Taxonomy

Rarity

Abundance rates how many are in suitable habitat. Find difficulty rates how hard it is to locate one on a daylight snorkel or freedive through 50 ft. A higher find score means a harder search. The rarity category also reflects the kind of encounter; it is not an average of the 2 scores.

Seasonality

Location

Smooth hammerheads occur inshore and well offshore, over continental and island shelves. The depth figure is the surprising one. Despite reaching 16.4 feet, this species usually holds in the top 66 feet, and although it has been recorded to about 656 feet and is often associated with the bottom down to roughly 456 feet, the water it normally occupies is shallow enough for a person to be in.

The head is the identifying feature and it separates this hammerhead from its relatives. A smooth hammerhead has no notch at the center of the front edge of its head, though it does have prominent indentations to either side. The scalloped hammerhead has that central notch, which is where its name comes from. The snout is short, between a fifth and less than a third of the width of the head, and the animal is olive-gray or dark gray above and white below, with dusky undersides to the pectoral fin tips.

The diet is the other thing worth knowing, because it explains the shape. Smooth hammerheads prefer small sharks, skates and stingrays, and take bony fishes, shrimps, crabs, barnacles and cephalopods as well. A shark whose favorite prey lies flat on the bottom is a shark that benefits from a wide head sweeping the sand.

Deep Dive

The hammer is the whole animal, and the flattened head has a name of its own: the cephalofoil.

What it plainly does is move the eyes and the nostrils out to the ends of a wide bar instead of clustering them on a pointed snout. Researchers have proposed several reasons a shark would benefit from that, including a wider spread of its senses and better lift while turning, and the question is not settled. What is documented here is what this particular hammerhead eats: it prefers small sharks, skates and stingrays, animals that lie flat on the bottom. A head shaped to sweep a wide path over sand and a diet of things buried in sand are at least a suggestive pairing.

The name says the same thing twice over. The genus appears to be a misspelling of the Greek word for hammer, and the species name comes from the ancient Greek name for hammerhead sharks, built on the word for a yoke, the wooden crosspiece laid over the necks of a pair of oxen. Somebody looked at this animal a very long time ago and reached for the same comparison everyone still reaches for.

Reproduction sits between the extremes this Ichthyopedia covers. Smooth hammerheads are viviparous with a placenta, like the blue shark and the smoothhounds, so the pups are fed directly by the mother rather than on unfertilized eggs. Litters run 20 to 50 pups after a gestation of 10 to 11 months, with the young born at 20 to 24 inches. One source in the same record puts the litter at 30 to 40. Maturity comes at somewhere between 8.2 and 9.8 feet, and the maximum recorded age is 21 years.

Set that against the mako, which produces perhaps 10 to 18 pups every 3 years, and the hammerhead looks productive. Set it against the assessment that made it Vulnerable in 2018 and the productivity is clearly not enough on its own. A species can produce 50 pups a litter and still be losing ground.

One behavioral note is worth ending on because it is the version of this animal a California diver is most likely to meet. Young smooth hammerheads gather in large aggregations of hundreds of individuals and migrate north in summer. The hammerhead in California waters is usually not a solitary 16 foot adult. It is a school of juveniles passing through in the warm season.

Where to Find Them

Researched habitat and range candidates

These locations have suitable habitat within the species range. An assignment is a possible encounter, not a confirmed sighting at every beach. Season, depth, and local conditions still matter. Historical habitat without present-day evidence is excluded.