Pantropical Spotted Dolphin, Stenella attenuata
Pantropical Spotted Dolphin, Stenella attenuata. Underwater photograph taken in coastal waters off Kona, Hawaii, September 2015. Photography and identification courtesy of Bob Hillis, Ivins, Utah.
Phylogeny: The Pantropical Spotted Dolphin, Stenella attenuata (Gray, 1846) is a member of the Delphinidae Family of Oceanic Dolphins. The genus Stenella is one of eighteen genera in the Delphinidae Family, and there are five species in the Stenella genus. They are known in Mexico as Delphín Manchado and Delphín Pintado. The genus name Stenella is a combination of Greek and Latin and roughly translates to “little narrow one”. This refers to the slender build and narrow snout of these dolphins. The species name attenuata comes from the Latin word meaning “thinned” or “tapering”, and again refers to their narrowness.
Morphology: Pantropical Spotted Dolphins are slender dolphins with fairly long, slender beaks. The dorsal fin is relatively small and fairly falcate (posteriorly concave). The back “cape” is dark gray, as are the fins. The belly is light gray. Varying amounts of whitish spots cover the body of adult specimens. Some may lack spots completely. Most specimens will also display a white tip on their beak, looking like a golf ball. Many individuals will have light colored scars from Cookie-cutter Sharks. Pantropical Spotted Dolphins reach a maximum of 2.57 m (8 feet 5 inches) in length, and 118 kg (260 lbs) in weight.
Habitat and Distribution: Pantropical Spotted Dolphins are an open water species, generally found well offshore. They are gregarious and may be found in schools of hundreds or thousands spread out over large areas of ocean. Usually they segregate themselves into smaller groups within the school, based on age and sex. They are often associated with schools of tuna and Spinner Dolphins. These dolphins are known for leaping high out of the water, possibly to remove parasites. They spend most of their time in the top 50 m (164 feet) of water, though they have been recorded diving to 342 m (1,122 feet). Pantropical Spotted Dolphins are found worldwide, in tropical and warmer temperate seas. There are currently two recognized subspecies of Pantropical Spotted Dolphins. Both have been recorded in Mexican waters. The Offshore Spotted Dolphin, Stenella attenuata attenuata (Gray, 1846), is found along all of Mexico’s east coast and the southern portions of Mexico’s Pacific Coast. The Coastal Spotted Dolphin in found in a narrow coast strip that is less than 200 km wide in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Magdalena Bay, Baja California Sur along the central and northwest coasts of the Baja Peninsula and in north of Loreto, Baja California Sur, in the Sea of Cortez. The Coastal or Inshore Spotted Dolphin Subspecies Stenella attenuata graffmani (Perrin, 1990) is ENDEMIC to Mexico’s Pacific Coast.
Diet: Pantropical Spotted Dolphins are predatory carnivores that consume cephalopods, crustaceans and fish. Most hunting occurs at night when their prey ascends toward the surface.
Predators: Pantropical Spotted Dolphins are eaten by large sharks, False Killer Whales and Killer Whales. They are also subject to bites from Cookiecutter Sharks, which are not fatal but can be disabling.
Reproduction: As mammals, Pantropical Spotted Dolphins are gonochoric (male or female for life), and reproduce sexually, with internal fertilization. Breeding takes place year round. The gestation period is eleven months. New born calves are 85 cm (2 feet 9 inches) in length. Females reach sexual maturity between the ages of nine and eleven years, and males at fifteen years. Mature females give birth every twenty-six to thirty-six months.
Ecosystem Interactions: Pantropical Spotted Dolphins can host a variety of internal parasites including cestodes, nematodes, and trematodes. They also host epibionts such as cerripedes barnacles, remoras, shark suckers, and whale lice.
Human Interactions: Pantropical Spotted Dolphins are often the subject of commercial dolphin watching tours. They are still hunted in Asia. In most locations, their greatest threat is entanglement in commercial fishing equipment. From a conservation perspective the Pantropical Spotted Dolphin is currently considered to be of Least Concern with widely distributed increasing populations.
Synonyms: Steno consimilis.