DOLPHIN DEMISE - by B.L. Bruigom Ó2005
Captain Scott Smith has been studying the species Stenella Frontalis, the Atlantic Spotted dolphin for over 25 years. The statistics for 2005 are in and the numbers are frightening. Nearly 1/3 of the spotted dolphin population seems to have “disappeared”. Spotted dolphins are commonly recognized by their spots that develop as they age and are considered a near-shore species ranging in the tropical waters of the Atlantic.
The Little Bahama Bank, home of the spotted dolphin, is near major shipping routes that have been used since the Americas were “discovered”. This is where Captain Scott goes every year to identify the individuals, catalog behaviors and study these amazing mammals.
The country of the Bahamas lies just fifty miles from the south east coast of Florida. The Bahamas consist of more than 700 islands that stretch over 100 miles. These islands dot the edges of what is referred to as Banks, vast areas of shallow water, 10-30 feet deep. The edges of the Banks are lined with cays, rocks, reefs and wrecks which then drops off to water that is 200+ feet deep. The northern most of these is called the Little Bahama Bank. The 40-mile long western edge of the Little Bahama Bank is where the southern, central and northern groups of spotted dolphin call home. To the south is the island of Grand Bahama, the port of West End and along the edge are small cays. As you travel north you head into the wide-open Atlantic Ocean. Between Florida and the Bank runs a major ocean current called the Gulf Stream. The Gulf Stream moves vast amounts of water from south to north. This warm clear water, rich in life, is brought to the edge of the Banks providing an abundant food source to the dolphins as well as the other marine life. There is a sand bar on the Little Bahama Bank that is referred to as White Sand Ridge, it’s where most of the dolphins are found.
On average Captain Scott will see 60 resident dolphins throughout the year. His ID catalog has over 125 dolphins in it. Some are transient dolphins moving through the area that he may see only once every several years. He is very familiar with this population and it’s residents, many he can recognize by sight alone. Captain Scott reports, “My first indication that something was wrong came in the spring. We did not see the large groups of 30-40 dolphins that we normally see at that time of the year. We never saw groups of more than 10-12 dolphins. The residents have dropped in number to a shocking 47 and it’s not just older ones missing, dolphins of all ages went unseen this year. To even find those residents we had to travel 10 miles further north.” That may not seem far to travel, but for spotted dolphins recorded in the area since the 1700’s by salvage divers working the shallow waters of old sailing ship wrecks, that distance is staggering.
When asked why, Captain Scott replies, “has the demise of the spotted dolphin occurred from man, natural disasters, a shift in predator hunting grounds or all of the above? It’s yet to be determined.” Here are some of his observations.
With the Little Bahama Bank so close to Florida, its popularity as a great area to fish and dive grew during the 1960’s. During the Mid 70’s, salvage diver Robert Marx and his crew were looking for gold from an old Spanish Galleon. They would spend hours searching the bottom, while curious dolphins moved in and out of the area to see what they were up to. As the dolphins appeared, the divers would swim and interact with them. In 1979 Robert Marx starting spreading the word and by the late 1970’s and early 1980’s charter boats were running a few trips a year to swim with these very friendly, wild dolphins.
During the late 1980’s and the boom of the live-aboard dive/charter boats, word spread of these unbelievable encounters. More and more people wanted the experience of swimming with a wild dolphin. With each passing decade, as more and more people get their own boats the White Sand Ridge has become a very crowed area in the summer months.
Are these numbers of boats and people pushing the very dolphins they have come to enjoy out of the area? Dolphins like to swim at about 10 knots and have bursts of speeds up to 30mph. The super fast boats, like cigarette boats, can travel at such high speeds they can cause propeller damage to a dolphin unable to get out of the way quick enough.
Or is it the bottlenose dolphins, usually found farther south, but are now seen in abundance on the ridge? The bottlenose dolphin is more aggressive and much larger in size than the spotted dolphin; they may be “bullying” them out of the area.
Is it the navy who this year started new sonar experiments? Before electronic navigation there existed light towers that were maintained by man. Dolphins communicate with a wide variety of sound, body language and touch. Our human ears, if we’re lucky, can hear 20 kHz sounds. Dolphin ears, two minuscule holes located a couple of inches behind and below the eyes, are capable of hearing sounds well over 100 kHz. They are connected to a very sophisticated sensory system of echolocation. Dolphins transmit sound from air sacks, it then bounces off, or echoes off, the surrounding environment or an individual object. By making a series of whistles, barks, squeaks and other sounds that we can’t possible hear, a dolphin is able to hunt, learn the lay of the land, know where they are in relation to the group and much more. Are these test affecting the dolphin’s sonar to the extent they must get “out of range” to utilize their own very sensitive sonar systems?
One thing for certain is that the predators are out in abundance. Captain Scott says, “Where we use to see only a few tiger sharks a year we now see several a month. This can be a result of irresponsible boaters who toss their waste into the shallow waters of the White Sand Ridge. What they don’t realize is that if there is any meat product, any cleaned fish debris, they are creating chum and inviting the sharks. Boaters need to be responsible and dump natural waste over very deep water ONLY!” A very knowledgeable and respectful local boater, Lara Pike, reported that her small family boat was actually attacked by a bull shark. Knowing Captain Scott was in the area for his research she radioed his boat and relayed the information as it was happening. She reported how the bull shark had aggressively turned 4 times charging, trying to bite the front of the boat. After several unsuccessful passes it went to the rear where the diving platform still shows the teeth imprints from the bite it took. When it comes to unpredictability, extreme aggression and territorialism the bull shark takes 2nd place only to the Great White Shark. To see one on the ridge is very frightening.
Over the last several years sightings of a small group of killer whales has been repeatedly reported to Captain Scott. They have been found between Florida, the Carolinas and all over the Bahama area. Captain Scott wonders if all the natural disasters have forced a shift in the food chain.
In 2004 hurricanes Frances and Jeanne rolled over the White Sand Ridge. Frances moving at a snails pace. The problem with hurricanes is that dolphins, like us, need to breath air. They can only hold their breath for 3-5 minutes. During storms they always head for deep water. NO one is able to track them during hurricanes, but it is suspected that as they come up for air they ingest great amounts of water through their blowholes. Blowholes are designed to take the place of nostrils, the air is pushed in and out rapidly, and this exchange takes place in approximately 1 second. Their forehead, the Melon, is hydro-dynamically formed to split the water flow in front of the blowhole, located on top. A dolphin exhales explosively as it surfaces and then rapidly inhales before diving again. The blowhole closes off enabling dolphins to stay submerged. It is very likely that high winds, rain and waves allow too much water into their lungs, which can lead to pneumonia or drowning.
Captain Scott says “it’s too soon to know the answers, but you can be assured that I will be looking at all of these factors very closely and if need be will work with the Bahamian government to rectify as many issues as possible! The good news is that we’ve seen a lot of births, so if the babies make it through their first two years of life we will always have these magnificent creatures as part of our lives.” Something that is near and dear to the very heart and soul that makes Captain Scott the researcher he is.