The number of young born in a litter is dependant on the size of the female, larger females bearing more pups. However most litters are between 1 and 14 individuals that are approximately 20 to 30 cm in length.
The average litter is pups. Sexual maturity in males is reached at a total length of about 64 cm and 10 years of age. Females reach sexual maturity at a later age, around 16 years, at which time they are about 82 cm in total length. Reproduction occurs offshore in the winter.
The spiny dogfish is a major predator on some commercially important species such as herring, Atlantic mackerel and squid. It has been harvested for the last years for its oil rich liver which was used in lamp oil and machine lubricants.
The oil was later used as a source of vitamin A. Today spiny dogfish is valued as food in many countries. The spiny dogfish is the target of a directed fishery in Atlantic Canada, and has been the subject of considerable research in our laboratory.
The images below show the internal organs of mature dogfish and stages of embryo development. Though females are slightly larger than males, the spiny dogfish is a relatively small shark, usually reaching only 3 to 4 feet in length and about 8 pounds in weight.
Spiny dogfish have long, thin cylindrical bodies with grey backs and white bellies. White spots or bars along the sides of the spiny dogfish—though they fade as the shark ages—help distinguish it from other similar species. This shark is named, in part, for spines located on its two dorsal fins that can inject venom into predators. Dogfish get their name because they often travel and hunt in packs. Spiny dogfish hunt alone or in packs of up to a thousand for schooling fish, smaller sharks, octopuses, squid, crabs and other prey.
Sometimes, spiny dogfish will ram their prey with their nose. 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 months which is longer compared to other shark species. Usually spiny dogfish do not exceed a length of approximately cm, whereby sexual maturity is usually reached by males measuring 60 to 70 cm and females measuring 70 to 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 young. Global populations have declined by more than 30 percent over the last 75 years. In some parts of the world, this shark has been targeted for its meat and fins. In , Oceana applauded steps taken by the Atlantic States Marine Fisheries Commission to prohibit the finning of spiny dogfish. Other fisheries take the spiny dogfish as unwanted bycatch before discarding them back to sea.
Pacific spiny dogfish reach a maximum length of 4. Pacific spiny dogfish can live more than 80 years, while the Atlantic spiny dogfish only lives for 35 to 40 years. Males reach maturity much sooner at age Atlantic spiny dogfish can be found anywhere from the surface to more than 3, feet m deep.
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