17 October
Today is International Sawfish Day! That might not sound too exciting to you because the vast majority of people have never even heard of sawfish, let alone understanding why they have their own awareness day! But Sawfish are so worth a few minutes of your time! They are absolutely fantastically bizarre animals! So please allow me to introduce you to these unique and wonderful creatures... I'm sure you will come love them!
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Saw-Tastic!
Undoubtedly the first thing you will notice about the sawfish is their spectacular saw (known as a "rostrum") sticking out of the front of their head. It would be pretty hard to miss! Sawfish use their incredible rostrum to slash their prey into bite-size pieces and dig-up hidden food that is buried in the sandy substrate. It is quite impressive! (Compagno, 1984)
The sawfish rostrum is an extension of the facial cartilage, armed with incredible "rostral teeth" on both sides. Don't be fooled by the name though, because these are not actually true teeth. In fact, they are "placoid scales". These are tiny, plate-like structures, which also make up the skin of sharks and rays. These structures are what give their hides both strength and flexibility (Slaughter & Stinger, 1968; Compagno, 1984).
In the distantly related sawsharks (Family Pristiophoridae), the rostral teeth are actually modified teeth and are therefore, lost and replaced continuously throughout the shark's life (to learn more check out, An Endless Supply of Teeth). However, in sawfishes the rostral teeth are not replaced if broken and they continue to grow ever larger throughout their lifetime (Slaughter & Stinger, 1968; Compagno, 1984). To learn more about how to tell these similar fishes apart, you can head to Sawfish or Sawshark?
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Amazing Sensory Abilities
Sawfish have seven senses with which to detect their prey! As well as the five senses that human beings enjoy (sight, touch, taste, smell and hearing), sawfish are also able to detect minute electromagnetic fields in the water through their "Ampullae of Lorenzini". This allows them to find prey, even when it is well hidden. They are also able to sense water displacement through their "lateral line", so can note changes in air and water pressure. Quite the super power!
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Wedgefish Relatives
Although they have an elongated body and powerful tail, much like a shark, sawfishes are actually a type of ray (or "Batoid"). They are assigned to the order Rhinopristiformes. Genetic analysis has shown us that sawfishes are closely related to wedgefishes and guitarfishes, and only distantly related to angel sharks or wobbegongs, which might look more similar at a glance (Stein et al, 2018). To learn more you can check out Kissing Cousins and the Rhino-Saws.
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Friendly Fishes
Sawfish are not dangerous to human beings (except to those who fish and haul them onto boats, at which point their large size, great strength and sharp rostral teeth could certainly cause injuries). However, humans and sawfish very rarely come into contact, as they do not like to spend time around shallow beaches where people swim.
When SCUBA divers are lucky enough to encounter sawfish, they are usually placid. So much so, that the Florida Museum has even started an initiative for snorkelers and divers to report their sawfish sightings as part of a citizen science data collection project called The International Sawfish Encounter Database (ISED).
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Independent Women
Sawfish, like all other species of rays, reproduce sexually by "ovoviviparity". This means that a male and female come together to copulate and the female incubates eggs, which hatch internally, before being born as live youngsters (Compagno, 1984; Fields et al, 2015).
However, what is especially interesting about sawfish, is that they are capable of switching to "asexual reproduction", when they cannot find a mate. Females that live in such low population densities that they simply do not come into contact with a male during the mating season, will reproduce on their own through a process known as "facultative parthenogenesis" (Fields et al, 2015). To learn more, you can head over to Like A Virgin.
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Stupendous Size!
Sawfish can be really enormous! In 2021, a large female smalltooth sawfish (Pristis pectinata), which had sadly been found dead in the shallow waters of the Florida keys, was the largest ever measured at a whopping 6 metres long! They are truly magnificent! (Compagno, 1984)
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High Extinction Risk
Sawfish rostrums, like elephant ivory and rhino horns, have held a great value as curios on the global market. Consequently, sawfish have been relentlessly hunted for their saws in the past, which has contributed to their population declines (It is beyond me why you would want something so morbid decorating your home, but there you have it!).
Today sawfish are still threatened by overfishing, both for their saws and for their fins. They are also very vulnerble to being killed as bycatch, as their rostrums are so easily entangled in fishing gear (Dulvy et al, 2016).
As a result, sawfishes have now vanished from at least 22% of the countries where they were once common. When a species becomes locally extinct, this is known as "extirpation" (Dulvy et al, 2016).
All of the five species of sawfishes are now considered threatened with extinction, with The International Union for the Conservation of Nature (IUCN) flagging the smalltooth sawfish, green sawfish (P. zijsron) and largetooth sawfish (P. pristis) as Critically Endangered, and the dwarf sawfish (P. clavata) and narrow sawfish (Anoxypristis cuspidata) as Endangered on their Red List of Threatened Species (Dulvy et al, 2016).
On this International Sawfish Day, I hope you have learnt something about these magnificent animals and have begun to find them fascinating. If so, I hope you will feel as anxious and devastated as I do about their terrible population declines in the wild. Please DO share this article and tell your friends all about the plight of sawfish.
If you would like to get involved in sawfish conservation, you can:
Support the Sawfish Conservation Society.
Contribute your sawfish sightings to the Shark Trust See A Saw campaign.
Contact your political leaders to demand they take action to protect sawfishes. You could even include a petition!
References
Compagno LJV (1984). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species known to Date. FAO Species Catalogue. Access online.
Dulvy NK, Davidson LNK, 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.
Fields AT, Feldheim KA, Poulakis GR & Chapman DD (2015). Facultative parthenogenesis in a critically endangered wild vertebrate. Current Biology, 25:11, PR446-R447. Access online.
Slaughter BH & Springer S (1968). Replacement of rostral teeth in sawfishes and sawsharks. Copeia, 3, 499-506. Access online.
Stein RW, Mull CG, Kuhn TS, Aschliman NC, Davidson LNK, Joy JB, Smith GJ, Dulvy NK & Mooers AO (2018). Global priorities for conserving the evolutionary history of sharks, rays and chimaeras, Nature Ecology & Evolution. Access online.
By Sophie A. Maycock for SharkSpeak
