Featured Species Friday: Spiny Dogfish (Squalus acanthias)

This week’s featured species is the Spiny Dogfish (Squalus acanthias), sometimes referred to as the piked dogfish or the whitespotted spurdog (Tricas, et al., 1997). Perhaps it is misnomer of “dogfish,” but the spiny dogfish is often mistaken for a bony fish species rather than a shark species. But make no mistake, this small cartilaginous fish is definitely an elasmobranch!

spiny-dogfish
Monterey Bay Aquarium (Photographer). (n.d.). Spiny Dogfish [Digital Image]. Retrieved from https://www.montereybayaquarium.org/

 

The spiny dogfish is a small species of shark, only reaching about 4 feet when fully grown, which leaves it vulnerable to attack from other large predators, including other sharks. When it feels threatens, the spiny dogfish will thrash its body and arch its back towards its potential predator in an attempt to protect its with a sharp set of spines at the base of its dorsal fins. These spines are also mildly venomous, thanks to a gland at the base of each spine (Parker, 2008)! Ouch!

spiny-dogfish-spine
The spiny dogfish has sharp spines at the front of its dorsal fins [Digital Image]. (n.d.). Retrieved from https://fishingmag.co.nz/

 

The spiny dogfish is known to form large single-sex schools outside of the breeding season when food in abundant. Though they may be relatively small sharks, they are known for their ferocious appetites! Schools of spiny dogfish have been known to destroy fishing grounds, making them the bane of fishermen in many parts of the world (Parker, 2008).

Spiny Dogfish
Murch, A. (Photographer). (n.d.). Schooling Spiny Dogfishes [Digital Image]. Retrieved from http://www.elasmodiver.com/

 

With a worldwide distribution in temperate waters, the spiny dogfish is possibly one of the the most abundant shark species in the world (Skomal, 2016). And fisheries industry has taken advantage of their abundance and marketability the world over. Not only are the spiny dogfish the most popularly used shark species for educational purposes in the science classroom – I, myself, dissected one in college as an undergrad – but they are also sold all over the world for their meat and fins. In Europe they are often sold as “rock salmon” or “sea eel” and in the UK specifically, they are commonly used to make fish and chips (Parker, 2008; Skomal, 2016).

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Alamy (2014). DogFish and Chips [Digital Image]. Retrieved from http://dailymail.co.uk/

The harvesting of the spiny dogfish has led to collapses of regional populations due to overfishing. Like many other shark species, the spiny dogfish takes several several to reach sexual maturity. But they also have one of the longest gestation periods of any elasmobranch species – 24 months (Tricas, et al., 1997)! A female spiny dogfish will take 2 years to incubate up to 20 pups before giving birth to live young. So the spiny dogfishes are slow to rebound from population declines due to fisheries. However, to have an financially feasible fisheries industry, large numbers of dogfishes must be landed (Skomal, 2016).

spurdog_squalus_acanthias_11-08-15_4
Fenwick, D. (Photographer). (.n.d). Spiny Dogfish in fishing net [Digital Image]. Retrieved from http://www.aphotomarine.com/

 

So what to do? Can we have both a shark fisheries industry and stable shark populations? At the height of spiny dogfish harvest, nearly 50,000 tons (45,360 metric tons) were taken by Britain alone in a single year (Parker, 2008). Surely an unsustainable harvest!  But there is hope for spiny dogfish. On the east coast of the United States, spiny dogfish populations are beginning to rebound following strict fishing regulations placed on the industry (Skomal, 2016; Parker, 2008). Species conservation management practices are showing promise for population rebound!

 

NOAA Fisheries. Shark Conservation and the Spiny Dogfish [Video Clip]. Retrieved from https://www.youtube.com/

Shark Stats

Authority: Linnaeus, 1758

Family: Squalidae; 28 species

Length: Average 4.0 feet (1.2 m); up to 5.0 feet (1.5 m)

Weight: 11 – 22 lbs (5 – 10 kg)

Habitat: Continental and island shelves and slopes; coastal waters, bays, river mouths and inlets

Depth: Typically 100 – 300 feet (30.5 – 92 m), occasionally up to 3,000 feet (915 m)

Reproduction: Ovoviviparous

Gestation: 24 months – longest known gestation period of elasmobranch, basking and frilled sharks suspected to have longer gestation periods, but still unknown

Litter Range: 1 – 20 pups

Home Range: World wide in warm temperate waters

Diet: Small bony fishes and invertebrates

IUCN Status: Critically Endangered in Northeastern Atlantic; Endangered in several locations; Least Concern in Australia and South Africa; Vulnerable everywhere else

(Parker, 2008; Fordham, Fowler, Coelho, Goldman, & Francis, 2016; Skomal, 2016)

Thanks for taking the time to check out one of the little guys this week! Sharks come in all shapes and sizes, and I just love that! If you missed last week’s featured species, go check out the stunning Oceanic Whitetip Shark! Haven’t seen your favorite species featured yet? Leave me a comment or send me a message and let me know what species you’d love to see featured!

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!

Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.

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Featured Image Source

Murch, A. (n.d.). Spiny Dogfish [Digital Image]. Retrieved from http://www.elasmodiver.com/

Literature Cited

Fordham, S., Fowler, S.L., Coelho, R.P., Goldman, K. & Francis, M.P. 2016. Squalus acanthias. The IUCN Red List of Threatened Species 2016: e.T91209505A2898271. http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T91209505A2898271.en

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

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.

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