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WHAT IS ELASMODIVER?

Not just Shark Pictures: Elasmodiver contains photos of sharks, skates, rays, and chimaera's from around the world. Elasmodiver began as a simple web based shark field guide to help divers find the best places to encounter the different species of sharks and rays that live in shallow water but it has slowly evolved into a much larger project containing information on all aspects of shark diving and shark photography.

There are now more than 10,000 shark pictures  and sections on shark evolution, biology, and conservation. There is a large library of reviewed shark books, a constantly updated shark taxonomy page, a monster list of shark links, and deeper in the site there are numerous articles and stories about shark encounters. Elasmodiver is now so difficult to check for updates, that new information and pictures are listed on an Elasmodiver Updates Page that can be accessed here:

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Shark picture - green sawfish

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SPINY DOGFISH

Spiny Dogfish

Atlantic Spiny Dogfish

View all available Spiny Dogfish Pictures

Common Names: Spiny dogfish, Common spiny dogfish, Piked dogfish, Mud shark.

Latin Name: Squalus acanthias

Family: Squalidae

Identification: Long, flattened, pointed snout. Grey to brown above usually with small white spots. White spots may follow lateral line.  Eyes large. Mildly venomous spines on first and second dorsal fins. Anal fin absent. Belly white.

Size: Maximum length 1.6 meters. size at birth 22-33 cm. Maximum recorded age 66 years.

Habitat: Often cruise over sand and mud bottoms. Also frequently encountered over rocky reefs. From 0 to 900 meters.  Inhabits estuarine, coastal and offshore waters sometimes migrating over great distances Newfoundland tagged individuals have been captured years later in Iceland. Normal migration patterns are usually more localized; Western Atlantic groups migrate between Canada and the US.

Abundance and distribution: North and South Atlantic Ocean and South Pacific and Southern Ocean around Australia. Some populations may eventually be recognized as new species or distinct 'sub species'. An example of this is the recent resurrection of the North Pacific Spiny Dogfish ~ Squalus suckleyi.

The spiny dogfish's western range extends along the east coast of North America from Labrador to the Gulf of Mexico. Some populations are locally abundant while others have experienced steep declines leading to drastically reduced fishing quotas (especially in Europe). In the UK and Europe Spiny dogfish are the principal fish utilized in "fish and chips". They are also ground up to be used in fertilizers.

Behavior: Cruises over soft bottoms either alone or in small groups. Occasionally schools (often segregated by sex) in response to food supply such as squid or salmon runs. May also form schools with other species such as leopard sharks and smoothhounds. Diet consists mainly of bony fishes. Other foods include octopus, squid and crustaceans. 

Reproduction: Ovoviviparous. Litter size from 1- 20. Spiny dogfish have a slow maturity rate (around 12 years) which makes them very vulnerable to over fishing. They also have the longest gestation period of any known vertibrate 18-24 months. 

Conservation Status: Listed by the IUCN as 'Vulnerable': Most stocks are highly migratory, but there is no regional fisheries management for the species. Management is in place in only a few range states and in only a limited part of the range of highly migratory stocks. Although naturally abundant, this is one of the more vulnerable species of shark to over-exploitation by fisheries because of its late maturity, low reproductive capacity, longevity, long generation time (25 to 40 years) and hence a very low intrinsic rate of population increase (2 to 7% per annum). Population segregation and an aggregating habit make mature (usually pregnant) females highly vulnerable to fisheries even when stocks are seriously depleted. This aggregating habit also means that catch per unit effort (CPUE) is not an adequate indicator of stock status; high CPUE can be maintained even when populations are severely depleted. Some targeted Squalus acanthias fisheries have been documented for over 100 years. Fisheries stock assessments report a decline in total biomass of >95% from baseline in the Northeast Atlantic, where catch effort is effectively unlimited. Mediterranean and Black Sea stocks are also unmanaged, with a >60% decline reported in a Black Sea stock assessment for 1981 to 1992. There has been a decline in biomass of mature females of 75% in just 10 years in the Northwest Atlantic, where US federal efforts to manage the stock are hampered by high bycatch, continued exploitation in Canadian Atlantic waters, and regular defiance of scientific advice by US Atlantic states. European demand continues to fuel markets around the world. Fisheries and population trend data indicate that the southern part of the Northeast Pacific stock has also declined through overfishing, but stocks appear stable off Alaska. The only data identified from the Northwest Pacific are from Japan, where landings of spurdog declined ~80% between 1952 and 1965, and inshore spurdog CPUE declined 80 to 90% from the mid 1970s to late 1990s. Unregulated and expanding target and bycatch fisheries take spiny dogfish in South America (Europe reports imports from this region), where population declines are reported. New Zealand manages the species, which is taken in target and bycatch fisheries, through its Quota Management System. There is only limited fishing pressure in Australia and South Africa, with most catches discarded.

Citation: Fordham, S., Fowler, S.L., Coelho, R., Goldman, K.J. & Francis, M. 2006. Squalus acanthias. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. <www.iucnredlist.org>.

Photographs: Rhode Island, New England, USA. North Atlantic Ocean

Similar species: The virtually identical North Pacific Spiny Dogfish Squalus suckleyi does not occur in the same areas as the spiny dogfish. The Smooth Dogfish or dusky smoothhound mustelus canis which has a sympatric range from the Bay of Fundy to the Gulf of Florida and from Southern Brazil to Argentina is easily recognizable as it lacks fin spines.

Elsewhere, there are many other similar dogfish species but most do not enter shallow water.

Reaction to divers: These are curious and harmless sharks that will often closely approach divers and on occasion accompany them on their dives. If divers are buzzed by a dogfish they can often be recalled by tapping two stones together. The dogfish seem to find this irresistible and will repeatedly return to satisfy their curiosity. If engaging in dogfish feeds it is possible to play tug of war with these little sharks. Care should be taken to avoid their mildly venomous spines. 

Diving logistics: Spiny dogfish are sometimes attracted to inshore shark feeds organized in New England.

As spiny dogfish schools are reported to reach plague like proportions in some areas, it may be possible to easily attract quite large numbers although the appearance of the schools is hard to predict. If planning to chum, try the summer months when the Gulf Stream has moved in towards shore.

Other diving locations submitted by readers:

Read about the spiny dogfish debate

References: 

Resurrection and redescription of Squalus suckleyi (Girard, 1854) from the North Pacific, with comments on the Squalus acanthias subgroup (Squaliformes: Squalidae)
DAVID A. EBERT 1, 2, 3, 8, WILLIAM T. WHITE 4, KENNETH J. GOLDMAN5, LEONARD J.V. COMPAGNO6, TOBY S. DALY–ENGEL7 & ROBERT D. WARD4

Migration Patterns of Spiny Dogfish (Squalus acanthias) in the North Pacific ocean - G.A. McFarlane and J.R. King. - Fisheries and Oceans Canada.

 

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