Dogfish are a diverse group of small sharks found worldwide in various marine environments. They are common and widespread, often encountered by those exploring ocean life. These cartilaginous fish inhabit global coastlines and deeper waters.
Defining Dogfish
The term “dogfish” refers to several species of small sharks, primarily those in the family Squalidae (spiny dogfish). The common name can also encompass species within the Scyliorhinidae (catsharks) and Triakidae (houndsharks) families. These sharks are characterized by their slender, streamlined bodies and a pointed snout.
A distinguishing feature of many dogfish, particularly the spiny dogfish, is the presence of two dorsal fins, each often preceded by a sharp spine. These spines can secrete a mild venom, serving as a defensive mechanism. Unlike many other shark species, dogfish lack an anal fin, which aids in their identification.
Dogfish typically exhibit a gray to brownish coloration, sometimes with distinctive white spots along their sides that may fade with age. Their skin is generally rough due to dermal denticles. Most dogfish are smaller than other sharks, commonly ranging from 60 to 120 centimeters (2 to 4 feet) in length, though some can reach up to 160 centimeters (over 5 feet).
Life in the Ocean
Dogfish inhabit a wide range of marine environments, from shallow coastal waters to depths exceeding 4,000 feet (1,200 meters). While often found near the ocean floor, they are capable of navigating throughout the entire water column. Their global distribution spans the temperate and subarctic regions of the North Atlantic and North Pacific Oceans, extending from Greenland to Argentina and Alaska to New Zealand.
As opportunistic predators, dogfish consume readily available prey. Their diet primarily consists of small schooling fish (herring, mackerel, capelin), various crustaceans (crabs, shrimp), and cephalopods (squid, octopus). Smaller dogfish tend to feed more on crustaceans, while larger individuals incorporate more fish and even jellyfish. They employ active foraging behaviors, sometimes ramming prey with their snout, and can detect electromagnetic fields from potential food sources.
Dogfish are known for their distinctive schooling behavior, often gathering in large aggregations. This collective action aids in protection from larger predators and in their foraging strategies, as they are known to hunt in coordinated “pack-like” formations, a behavior that contributed to their common name. Their navigation involves extensive seasonal migrations, with dogfish traveling thousands of miles in response to changing water temperatures, ensuring access to favorable feeding grounds.
Reproduction and Lifespan
Dogfish reproduce through ovoviviparity, where eggs hatch inside the mother’s body. The developing pups are nourished by a yolk sac and remain within the uterus until they are fully formed, after which the mother gives birth to live young. This internal development offers protection for the offspring during their early stages.
The gestation period for some dogfish species, particularly the spiny dogfish, is remarkably long, often 18 to 24 months. This duration is among the longest known for any vertebrate. Litter sizes vary by species and the size of the female, typically 2 to 12 pups, averaging 5 to 7 live births.
Upon birth, dogfish pups are well-developed and capable of independent hunting, allowing them to integrate quickly into their marine environment. Dogfish also exhibit long lifespans; spiny dogfish can live for 30 to 40 years on average, with some individuals in the Pacific reaching over 70 or even 80 years.
Dogfish and Humans
Dogfish interact with humans through commercial fisheries and scientific research. Commercially, they are a significant food source in some regions, especially in Europe, where their mild, white flesh is a common ingredient in “fish and chips,” sometimes marketed as “rock salmon” or “huss.” Historically, dogfish liver oil was also harvested for industrial uses and as a source of Vitamin A.
Dogfish serve as important subjects in scientific research. Their unique biological features, such as rectal glands, offer insights into human kidney function, and a compound they produce, squalamine, has demonstrated antibiotic and anti-cancer properties. Dogfish are generally not considered dangerous to humans; their small teeth are not designed for harming people, and they tend to be shy.
While spiny dogfish possess venomous spines that can cause painful wounds if mishandled, these are primarily defensive mechanisms. Some dogfish populations have faced challenges from historical overfishing due to their slow growth, late maturity, and long gestation periods. This led to some populations being classified as vulnerable, but management efforts, including quotas and regulations, have allowed stocks to rebuild in certain areas, such as the Eastern U.S. Atlantic.