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Smooth Dogfishes, Mustelus canis

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Description & Behavior

Smooth dogfishes, Mustelus canis (Mitchill, 1815), aka dusky smooth-hounds, Atlantic smooth dogfishes, dogfishes, dusky smooth hounds, dusky smoothhounds, grayfishes, nurse sharks, smooth dogs, smooth hounds, and smoothhounds, measure about 150 cm in total length and weigh a maximum of 12.2 kg. This is a small shark species with two well-serrated dorsal fins that are almost equal in size. Their first dorsal fin is slightly larger. Their second dorsal fin is found slightly in front of their anal fin, which is about half the size of their second dorsal fin. There tail has two tail lobes; the lower lobe is rounder and shorter than the upper lobe and the rear lobe has a deep notch near the tip. This species has a tapering, blunt snout and a spiracle behind each narrow eye.

Species within the genus Mustelus are characterized by their flat, blunt dentition, which is much different than other shark species that have sharp, blade-like teeth. The small teeth of the smooth dogfish are of similar size in the upper and lower jaw and are asymmetrical in shape with a rounded apex. They have between 8-10 rows of teeth used to crush and grind their food rather teeth used to bite and tear as in other shark species.

Although the geographic range of the smooth dogfish overlaps that of the spiny dogfish, Squalus acanthias, the two are easily distinguished by the presence of a single spine in front of each of the two dorsal fins of the spiny dogfish.

M. canis has a subspecies, M. canis insularis, which is identical to M. canis with the exception of a slightly higher dorsal fin and a longer caudal fin tip in M. canis insularis. In addition, M. canis insularis also has more vertebrae than M. canis. M. canis is also confused with M. norrisi, the Florida smoothhound, which has a lower caudal lobe with a sharp point at the tip.

The smooth dogfish varies in color from gray to brown with a yellow-gray to white ventral side. This species can change its color by contracting its melanophores to blend into its surroundings.

Smooth dogfish are born with a first dorsal fin that is dusky gray in color at the edges. The apex of the second dorsal fin is also dusky gray and has a white rear edge with a white-edged tail fin. These markings fade by the time the shark is about two feet in length.

World Range & Habitat

Smooth dogfishes, Mustelus canis, are found in subtropical waters between 42°N-44°S and 100°W-46°W up to a max depth of 579 m deep. They are a migratory species found in abundance off the coasts of the US. Their range includes the western Atlantic from Massachusetts to Florida, the northern and western Gulf of Mexico, the coasts of Venezuela, Cuba, Jamaica, Barbados, Bermuda, Bahamas, and southern Brazil to northern Argentina, and the Antilles. Smooth dogfish tends to inhabit continental and insular (island) shelves and upper slopes in depths that range from shallow inshore waters and the intertidal zone around 18 m up to a max depth of 579 m. Although this species has been seen in freshwater, it is unlikely that smooth dogfishes can survive in fresh water for extended periods.

Feeding Behavior (Ecology)

Smooth dogfishes feed nocturnally on large crustaceans, including crabs and lobsters, and shrimp, small fishes, and mollusks. They are preyed on by other shark species including: Carcharhinus plumbeus, C. carcharias, C. obscurus, C. limbatus, and Sphyrna mokarran.

Life History

Smooth dogfish, Mustelus canis, have a low, minimum population doubling time of 4.5-14 years. This species is viviparous and gives birth to 4-20 pups per litter after a gestation of 10-11 months. Mating occurs between May and July. Females are able to store live sperm, although it is unknown whether stored sperm can be used to actually fertilize their eggs. Pups are born measuring 34-39 cm in length and grow quickly. Males reach sexual maturity between 2-3 years of age or 68-93 cm, females between 4-5 years and 70-130 cm. Female smooth dogfish are thought to live about 16 years, males 10.

Viviparous: the embryo develops inside the body of the female from which it gains nourishment from a yolk-sac placenta.

Population doubling time: a measure of a species' resilience, or its capacity to tolerate exploitation.

Conservation Status & Comments

Smooth dogfishes are caught commercially and as a gamefish. They are probably considered bycatch in most fisheries.

The smooth dogfish is listed as Near Threatened (NT) by the IUCN Red List of Threatened Species:

NEAR THREATENED (NT) - A taxon is Near Threatened when it has been evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.

References & Further Research - image database of sharks, skates, rays, and chimaera's from around the world by Andy Murch

Research Mustelus canis » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS

Search for Smooth Dogfishes » ARKive ~ ~ Bing ~ dmoz ~ Flickr ~ Google ~ NatureFootage ~ Picsearch ~ Wikipedia ~ Yahoo! Images ~ YouTube

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