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Characteristics, distribution and ecology
Taxonomische classification
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Author: Smith and Radcliffe, 1912

Field Marks:
Two dorsal fins with ungrooved large spines, first dorsal spine origin behind pectoral rear tips, white spots on grey sides, oblique-cusped cutting teeth in both jaws, no subterminal notch on caudal fin, no anal fin, and upper precaudal pit and lateral keels on caudal peduncle.

Diagnostic Features:
Body fairly slender. Snout subangular, pointed, narrow, and moderately long, diagonal distance from snout tip to excurrent aperture of nostril greater than that from excurrent aperture to upper labial furrow, preoral snout about 1.2 to 1.3 times mouth width, preorbital snout less than twice eye length; eyes about equidistant between snout tip and first gill slits; nostrils nearer snout tip than mouth; anterior nasal flap with posterior secondary lobe minute or absent. First dorsal spine short, much shorter than fin base and with tip falling far below apex of fin; second moderately long, about as high as fin, and less than 5% of total length; first dorsal fin more posteriorly situated, with origin over or behind pectoral free rear tips and spine origin behind tips; first dorsal low, height less than half length from origin to rear tip; second dorsal markedly smaller than first, with height less than 5% of total length; pectoral fins narrow and falcate, posterior margins slightly concave, rear tips narrowly rounded; pelvic midbases closer to second dorsal base than to first; caudal fin narrow-lobed and moderately long, with a long ventral lobe and strongly notched postventral margin. Upper precaudal pit well developed on caudal peduncle. Lateral trunk denticles small, tricuspidate and with deeply scalloped posterior borders in adults. Colour grey above, white below, usually with conspicuous white spots present on sides of body, dorsal and fins without white edges but dusky-tipped in young and plain in adults. Size moderate to large, up to 1.5 m but mostly smaller.

Geographical Distribution:
Antetropical. Western Atlantic: Greenland and Labrador (Canada) to Florida (USA), Cuba; Uruguay and Argentina. Eastern Atlantic: Iceland and Murman Coast (USSR) to Morocco, West Sahara, Canary Islands, Mediterranean and Black Sea; Cape coast of South Africa. Western Pacific: Bering Sea to Japan, Sea of Okhots, Republic of Korea and northern China; southern Australia, New Zealand, ? Papua New Guinea. Eastern Pacific: Bering Sea to southern Baja California, possibly Gulf of California; Chile.

Habitat and Biology:
An extremely abundant, boreal to warm-temperate, inshore and offshore dogfish of continental and insular shelf waters and the upper slopes, from the surface down to the bottom but usually near the bottom; found from the intertidal down to at least 900 m.

This is possibly the most abundant living shark, despite its restricted range, and the only one that supports fisheries of a size rivaling those of the more commercially important bony fishes. Bigelow and Schroeder (1948) noted that in a time of peak abundance in 1904-1905 an estimated 27 000 000 dogfish were taken off the Massachusetts coast each year. The piked dogfish is probably the best-known of living sharks, particularly from a morphological, experimental and fisheries-biological viewpoint, though its ecological relationships and ethology is far less well known than some other sharks, particularly certain tropical carcharhinids and sphyrnids. Knowledge of its biology clearly reflects the concerns of fisheries and the interests of fisheries biologists, as well as its great abundance, but even with the massive corpus of information available great gaps remain in our knowledge of its biology. The literature on this shark is so enormous that only a small amount of the available information can be presented here.

The existence of differentiated, possibly subspecifically distinct, antetropical populations of this temperate shark with little if any mixing at present probably also allows for considerable variation in biology for different areas. Principle contiguous populations are apparently those of the North Atlantic, eastern South Pacific, eastern South Atlantic coast of South America, Cape coast of South Africa, temperate south coast of Australia, temperate southern New Zealand, and the North Pacific. Some of these larger areas apparently have differentiated stocks or subpopulations with complex migration patterns and possibly limited mixing. The various geographic populations or clusters of populations havebeen given separate subspecific or specific names, but there is no agreement at present as to which of these should be recognized. The North Pacific piked dogfish has been often distinguished as Squalus suckleyi (or sucklii) or Squalus acanthias suckleyi, but the validity of this is d isputed.

The piked dogfish is described as a slow, inactive swimmer, which nevertheless keeps a steady pace in its nomadic, erratic and regular movements. If not greatly traumatized in capture and transportation to holding facilities it can survive for a few years in captivity, provided it is given proper care and an adequate containment. In captivity it swims strongly but slowly; one kept for over a year was seen to occasionally orient itself vertically at the surface and poke its snout and head out of the water. The dogfish forms immense feeding aggregations or packs in rich foraging grounds and may be present in thousands. Longline sets of 700 to 1500 hooks with nearly every hook bearing a dogfish have been reported from the western North Atlantic. Dogfish often occur in schools segregated by size and sex, including those of small juveniles of both sexes in equal numbers, mature males, larger immature females, and large mature females. Mixed schools of adults have also been reported, but at best these are probably less common than segregated schools. These schools are dense and localized in a given area, and move erratically over short periods of time, possibly reflecting pursuit of schooling prey fishes. In general, males occur in shallower water than females, with the exception of large pregnantfemales. Pregnant females may congregate in enclosed shallow bays like San Francisco Bay in California, and drop their young there. Dogfish are also found as solitary individuals and may also associate with schools or aggregations of other temperate sharks such as the leopard shark (Triakis semifasciata) and the brown smoothhound (Mustelus henlei) in the eastern North Pacific.

Although the piked dogfish is often found in enclosed bays and estuaries, and can tolerate brackish water, it apparently cannot survive freshwater for more than a few hours and does not occur there. During the rainy winter and spring of California dogfish may leave San Francisco Bay and other shallow bays and estuaries as the salinity drops, but return in late spring and summer.

Much has been written of the seasonal, bathymetric, and localized movements of this shark. An important correlate of dogfish movements seems to be water temperature; the sharks favour a temperature range with a minimum of 7 to 8°C and a maximum of 12 to 15°C, and apparently make latitudinal and depth migrations to stay within their optimum range. Thus in the western North Atlantic dogfish move inshore from their wintering grounds in deep water off the US Middle Atlantic and southern States as the water warms in spring, pressing northward aiong the coasts of Newfoundland and Labrador, Canada, and southward along the US Atlantic coast occasionally to Cuba. As the water warms in the south over the optimum in late spring and summer, the dogfish apparently retreat into deepwater, reappear coastally in autumn as the water temperature descends to optimum, and disappear into deep water when the surface temperature goes below optimum. In the northern part of their range in the western North Atlantic large females appear first inshore, followed by adult males. There may be unseasonal invasions of dogfish inshore during the winter for unknown reasons.

Tagging studies off the British Isles suggests separate winter migrations of stocks to the Irish Sea and the Norwegian coast and a return and mixing of these stocks on fishing grounds northwest of the British Isles in summer. Tagging studies in Puget Sound and adjacent areas in the Canadian eastern North Pacific suggest that the dogfishin the Sound itself and the adjacent Strait of Georgia are year-round residents with local internal movements, but the Sound and Strait sharks form separate stocks or subpopulation with little mixing with each other or with seasonally migrating offshore dogfish. Discovery of largely resident and seasonally migrating dogfish groups has also occurred off the US States of Washington and California. Some tagged sharks in the eastern North Pacific have made spectacularly long net movements, in one case a 6500 km movement to Honshu, Japan where the shark was captured seven years after it was tagged off Washington State. Long-range movements have also been reported in the western North Atlantic, up to at least 1600 km.

An ovoviviparous shark, with litters of 1 to 20 young. There is much regional variation in reported litter sizes that may be correlated with other factors than maternal size, but in general larger mother sharks have larger litters of fetuses that attain a larger size before birth than smaller ones. The gestation period is variously reported as 18 to 24 months, and may differ in areas. Mating of dogfish may occur in the winter. Birth in the dogfish may occur primarily during the cold months of the year, with considerable variation and with some young produced in spring and summer. The sex ratio at birth is 1:1. Young are delivered head first with a series of rhythmic contractions reminiscent of birth in mammals.

Age of piked dogfish is commonly determined by counting annual growth rings on the fin spines, though wear of the spines in large dogfish may limit the usefulness of this method. This is apparently a slow-growing and maturing species, that is very long-lived. Ages at maturity may vary regionally, and has been variously reported as 10 to 20 years for females and 11 or more years for males. Ketchen (1975), trying a variety of methods on British Columbian dogfish estimated an average of 14 years to maturation for males and 23 years for females. Maximum age is at least 25 to 30 years, with some estimates going much higher and approaching 100 years.

This shark is a powerful, voracious predator that feeds primarily on bony fishes, and is capable of dismembering rather large prey with its strong jaws and clipper-like teeth. Its bony fish prey includes herring, sardines, menhaden and other clupeids, true smelt (Osmeridae) and their eggs, hake, cod, pollock, ling, haddock and other gadoids, midshipmen, blennies, sand lances, mackerels, porgies, croakers, flatfishes and sculpins. It is thought to prey on most available bony fishes smaller than itself, and will often prey heavily on abundant schooling fishes, but newborn dogfish attack herring larger than themselves, as may adults with cod and haddock. They often destroy fish on longlines and in seines. Cartilaginous fishes are uncommonly taken by dogfish, with the occasional exception of ratfish (Hydrolagus colliei) off Washington State, USA. Their invertebrate prey include squids, octopuses, crabs, shrimps, amphipods, euphausiid shrimps, worms, sea snails, polychaetes, and even sea cucumbers, jellyfishes and comb jellies. In the western North Atlantic these sharks may feed very little in the winter on their deepwater wintering grounds as judged by their thinness when they return to shallow water.

This is not a 'dangerous' species in the sense of attacking people in the water, but is a hazard to those who catch it because of its sharp teeth and toxic fin spines.The piked dogfish can curl itself and whip its tail about to inflict wounds with the long, sharp, second dorsal spine. The toxin is mildly irritating to most people, but some people can have a strong allergenic reaction to it and require hospital care. The main impact of this shark on people is economic, however: both negative, as it displaces or chases off other fishes, gets hooked or netted in gear intended for other species, damages fishing gear, and destroys hooked and netted fishes; and positive, as a fisheries species. Suggestions have been made to 'control' the numbers of dogfish in the western North Atlantic, by a variety of sometimes bizarre methods, though the necessity of doing this is largely a result of prejudice against dogfish as human food and unreasoned hatred for these sharks. However, this is disappearing, and developing fisheries may eventually require restrictions as western North Atlantic dogfish stocks are depleted like heavily exploited European stocks. The high standing populations of this shark may suggest a limitless resource to some, but the low fecundity, long gestation period, long life, and slow maturation of the piked dogfish belies this.

Apart from human beings, this shark is preyed on by a number of larger sharks, some bony fishes, seals and killer whales.

Size:
May exceptionally reach 160 cm in the eastern north Pacific, but most individuals there are smaller, and other populations apparently reach smaller maximum sizes. Size of males at maturity from 59 to 72 cm and maximum size of mature males from 83 to 100 cm; size of females at maturity from 70 to 100 cm and maximum size of mature females from 101 to 124 cm; size of young at birth 22 to 33 cm.

Interest to Fisheries:
This is one of the most important sharks because of its abundance in colder waters, utilization in various fisheries, and damage it does to gear and catches of other fishes. It is heavily fished in the eastern North Atlantic at least 34 288 metric tons listed by species name in the 1978 FAO fisheries catch statistics for Europe, plus an uncertain tonnage of the species listed under "dogfish sharks" that primarily includes this species but may also include Scyliorhinus species), less so in Canadian, US, New Zealand, Japanese and Korean waters, and no doubt fished elsewhere where it occurs. It is captured primarily in bottom trawls and with line gear (handlines and longlines set near the bottom), but also commonly taken in gillnets; it is also readily captured by sportsfishing gear. It is utilized fresh, fresh frozen, smoked, boiled marinated, dried salted, and in the form of fish cakes for human consumption; it is also utilized in liver oil, pet food, fishmeal, fertilizer and leather.

Type material:
Holotype: Unknown. Type Locality: "Oceano europaeo".

Piked dogfish (Squalus acanthias)