Spadenose shark

Lore & Background

The spadenose shark was first scientifically described in 1838 by German biologists Johannes Peter Müller and Friedrich Gustav Jakob Henle. Its generic name Scoliodon derives from Greek skolex ('worm') and odon ('tooth'), while the specific epithet laticaudus comes from Latin latus ('broad') and cauda ('tail'). Phylogenetic analyses indicate it is one of the most basal members of its family, and anatomical similarities suggest it is the closest living relative of the hammerhead sharks, which diverged from other carcharhinids before the Middle Eocene (48.6–37.2 million years ago).

This species has a broad, highly flattened, trowel-shaped snout, small eyes and nares, and poorly developed furrows at the mouth corners. Its teeth have a single slender, blade-like, oblique cusp without serrations. The first dorsal fin is positioned closer to the pelvic than the pectoral fins, and the second dorsal fin is much smaller than the anal fin. The back is bronze-gray, the belly white, and the fins plain. Maximum known length is 74 cm, though unsubstantiated reports indicate individuals reaching 1.2 m.

The spadenose shark is found from Tanzania to South and Southeast Asia, as far east as Java and Borneo and as far north as Taiwan and Japan, typically in shallow coastal waters 10–13 m deep. It is frequently reported from lower reaches of rivers in Malaysia, Sumatra, and Borneo, though whether it tolerates fresh water is unclear due to lack of salinity data.

Reader's Guide

The spadenose shark is harmless to humans but is heavily exploited by artisanal and commercial fisheries across its range, using gillnets, longlines, bottom nets, fish traps, trawls, and hook-and-line. Its meat is eaten or used as bait, its fins are valued for shark fin soup, and its carcasses are processed into fishmeal. The meat can also be processed with glacial acetic acid to obtain a gel powder used as a protein supplement, a biodegradable film, or a binder in foods. Despite its commercial importance, overall fishery statistics are lacking. A 1996 report found it to be the most common coastal shark on Chinese markets. Substantial numbers are caught by Indian and Pakistani fisheries; from 1979 to 1981, an average of 823 tons was caught annually off Verval, India. It is also caught as bycatch, particularly in gillnet fisheries off Kalimantan. The International Union for Conservation of Nature has assessed this species as Near threatened. Its relatively short reproductive cycle may render it more resilient to fishing pressure than other sharks, though its low fecundity still merits caution. Coastal development may also negatively affect it due to its inshore habitat preferences.

Did You Know?

• The spadenose shark has the most advanced form of placental viviparity known in fish, with newly ovulated eggs measuring only 1 mm in diameter.
• Its placental stalk has an unusual columnar structure covered by numerous long appendiculae supporting a massive capillary network.
• The species is also known as mori in Goa.
• Males mature sexually at a length of 24–36 cm, and females at 33–35 cm.