Blotchy Swellshark: Cephaloscyllium umbratile

Family: Scyliorhinidae

Common name(s)

Blotchy Swellshark, Japanese Swellshark.

Binomial

Cephaloscyllium umbratile.

Synonyms

Cephaloscyllium formosanum

Identification

Stout body. Snout bluntly rounded but relatively long for this genus of catshark. Mouth width much greater than snout length. First dorsal origin approximately level with middle of pelvic fin base. Second dorsal fin level with middle of anal fin base. Anal fin larger than second dorsal. Anal fin apex rounded. Lower caudal lobe indistinct. Dorsal surface densely covered in irregular grey/brown blotches. Blotches may form subtle dark saddles. Upper caudal subterminal notch well defined.

Size

Maximum length 120cm. Size at birth 20-22cm.

Blotchy Swellshark, Cephaloscyllium umbratile, aka Japanese swell shark. Tateyama, Chiba Prefecture, Honshu, Japan, Sea of Japan.

Conservation Status

DATA DEFICIENT

Although no data are available to assess population trends, the Japanese swellshark is apparently still abundant in areas that are heavily fished by trawlers. Small scyliorhinid species have proven resilient to population decline, even where they are heavily fished (for example the Smallspotted Catshark (Scyliorhinus canicula) in the northeast Atlantic). However, records of Japanese Swellshark apparently include C. umbratile and a smaller undescribed sympatric species. The two species may be confused and C. umbratile is a larger catshark, and may be more vulnerable to depletion. Therefore this species is assessed as Data Deficient until further information is available on its life-history, catches in fisheries and population trends.

Habitat

Temperate continental shelf on sandy and muddy bottoms and rocky reefs. From 40-440m.

Distribution

The blotchy swellshark is confined to the northwest Pacific. From Japan to southern Korea, China, and Taiwan. May occur further south in Southeast Asia but sightings need confirmation as this species may be confused with other swell sharks from the region.

Reproduction

Oviparous. Hatching times and seasonality is poorly understood. Eggs may be deposited year round.

Diet

The Japanese swell shark consumes a wide variety of small fishes, sharks, molluscs and crustaceans. Japanese mackerel appear to be an important food source.

Behavior

Poorly known.

Reaction to divers

Easy to approach when resting on the reef. Not known to respond to chum.

Diving logistics

Although the blotchy swellshark occurs within the depth limit of recreational diving, encounters are extremely rare. Most encounters take place off the south coast of Honshu Island between Shizuoka and Chiba areas. However, this may just be because the area is heavily dived.

Divers hoping to see this species should dive in the winter when cooler water sharks are more likely to be in shallower water. Try searching under overhangs and in large crevices close to (or beyond) recreational depths.