Sharpnose sevengill shark

Heptranchias perlo is a small, slender shark recognised by its 7 pairs of gill slits, a single dorsal fin and very large eyes ^[1]. It lives near the bottom on the outer shelf and the upper slope, down to about 1000 m, and is almost worldwide in tropical and temperate seas ^[1]. In Peru it appears in the updated checklist of the country's cartilaginous fishes ^[2]; WoRMS places it in the family Hexanchidae, order Hexanchiformes ^[3].

It is a small, slender shark with 7 gill slits, a very narrow head and snout, and very large eyes ^[1]. It has one dorsal fin, set off from the start of the tail fin by more than 2 times its own base length, and adults have a short lower tail lobe ^[1]. The lower-jaw teeth are larger than the upper ones, flattened and comb-like, with a long main cusp and several small cusplets and no serrations on the inner edge ^[1]. It is grey-brown above and pale below; young fish have dark tips on the dorsal fin and the terminal tail lobe, which fade with age ^[1].

The probable maximum size is 137 cm, and most adults are under 110 cm ^[1]. In a sample from the central-western Mediterranean, the 31 fish measured between 54.5 and 113.3 cm in total length ^[4].

Similar species

• Notorynchus cepedianus: Notorynchus cepedianus is the only other shark with 7 pairs of gill slits, but it has a much heavier body, reaches about 2.9 m, has a broad, rounded head, very small eyes and usually many small black spots ^[1].
• Hexanchus griseus: Hexanchus griseus has 6 pairs of gill slits, a broader head and snout, smaller eyes and lower teeth serrated on the inner edge; it is also much larger ^[1].

Outside the eastern North Pacific, its range is almost circumglobal in tropical and temperate seas, with a mainly continental distribution ^[1]. It is chiefly a deepwater species of the outer shelf and upper slope down to 1000 m, although it sometimes occurs in shallow water ^[1]. Off Sardinia, in the Mediterranean, the 31 fish studied were caught between 336 and 600 m depth, and the authors regard the eleven species they studied, this one included, as rare or occasional in that sea ^[4].

For Peru, the updated checklist of cartilaginous fishes from the south-east Pacific includes the species, based on the 2001 annotated catalogue of Peruvian marine fishes ^[2].

It is ovoviviparous: litters hold 9 to 20 young, about 27 cm long at birth ^[1]. It apparently swims actively near the bottom and, when caught, is aggressive and quick to bite ^[1].

In the Sardinian sample, 25 of the 31 fish were females and 6 were males, and only 3 were mature: the 2 largest males, at 90.4 and 95.0 cm, were actively spawning, and the largest female, at 113.3 cm, was regressing ^[4]. Immature fish were caught in every season, and one active male was smaller than the published size at first maturity ^[4]. The vertebrae were so poorly calcified that no stain revealed growth bands, so age could not be estimated ^[4].

It feeds on bony fishes, including hake, and on squid ^[1]. Of the 31 stomachs examined off Sardinia, 13 held food; the main prey were ommastrephid cephalopods such as Todarodes sagittatus, bony fishes, and other elasmobranchs such as Etmopterus spinax and Galeus melastomus ^[4].

The authors group it with other deepwater sharks that eat large, fast prey, and note that body size, depth range and diet all affect how vulnerable a species is ^[4].

Its global IUCN Red List category is Near Threatened ^[5].

In Sardinian waters, the authors note that the rare species they studied, this one included, have low or nil commercial value, are not directly targeted and are usually part of the bycatch discarded at sea ^[4]. In the western Indian Ocean it is taken in bottom trawls and no separate statistics are kept for the species ^[1].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

It is aggressive and quick to bite when caught, but too small to be very dangerous ^[1].

In the western Indian Ocean it is taken in bottom trawls, no separate statistics are reported for the species and its use is not recorded ^[1]. In Sardinia the authors describe the rare species they studied, this one included, as having low or nil commercial value and not being fished directly ^[4].

The chondrichthyan checklist published in 2015 includes the species for Peru, but only as a presence in the country, with no locality or depth ^[2]. In the Mediterranean it was caught between 336 and 600 m ^[4], and FAO describes it as chiefly a deepwater species that sometimes occurs in shallow water ^[1]. None of the sources consulted says whether it has been seen by divers in Peru ^[2].