The real spiny dogfish (Squalus acanthias).
© Shark Info / J. Stafford-Deitsch
The spiny dogfish is known primarily by virtue of its largest representative, the real spiny
dogfish, Squalus acanthias. But the name "spiny dogfish" is not reserved for this
one specific species alone. It covers an entire family of spiny dogfish including, for
example, such different forms as Greenland sharks or cookie-cutter sharks. The name
"spiny" shark is actually misleading since contrary to expectations, not all
species of the group have the typical spines in front of the dorsal fin. Although the
species in this family in part look different, they do have one thing in common: the
suction holes behind the eyes and the lack of an anal fin. Most species of spiny dogfish
actually live quite deep in the ocean. Obviously, this makes their observation in their
natural environment very difficult and much of our knowledge on this species is thus
speculative. Generally speaking, very little is known about its biology. The best researched
species is the real spiny dogfish, Squalus acanthias, whereby here too, knowledge is mostly
limited to information relevant to fishing.
Distribution of the spiny dogfish (Squalus acanthias).
Source: FAO Species Identification and Data Programme.
© Shark Info / J. Stafford-Deitsch
The distribution of the real spiny dogfish is limited (see map) since these animals
generally prefer a water temperature ranging between 7 and 15 degrees. Nevertheless, they
may well have the largest population of any given shark species. The annual catch along the
Massachusetts (USA) coast alone used to amount to approximately 27,000 tons.
The age limit of these animals is still very speculative. Literature sources cite
values of 30 and sometimes even a 100 years.
Much knowledge on the biology of the spiny dogfish is only fragmentary. In 1998,
for example, it was discovered that the animals have two separate feeding methods: On the
one hand they suck in their food by quickly lowering the lower jaw to produce a kind of
suction, and on the other hand some potential prey is rammed before being eaten. Their food
palette appears to consist of school fish as well as spineless animals such as crabs or
Spiny dogfish reproduce in a way which makes them extremely vulnerable to
fishing methods. The age at which they reach sexual maturity is very difficult to determine.
Some observations point to 10 to 20 and even 30 years. Such fluctuations may indicate that
their habitats are marked by differences. External factors such as water temperature and
food supplies may influence sexual maturity as well as the size of the litter which may
range between one and twenty animals. Generally, they have an above-average pregnancy period
of 18-24 months which is longer compared to other shark species. Usually spiny dogfish do
not exceed a length of approximately 120 cm, whereby sexual maturity is usually reached by
males measuring 60 to 70 cm and females measuring 70 to 100 cm. Length at birth may be
around 22 to 23 cm. If these factors are integrated - late sexual maturity with small litter
sizes and a long pregnancy time - it is by no means surprising that excessive fishing has a
destructive influence on spiny dogfish populations. Their "slow" reproduction rate
does not allow easy restoral of its unstable populations.
Their numbers are negatively influenced both by fishing and their relatively small
size, which makes them easy prey for other sharks, sea lions and swordfish.
Spiny dogfish often live in swarms consisting of thousands of animals. These
swarms are formed in order to hunt together, but also as protection against enemies. Certain
swarms consist of pregnant females in search of their nesting grounds, which include the San
Francisco Bay. Females and males usually live in separate swarms. Mixed groups are rare.
Males prefer flatter regions while females only return to flat coastal areas to bear their
Spiny dogfish undertake long migrations, influenced partly by the availability of
food and partly by water temperatures, but their migration path has not yet been studied
sufficiently. One tagged animal was found to have migrated 6,500 km, but the reasons behind
this behavior remain purely speculative.
Spiny dogfish are usually quite harmless, but a poison is secreted
at the base of the spines which may lead to complications in humans suffering from
Cheryl D. Wilga and Philip J. Motta (1998). Conservation and variation in the
feeding mechanism of the spiny dogfish Squalus acanthias. J. Exp. Biol 201 (9): 1345-1358.
Compagno, L. J. V. (1984). Sharks of the world. FAO
Species Catalogue. Vol. 4(2): 111-113.
(1988). Reproductive biology of Squalus acanthias from the east coast, South Island, New
Zealand. N. Z. J. Mar. Freshwater Res. 22: 537-549
Walker, T. I., Taylor, B. L., Hudson, R. J. and J. P. Cottier
(1998). Implications on recent increases in catches on the dynamics of Northwest Atlantic spiny
dogfish (Squalus acanthias). Fish. Res. 39 (2): 139-164.
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