This week’s Featured Species is celebrating International Sawfish Day, which happened earlier this week on October 17th. Today we examine the largest of the sawfishes, the Green Sawfish (Pristis zijsron)- which I highly recommend you see in person if you can. These animals are just awe-inspiring. No videos or photos I can show you will be able to capture the true beauty of seeing one glide over you, but I will do my best! If you are ever in Chicago, stop by Shedd Aquarium’s Wild Reef, especially early in the morning. Ginsu is a sight!
The green sawfish is the largest of the sawfishes. There are five extant- or living – species of sawfishes in two genera: Anoxypristis and Pristis. Anoxypristis sawfish, or the narrow sawfish, are characterized by long narrow rostra that have no teeth on the first quarter where the rostrum attaches to the body. Teeth become more abundant as you move away from the body towards the end of the snout. There is only one extant species of Anoxypristis sawfish. The pristis sawfish, which has the remaining four species of living sawfishes, including the green sawfish. All species of living sawfishes are either endangered or critically endangered (Simpfendorfer, 2013).
Sawfishes are often confused with sawsharks due to their strong dorsal fins and shark-like caudal tails; however they are members of the ray family (Tricas, et al., 1997). It is easy to spot the differences if you know what you are looking for. Both sawfish and sawsharks have five pairs of gills. However, the gills of sawsharks are located on the sides of their heads, while the gills of swfishes are located underneath their bodies just like other skates and rays (Parker, 2008; Tricas, et al., 1997). Their rostra are also structured differently. Sawfishes have long, strong rostra with teeth that are uniform along both sides (Klimley, 2013). Sawsharks have teeth of varying sizes along both sides of the rostra and fleshy tendrils that trail down from about half way up their rostrum (Parker, 2008). But one of the most telling characteristics, is size. Sawfishes are overall much larger than sawsharks. Most species of sawsharks grow no more than 4.5 feet (1.4 m), while the some species of sawfishes, like the green sawfish, can grow more than 20 feet (6 m). Sawfish and sawsharks are the perfect example of convergent evolution: two unrelated species that evolution similar structures along their own evolutionary path ways. Essentially two species are out doing their own thing for millions of years, evolve to fit into their ecological niches, and show up to the party wearing very similar outfits! In the photo below, you can see the differences between the sawshark on the left and the sawfish on the right.
Modern sawfishes first appeared in the fossil record sometime between the beginning of the Cenozoic, about 66 million years ago, and the beginning of the Eocene, about 56 million years ago. Just like sharks, their cartilaginous skeletons did not fossilize well so much of what we know of their history is from their teeth. Unlike traditional shark teeth which are constantly worked and shed, the teeth along a sawfish’s rostrum are embedded into deep sockets. If one of these teeth are lost, it is not replaced. Which makes fossils, like this 66 million year old Ischyrhiza found in the Dukamaje Formations of Niger, Africa, rare. The flared root area would be deeply embedded into the rostrum. It is my absolute favorite!
The green sawfish has an excellent build for hunting. Unlike the traditional ray build, with large, flapping pectoral fins; the green sawfish has relatively small, rigid pectoral fins that are more shark-like that help provide lift and direction. They also have a well defined dorsal fin to enhance swimming efficiency. Their tail muscles are also arranged more closely to that of a shark. They move forward by undulating the entire back half of their bodies from side to side, rather than flapping their pectoral fins (Tricas, et al., 1997). The green sawfish uses its rostrum in a number of ways to hunt. By using the top of the snout like a bat, stun a fish, knocking it out of the school. They also have tremendous dexterity to shake their rostrum laterally from side to side in an aggressive, saw-like attack. This lacerates its prey before consuming it (Klimley, 2013).
edyong209 (Videographer). (2012 March 5). How the Sawfish Uses its Saw [Video Clip]. Retrieved from https://www.youtube.com/
Sawfishes, like many species of elasmobranchs, are aplacental viviparous. Which means their young develop inside eggs, attached to yolk sacs, inside the mother’s womb until they are ready to hatch. Then the mother gives birth to fully developed, live young. Think about that for a second… fully developed sawfish, coming out of you… with those rostra. Yikes!! As if child birth wasn’t bad enough! But don’t worry too much for mom. Nature can be cruel, but it isn’t that cruel. When the young are born, their rostra are soft, and they are covered with a membranous sheath that protects both the pup and mom. When the pup is born, the membrane comes off, the snout straightens, and the teeth harden soon after birth (Tricas, et al., 1997). In the video below, the incredible team at Field School in the Bahamas managed to capture the birth of 5 smalltooth sawfish on film.
Field School (Videographer). (2016 Dec 29). Andros Expedition Report: Sawfish Birth [Video Clip]. Retrieved from https://www.youtube.com/
The green sawfish and the other four species of sawfish are all threatened with extinction due to habitat destruction from agricultural pollution, climate change induced habitat shifting, and fishing pressures. The toothed rostrum of the sawfishes makes entanglement in gillnets and trawl nets very easy (Simpfendorfer, 2013). There are several conservation initiatives in place to protect these species.
- All sawfishes are protected until Appendix 1 of the Convention on the International Trade in Endangered Species (CITES), this means CITES parties are obligated to ban all international commercial trade of sawfish and their products. It does not require countries to make the species “no take,” but it does require CITES parties to strictly protect sawfish nationally, though many countries still struggle to do so. A black market trade for their fins, flesh, rostrum, liver, eggs, and skin (Simpendorfer, 2013).
- Education initiatives aimed at sawfish-specific encounters with fisheries are thought to help increase the chance of survival when released from nets (DEEDI, 2010). These protocols have been distributed through print media, video training, and even during face to face training sessions.
- Some zoos and aquariums have also begun work on conserving the species. Green sawfish are difficult to study in the wild, and we still do not know much about their life histories. Zoos and aquariums can off a glimpse into their life histories and can provide an opportunity to protect the genetic diversity. Studies of Australian populations suggest that there is low to moderate genetic diversity in these populations and suggest that populations are highly fragmented (Phillips, Chaplin, Morgan, & Peverell, 2011; Phillips, 2012). Low genetic diversity could lead to localized extinction if populations do not have the genetic strength to rebound from outside pressures.
- Finally, marine protected areas are increasing the habitats where sawfish are free from fishing pressures (Bond et al., 2017). Marine protected areas make up a very small fraction of the world’s oceans, the more areas we can make safe for our endangered marine life, the better off we will all be.
The Deep (Videographer). (2015 Aug 26). Saving the Endangered Green Sawfish [Video Clip]. Retrieved from https://www.youtube.com/
I’m delighted to announce a partnership with the wonderfully talented Julius Csotonyi! Julius creates stunning shark coloring sheets that are fun and educational for all ages. From time to time you’ll see Julius’ work featured right here and on my other social media platforms! You can find more coloring sheets in the store! You are welcomed to download these beautiful sheets and enjoy them with family and friends.
Authority: Bleeker, 1851
Family: Pristidae, 5 species
Length: Up to 23 feet (7 m) though anything over 20 feet (6 m) is rare
Weight: 700 lbs (317 kg) +
Habitat: Shallow coastal waters and estuaries
Depth: 0 – 230 feet (0- 70 m)
Reproduction: Aplacental Viviparous
Litter Range: Approximately 12 pups
Home Range: Indo-West Pacific from Southern Africa to Australia
Diet: Small bony fishes and invertebrates
IUCN Status: Critically Endangered; toothed rostrum is easily ensnared by gillnets and demersal trawl nets set by commercial fisheries.
Thanks so much for checking out the green sawfish! Remember to swim over to last week’s featured species: the Dusky Smoothhound Shark. If there is a species of shark you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species.
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finatics!
Featured Image Source
Shedd Aquarium (Photographer). (2017 November 14). Ginsu the Green Sawfish [Digital Image]. Retrieved from https://www.facebook.com/
Bond, M. E., Valentin-Albanese, J., Babcock, E. A., Abercrombie, D., Lamb, N. F., Miranda, A., … Chapman, D. D. (2017). Abundance and size structure of a reef shark population within a marine reserve has remained stable for more than a decade. Marine Ecology Progress Series, 576, 1–10.
Department of Employment, Economic Development and Innovation (DEEDI). (2010). A Guide to Releasing Sawfish. Gulf of Carpentaria Inshore and Offshore Set Net Fishery. The State of Queensland, Department of Employment, Economic Development and Innovation, Brisbane.
Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Phillips, N. (2012). Conservation genetics of Pristis sawfishes in Australian Waters (Doctoral dissertation, Murdoch University).
Phillips, N. M., Chaplin, J. A., Morgan, D. L., & Peverell, S. C. (2011). Population genetic structure and genetic diversity of three critically endangered Pristis sawfishes in Australian waters. Marine Biology, 158(4), 903-915.
Simpfendorfer, C. (2013). Pristis zijsron The IUCN Red List of Threatened Species 2013. Retrieved from http://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T39393A18620401.en
Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.
Welten, M., Smith, M. M., Underwood, C., & Johanson, Z. (2015). Evolutionary origins and development of saw-teeth on the sawfish and sawshark rostrum (Elasmobranchii; Chondrichthyes). Royal Society open science, 2(9), 150189.