History of IRL Dolphin Studies

History of Dolphin Studies in the Indian River Lagoon

Field Study - Indian River Lagoon Dolphins


I began to study the bottlenose dolphins in the IRL in 1974 in cooperation with SeaWorld. Money for dolphin studies is always in short supply and one of the easiest (and smelly!) ways to learn about them is to pick up the animals that are found dead on the beaches. They are also called stranded or beached dolphins. Dolphins die from many kinds of natural diseases but some as a result of human activities (entanglement in nets, for example). I picked up dead dolphins in south Florida from my base at the University of Miami and SeaWorld collected dead dolphins from the IRL from its base in Orlando. SeaWorld also rescued live stranded dolphins and manatees for rehabilitation. Since dolphins were protected by federal law in 1972, we all worked under permits issued to us by the U.S. government. We would weigh and measure each dead dolphin and perform a necropsy (a dolphin autopsy) to collect tissue samples, parasites and stomach contents. When we were done, we cleaned the skull and collected the teeth. In our studies of dolphins, biology is very important to know how old the dolphin is. A dolphin is born with one set of teeth (20-25 in each of 4 rows in the bottlenose dolphin) that continue to grow a little bit each year. The growth is not in the top (or crown) of the tooth but in the root. The part of the tooth that is in the jaw beneath the gum.

Determining the Age of a Dolphin

We can tell how old a dolphin is by cutting a thin section from the root of the tooth and looking at it under a microscope. We use a saw with a diamond blade to cut the tooth. The pulp cavity (the inside of the root of the tooth) fills in a little bit each year as the dolphin gets older. This is like the growth of a tree except that the tree grows on the outside. And, just like counting the growth layers in a tree we can count the growth layers in a dolphin's tooth. Other scientists have told us that a dolphin gets one growth layer each year. From this information we can tell how long dolphins live and calculate the "average" life span. Using the dolphins' ages and other data collected from the necropsy we can calculate growth rates and determine when they become sexually mature.

Growth layers are used to determine an age approximation for dolphins
without any previous observational history (i.e. unknown birthdate).

Studying Live Dolphins

However, studying dead dolphins doesn't tell us everything we need to know about dolphin biology. We have to study live dolphins too. The federal law that protected dolphins also allowed people to collect some alive for public display in oceanariums and for research. In order to be sure that too many dolphins weren't collected, the government had to learn about the dolphins first and the Indian River Lagoon was one place where people collected dolphins for public display and research.

In 1979 the National Marine Fisheries Service issued a research contract to the Hubbs-SeaWorld Research Institute. The Institute subcontracted with me and with SeaWorld to study the bottlenose dolphins in the Indian River Lagoon. The government wanted to know if the dolphins spent their entire lives in the IRL and they wanted us to test a method known as freeze-branding to mark individual dolphins. Freeze-branding is used to mark many different animals, including cattle. It is a cold process compared with the hot brands often used on cattle. We use a branding "iron" made from brass and cool it in liquid nitrogen. The process briefly freezes the animal's skin and kills the cells that make pigment. The end result is a white mark in the shape of the branding "iron".

We started in August 1979 near Titusville and caught 25 dolphins in two weeks. The dolphins were surrounded with a long net let out from the back of a fast boat. When the dolphins were surrounded we gradually closed the net until we could place the animals in canvas stretchers and lift them aboard the boat. We were careful to avoid setting our nets around dolphin herds that contained calves. Sometimes the dolphins escaped before we could close the net and sometimes they went under it. Only rarely did they jump over the net.

Once onboard our research boat each dolphin was weighed, measured and given a physical examination by SeaWorld veterinarians. The veterinarians collected blood samples and pulled a tooth (after the dolphin's jaw was anesthetized). The last thing we did was to freeze-brand each dolphin on both sides of the dorsal fin and on both sides of the base of the dorsal fin. The whole process took 20-30 minutes per dolphin and then they were back in the water.

The freeze branded number on the dolphin's dorsal fin allows us to easily
track individual dolphins over a long observational period.

We marked an additional 50 dolphins in 1980 and then recaptured some branded dolphins in 1981 for a close-up look at the brands. Catching and releasing the dolphins was fast-paced but over in a relatively small amount of time. The bulk of the time in the field was spent looking for branded dolphins. We used a field crew of 2-3 people and collected dolphin observations throughout the year as long as the weather was good. In the first three months of the study in 1979 we made over 400 dolphin herd sightings.

During the two years of the study we made over 1,200 herd sightings and took hundreds of photographs. We resighted most of the branded dolphins at least once and many of them were seen on several occasions. During our entire study we never had a sighting of a marked dolphin outside of the Indian River Lagoon. In the years since the study several of the marked dolphins have been found dead (from natural causes) and boaters continue to see some of the branded dolphins, particularly 'Number 56', even in December 1996. In the coming weeks we hope to encounter dolphin Number 56 and some of the other dolphins branded 17 years ago. We will also find many dolphins that weren't even born then. This time we will only be photographing the dolphins, and collecting data on their movements, feeding, and socializing patterns. We hope to be able to learn even more about the behavior of these animals - things that can only be learned from a long-term study.

One of the earliest images of 'dolphin 56'.