BROADFIN SAWTAIL CATSHARK
Slender deep-water shark
The Broadfin Sawtail catshark (Galeus nipponensis) is a species of catshark belonging to the family Scyliorhinidae. It is found in southeastern Japan in deep water on the bottom. It is characterized by a long, pointed snout, a series of indistinct, dark saddles along its back and tail, and a prominent crest of enlarged dermal denticles along the dorsal edge of its caudal fin. Adult males have very long claspers that reach past the anal fin covered by aprons.
Family: Scyliorhinidae – Catsharks
Common Name– Ground Sharks
Common Name– Catsharks
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: Mature specimens have measured between 53-55 cm. The maximum reported has been 65.5 cm.
Current Rare Mythical Sightings: The Broadfin Sawtail catshark has been lumped together with the Gecko catshark (G. eastmani), under whose name authors such as Toshiji Kamohara had described it since 1950. This shark was formally described as a new species in a 1975 volume of the scientific journal Memoirs of the Faculty of Fisheries, Hokkaido University by Kazuhiro Nakaya, who gave it the specific epithet nipponensis from Nippon (Japan). The type specimen is a 60 cm/2-foot-long adult male caught off Mimase in Kōchi Prefecture, on December 20, 1972. Within the genus, this species is closest in morphology to the Longnose Sawtail catshark (G. longirostris).
Teeth and Jaw: The mouth lining is white. The large mouth forms a long, wide arch. There are well-developed furrows present at the corners. The small teeth each have a narrow central cusp flanked by usually one, sometimes more, smaller cusplets on both sides.
Head: The snout is long and pointed. The tip to the nostril is greater than the eye length. There are large nostrils that have triangular skin flaps on their anterior rims. The large eyes are horizontally oval and equipped with nictitating membranes. Beneath each eye is a subtle ridge, and behind is a small spiracle.
Denticles: There is a distinct crest of enlarged dermal denticles along the upper margin of the tail. They are not below. The dermal denticles are small and overlapping, each with a leaf-shaped crown bearing a median ridge and three marginal teeth.
Tail: The tail is elongated. The caudal peduncle is almost cylindrical, and leads to a low caudal fin with a small lower lobe and a ventral notch near the tip of the upper lobe.
Demographic, Distribution, Habitat, Environment and Range: The Broadfin Sawtail catshark can be found in the northwest Pacific. They are common off Japan in southeast Honshu and Kyushu-Palau Ridge (34°N – 7°N) in deep water on the bottom between 362-540 m. They are considered bathydemersal.
Diet: They more than likely predate bony fishes, cephalopods, and crustaceans, with immature and mature sharks being primarily piscivorous. Some of the fish include Sardinops melanostictus, Glossandon semifasciatus, Chlorophthalmus albatrossis. Other prey includes squid, krill, decapods and isopods.
Aesthetic Identification: The Broadfin Sawtail catshark is slender, greyish-white dorsally, with many obscure dusky saddles and blotches. They are white ventrally. There are black anterior margins to the dorsal and anal fins, the lower caudal lobe and the rear tip. There are no black fin tips. The five pairs of gill slits are short, with the last pair over the pectoral fin bases. The first dorsal fin is roughly triangular, with gently convex anterior and posterior margins, and originates over the midpoint of the pelvic fin bases. The second dorsal fin is slightly smaller than the first and similar in shape, and originates over the latter portion of the anal fin base. The pectoral fins are medium-sized and broad. The pelvic fins are sizable and relatively low, with angular corners. Mature males have slender, greatly elongated claspers with bases covered by broad extensions of the pelvic free rear tips, called aprons, and a long space between the pelvic fin bases and a short anal fin. The base of the anal fin measures 8–10% of the total length, much less than the distances between either the pelvic and anal fins or the two dorsal fins. The anal fin of the male is 2% shorter than that of the female, which may be related to the function of the unusually long claspers.
Biology and Reproduction: They are oviparous. They possibly lay pairs of eggs, one per oviduct. Only a single egg may mature within each oviduct at a time. The egg case is vase-shaped and measures roughly 3.5 inches long and 0.79 inches across, with thick, opaque, brown walls bearing fine, lengthwise grooves. The top is squared off, while the bottom is rounded with a short projection. Females lay eggs throughout the year, with a peak in December and January. The young shark hatches at about 13 cm/5.1 inches long. Males mature sexually at 51–62 cm/1.7-2 feet long, and females at 55–61 cm/1.8-2 feet long.
Behavioral Traits, Sensing and Intelligence: Unknown.
Broadfin Sawtail Catshark Recorded Attacks on Humans: Not a threat to humans.