Spiny dogfish
The spiny dogfish, spurdog, mud shark ("Squalus acanthias") or piked dogfish, is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several species, "Squalus acanthias" is distinguished by two spines (one anterior to each dorsal fin) and no anal fin. It lives in shallow waters and further offshore in most parts of the world, especially in temperate waters. Those in the northern Pacific Ocean were reevaluated in 2010 and found to constitute a separate species, now called the Pacific spiny  dogfish ("Squalus suckleyi). Description and behaviour. The spiny dogfish has dorsal fins, no anal fin, and white spots along its back. The caudal fin has asymmetrical lobes, forming a heterocercal tail. The species name "acanthias" refers to the shark's two spines. These are used defensively. If captured, the shark can arch its back to pierce its captor with spines near the dorsal fins that secrete a mild venom into its predator. This shark is known to hunt in packs that can range up into the thousands. They are aggressive hunters and have a sizable diet that can range from  squid, fish, crab, jellyfish, sea cucumber, shrimp and other invertebrates. Males mature at around 11 years of age, growing to in length; females mature in 18–21 years and are slightly larger than males, reaching . Both sexes are greyish brown in color and are countershaded. Males are identified by a pair of pelvic fins modified as sperm-transfer organs, or "claspers". The male inserts one clasper into the female cloaca during copulation. Reproduction is aplacental viviparous, which was once called ovoviviparity. Fertilization is internal. The male inserts one clasper into the female oviduct orifice and injects sperm along a groove on  the clasper's dorsal section. Immediately following fertilization, the eggs are surrounded by thin shells called "candles" with one candle usually surrounding several eggs. Mating takes place in the winter months with gestation lasting 22–24 months. Litters range between two and eleven, but average six or seven. Spiny dogfish are bottom-dwellers. They are commonly found at depths of around , but have been found deeper than . Life span estimates based on analysis of vertebral centra and annuli in the dorsal spines range from 35 to 54 years. Commercial use. Spiny dogfish are sold as food in Europe, the United States , Canada, New Zealand, Venezuela and Chile. The meat is primarily eaten in England, France, Italy, the Benelux countries, and Germany. The fins and tails are processed into fin needles for cheaper versions of shark fin soup in Chinese cuisine. In England, dogfish are bought in fish and chip shops as "huss", and previously as "rock salmon" until the term was outlawed. In France, they are sold as "small salmon" ("saumonette") and in Belgium and Germany as "sea eel" ("zeepaling" and "Seeaal", respectively). Spiny dogfish bodies are ground into fertilizer, liver oil and pet food. Because of their availability, cartilaginous skulls  and small sizes, they are popular vertebrate dissection specimens in high schools and universities. Reported catches varied between 31,700 tonnes in 2000 and 13,800 tonnes in 2008. Bottom trawlers and sink gillnets are the primary tools. In Mid-Atlantic and Southern New England fisheries, they are often caught with larger groundfish, classified as bycatch, and discarded. Recreational fishing accounts for an insignificant portion of the spiny dogfish catch. The Cape Cod Commercial Fishermen's Alliance promotes sustainable use of the dogfish in restaurants and fish markets in the Cape Cod area of Massachusetts, as of 2017, paid for by the  National Oceanographic and Atmospheric Administration. It aims to persuade diners to buy less-popular fish. Conservation status and management. Once the most abundant shark species in the world, populations of "Squalus acanthias" have declined significantly. They are classified in the IUCN Red List of threatened species as Vulnerable globally and Critically endangered in the Northeast Atlantic, meaning stocks around Europe have decreased by at least 95%. This is a direct result of overfishing to supply northern Europe's taste for rock salmon, saumonette, and zeepaling. Despite these alarming figures, very few management or conservation measures are in place for "Squalus  acanthias". In EU waters, a Total Allowable Catch (TAC) has been in place since 1999, but until 2007 it only applied to ICES Areas IIa and IV. It was also set well above the actual weight of fish being caught until 2005, rendering it meaningless. Since 2009 a maximum landing size of has been imposed in order to protect the most valuable mature females. The TAC for 2011 was set at 0 tons, ending targeted fishing for the species in EU waters. It remains to be seen if populations will be able to recover. In the recent past the European  market for spiny dogfish has increased dramatically, which led to the overfishing and decline of the species. This drastic increase led to the creation and implementation of many fishery management policies placing restrictions on the fishing of spiny dogfish. However, since the species is a late-maturing fish, it takes a while to rebuild the population. In 2010, Greenpeace International added the spiny dogfish to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from  unsustainable fisheries." In the same year, the Convention on Migratory Species (CMS; also known as the Bonn Convention) listed the species (Northern Hemisphere populations) under Annex I of its Migratory Shark Memorandum of Understanding. In recent years, however, the US has implemented fishing controls and The proposed quota for 2011 was with a trip limit of , an increase over past years in which the quota has ranged from , with trip limits from . In 2010, NOAA announced the Eastern US Atlantic spiny dogfish stocks to be rebuilt, and in 2011, concerns about dogfish posing a serious predatory threat to other stocks  resulted in an emergency amendment of the quota with nearly being added. In June 2018, the New Zealand Department of Conservation classified Squalus acanthias Linnaeus as "Not Threatened" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System. Fossil range. As a cartilaginous fish, shark tissues usually do not fossilize. "Squalus acanthias" fossils date back to the Miocene 11 MYA.