Dogfish
Order: Scyliorhiniformes Family: Scyliorhinidae Genus &Species: Scyliorhinus spp.
The dogfish is a small sea-bed dwelling shark that preys on fish as well as molluscs and other invertebrates. As well as gills, some dogfish have a breathing hole behind each eye.
| Habitat In the temperate waters of the Atlantic, the lesser spotted, greater spotted and chain dogfish are rarely found at depths of more than 100m, although lesser spotted dogfish have been known to scavenge at 400m on the Mediterranean seabed. |
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| Dogfish are also attracted to shipwrecks and jetties, which harbour many
of their prey species. They also swim surprisingly close to the shore to exploit rich
pickings of crustaceans. |
Behaviour
Dogfish are active day and night and spend most of their lives foraging.
Like all sharks, they lack a swim bladder, the organ that provides most fish with
buoyancy. Instead they rely on enlarged livers to keep them afloat. Dogfish
however, beingsmall bottom-dwelling feeders, have proportionally smaller livers than most
of their relatives. While large sharks seem to glide effortlessly through the water
on wing like fins, dogfish swim with slow snake- like movements, hugging the terrain of
the seabed. Adult dogfish are generally solitary, except in the breeding season,
when several males may compete to mate with a female. In some areas large groups may
occur closer to shore in winter before moving farther out again in the spring. Young
dogfish tend to form shoals as defence against large predatory fish,such as bass, and
seabirds such as gulls.
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Feeding Dogfish are sluggish hunters that cruise over the seabed through clumps of weed, where they surprise crabs and prawns. With their array of tiny teeth, they can crack the shells of mussels and whelks or seize flatfish. |
| They readily enter surface waters to snap up fish scraps discarded by
trawlers. An excellent sense of smell helps them track their victims. In addition,
sophisticated sensors in the snout pick up electric pulses generated by the movements of
prey. These adaptations help dogfish find food blind in murky coastal waters. |
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Breeding Unlike fiish that produce vast numbers of eggs in the hope that a handful will survive the sea's many perils, the dogfish lays few eggs but goes to great lengths to give its young a headstart in life. By depositing his sperm deep inside the female, the male dogfish ensures that a high proportion of her eggs are fertilized. Pairs remain in the mating position for up to 20 minutes, despite being nipped by other males. |
| The female swims into shallows with plenty of seaweed and other aquatic vegetation in which to lay her 18 to 20 eggs. Each egg , roughly the size of a hen's egg yolk, is encased in a leathery purse. Tendrils on each corner of the purse anchor it on rocks or plant matter, securing it from currents while the embryo develops. The hatchling is 10-15cm long at birth, and after a few days is able to feed on small invertebrates. |
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