Bahamas Marine Mammal Survey

Bottlenose Dolphins leaping

In 1991, the Principal Investigators conducted a preliminary vessel survey of marine mammals in the northeastern Bahamas to document which species inhabit these waters. Concurrently, marine mammal sighting forms were distributed to yachtsmen and fishermen throughout The Bahamas in an effort to obtain species distribution information over more of the island chain. A primary goal of this preliminary survey was to find an area suitable to begin a long term photo-identification study to determine the residency and demographic status of selected marine mammal species. The preliminary survey documented the occurrence of 17 different species of dolphins and whales in Bahamian waters (Claridge and Balcomb, 1993), and indicated that the waters around Great Abaco Island offered a high diversity of species that warranted further investigation.

With the support of Earthwatch, in 1992 the Bahamas Marine Mammal Survey began a photo-identification study in central Abaco concentrating primarily on an inshore population of Atlantic bottlenose dolphins (Tursiops truncatus). During five years of study, we successfully photo-identified most individuals in the study area, allowing us to determine with confidence that there is a resident inshore community of about 90 dolphins in east-central Abaco (Claridge, 1994a). This is the first population estimate determined for this species in The Bahamas, allowing the Bahamas Department of Fisheries to manage this species more effectively.

Bottlenose dolphins (Tursiops truncatus) surfacing

In addition to the bottlenose dolphin studies conducted in central Abaco, the Bahamas Marine Mammal Survey also surveyed the offshore Atlantic waters and successfully photo-identified over 400 individuals of 11 different oceanic cetacean species (Claridge and Balcomb, 1995a). We resighted individual Atlantic spotted dolphins (Stenella frontalis), Risso’s dolphins (Grampus griseus) and dense-beaked whales (Mesoplodon densirostris) over consecutive years. Concerning the latter, perhaps the most exciting results of the oceanic surveys was frequent encounters with beaked whales (Family Ziphiidae), which are deep diving and relatively enigmatic creatures that flourished in the Miocene epoch and are now considered rare. We photo-identified over 60 individual dense-beaked whales and found inter-year and intra-year matches with 16 of them, including mother/calf pairs (Claridge and Balcomb, 1995b). This is an unprecedented research opportunity, somewhat like a herpetologist being able to study living dinosaurs.

Home of the Bahamas Marine Mammal Survey

In December, 1996 we moved our base of operations from central Abaco to the southeastern end of Great Abaco Island, and began survey work based at Hole in the Wall lightstation. We proposed to shift the emphasis of the survey efforts and photo-identification study from coastal waters to the oceanic waters in order to learn more about the deep-diving odontocete species. To the south and west of Hole in the Wall lie two extremely deep channels known as Northeast and Northwest Providence Channels, respectively. These channels are relatively sheltered from the Atlantic Ocean providing better sea conditions to survey oceanic waters than what we experienced off central Abaco. We hoped to learn if these channels supported that same species diversity as off central Abaco, and if we would find resident populations or perhaps some of the same individuals. We planned to conduct both shore-based searches from the 168-foot lighthouse as well as vessel surveys.

Hole in the Wall lighthouse

When we began the 1996/97 field season at Hole in the Wall, we had to endure the expected difficulties of learning a new study area resulting in fewer encounters, but as the season developed we realized that the waters off south Abaco would present us with rewarding discoveries. During our 1996/97 field season, we documented the presence of twelve different species of cetaceans in Northeast and Northwest Providence Channels. Two of these species had never been recorded off central Abaco, suggesting that these deep channels may actually support a greater diversity of marine mammal species than the Atlantic waters of central Abaco. We photo-identified individuals from nine different species and had intra-season resights of sperm whales, bottlenose dolphins, and Atlantic spotted dolphins.

Atlantic spotted dolphins (Stenella frontalis)

It became apparent that Northeast and Northwest Providence Channels provide year-round habitat for sperm whales. We sighted sperm whales from the lighthouse during all months of the "winter", and began encountering nursery groups of mother/calf pairs during vessel surveys in May. We had more sperm whale encounters between May and August of 1997 than we had had in all previous years off central Abaco combined. Matches were found between individuals photographed in July and August, suggesting that at least some of the adult females are remaining in the area for a period of time. We now have a catalogue of 40 sperm whale tail flukes and will attempt to match these with any found in future surveys. We also collected patches of sloughed skin for DNA analyses.

Sperm Whale (Physeter macrocephalus) raises its tail

We were intrigued to discover an apparent difference in social structure, feeding behaviour and habitat use of the bottlenose dolphins between central Abaco and south Abaco. In south Abaco the bottlenose dolphins are found in groups three times the average group size of central Abaco, appear to have different mating strategies, and occasionally socialize with Atlantic spotted dolphins. The average group size of spotted dolphins encountered off south Abaco were considerably lower, which may be why they choose to associate with the larger, more domineering bottlenose dolphins.
We found resights of two species that had been previously photographed outside the south Abaco study area. Seven bottlenose dolphins, part of a larger group encountered off Hole in the Wall in June, were previously photographed and encountered on numerous occasions by Kelly Rossbach, a graduate student doing a bottlenose dolphin study off the northwestern edge of Little Bahama Bank, 140 miles away! We also found a melon-headed whale in May 1997 off Hole in theWall (part of a group of 150) that we had photographed in July 1995 off central Abaco. This is the only resight that has ever been documented for this species anywhere in the world; further analysis of the photographs may reveal resights of more individuals.

The Bahama Parrot (Amazona leucocephala bahamensis) is an endangered and endemic species that is found only on the islands of Great Abaco and Great Inagua.

It is known that one species of pinniped, the Caribbean monk seal (Monachus tropicalis), occurred in the Bahamas in past centuries, but they were slaughtered to presumed extinction for their meat and oil. We have had several anecdotal reports of monk seal sightings in the last decade, but been unable to confirm any reports, and it is generally accepted that this species is extinct. West Indian manatees (Trichechus manatus), also occurred historically in Bahamian waters, but throughout the Caribbean and the southeast United States their numbers have windled and they are endangered throughout their range. From reliable sightings reports and two strandings, we now know of at least 10 documented occurrences of this species in the past 20 years in the Bahamas, with the majority of sightings occurring in the last 3 years. However, manatees are still considered extremely rare visitors.
With ocean habitats being threatened worldwide by pollution and overexploitation, it is important for each nation to inventory what remains in their sovereign waters, and it is incumbent on the international community to inventory the international waters. In 1994, The Bahamas hosted the World Biodiversity Conference and announced plans for a nationwide conservation strategy plan to determine the biodiversity of the country. The results of our survey will contribute significantly to the national biological survey efforts to be undertaken.

Whales of the Bahamas, a report by Diane Claridge.

Have a look at the Highlights of the 1997 Field Season.

Email the Bahamas Marine Mammal Survey:

Visit the Bahamas Marine Mammal Survey Webpage.
See also Earthwatch Institute.
For a volunteer's view look at David Hoffmann's page on Bahamas Marine Mammal Survey

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