Portuguese Dogfish

The Portuguese dogfish typically reaches a length of 0.9 m (3.0 ft) for males and 1.0 m (3.3 ft) for females, though specimens up to 1.2 m (3.9 ft) long have been recorded. Sharks in the Mediterranean are smaller, growing no more than 65 cm (26 in) long. This species has a flattened, broadly rounded snout that is shorter than the mouth is wide. The nostrils are preceded by short flaps of skin. The eyes are large and oval in shape, positioned laterally on the head and equipped with a reflective tapetum lucidum that produces a yellow-green "eye shine". The mouth is wide and slightly arched, with moderately thick, smooth lips and short furrows at the corners extending onto both jaws. The upper teeth are slender and upright with a single cusp, numbering 43–68 rows. The lower teeth have a short, strongly angled cusp and number 29–41 rows; their bases interlock to form a continuous cutting surface. The five pairs of gill slits are short and nearly vertical. The body of the Portuguese dogfish is thick and cylindrical except for the flattened belly. The two dorsal fins are small and of similar size and shape, each bearing a tiny grooved spine in front. The first dorsal fin originates well behind the pectoral fins, while the second dorsal originates over the middle of the pelvic fin bases. The pectoral fins are medium-sized with a rounded margin. There is no anal fin. …

One of the widest-ranging deepwater sharks, the Portuguese dogfish is patchily distributed around the world. In the western Atlantic, it occurs from the Grand Banks of Newfoundland to the U.S. state of Delaware. In the eastern Atlantic, it is found from Iceland to Sierra Leone, including the western Mediterranean Sea, the Azores and Madeira, as well as from southern Namibia to western South Africa. In the Indian Ocean, this species has been caught off the Seychelles. In the Pacific, this shark occurs off Japan, New Zealand, and Australia from Cape Hawke, New South Wales, to Beachport, South Australia, including Tasmania. The deepest-living shark known, the Portuguese dogfish has been reported at depths of 150 m (490 ft) to 3,675 m (12,057 ft) from the lower continental slope to the abyssal plain, and is most common between 400 m (1,300 ft) and 2,000 m (6,600 ft). This species is found deeper in the Mediterranean, seldom occurring above a depth of 1,500 m (4,900 ft) and being most common at 2,500–3,000 m (8,200–9,800 ft). The deep Mediterranean has a relatively constant temperature of 13 °C (55 °F) and a salinity of 38.4 ppt, whereas in the deep ocean the temperature is generally only 5 °C (41 °F) and the salinity 34–35 ppt. The Portuguese dogfish is essentially benthic in nature, though young sharks can be found a considerable distance off the bottom. …

Living almost exclusively in the aphotic zone where little to no sunlight penetrates, the Portuguese dogfish is relatively common and the dominant shark species in deeper waters. The large, squalene-rich liver of this shark allows it to maintain neutral buoyancy and hover with minimal effort; males contain more squalene in their livers than females. A tracking study in the Porcupine Seabight has found that the Portuguese dogfish has an average swimming speed of 0.072 m/s (0.24 ft/s), and does not remain in any particular area for long. This species may be preyed upon by larger fishes and sharks. Known parasites of this species include monogeneans in the genus Erpocotyle, and the tapeworms Sphyriocephalus viridis, S. richardi, and Anthobothrium sp. An active predator of mobile, relatively large organisms, the Portuguese dogfish feeds mainly on cephalopods (including Mastigoteuthis spp.) and bony fishes (including slickheads, orange roughy, lantern fishes, and rattails). It has also been known to take other sharks and invertebrates (such as the medusa Atolla wyvillei), as well as scavenging from whale carcasses. …