Welcome to the first installment of Featured Species Friday! There are over 400 species of sharks and over 500 skates and rays. There are more species discovered every year. Most of us are only familiar with a handful of species from Shark Week and similar programming. My Master’s work is focused on inspiring elasmobranchii conservation through education and personal connections. I thought a great way to not only push myself to continue to expand my knowledge of these amazing animals, but also to share that knowledge with all of you, was to create a new series featuring a different species of elasmobranch each week. This week’s featured species is the Longnose Sawshark, also known as the Common Sawshark (Pristiophorus cirratus).
The sawsharks are of the Order Pristiophoriformes, Family Pristiophoridae which contains 5 species of sawsharks (Stevens, 1997):
- Sixgill Sawshark Plioterma warreni
- Japonese Sawshark Pristiophorus japonicus
- Shortnose Sawshark Pristiophorus nudipinnis
- Bahamas Sawshark Pristiophorus schroederi
- Longnose (or Common) Sawshark Pristiophorus cirratus
All members of the Pristiophoridae family are characterized by broadly similar anatomy and habits. Their bodies are flattened from the top to the bottom; this is also referred to as dorsoventrally. They also have the distinctive long, saw-like snouts, or rostrums. In the Longnose Sawshark the rostrum typically forms more than a quarter of the overall body length (Parker, 2008).
These sharks have adapted their fins to their their bottom dwelling lifestyle. They have developed a long upper lobe of the caudal (or tail) fin, and have lost the anal fin all together (Mojetta, 1997). Typically, bottom dwelling sharks have long upper lobes of their caudal fins and very little lower lobe. They usually hold the upper lobe at a very low angle, sacrificing speed, but gaining maneuverability (Kardong & Romer, 2006). In the following video clip you can see how the Longnose sawshark moves with almost eel-like body movements, hugging the ocean floor.
DIVErsion (2015, November 6). Longnose Sawshark on the Dunsborough Artificial Reef. Retrieved on June 22, 2017 from https://www.youtube.com/watch?v=oxPE8eOnCv4
Because of their flattened bodies and saw-like rostrums, sawsharks are often confused with sawfishes, which are in the ray family (Tricas, Deacon, Last, McCosker, Walker, & Taylor, 1997). However there are several differences that are easy to identify once you know what you’re looking. Sawsharks have five pairs of gills located on the sides of their heads (Parker, 2008), unlike sawfishes which have the gills located underneath the bodies like skates and rays (Tricas, et al., 1997). Sawsharks also have a pair of long, fleshy barbels or tendrils that are used in hunting located halfway up the rostrum. Sawfishes do not have these long tendrils (Parker, 2008). In the photo below, you can see the sawshark on the left with the long trendils trailing down from the rostrum half way down; the gill slits are also visible on the sides of the individual at the bottom of the photo. On the right you can see there are no trendils, but uniform spiked teeth along the entire rostrum, as well as gill slits underneath the body of the sawfish.
One of the most incredible things about this species is how they give birth. A mother gives live birth to anywhere from 3 to 22 pups ranging from 12 to 14 inches in length. And these pups are born with their saw rostrums ready to use! At least Nature has a sense of humor! The teeth of the rostrums are actually folded back along the blade in the womb and through the birth canal in order to avoid injuring mom during birth (Parker, 2008). Once these pups are born, they leave mom and are ready to begin the hunt.
While the IUCN lists the longnose sawshark among the “Least Concern” category, these sharks are still sometimes accidentally caught in fishing nets. Fishermen place gillnets while fishing for gummy sharks (Mustelus antarcticus), but sometimes the longnose sawsharks are accidentally snared in the fine mesh of the gillnets and become what is referred to in the fisheries industry as “bycatch” (Walker, 2016). Bycatch refers to fish species other than the primary target that are caught as a result of the harvesting of the target species (Blackhart, Stanton, & Shimada, 2006).
Length: 3 to 4.5 feet (0.9 to 1.4 meters)
Weight: Up to 22 lbs (10 kg)
Habitat: Continental Shelf
Depth: 130 to 980 feet (39 to 299 meters)
Gestation: Approximately 12 months
Litter Range: 3 to 22 pups per birth 12 to 14 inches (30 to 36 cm) long
Home Range: Southern Coasts of Australia and neighboring islands in south-east Indian Ocean and south-west Pacific Ocean
Diet: Small fish, cornets, shrimp, prawns, and squid
IUCN Status: Least Concern
(Walker, 2016; Parker, 2008)
Which species are you most interested in learning more about? Leave me a comment and let me know! Maybe you’ll see your species featured next week!
Featured Image Source
Longnose Sawshark [Digital Image] (n.d.) . Retrieved from http://laguna-akul.ru
Blackhart, K., Stanton, D.G., and Shimada, A. M. (2006). NOAA fisheries glossary: NOAA technical memorandum NMFS-F/SPO-69. Retrieved from http://www.st.nmfs.noaa.gov/st4/documents/FishGlossary.pdf
Frederico, L., & Hassall, G. (Eds.). (1998). Reader’s Digest Explores: Sharks (1st ed.). Reader’s Digest.
Kardong, A. K. V., & Romer, A. S. (2006). Comparative vertebrate anatomy. BIOL, 3510(001), 53408.
Mojetta, A. (1997). Sharks: History and biology of the lords of the sea. (E. McNulty, Ed.). San Diego: Thunder Bay Press.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Stevens, J. D. (Ed.). (1997). Sharks (6th ed.). New York: Facts on File.
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.
Walker, T.I. 2016. Pristiophorus cirratus. The IUCN Red List of Threatened Species 2016: e.T39327A68640973.Downloaded on 22 June 2017.