Taxonomy

Rarity

Abundance rates how many are in suitable habitat. Find difficulty rates how hard it is to locate one on a daylight snorkel or freedive through 50 ft. A higher find score means a harder search. The rarity category also reflects the kind of encounter; it is not an average of the 2 scores.

Seasonality

Location

Adults live on or near the bottom between about 49 and 4,080 feet, and are usually between 164 and 656 feet. Juveniles do something different: they hold in open water in the top 82 feet and only settle to the bottom as they mature. Dogfish may be alone or in groups.

The diet is opportunistic with no particular target. Larger animals eat mostly fish, and the rest of the menu is squid, octopus, jellyfish, comb jellies, shrimps, krill, small shrimp-like crustaceans called amphipods, and bristle worms. That is the list of a predator that eats whatever is in front of it.

The name comes from the equipment. A spiny dogfish carries a spine in front of each of its 2 dorsal fins, and the first one is described as moderate in size and narrow at the base. FishBase lists the species as harmless to people. Popular accounts often describe these spines as venomous; that was not verified for this entry, so what is said here is simply that the spines are there and are worth handling carefully.

Deep Dive

The number that defines this species is 35.5, and it is a number about patience.

Male Pacific spiny dogfish reach breeding size at a median age of 18.5 years. Females reach it at a median age of 35.5 years. A female dogfish spends 3 and a half decades growing before she produces a single pup, and then rests a year or more between pregnancies for the rest of her life. There is no fish in this Ichthyopedia that takes longer to start. A market squid, at the other extreme, completes its entire existence in 9 months.

This is what fisheries scientists mean by low productivity. A species that cannot replace a removed adult for 35 years does not respond to good management on a human timescale, whatever the current conservation listing says.

There is a naming problem attached to this shark that is worth knowing about, because it will trip up anyone reading older material. Until recently, the spiny dogfish of the North Pacific was treated as the same species as the Atlantic one. In 2010 a study by Ebert and colleagues resurrected an older name, and the North Pacific animal became its own species again. Every California source written before that calls this fish by the Atlantic name. The practical consequence is that a great deal of the famous dogfish biology in circulation, including the often-quoted claim that they live to about 100 years and carry their young for 2 years, belongs to the Atlantic species and has not been established for this one. FishBase carries no maximum age for the Pacific animal at all.

The last note is a small piece of industrial history. Dogfish liver is rich in oil, and around Nanaimo in British Columbia that oil once served as fuel for mine lamps. A fish nobody wanted to eat was still worth catching, and a shark that takes 35 years to breed was being rendered for lamp oil long before anyone had measured how long it took to replace one.

Where to Find Them

Researched habitat and range candidates

These locations have suitable habitat within the species range. An assignment is a possible encounter, not a confirmed sighting at every beach. Season, depth, and local conditions still matter. Historical habitat without present-day evidence is excluded.