There are many species of dolphins
Take a moment and picture a dolphin in your head. What did it look like in your mind's eye? A dolphin with a grey body, slightly darker on top and lighter on the belly? A head with a rounded forehead, and a short sturdy rostrum with a “built-in smile”? A body that is longer than a human’s but shorter than a minivan? Well, all of these features specifically describe only one of the more than 40 different kinds of dolphins. This is the famous bottlenose dolphin, featured for more than 50 years in numerous TV shows, movies, aquariums and marine life parks. These are marvelous animals and yet, they only represent one of over 40 species in the family Delphinidae, the Oceanic Dolphin Family. This blog will explore some of the variation among these species, all of which has come about through adaptations to the particular habitat they live in and niche (the functional role they play there) they occupy.
Bottlenose dolphins off Hawaiʻi. Photo credit: Kula Naiʻa Foundation.
Let me start by highlighting some of the very obvious vast differences between species within the family Delphinidae. For example, these species have a wide array of coloration patterns. Many species have a uniform color all over. It can vary from light grey to black, to greyish blue and even pink. The color may change slightly from a lighter shade on the belly to a darker shade on the back. This is called countershading. Other species sport patterns that can range from hourglass shapes in dramatic black and white or yellow/tan and bluish grey, to a variety of stripes and, sometimes spots, on their sides.
The color and coloration patterns vary widely among the many species of Oceanic dolphins. From top left: Common Bottlenose dolphin, Hector’s dolphin, Taiwanese Humpback dolphin, Pantropical spotted dolphin, and Northern Right whale dolphin (Illustrations courtesy of NOAA). Striped dolphin, Hourglass dolphin, and Long-beaked common dolphin (Illustrations courtesy of Uko Gorter).
The reasons for this variation are likely manifold, but include where and how they live. The countershading can serve as a camouflage, blending in with the background from all directions: dark on top, blending in with the darker colors below and a lighter color on the belly, blending in with the lighter colors above, near the surface. Some of the more muted color patterns may serve to break up the body of individuals, while bolder color patterns might help to corral schooling fish, squid and shrimp while feeding.
The striped, common and spotted dolphins are generally found further offshore, in larger schools. These species can also be found in mixed species aggregations, where species identity may be an issue. The spotted dolphin species (the Pantropical spotted and the Atlantic spotted) accumulate their spots slowly as they grow older, so that it is possible to estimate their level of maturity from the accumulation of spots.
The size of dolphins also varies widely, from Hector’s dolphin (1.2-1.6m, 50kg), weighing as much as a large dog, to the killer whale, or Orca, where males (up to 10m and 10,000kg) can weigh as much as the largest male African elephant ever recorded. This size difference may correlate with the size of prey they feed on and Killer whales have been observed to attack and feed on large whales.
Hector's dolphin and a male Killer whale, or Orca (Courtesy of NOAA), compared to an outline of an adult human (6 ft/ 1.8m, 75kg) for scale.
So being aware of the wide range of variation in size, shape and coloration among Oceanic dolphins will hopefully help in the understanding of how differently they live their lives. This in turn has profound implications for their survival and conservation. I will look more closely at some of these adaptations and what they say about how these species live their lives, in future blogs. Being aware of different dolphin species also gives one the ability to be more conscious of how they should be treated or regarded.