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.
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.
