Scalloped Hammerhead

The scalloped hammerhead is easily distinguished from other hammerhead sharks by the central indentation on the anterior margin of the head. There are also two indentations on either side of the central indentation, which gives the "scalloped" look. They have a very large first dorsal fin that is slightly hooked and a smaller second dorsal fin. Scalloped hammerhead sharks are typically uniform grey, grayish brown, bronze, or olive with a white underside for countershading. Typically, males measure 1.5 to 1.8 m (4.9 to 5.9 ft) and weigh about 29 kg (64 lb) when they attain sexual maturity, whereas the larger females measure 2.5 m (8.2 ft) and weigh about 36.2 kg (80 lb) at sexual maturity. The maximum length of the scalloped hammerhead is 4.3 m (14 ft) and the maximum weight is 152.4 kg (336 lb), per FishBase. A female caught off Miami was found to have measured 3.26 m (10.7 ft) and reportedly weighed 200 kg (440 lb), though was in a gravid state then. These sharks have a very high metabolic rate, which governs behavior in acquiring food. They occupy tertiary trophic levels. The scalloped hammerhead shark, like many other species, uses the shore as a breeding ground. Due to high metabolic rates, young scalloped hammerhead sharks need a lot of food, or they will starve. S. …

The scalloped hammerhead is a coastal pelagic species; it occurs over continental and insular shelves and in nearby deeper water. It is found in warm temperate and tropical waters, worldwide from 46°N to 36°S. It can be found down to depths over 500 m (1,600 ft), but is most often found above 25 m (82 ft). During the day, they are more often found close to shore, and at night, they hunt further offshore. Adults are found alone, in pairs, or in small schools, while young sharks occur in larger schools. Juveniles and pups thrive in shallow coastal waters, such as bays and mangroves, which provide shelter from predators and waters high in nutrients from deposited sediments. Research carried out by the nongovernmental organization Misión Tiburón, using conventional and acoustic shark tagging methods, found that adult scalloped hammerheads migrate from the pelagic waters surrounding Cocos Island to the mangroves in the tropical fjord of Golfo Dulce - a tropical fjord on the Pacific Coast of Costa Rica. Here, female sharks give birth to live young; juveniles remain in the shallow root system of the mangroves for around three years. After this time they leave Golfo Dulce and migrate back to Cocos Island, to feed in pelagic waters.

The gestation period is reported to be around 12 months. Scalloped hammerheads give live birth. Compared to other species, the scalloped hammerhead produces large litters (12–41 pups), and this is most likely due to high infant mortality. Like most sharks, parental care is not seen. Nursery grounds for this species are predictable and repeated over the years, and they are faithful to their natal sites. Their natal sites still cause high infant mortality; a lack of resources prevents all the young from surviving. As a result, only the fittest grow to maturity. Also, should a population get depleted, it recovers through reproduction and not immigration. This species does not seem to attack each other even in periods of starvation. In addition, scalloped hammerheads have migratory behaviors. As a result, deprivation results from migration and young growth. While the Taiwan scalloped hammerhead seems to have an earlier maturity rate, it is still reported to be slow to mature.