Nursehound

Appearance

The nursehound attains a length of 1.6 m , though most measure less than 1.3 m . This shark has a broad, rounded head and a stout body that tapers towards the tail. The eyes are oval in shape, with a thick fold of skin on the lower rim but no nictitating membrane. Unlike in the small-spotted catshark, the large flaps of skin beside the nares do not reach the mouth. In the upper jaw, there are 22–27 tooth rows on either side and 0–2 teeth at the symphysis ; in the lower jaw, there are 18–21 tooth rows on either side and 2–4 teeth at the symphysis. The teeth are Y-shaped and smooth-edged; the anterior teeth have a single central cusp, while the posterior teeth have an additional pair of lateral cusplets. Towards the rear of the jaws, the teeth become progressively smaller and more angled, with proportionately larger lateral cusplets. The five pairs of gill slits are small, with the last two over the pectoral fin bases.

The two dorsal fins are placed far back on the body; the first is larger than the second and originates over the bases of the pelvic fins. The pectoral fins are large. In males, the inner margins of the pelvic fins are merged into an "apron" over the claspers. The caudal fin is broad and nearly horizontal, with an indistinct lower lobe. The skin is very rough, due to a covering of large, upright dermal denticles. The nursehound has small black dots covering its back and sides, interspersed with brown spots of varying shapes larger than the pupil, on a grayish or brownish background. The pattern is highly variable across individuals and ages; there may also be white spots, or the brown spots may be expanded so that almost the whole body is dark, or a series of faint "saddles" may be present. The underside is plain white.

Distribution

The nursehound is found in the northeastern Atlantic from southern Norway and Sweden to Senegal, including off the British Isles, throughout the Mediterranean Sea, and the Canary Islands. It may occur as far south as the mouth of the Congo River, though these West African records may represent misidentifications of the West African catshark . Its range seems to be rather patchy, particularly around offshore islands, where there are small local populations with limited exchange between them. The nursehound can be found from the intertidal zone to a depth of 400 m , though it is most common between 20 m and 60–125 m . This bottom-dwelling species prefers quiet water over rough or rocky terrain, including sites with algal cover. In the Mediterranean, it favors algae-covered coral.

Behavior

Primarily nocturnal, nursehounds spend the day inside small holes in rocks and swim into deeper water at night to hunt. Sometimes two sharks will squeeze into the same hole, and several individuals will seek out refuges within the same local area. In one tracking study, a single immature nursehound was observed to use five different refuges in succession over a period of 168 days, consistently returning to each one over a number of days before moving on. Nursehounds may occupy refuges to hide from predators, avoid harassment by mature conspecifics, and/or to facilitate thermoregulation. In captivity, these sharks are gregarious and tend to rest in groups, though the individuals comprising any particular group changes frequently. This species is less common than the small-spotted catshark.

The nursehound feeds on a variety of benthic organisms, including bony fishes such mackerel, deepwater cardinalfishes, dragonets, gurnards, flatfishes, and herring, and smaller sharks such as the small-spotted catshark. It also consumes crustaceans, in particular crabs but also hermit crabs and large shrimp, and cephalopods. Given the opportunity, this shark will scavenge. Adults consume relatively more bony fish and cephalopods, and fewer crustaceans, than juveniles. Known parasites of this species include the monogeneans ''Hexabothrium appendiculatum'' and ''Leptocotyle major'', the tapeworm ''Acanthobothrium coronatum'', the trypanosome ''Trypanosoma scyllii'', the isopod ''Ceratothoa oxyrrhynchaena'', and the copepod ''Lernaeopoda galei''. The netted dog whelk preys on the nursehound's eggs by piercing the case and extracting the yolk.

Habitat

The nursehound is found in the northeastern Atlantic from southern Norway and Sweden to Senegal, including off the British Isles, throughout the Mediterranean Sea, and the Canary Islands. It may occur as far south as the mouth of the Congo River, though these West African records may represent misidentifications of the West African catshark . Its range seems to be rather patchy, particularly around offshore islands, where there are small local populations with limited exchange between them. The nursehound can be found from the intertidal zone to a depth of 400 m , though it is most common between 20 m and 60–125 m . This bottom-dwelling species prefers quiet water over rough or rocky terrain, including sites with algal cover. In the Mediterranean, it favors algae-covered coral.Primarily nocturnal, nursehounds spend the day inside small holes in rocks and swim into deeper water at night to hunt. Sometimes two sharks will squeeze into the same hole, and several individuals will seek out refuges within the same local area. In one tracking study, a single immature nursehound was observed to use five different refuges in succession over a period of 168 days, consistently returning to each one over a number of days before moving on. Nursehounds may occupy refuges to hide from predators, avoid harassment by mature conspecifics, and/or to facilitate thermoregulation. In captivity, these sharks are gregarious and tend to rest in groups, though the individuals comprising any particular group changes frequently. This species is less common than the small-spotted catshark.

The nursehound feeds on a variety of benthic organisms, including bony fishes such mackerel, deepwater cardinalfishes, dragonets, gurnards, flatfishes, and herring, and smaller sharks such as the small-spotted catshark. It also consumes crustaceans, in particular crabs but also hermit crabs and large shrimp, and cephalopods. Given the opportunity, this shark will scavenge. Adults consume relatively more bony fish and cephalopods, and fewer crustaceans, than juveniles. Known parasites of this species include the monogeneans ''Hexabothrium appendiculatum'' and ''Leptocotyle major'', the tapeworm ''Acanthobothrium coronatum'', the trypanosome ''Trypanosoma scyllii'', the isopod ''Ceratothoa oxyrrhynchaena'', and the copepod ''Lernaeopoda galei''. The netted dog whelk preys on the nursehound's eggs by piercing the case and extracting the yolk.

Evolution

Like other members of its family, the nursehound is oviparous. Known breeding grounds include the River Fal estuary and Wembury Bay in England, and a number of coastal sites around the Italian Peninsula, in particular the Santa Croce Bank in the Gulf of Naples. Adults move into shallow water in the spring or early summer, and mate only at night. The eggs are deposited in the shallows from March to October. Although a single female produces 77–109 oocytes per year, not all of these are ovulated and estimates of the actual number of eggs laid range from 9 to 41. The eggs mature and are released two at a time, one from each oviduct. Each egg is enclosed in a thick, dark brown case measuring 10–13 cm long and 3.5 cm wide. There are tendrils at the four corners, that allow the female to secure the egg cases to bunches of seaweed .

Eggs in the North Sea and the Atlantic take 10–12 months to hatch, while those from the southern Mediterranean take 7 months to hatch. The length at hatching is 16 cm off Britain, and 10–12 cm off France. Newly hatched sharks grow at a rate of 0.45–0.56 mm per day, and have prominent saddle markings. Sexual maturity is attained at a length of 77–79 cm , which corresponds to an age of four years if hatchling growth rates remain constant. This species has a lifespan of at least 19 years.