One of the best-loved marine animals in Florida is the Atlantic Bottlenose Dolphin, which can often be seen playfully following boats or riding along on the bow wave, and sometimes interacting with human divers or swimmers.
The Daily Bucket is a regular series from the Backyard Science group. Here we talk about Mother Nature in all her glory, especially the parts that live nearby. So let us know (as close as you are comfortable) where you are and what's going on around you. What's the weather like? Seen any interesting plants, bugs or critters? Are there birds at your feeders? Deer, foxes or peahens in your yard? Seen any cool rocks or geological features? Post your observations and notes here. And photos. We like lots of photos. :)
Bottlenose Dolphin
There are about 40 different species of Dolphin, all in the family Delphinidae. They are mammals, not fish, and are closely related to the whales (in fact the "Killer Whale" or Orca is actually not a whale, it is the largest member of the Dolphin family). The fossil record shows that Dolphins are some of the most recent whales to have evolved, appearing only within the past 9-10 million years. In that time they have diversified to fill nearly every available aquatic habitat, from shallow tropical seas to ice-filled Arctic oceans to large freshwater rivers.
The Atlantic Spotted Dolphin and the European Common Dolphin can sometimes be found in Florida's coastal waters, but by far our most often-encountered is the Atlantic Bottlenose Dolphin (Tursiops truncatus). This species is familar to everyone from its many TV and movie appearances, from "Flipper" to "A Dolphin Tale". The Bottlenose Dolphin is about ten feet long, blueish-gray on top and whitish below. The males can be recognized by the two distinct slits in their bellies; the females have only one. The species is found throughout most of the world's oceans, from as far north as Norway to as far south as South Africa. In the Indian Ocean it is replaced by the Indo-Pacific Bottlenose, Turciops aduncus, and the dolphins near Melbourne, Australia, are classified as the Burrunan Bottlenose, Tursiops australis. DNA analysis shows some differences between the Atlantic populations that live near the coastlines and those which prefer the deeper ocean, and there are also some physical differences in size and coloring: it is possible that they are two distinct species and are reproductively isolated. The Pacific Bottlenose Dolphin is also classed by some taxonomists as a separate species, Turciops gillis.
Sometimes dolphins are referred to as a "porpoise", but the true porpoises are a separate biological family.
Dolphins are very long-lived animals. Wild Bottlenose Dolphins have been observed at fifty years, though the typical lifespan seems to be around 25-30. The females also seem to be capable of breeding for virtually their entire adult lives. The young are born live after a pregnancy of 12 months, and the calf then stays with its mother for up to 5 years, reaching sexual maturity at around age 10, though this can vary according to gender and geography. Bottlenose Dolphins have been known to hybridize with a number of other Dolphin species, both in captivity and in the wild.
What makes Dolphins so interesting to humans, though, is their extraordinary level of intelligence. The Encephalization Quotient (the ratio of brain size to body mass) in Dolphins is one of the highest in the animal kingdom. They are also highly social, living in "pods" of up to 20 individuals. The females tend to congregate in groups called "bands", while adult males tend to form cooperative pairs. I have often seen Bottlenose Dolphins hunting cooperatively, with one or two individuals herding a school of fish up against a seawall to allow another individual to dart in and catch the prey. At one fishing village in Brazil, the Dolphins have learned to signal to the fishing boats where to cast their nets, so they can prey on the panicked fish that manage to escape. This particular pod has been passing down this behavior to its young for over 150 years. Dolphins in Australia have also been observed using sea sponges plucked from rocks as tools to hunt in the bottom muck.
While Bottlenose Dolphins have excellent hearing and eyesight, like all Dolphins they experience their world mostly through echolocation. By sending out a series of high-frequency clicks through a fatty organ in their forehead called the "melon", they are able to read the echoes through their teeth and jawbones like sonar, and seem to be able to detect detailed sonogram images of obstacles, other Dolphins, prey, and potential predators. Although a dolphin's echolocation clicks are one of the loudest sounds made by any animal, they happen at a frequency too high for human ears to detect. Each individual has its own "signature whistle" that refers to itself, and the Dolphins all communicate with each other through a series of squeaks and squeals, some of them audible to humans. These sounds are produced by the nasal opening at the top of the head, known as the "blowhole".
In most areas, Bottlenose Dolphins have few natural predators, though large sharks or Orcas occasionally eat them. (Dolphins have very effective immune systems and can usually survive bites and injuries that would kill most other animals.) In Japan, Dolphins are eaten as food, usually in the form of raw sashimi, but the primary danger to Dolphins from humans comes from net fishing, which often entangles and drowns the air-breathing mammals. Today fisheries are required to use nets which are designed to allow Dolphins to escape. All dolphins and whales are protected by the Marine Mammals Act.
Virtually every coastal town in Florida has "dolphin boats" which take tourists out to watch the Dolphins. There are also a number of places, like Sea World and Marine Land, which have captive Dolphins on display and sometimes allow human interaction with them. The practice of keeping captive Dolphins has, however, generated a lot of controversy as many have argued that intelligent and social species like Dolphins should not be confined. In the Keys, by contrast, there are places where wild Bottlenose Dolphins, drawn by curiosity and playfulness, voluntarily enter into shallow coves to interact with humans.
Florida also has a number of facilities for rescuing and rehabilitating Dolphins who have been orphaned or injured. The most famous rescue, a young female named "Winter" who lost her tail and was fitted with an artificial prosthetic at Clearwater Aquarium, was the subject of a Hollywood movie.
NOTE: As some of you already know, all of my diaries here are draft chapters for a number of books I am working on. So I welcome any corrections you may have, whether it's typos or places that are unclear or factual errors. I think of y'all as my pre-publication editors and proofreaders. ;)