"...


A bowmouth guitarfish (Rhina ancylostoma) (Image source: www.sharkconservationfund.org)

The term Rhinopristiformes, refers to an orders of rays, which are more commonly known as the wedgefish (Family Rhinidae), guitarfish (Families Glaucostegidae and Rhinobatidae), sawfish (Family Pristidae), banjo rays (Family Trygonorrhinidae) and, depending which taxonomist you ask (scientists like to argue about which animals are more closely related to others and how they evolved), also the fanrays (Family Platyrhinidae) and panrays (Family Zanobatidae) (Naylor et al, 2012).


Rhinopristiformes : ῥῑνο (rhino) = 'nose', πρίστις (pristis) = 'sawfish' [Greek]


Evolutionary relationships of the Rhinopristiformes to other rays, and to sharks (Jabado, 2019)

The group are closely related to other rays and share many of their features. For example, they have extended pectoral fins which are connected to their body, resembling the long wings of other rays and they have relatively flattened bodies around the head and rostrum, similar to their ray relatives. However, at a glance they could also be mistaken for a type of shark thanks to their muscular tail and distinct dorsal fins, which make them strong swimmers. They almost look like a mixture between the two, so they are sometimes called the 'shark-like rays' (Jabado, 2019, Kyne et al, 2019).


Bottlenose wedgefish (Image Credit: Alex Kydd, Source: Pintrest)

The wedgefish are so-named for their wedge-shaped face, which they use to dig prey out of sand and gravel. The guitarfish and giant guitarfish have a similarly-shaped rostrum, but they differ from the wedgefish, as they are larger and lack any spots or stripes on their skin (Jabado, 2019, Kyne et al, 2019).


The Rhinopristiformes are found in tropical waters, on continental shelves or around coral reefs. The guitarfish often live in shallower, inter-tidal habitats and the broadnose wedgefish (Rhynchobatus springeri) has also been found in estuaries.



"Species richness" (meaning the number of different species found in one area) of wedgefishes and guitarfishes is highest throughout the Indo-West Pacific, and the Mediterranean Sea is also an important area. They also have a stronghold around Australia where their extraction in fisheries is quite limited (Jabado, 2019, Kyne et al, 2019).

Areas where species richness of wedgefish and giant guitarfish is highest (Kyne et al, 2019)

The other members of this group, the sawfish (despite being very closely related) have strikingly different in looks! Whilst still having the ray-like pectoral fins, and shark-like tail and dorsal fins, they also have a remarkable extended rostrum, armed with "rostral teeth" (Naylor et al, 2012, Dulvy et al, 2016).

Sawfish (Image Source: www.hakaimagazine.com)

This organ is vital for hunting, as the sawfish uses it to dig up hiding animals and swings it through the water to immobilise their prey. This is a very similar adaptation as can be found in the sawsharks (Order Pristiophoriformes). (To learn more about how to tell rostrum-bearing rays and sharks apart, you can check out Sawfish or Sawshark? ).


Sadly, in the past these magnificent saws were valued as a curio around the world. So, just like rhinos for their horns and elephants for their ivory, many, many sawfish were hunted for the sake of decorating people's homes (*sigh* *facepalm*!) (Dulvy et al, 2016, Jabado, 2019, Kyne et al, 2019).


And to this day, the Rhinopristiformes are still seriously threatened by fisheries. Whilst they were once common in soft-bottom tropical waters, they have been subjected to extreme fishing pressure throughout most of their range, which is completely unregulated in many countries. They are fished for the meat in developing nations and also for their fins, which are known as 'white fins' and are very especially valuable on the global shark fin market. They are also at risk from habitat degradation and loss, from dredging, land reclamation and mangrove habitat deforestation (Jabado, 2019, Kyne et al, 2019).



These incredible creatures are now considered some of the most threatened animals globally! Today, more than 88% of the Rhinopritiformes species which have been assessed for the IUCN Red List are considered endangered!


"Sawfishes, wedgefishes, and guitarfishes are amongst the most threatened families and are of global conservation concern"

- Kyne et al, 2019

Sawfish are extinct (RED) in some of their range (Dulvy et al, 2016)

Sawfish are often considered the most threatened marine species in the world and it is thought they have been "extirpated" (have become locally extinct within certain parts of their range) in several locations (Dulvy et al, 2016).


Recently, scientists have also discovered that the wedgefishes and guitarfishes are not doing any better than their sawfish cousins! In a recent assessment undertaken through the IUCN's Shark Specialist Group, scientists have found that every wedgefish and guitarfish (apart from one species (Rhynchobatus palpebratus)) should be reclassified as critically endangered, as they have all suffered a population reduction in excess of 80% over the last 45 years! Some species of wedgefishes and giant guitarfishes have also already suffered extirpation in certain areas of their ranges, and it is thought that 96% face an extremely high risk of extinction (Jabado, 2019, Kyne et al, 2019).


"Without immediate action, there is an extremely high likelihood of global extinction for most species [of wedgefish and guitarfish]"

- Kyne et al, 2019


So, can we save these wonderful animals? Scientists say yes!... This damage is theoretically reversible if management measures are implemented as soon as possible! The first step in this process will be to gather more information about these animals. We know very little about the ecology of wedgefishes and guitarfishes. It is impossible to design management strategies for these species if we do not know their reproductive output, longevity and the locations of their critical habitats. If we can discover more about them, we will be able to design more successful conservation plans for these animals (Jabado, 2019, Kyne et al, 2019).


Another serious problem is a lack of knowledge about how to identify different species. Many sawfish, guitarfishes and wedgefishes look quite alike and it can be challenging to identify them to species level in the field. This means many fishers do not accurately report their landings, which can make it very challenging to monitor catches and to track declines. Similarly, we also lack baseline data about the original sizes of these populations. This is because no-one thought to count all the Rhinopristiformes before they started fishing them. This means we actually do not know exactly how much their populations have declined. It will be very important in the future to educate fishers about how to accurately report their catches, to monitor all Rhinopristoformes fisheries very closely and to assess the stocks of each different species, so that we are able to better monitor their populations (Dulvy et al, 2016, Jabado, 2019, Kyne et al, 2019).


Wedgefish and guitarfish are commonly fished for their extremely valuable 'white fins' (Jabado, 2019)

Most importantly, if we are to save these remarkable creatures from the brink of extinction, their extraction in fisheries must be brought down to a sustainable level in every single country throughout their range. Rhinopristiformes species richness is highest in countries which rank amongst the top shark fishing nations globally including: Indonesia, India, Pakistan, Malaysia, Thailand, Sri Lanka, and Iran. There are very lax management measures in place in many of these countries and several nations have absolutely no management plans at all, so their Rhinopristiform fisheries are completely unregulated! It will be vital to come up with an international plan of action for these animals, including strict fisheries quotas and trade regulations, so that they have consistent protection throughout their whole range. BUT it will only be possible if a majority of the affected nations can agree to these management measures... and that will involve an enormous international collaboration. Species extinctions are a global issue that affect every single one of us and it will only be possible to save endangered animals if we are able to all work together towards a common goal! It is worth the work... these magnificent and bizarre creatures are just too glorious to not save!



There has been good news for one species of wedgefish, which was previously thought extinct! To learn more you can check out I Will Be Back!



References

Dulvy NK, Davidson LHK, Kyne PM, Simpfendorfer CA, Harrison LR, Carlson JK & Fordham SV (2016). Ghosts of the coast: global extinction risk and conservation of sawfishes. Aquatic Conservation: Marine and Freshwater Ecosystems, 26, 134–153. Access online.


Jabado RW (2019). Wedgefish and Giant Guitarfish: A Guide to Species Identification. Wildlife conservation Society, New York USA. Access online.


Kyne PM, Jabado RW, Rigby CL, Dharmadi, Gore MA, Pollock CM, Herman KB, Cheok J, Ebert DA, Simpfendorfer CA & Dulvy NK (2019). The thin edge of the wedge: extremely high extinction risk in wedgefishes and giant guitarfishes. BioRxiv Preprint. Access online.


Naylor GJP, Caira JN, Jensen K, Rosana KAM, Straube N & Lakner C (2012). In: Carrier JC, Musick JA & Heithaus MR (Eds.). Elasmobranch phylogeny: A mitochondrial estimate based on 595 species. Biology of Sharks and Their Relatives, 2nd Edition. CRC Press, Boca Raton, Florida. pp. 31–56.


By Sophie A. Maycock for SharkSpeak.

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