Spiny Dogfish: Squalus acanthias

Family: Squalidae

Common names

Spiny Dogfish, , Piked Dogfish, Spurdog.

Binomial

Squalus acanthias.

Synonyms

Acanthias americanus, Acanthias antiguorum, Acanthias commun, Acanthias lebruni, Acanthias linnei, Acanthias vulgaris, Spinax mediterraneus, Squalus acanthias acanthias, Squalus acanthias africana, Squalus acanthias chilensis, Squalus acanthias ponticus, Squalus acanthis, Squalus achantias, Squalus antiquorum, Squalus barbouri, Squalus canis, Squalus fernandinus, Squalus kirki, Squalus suckleyi acanthias, Squalus tasmaniensis, Squalus wakiyae, Squalus whitleyi.

Identification

A slender squaloid shark with a long snout, fairly large eyes, and a narrow anterior nasal flap. Snout length greater than mouth width. Two dorsal fins with short anterior spines. Second dorsal fin much smaller than first dorsal. First dorsal fin origin posterior to free rear tip of pectoral fin. Second dorsal origin midway between pelvic fin insertion and free rear tip. Pectoral fins have mildly concave posterior margins and rounded free rear tips. Anal fin absent. Pectoral fins broad with rounded free rear tips.
Dorsal coloration grey or greyish-brown, usually with a few small, white spots along lateral line and upper back. Ventrum pale. Tip of first dorsal and upper caudal lobe often dusky or black. Posterior margins of pectoral fins and caudal fin often pale.

Size

Maximum length 200cm but most adults do not exceed 100cm. Size varies significantly by region. Size at birth 18-33cm.

Spiny Dogfish, Squalus acanthias. Aka spurdog. Rhode Island, New England, USA, North Atlantic.

Conservation Status

VULNERABLE

The Spiny Dogfish has been heavily fished across most of its range in commercial trawl, line, and net fisheries. As a schooling species, it is particularly succeptible to mass capture that can quickly lead to regional population depletions.

The large-scale directed fishery in the North Atlantic that led to a population crash has been severely curtailed with strict catch limits in the northwest Atlantic and a retention ban in European waters. Bycatch in multi-species fisheries in the North Atlantic continues, but with proper management, the western population has recovered well.

New Zealand continues to manage their Spiny Dogfish fishery through realistic quotas, but elsewhere, management is poor.

Habitat

A temperate water species. Found inshore in enclosed bays and estuaries, to well offshore along the continental and insular slopes. From the surface to 1,978m.

Distribution

The spiny dogfish has a wide distribution in the temperate coastal regions around the North Atlantic Ocean and Mediterranean Sea. There are also isolated populations in the southern hemisphere, on both sides of South America, on the southern tip of Africa, along the south coast of Australia, and in New Zealand.

Reproduction

An aplacental viviparous species. Litter size 2-16. Gestation ranges between 12-24 months depending on the region.

Diet

Spiny dogfish are opportunistic predators that will feed on whatever is locally available. Stomach content analysis has included a wide range bony fishes (including species that are larger than themselves) and squids, shrimps, crabs, amphipods, snails, and worms. When food is scarce, they will even consume calorie-poor prey such as jellyfishes and ctenophores. Spurdogs are generally bottom feeders but they will rise to the surface to gorge on clouds of krill.

Behavior

North American Spiny dogfish migrate northward in the summer. They may be solitary but when a particular food is abundant they form immense feeding schools.

Reaction to divers

Shy and difficult to approach, but occasionally makes close passes. Becomes much bolder in baited situations, even wrestling fish from a diver’s hand.

Diving logistics

Sightings in European waters are rare, but is possible to run into dogfish while wreck diving in New England. When this occurs, the encounters are usually brief and more distant than one would like.
Spiny dogfish can easily be baited in, by chumming around shallow wrecks in the summer months. I tried chumming on a wreck off of Rhode Island and managed to attract around a dozen sharks. They were initially shy, but soon became very comfortable around our small group, even accepting food by hand.