Bottlenose Guitarfish: Rhinobatos schlegelii

Family: Rhinobatidae

Common name(s)

Bottlenose Guitarfish, Brown Guitarfish, Yellow Guitarfish.

Identification

A medium-sized guitarfish. Long, wedge-shaped snout with a bulbous, protruding tip. Rostral ridges almost parallel, narrowly separated along their entire length. Eyes large. Preorbital length 4.3-5 x orbit length. Spiracles with 2 small skin folds on posterior margin; inner fold indistinct. Nostrils positioned obliquely. Nasal curtain absent. Anterior nasal flaps extend over nostril opening but not beyond.
Anterior margins of disc straight or weakly convex except at bulbous tip. Pectoral apices broadly rounded. Skin completely covered in small denticles. Small thorns around orbits and above spiracles, on shoulders, and along midline and tail to first dorsal origin.
Tail robust and long; 1.6-1.7 x disc length. Dorsal fins large and well separated, with acutely rounded apices. Caudal fin triangular, without a defined lower caudal lobe, upper tip mildly acute.

Colour

Dorsum pale, greyish-brown, or yellow-brown, often with a dense pattern of diffuse, darker brown blotches. Rostral cartilage very pale but with subtle blotches. Ventrum white, sometimes with a dusky tear-shaped spot on snout tip.

Size

Maximum length 100cm. Size at birth unknown.

Habitat

Tropical/temperate seas. Benthic on soft sand or mud substrates, sometimes adjacent to reefs. From close inshore to 230m on the continental shelf.

Distribution

Northwestern Pacific. The bottlenose guitarfish occurs from central Japan to Taiwan, including South Korea and southern China. Records from the Philippines and India are likely misidentifications.

Conservation Status

CRITICALLY ENDANGERED

The Brown Guitarfish (Rhinobatos schlegelli) is captured in industrial, artisanal, and subsistence fisheries with multiple gears, including trawl, gillnet, and longline, and is retained for the meat and fins.
There is a high level of fisheries resource use across the range of the Brown Guitarfish. Landings data of all skates combined from the Taiwan Exclusive Economic Zone (EEZ) and reconstructed catches of all sharks, skates, and rays from the Japan, China, and Republic of Korea EEZs indicate declines of 40–90% over the past three generation lengths (30 years). These levels of decline are not species-specific but are informative for understanding the broader levels of decline in batoids in the region. Severe reductions of guitarfishes have occurred elsewhere in the Indo-West Pacific due to fishing pressure. The Brown Guitarfish is subject to intense fishing pressure across its entire spatial and depth range and there is serious concern for its ability to sustain historic and current levels of fishing pressure. The species is rare in Japan, has virtually disappeared from South Korea over the past 20–25 years, and has declined by 75–96% over the past three generation lengths (30 years) in a part of Taiwan where mainly gravid females are landed.
Overall, it is inferred that the Brown Guitarfish has undergone a population reduction of >80% over the past three generation lengths (30 years) due to levels of exploitation, and it is assessed as Critically Endangered A2bd.

Citation

Rigby, C.L., Walls, R.H.L., Derrick, D., Dyldin, Y.V., Herman, K., Ishihara, H., Jeong, C.-H., Semba, Y., Tanaka, S., Volvenko, I.V. & Yamaguchi, A. 2021. Rhinobatos schlegelii. The IUCN Red List of Threatened Species 2021: e.T104005557A104006031. https://dx.doi.org/10.2305/IUCN.UK.2021-1.RLTS.T104005557A104006031.en. Downloaded on 29 May 2021.

Reproduction

Aplacental viviparous. Litter size up to 1-14 pups. Gestation period ~12 months.

Diet

Unknown.

Behavior

Poorly known.

Reaction to divers

Fairly easy to approach.

Diving logistics

The bottlenose guitarfish is occasionally seen at dive sites on the Izu Peninsula and off Chiba, on the south coast of Honshu, Japan.