BOTTLENOSE DOLPHIN
(Tursiops truncatus)
Basic Information: Description and Habitat
Description
Dolphins are large marine mammals. They range in color from light to dark grey, and can get speckles on their backs as they age. Dolphins range in size based on their habitat, ranging in size from a 225 cm length in Shark Bay Australia to up to 410 cm in the northeastern Atlantic Ocean. Typically, dolphins in colder and deeper habitats are larger and longer than those in warmer and shallower habitats. In some areas, there is further dimorphism between the sexes, with males larger than females (for example, Sarasota Bay, Florida). In other areas, there is no discernible difference (Shark Bay, Australia). Researchers can differentiate between individual dolphins by the scars on and shape of their dorsal fin. Use of this method through photo-identification has facilitated long-term studies of communities (Connor, et al. 2000).
Dolphins typically have a long life. Individuals have been known to live more than years, with females averaging 50 years and males 40 years in Sarasota Bay, Florida. Sexual maturity occurs earlier for females (5 to 13 years) than for males (8 to 13 years).
Two different types of bottlenose dolphins have been identified, with genetic and physical (both internal and external) differences. The coastal dolphin is the one most commonly studied. It usually stays near the coast. It is both shorter and thinner and lives in warmer and shallower water. Much less is known about the offshore dolphin. It is larger and lives in deeper, colder water (Wells, et al. 1999), and usually exists in larger groups (Connor, et al. 2000). These two different forms of bottlenose dolphin might reflect different subspecies and this question is currently being studied (Connor, et al. 2000).
Due to their high activity during the day, researchers have classified dolphins as diurnal animals (Reynolds, et al. 2000). A dolphin day is typically divided into several activities, and the time allocated to these different activities changes with the seasons. The primary activities include socializing, traveling and feeding. Over the year, dolphins spend the majority of their time traveling. During the summer, time spent socializing increases as feeding time decreases. During the fall, socializing greatly decreases as feeding time increases, possible in reaction to more energy needed to keep bodies warm as waters begin to cool. Typically, feeding occurs in the morning and socializing in the mid to late afternoon, but variations on this pattern can occur. In warmer waters, the shift between activities does not occur as much during the fall and the summer(Braeger 1993).
Habitat
Bottlenose dolphins are found in tropical and temperate oceans around the world. They are typically in the coastal or pelagic zone (Connor, et al. 2000).
Food
Dolphins are predators and eat a variety of fish and squid. As well as individual hunting, dolphins will work together to herd fish. Some individuals have exhibited more unusual techniques. For example, dolphins in Shark Bay, Australia, have appeared to use a sponge attached to their rostra to help feed. A rare instance of tool-use outside of humans, dolphins may use the sponge to gather food from the bottom of the ocean floor (Smolker, et al. 1997).
Predators
Large sharks (such as the great white shark (Carcharodon carcharias), bull (C. leucus), dusky (C. obscurrus), and tiger (Galeocerdo cuvieri) are the primary predators of bottlenose dolphins (Connor and Heithaus 1996; Conner, et al. 2000). Young and mothers with young are particularly vulnerable (Connor and Heithaus 1996), as are dolphins in deeper water. Killer whales have also been connected to bottlenose dolphin predation, though an attack has never directly observed (Connor, et al. 2000).
Reaction to predators is usually to flee, especially to shallow water. A group will sometimes divide into two separate groups to avoid a predator. Dolphins have been observed to attack and kill small sharks by ramming the shark. (Connor and Heithaus 1996). Also, there is evidence that groups living contributes both to predator protecting and increasing survival after a predator attack (Lilly 1963).
An offshore bottlenose dolphin photographed in the wild
Photo by David Hofmann. Used with Permission
A coastal bottlenose dolphin photographed in captivity
Photo by David Hofmann. Used with Permission