| Prickly shark | |
|---|---|
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Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Echinorhiniformes |
| Family: | Echinorhinidae |
| Genus: | Echinorhinus |
| Species: | E. cookei |
| Binomial name | |
| Echinorhinus cookei Pietschmann, 1928 | |
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| Range of the prickly shark[2] | |
Theprickly shark (Echinorhinus cookei) is one of the twospecies ofsharks in thefamilyEchinorhinidae (the other one is thebramble shark), found in thePacific Ocean overcontinental and insular shelves andslopes, and insubmarine canyons.Bottom-dwelling in nature, it generally inhabits cool waters 100–650 m (330–2,130 ft) deep, but it also frequently enters shallower water in areas such asMonterey Bay offCalifornia. This stocky, dark-colored shark grows up to 4.0 m (13.1 ft) long, with two smalldorsal fins positioned far back on its body and noanal fin. It is characterized by a dense covering of thornlikedermal denticles, hence itscommon name.
Nocturnally active, the prickly shark rests during the day in deeper offshore waters and performs adiel migration to shallower inshore waters at dusk. Individual sharks have a smallhome range and tend to remain within a given local area. This species consumes a variety ofbony andcartilaginous fishes, andcephalopods. Since it moves slowly, it may use suction to capture prey. It isaplacental viviparous, with females producing sizable litters. The prickly shark is not known to be dangerous to humans and has minimal economic value. It iscaught incidentally bycommercial deepwater fisheries, which are expanding and may potentially threaten its population. Thus, theInternational Union for Conservation of Nature (IUCN) has assessed this species asData Deficient.
AustrianichthyologistViktor Pietschmann described the prickly shark as a new species in two separate publications: a brief German account in a 1928 volume ofAnzeiger der Akademie der Wissenschaften in Wien and a more detailed English account in a 1930 volume ofBernice P. Bishop Museum Bulletin. Pietschmann named the shark in honor ofCharles Montague Cooke Jr., aconchologist at theBishop Museum.[3][4] However, prickly sharks were continually misidentified asbramble sharks (E. brucus) and referred to as such in scientific literature until 1960, whenJack Garrick redescribed the species. Since the originalholotype fromKauai,Hawaii had been lost, Garrick designated a 2.0 m (6.6 ft) long male fromPalliser Bay,New Zealand as anew type specimen.[5] Other common names for this species include Cook's bramble shark and spinous shark.[1][6]
The prickly shark has a flabby and cylindrical body, with the adults markedly bulkier than juveniles, and a short, moderately flattened head. The nostrils are placed far apart and preceded by small flaps of skin. Thespiracles are tiny and positioned well behind the eyes, which lacknictitating membranes. The mouth forms a broad arch, with very short furrows at the corners. There are 21–25 and 20–27 tooth rows in the upper and lower jaws respectively. The knife-like teeth each have a strongly angled main cusp flanked by up to three smaller cusplets on either side; the lateral cusplets are absent in young sharks. There are five pairs ofgill slits, with the fifth pair the longest.[7][8][9]
Thelateral line runs along each side of body in a conspicuous furrow. Thepectoral fins are short, while thepelvic fins are relatively large with long bases. The firstdorsal fin is small and originates at or behind the level of the pelvic fin origins; the second dorsal fin is similar to the first and positioned close behind. Theanal fin is absent, and the stoutcaudal peduncle lacks depressions at thecaudal fin origins. The caudal fin has a longer upper lobe without a notch in the trailing margin, and an indistinct lower lobe. The skin has a dense, uniform covering of non-overlappingdermal denticles measuring up to 0.4 cm (0.16 in) across, which are never fused together as in the bramble shark. Each denticle is thornlike, with strong ridges running down the central spine and radiating out over the star-shaped base. The denticles beneath the snout are very fine in adults. The prickly shark is plain brown or gray, often with a purplish tint, and has black trailing margins on the fins. The underside is paler, most obviously on the snout and around the mouth. It may reach a length of 4.0 m (13.1 ft). The maximum recorded weight is 266 kg (586 lb) for a 3.1 m (10 ft) long female.[7][8][9]
The prickly shark is widely distributed around thePacific Ocean. In the western and central Pacific, it has been reported offJapan,Taiwan,Victoria andQueensland inAustralia, andNew Zealand, as well as around the islands ofPalau,New Caledonia,Tonga,Hawaii, and possibly theGilberts. In the eastern Pacific, it is known to occur fromOregon toEl Salvador (including theGulf of California), around theCocos andGalapagos Islands, and offPeru andChile.[10] This species generally seems to be uncommon; an exception is inMonterey Canyon offCalifornia, where sharks of both sexes are abundant throughout the year.[1][11][12]
Favoring cooler temperatures of 5.5–11 °C (41.9–51.8 °F), the prickly shark is mostly found below depths of 100–200 m (330–660 ft), particularly in thetropics.[9][10] It has been recorded from at least 650 m (2,130 ft) down and may occur much deeper, possibly to 1,500 m (4,900 ft).[1][7] On the other hand, at higherlatitudes it frequently enters shallowinshore waters; for example, in Monterey Canyon it can be consistently found at depths of 15–35 m (49–115 ft), and offMoss Landing one individual was captured in water only 4 m (13 ft) deep.[7][9] This shark inhabitscontinental and insular shelves andslopes, where it swims close to the bottom. It can also be found insidesubmarine canyons, close to the walls. It prefers areas with a muddy or sandysubstrate.[9] It is tolerant of lowdissolved oxygen levels, allowing it to inhabitoceanic basins inaccessible to other sharks.[13]
The prickly shark is a slow swimmer and has been observed hovering just above thesea floor.[14] A tracking study in Monterey Canyon found that this species exhibits strongdiel migration patterns. The sharks were inactive during the day, resting in discrete refuge areas located near the sea floor in deep, offshore waters. They became active at dusk, swimming towards the coast to the head of the canyon and rising into the water column; this upward movement is likely related to feeding onschooling fishes. Individual sharks seldom strayed from the local area and had very smallhome ranges, no more than 2.2 km2 (0.85 sq mi).[11][12] The prickly sharks in Monterey Canyon regularly form aggregations that may number over thirty.[7]
The size and structure of the prickly shark's mouth andpharynx suggests that it uses suction to capture prey. This species feeds on a variety ofbenthic andpelagicbony fishes, includinghake,flounders,rockfishes,lingcod,topsmelt,mackerel, andherring, and oncartilaginous fishes, includingelephantfishes (Callorhinchus),spiny dogfish (Squalus acanthias), youngbluntnose sixgill sharks (Hexanchus griseus), andghost catshark (Apristurus)egg cases.[8][9]Octopuses andsquid, including theHumboldt squid (Dosidicus gigas) are also consumed.[7] Young prickly sharks may themselves fall prey to the bluntnose sixgill shark, while adults likely face few threats.[9] Reproduction in this species isaplacental viviparous, with the unborn young sustained byyolk. There is only one known record of a pregnant female, which wasgestating 114embryos; this ranks among the largest known litters from any shark. The young are probably under 40 cm (16 in) long at birth.[7] The length atsexual maturity has not been precisely determined but is thought to be around 2.0 m (6.6 ft) for males and 2.5–3.0 m (8.2–9.8 ft) for females.[15]
Interactions with divers show that the prickly shark behaves inoffensively towards humans, either tolerating contact or fleeing when closely approached.[7][9] It is susceptible toincidental capture bycommercialbottom trawls,gillnets, or line gear.[8] It has little commercial value since the meat is soft and poorly regarded.[9]
In June 2018 the New ZealandDepartment of Conservation classified the prickly shark as "At Risk – Naturally Uncommon" with the qualifiers "Data Poor" and "Secure Overseas" under theNew Zealand Threat Classification System.[16] TheInternational Union for Conservation of Nature (IUCN) has assessed the prickly shark asData Deficient, citing its patchy known distribution and the continuing expansion of deepwater fisheries.[1]
