The small-spotted catshark or lesser spotted dogfish, Scyliorhinus canicula, is a cat shark of the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Scyliorhinidae found on the continental shelves and uppermost slopes off Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 and the British Isles

British Isles

The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

 south to Senegal

Senegal

Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...

, including the Mediterranean between latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s 63° N

63rd parallel north

The 63rd parallel north is a circle of latitude that is 63 degrees north of the Earth's equatorial plane. It crosses the Atlantic Ocean, Europe, Asia and North America....

 and 12° N

12th parallel north

The 12th parallel north is a circle of latitude that is 12 degrees north of the Earth's equatorial plane. It crosses Africa, the Indian Ocean, South Asia, Southeast Asia, the Pacific Ocean, Central America, South America and the Atlantic Ocean....

. Its length is up to 1 m

Metre

The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

 (3.3 feet) and it can weigh more than 2 kg (6.5 lb).. It is found primarily over sandy, gravely or muddy bottoms at depths of a few metres down to 400 m..The S. canicula is one of the most abundant elasmobranchs in the Northeast Atlantic and Mediterranean Sea. The majority of the populations are stable in most areas..

Description

The S. canicula are small, shallow-water sharks with a slender shaped body with a blunt head. The two dorsal fins are located towards the tail end of the body. The texture of their skin is rough, similar to the coarseness of sandpaper.. The nostrils are located on the underside of the snout and are connected to the mouth by a curved groove. The underside is a lighter greyish-white colour and the upper side is greyish-brown with darker spots. Dorsal colour is sandy and tightly tan, with numerous small spots and dark brown or nearly black in colour. The teeth of S. canicula in males are larger than in females. In male S. canicula from West African waters, their jaws are stronger, larger and more calcinated. The reasons for the changes in their mouth dimensions during maturation could explain their feeding habits and adaptations for reproductive behavior.

Reproduction

Reproduction is oviparous. They deposit egg-cases that are protected by a horny capsule

Capsule

-Anatomy:* an eggshell* Articular capsules - every diarthrodial joint possesses a fibrous or ligamentous capsule, lined with synovial membrane, attached to the adjacent ends of the articulating bones* the sac that encloses the crystalline lens of the eye...

 with long tendrils

Tendrils

Tendrils is an irregular collaboration between noted Australian guitarists, Joel Silbersher and Charlie Owen. A difficult sound to describe, Tendrils features two seemingly chaotic but strangely melodic and complementary, guitar parts and occasionally stripped back percussion.Starting out billed...

. The deposited egg-cases are mostly on macroalgae in shallow coastal waters. When the egg-cases are deposited farther from shore, they are placed on sessile erect invertebrates. These eggs usually measure 4 cm by 2 cm, without ever exceeding 6 cm. These egg-cases can be found around the coasts of Europe. The embryos develop for 5–11 months, depending on the sea temperature and the young are born with a measurement of 9–10 cm. Spawning can take place almost all year round. However, there are can be seasonal patterns in spawning activity as well. For example, S. canicula females that are located off the Mediterranean coast of France, lay their eggs from March to June and in December. In the waters surrounding Great Britain, egg laying occurs in spring with a gap between August and October. In the Tunisian Coast, the sharks lay their eggs starting in spring, peaking in the summer and then slightly decreasing during Autumn. Males reach sexual maturity with a length of about 37.1-48.8. Females reach sexual maturity with a length of 36.4-46.7 cm.

Feeding

S. canicula is considered an opportunistic species which preys on a wide range of food, such as, molluscs, echinoderms, polychaetes, crustaceans, sipunculids and tunicates. However, decapod crustaceans and fishes are their main food. The dietary preferences change with age; younger animals prefer small crustaceans, older animals prefer hermit crabs and molluscs. It was also observed that the feeding intensity was highest during the summer due to the higher availability of prey life. Diet composition varies with body size. There are no significant differences in the feeding habits of the male and female S. canicula.
Behavioral analysis showed that the S. canicula uses a consistent behaviour pattern termed 'scale rasping', as a feeding mechanism. The sharks uses this mechanism by anchoring food items near their tail so that their rapid head and jaw movements can tear away bite-sized pieces from their prey. They are able to anchor food items near their body due to the tooth-like structures that are embedded in their skin. These structures normally assist with protection from predators, parasites and abrasions to the skin. This type of feeding in S. canicula can also be done due to their elongated body morphology.

Model Organism

The S. canicula is well-suited for comparative analysis of gastrulation

Gastrulation

Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.Gastrulation takes place after cleavage...

 for several reasons.

• It is harvested in large numbers along all the coasts of Europe, and it is the only elasmobranch species known to us from which any stage of development can be obtained in abundance at any time of year..
• Fertilization is internal in the dogfish, but eggs are laid at early stages of development, before the formation of the blastocoel. Once laid, they can go on developing normally in the laboratory, simply in oxygenated seawater.
• The size and accessibility of the embryo makes analysis easier.
• Five well-characterized stages can be distinguished between the onset of gastrulation and the beginning of neurulation
  Neurulation
  Neurulation is the stage of organogenesis in vertebrate embryos, during which the neural tube is transformed into the primitive structures that will later develop into the central nervous system....
  
  .

Threat Level

The S. canicula is one of the most abundant elasmobranchs in the northeast Atlantic and Mediterranean. It is regularly used by near-shore fisheries for human consumption. The majority of S. canicula that are taken by commercial fisherman and recreational anglers are discarded. However, studies have shown that post-discard survival rates are extremely high, around 98%. Although localized depletion may have occurred in some areas, surveys have shown that populations are stable or are even increasing throughout the majority of its range. However, continued monitoring of landing and discarded data is important to avoid any future decline. This species is currently listed under "least Concern" on the IUCN Red List of Threatened Species, because there is no evidence to indicate that the global population has declined significantly. There are currently no conservation actions in place.

External links

• IUCN Red List
• Animal Diversity Web entry for Scyliorhinidae