BROWN GUITARFISH

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Common English Names: Brown guitarfish, yellow guitarfish.

 

Latin Name: Rhinobatos schlegelii

Family: Rhinobatidae

Identification: Long, pointed snout with elongated rostral cartilage forming a slightly extended rostral tip. Pectoral fin posterior margins convex. Body behind pectoral fins tapers into a thick tail topped by two well developed dorsal fins of roughly equal size. Caudal fin triangular with indistinct lower lobe. Dorsal color yellowish brown with a mottled pattern of symmetrical, darker blotches. Ventrum pale. Rear border of spiracles have two visible folds.

Another form of R.schlegelii exists that has a significantly shorter snout. This may be a case of sexual dimorphism or it could represent a completely separate species.

Size: Maximum length 100cm.

Habitat: Listed as occurring at depths from 80-240m but this species is occasionally sighted by recreational divers much shallower than 40m around southern Honshu, Japan. On sandy bottoms often adjacent to rocky reefs.

Abundance and distribution: Restricted to the Northwest Pacific Ocean. Further study is needed to determine which of the two forms of R.schlegelii occur in which regions. It appears that the long-snouted form is centered around Japan and likely occurs off the coast of China, Korea and Taiwan.

Behavior: Lays on or partially buries in sand when not foraging for food.

Reproduction: Guitarfishes are ovoviviparous (yolk sac viviparity). After absorbing all of the yolk, embryos suckle from tiny club shaped villi (projections) that provide nutrients for the young as they develop.

IUCN Red List Status: The brown guitarfish (Rhinobatos schlegelii) has not yet been evaluated by the IUCN largely due to the confusion over the species complex and the extent of its range.

However, it is susceptible to capture in a variety of fishing gear including trawl, gillnet and line fisheries and rhinobatids are highly valued for their fins. Historical fishing pressure has been relatively intensive across its known range, although increases in fuel prices have reportedly led to some decrease in recent years off Japan. Other Rhinobatos species have proved vulnerable to population depletion as a result of their limiting life-history characteristics and serious declines have been reported in similar species where they are heavily fished. Consequently, the brown guitarfish may prove to be threatened when these taxanomic issues are resolved.

Photographs: Ito, Chiba Prefecture, Japan.

Similar species: The brown guitarfish needs to be reviewed to establish how many species actually exist. There appears to be a long snout and short snout species in Japan and what is likely another similar species in the Philippines.

Reaction to divers: Generally easy to approach with careful slow movements. May slowly move away or bolt upon very close examination.

Diving logistics: This guitarfish is occasionally encountered in Chiba and Izu; two peninsulas on the south side of Honshu, Japan.

In Chiba. There are a number of dive shops operating in the region. One recommended operator is Bommie Dive Center in Ito, Chiba Prefecture.