Scalloped Hammerhead Shark | Oceana
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Marine Life Encyclopedia

Sharks & Rays

Scalloped Hammerhead Shark

Sphyrna lewini

Distribution

Worldwide in tropical to warm temperate latitudes

ECOSYSTEM/HABITAT

Coastal pelagic

FEEDING HABITS

Active predator

TAXONOMY

Order Carcharhiniformes (ground sharks), Family Sphyrnidae (hammerhead sharks)

The hammerhead sharks are an unmistakable group of sharks that can be distinguished from all other fishes by the shape of their heads. The wide, hammer-shaped head gives these sharks their common name, and the scalloped hammerhead is named for the notches found along the front edge of its head.

Like all hammerhead sharks, the scalloped hammerhead is an active predator and gains several advantages from the shape of its head. The widely spaced eyes, nostrils, and other senses allow the scalloped hammerhead to more successfully locate its prey near, or buried in, the sea floor. Also, the scalloped hammerhead may use its head to pin stingrays to the bottom, allowing them to successfully eat those difficult to capture species. Finally, like most sharks, the scalloped hammerhead has special sensory cells that it can use to detect the electric field given off by all other fishes. The wide head likely allows this species to more accurately utilize this sense, again helping it to locate prey buried in the sand.

Historically, the scalloped hammerhead shark could be observed forming very large schools of hundreds (or more) adults, but this phenomenon makes the species vulnerable to targeted fishing, and many known grouping areas have been mostly depleted. Scientists are unsure why scalloped hammerheads form these occasional large groups, while maintaining solitary lifestyles for much of the time in between, but they seem to be social animals for at least part of the year. They mate via internal fertilization and give birth to live young, which spend several years living in coastal nursery habitat before moving to join the adult populations around deeper reefs, seamounts, and other open ecosystems.

Though scalloped hammerheads have been implicated (but not confirmed) in biting some people, they are very shy and normally are quite successful at avoiding people. In fact, they can be difficult for scientists to study because they are so shy. Furthermore, they have small mouths relative to their large body size (up to 13 feet/4 m) and do not hunt prey larger than stingrays, so they are unlikely to show aggression toward people.

Unfortunately, scalloped hammerheads have been overfished throughout much of their geographic distribution. Their fins are highly valuable, and their habit of forming regular, large groups makes it easy for fishers to take all of the individuals from a large area by fishing the right place at the right time. Conservation scientists have considered the scalloped hammerhead to be endangered with extinction for quite some time, and legal authorities have recently started to agree.  In July 2014, the United States listed several populations of the scalloped hammerhead as legally endangered, the first time that distinction has been extended to a shark species. With this protection and similar legal protection elsewhere in the international community, perhaps the scalloped hammerhead’s numbers can rebound and the large aggregations that have been lost in some places will return.

Resources:

IUCN Red List

NOAA Fisheries

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