The Dusky smoothhound (Mustelus canis), also sometimes referred to as the Smooth dogfish or the Dog shark, is a species of shark belonging to the family Triakidae. It is grey or olive-grey in color without any prominent markings. This is a highly active and migratory species of shark found in the northwest Atlantic. It has teeth unique to its specialized diet, and the ability to change colors.
Family: Triakidae – Houndsharks
Genus: Mustelus
Species: canis
Phylum– Chordata
Class– Chondrichthyles
Common Name– Ground Sharks
Family– Triakidae
Common Name– Houndsharks
Genus– Mustelus
Species– canis
Status: IUCN Red List NEAR THREATENED
Average Size and Length: They are born between 34-39 cm/1.1-1.2 feet. Males have been measured at 82 cm/ 2.7 feet, and females 90 cm/2.9 feet. The maximum recorded is 150 cm/4.9 feet.
Current Rare Mythical Sightings: The Dusky smoothhound has many common names. It was originally named Squalls canis. In Latin, mustelus translates to weasel and canis translates to dog. M. canis has an allopatric relationship with M. mustelus (the Smoothhound or Common smoothhound) and a sympatric relationship with M. norrisi (the Narrowfin smoothhound).
Teeth and Jaw: The upper labial furrows are longer than the lower labial furrows. There are 10 rows of teeth. The teeth are flat, blunt and low and are pavement-like that are great for crushing. The teeth in the upper and lower jaws are similar in size and are asymmetrical with rounded cusps. Tooth replacement is related to body growth. They grow about 10 cm per every six rows of teeth replaced. That is an increase of 0.03 mm per replaced tooth. Teeth are replaced at a rate of one row per 10 to 12 days.
Head: The head and snout are short and blunt. The internarial area is broad. The eyes are large and closely spaced, elongated and oval. There are small spiracles just behind the eyes.
Denticles: Along the body of the smooth dogfish, denticles are irregularly spaced and lance-shaped with two to six longitudinal ridges extending the entire length of the denticle.
Tail: The caudal fin has two asymmetrical lobes, the lower is smaller and rounder and the upper has a deep notch.
Demographic, Distribution, Habitat, Environment and Range: The Dusky smoothhound sits on the continental shelf of the northwest Atlantic from Canada to Argentina (42°N and 44°S and 100 and 46° W). They are most abundant on the East Coast, from Massachusetts to Florida, Brazil to Argentina, and in the Gulf of Mexico. There are several extensively separated distinct species. The continental shelf subspecies prefers mud and sand in water that is less than 59 feet in depth but can occur in water as deep as 656 feet. They are rarely seen on the upper most slopes to 1,181 feet. The Island subspecies prefers rough rocky bottoms on outer shelves and upper slopes between 449-2,651 feet, but mostly greater than 656 feet in depth. They could possibly occur in midwater off of Cuba. They have been documented in marine and brackish waters. They are demersal and oceanodromous.
Diet: Their diet is crustacean based. They will also eat polychaetes and mollusks. Some prey includes squid, worms, small fish, razor clams, and have been documented to occasionally have garbage in their stomachs.
They fall prey to larger sharks.
Aesthetic Identification: The Dusky smoothhound is large and slender. They are usually grey, or olive-grey without any markings dorsally, and white ventrally. The dorsal fins are unfringed and triangular in shape and are about the same size. The second dorsal fin is just slightly smaller than the first and twice as large as the anal fin. Newborn pups have dusky-tipped dorsal fins and caudal fin. The sub-species, the Caribbean Smoothhound is very similar and hard to distinguish (its location in the Caribbean is a tell-tale sign. The Dusky smoothhound has a higher first dorsal fin and a shorter terminal caudal lobe than the Caribbean smoothhound. Juveniles have indistinct white fin margins, where the juvenile Caribbean smoothounds have very distinct ones. They may have the ability to change colors using melanophores to help them camouflage.
Biology and Reproduction: They are viviparous with a yolk-sac placenta, having between 4-20 pups after a 10-month gestation period. Females can store sperm for up to a year. Mating is thought to happen in May and June. Males mature in 1 to 2 years, sometime 3, and females 4-5 years of age. They have a relatively low population doubling time of 4.5 to 14 years. Males can live up to 10 years and females up to 16 years.
Juvenile females have filiform uteri, small ovaries with undifferentiated oocyctes, egg cells, and narrow, thread-like oviducts with undeveloped oviducal glands. Adolescents have enlarged oviducal glands with distinguishable oocytes and no or few corpora lutea. Adults have large ovaries and vitellogenic oocytes. Spermatozoa has been observed in preovulatory females. Juvenile males have soft, small claspers and undeveloped testes with straight, thread-like ampullae ductus deferens. Adolescents’ testes have increased weight and claspers are extended and calcified but are still flexible. Adults have fully formed and calcified claspers and large and developed testes. (agaglia, C. R.; Damiano, C.; Hazin, F. V.; Broadhurst, M. K. (2011). “Reproduction in Mustelus canis (Chondrichthyes: Triakidae) from an unexploited population off northern Brazil“. Journal of Applied Ichthyology. 27 (1): 25–29).
This is the first shark to be documented to have viral infections. Nematodes are a common parasite.
Behavioral Traits, Sensing and Intelligence: The Dusky smoothhound is an extremely active shark. They are always on the move make the rounds for food, even in hidden locations. The northern population migrates inshore and north for the summer (mid-Atlantic to southern New England), and offshore south for the winter (Carolinas to the outlet of the Chesapeake Bay). They are not territorial in captivity, but they are documented and observed to show that the larger sharks are dominant.
There is some mention of these sharks being nocturnal hunters and scavengers.
There have been documented activity where humans have placed this shark into tonic immobility, the mean time to induce tonic immobility in this shark was 32.5 seconds. The mean duration of the tonic immobility was 61.9 seconds. Sharks that had the “limp” response also exhibited tonic immobility. The “limp” response is a criterion for the onset of tonic immobility. (Whitman, P. A.; Marshall, J.A.; Keller, E. C. (1986). “Tonic immobility in the smooth dogfish shark, Mutelus canis (Pisces, Carcharhinidae)“. Copeia (3): 829–832).
Speed: Highly active.
Dusky Smoothhound Future and Conservation: They are currently near threatened. They are abundant among their range. The largest females are fished regularly and heavily by gill nets and long lines in places like Massachusetts, New Jersey, Maryland, Virginia, and North Carolina, which has impacted the population numbers as a whole. They are mostly bycatch though. They are also kept in public aquaria.
Dusky Smoothhound Recorded Attacks on Humans: Not a threat to humans.