Those fins you see in the Matanzas River are not sharks. They are Bottlenose Dolphins. They are very playful animals and will play with almost anything. Dolphins and porpoises belong to the whale family (cetacean). All cetaceans are mammals. Dolphins and porpoises are the smallest of whales.
It is thought that millions of years ago dolphins were land animals. They were wolf-like creatures that hunted at the edge of the sea. Eventually their forelimbs became flippers which look like pointed paddles. Inside there are 5 sets of bones just like fingers. The skin is fused around the fingers to create a smooth surface which enables the dolphin to steer through the water. Their hind limbs are now tiny, useless bones behind their ribs.
All the power for propelling a dolphin forward comes from its muscular tail. The end of the tail is spread out into two wide flukes. The dolphin pushes the flukes up and down to move through the water. The dorsal fin on its back may help the animal keep its balance as it swims Bottlenose dolphins can get up to 12 feet long and weigh 1500 pounds. The skin is very smooth and firm and feels almost like rubber. This feature enables the dolphin to slide easily through the water. Their skin is insulated with thick blubber which keeps them warm. Dolphins have lungs and breathe air by using a blowhole at the top of their heads. This enables them to breathe at the surface without having to expose much of their bodies. To close its blowhole when diving, the dolphin uses powerful muscles to squeeze it shut. Salt water can irritate their eyes so they have a jelly-like substance in their eyes that looks like tears.
How they find their food is extraordinary. They use sound waves or sonar-echolocation. They make a clicking sound that starts in air sacs in their nasal cavity. Then it moves forward through a structure in their forehead called the melon. The echoes from the fish or object bounce back and travel through the lower jaw to the dolphin's inner ear. Sending out as many as 2,000 clicks per second, the dolphin can learn all about an object--its size, shape, speed, and direction--in just one second! It can detect a fish as small as a minnow from 10 feet away.
Dolphins often work as a team to catch fish. First they herd a school of fish into a tight group; then they circle the fish to keep them corralled. Each dolphin then takes a turn swimming in the middle to feed. Often you will see the dolphins chasing mullet close to the shore line to corner them. When a dolphin gets a fish, it turns it around to swallow head first.
You will usually see at least two or more dolphins together. They are very social animals. However, if a dolphin breaks the social rules, it may be cast out of the group. A bottlenose dolphin family usually consists of about 5 to 10 members, with 2 to 4 females and their offspring. Small groups of males swim separately.
Dolphins are quite vocal. They talk to each other by whistling, whines, groans, and jaw claps. When a dolphin is injured or sick, other dolphins might come to its aid. They will support the weak dolphin with their flippers and keep it afloat so it can breathe.
Since dolphins are mammals, they give birth to live young and nurse the young from mammary glands. A mother dolphin carries her single baby for 12 months. When she gives birth, the calf emerges tail first. The mother will nudge it and help it to the surface to take its first breath. A calf might weigh 30 to 50 pounds and is 35 to 50 inches long. They have no teeth for several weeks and nurse for 1 to 2 years. They stay with their mothers for 3 to 6 years. The mothers are very protective. If the baby strays away too often, the mother will trap it between her flippers or hold it under water for a few seconds. The young usually swim in the center with the female adults at the edges to protect them from danger. Dolphins' life span in the wild is anywhere from 20-30 years.
How can you tell the difference between a dolphin and a porpoise? One way is by the shape of their heads. Porpoises have smaller heads and shorter snouts. Also, all but one porpoise has a triangular fin on their backs instead of the curved fin of dolphins. Porpoises also have flat triangular teeth while dolphin teeth are cone- shaped.
The greatest threats to dolphins, like to other sea creatures, are pollution and gill nets. Thanks to recent laws regarding the nets used for catching tuna, thousands of dolphins are saved each year. However, much industrial waste and garbage are dumped into the ocean which pollute the dolphins' habitat and can cause disease and death.
If you would like to help protect the future of dolphins and porpoises, throw litter in receptacles and not on the ground or over the side of a boat. Also send letters to your representatives asking them to keep oceans clean and pollution free and to protect them from seining nets.
People come to Florida and see performing dolphins at Sea World or Marineland, but It is very special to be able to see dolphins in the wild like the dolphins we see here at Fort Matanzas National Monument.
Last updated: April 9, 2020