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LatestPhoto
A spinner dolphin (Stenella longirostris) leapts out of the water next to the bow. The spinner dolphin is a slender animal with a long slim beak.
Photo Copyright 2004 Bob Pitman - may not be reproduced without permission from author

March 30, 2004
Whale & Dolphin Diversity in the Maldives
Real Audio
  56k


Log Transcript

This is Genevieve Johnson speaking to you from the Maldives in the Indian Ocean.

This research leg, we are joined by visiting scientist, Bob Pitman of the National Marine Fisheries Service - NOAA Southwest Fisheries Center. Bob is a field biologist with over 30 years experience. He joins the Odyssey in the hope of documenting, photographing and collect biopsy samples from rarely seen beaked whales and tropical Indian Ocean killer whales (Orcinus orca)

Beaked whales are the least known of all cetaceans. Of the 21 species described so far in the family Ziphiidae, most are rarely observed at sea. With our new acoustic array (underwater microphones) specifically designed for recording beaked whales, we hope to capture their vocalizations. In particular, we aim to record Mesoplodon indopacetus, also known as Longman's beaked whale.

During most research legs, we focus our effort on sperm whales (Physeter macrocephalus). Sperm Whales are oceanic animals usually found far from shore. However, around atolls where the water is exceptionally deep close to shore as it is the Maldives, we usually find sperm whales within 3 to 5 miles of land. Beaked whales are also primarily deep diving squid eaters, but are rarely sighted in the company of sperm whales - perhaps to avoid prey competition. Beaked whales are often sighted within a mile of shore in the Maldives where the depth drops steeply and almost immediately from 500 to 2,000 meters. Surveying close to the reef also brings us into contact with several species of smaller cetaceans.

LatestPhoto
A Fraser's dolphin (Lagenodelphis hosei) rides the bow wave. This is a distinctive species with a stocky body, small apendages and a short beak.
Photo Copyright 2004 Bob Pitman - may not be reproduced without permission from author

As Odyssey sailed from Male, a mixed group of striped dolphins (Stenella coeruleoalba), bottlenose dolphins (Tursiops truncatus) and Risso's dolphins (Grampus griseus) approached. The solid, grey bottlenose and the elegant, leaping striped dolphins, rode the bow wave together while the Risso's milled around keeping their distance. We never see this scratched, beakless species ride Odyssey's bow wave.

Captain Mark Preedy turned Odyssey south and we proceeded to parallel the shoreline for the next 200 miles. A large school of Fraser's dolphins (Lagenodelphis hosei), joined us along the way. This species was only described in 1956 and wasn't seen alive until the early 1970's. Following this sighting was a group of 500 - 600 spinner dolphins (Stenella longirostris) and pan-tropical spotted dolphins (Stenella atenuatta). These two species often travel together, although we don't know exactly why. However, they offer the scientists and crew onboard some priceless photo opportunities.

The crew was excited to spot two groups of beaked whales, both identified as Cuvier's beaked whale (Ziphius cavirostris). We record the vocalizations of beaked whales while in close proximity to the Odyssey. However, the high frequency sounds known to be made by some beaked whale species are outside the range of human hearing. Therefore, the recorded data is sent back to SCRIPPS Oceanographic Institution in the United States for analysis.

As the search for beaked whales and killer whales continued, we sailed within one to two miles of the edge of the reef. We posted two crewmembers on the observation platform from sunrise to sunset on hourly rotations. Their job is to report all sightings to the helmsperson who records the information into a database.

The channels between islands where seawater flows in and out from the open ocean to the inner lagoon is usually an area of high productivity and an ideal place to sight certain cetaceans. While sailing by the channels, we spotted the small dorsal fins of two animals resting at the surface - a behavior called 'logging'. Bob Pitman immediately identified them as being dwarf sperm whales (Kogia simus). The dwarf sperm whale and pygmy sperm whale (Kogia breviceps) comprise their own family called Kogiidae and are the closest living relatives of the sperm whale. Relatively common but rarely seen, or often seen but rarely identified correctly, these small, inconspicuous animals are normally found a long way from shore except around atolls like the Maldives where deep water is very close to land.

We left the dwarf sperm whales only to see another set of dark dorsal fins in the distance. We sailed in their direction and identified them as pygmy killer whales (Feresa attenuata). Pygmy killer whales are small, shy animals, often confused with the slightly larger, similar looking melon-headed whale (Peponocephala electra). However, this group was comprised of 6-8 animals. The first clue in identifying the difference between the two species is that melon-headed whales usually number in the hundreds, while pygmy killer whales are always in small groups. They approached Odyssey briefly, just long enough for us to make a positive identification and take a few quick photographs.

LatestPhoto
A Bryde's whale calf (Balaenoptera edeni) surfaces to breath. Remora fish hitch a ride on the whale's back using a suction cup on the top of their head.
Photo : Chris Johnson

Later, False killer whales (Psuedorca crassidens) joined the growing list of sightings. We noted that one animal had a missing dorsal fin. Soon after, we spotted 'logging' animals close to the reef. After a close approach, we realized they were another mixed group. This time containing pilot whales (Globicephala machrorhynchus) and bottlenose dolphins - two species often observed in each others company for unknown reasons. We immediately noticed one of the dolphins was missing its dorsal fin as well. Moments later, a large male pilot whale surfaced, he too was missing a dorsal fin. The wound looked recent, it was ragged and torn. Bob Pitman speculated that perhaps there are killer whales in the area. They often bite the dorsal fin off fleeing prey such as whales and dolphins in an attempt to slow them down. "Nothing else is big enough or strong enough to attack an adult male pilot whale, and it doesn't look like a boat strike," suggested Bob.

Where these three animals the lucky survivors of an attack by killer whales?

So far, the crew detected two groups of sperm whales. On both occasions the faint clicks of a single animal identified at night, led us to a larger group by morning. Spending a day with each group, we collected biopsies from most of the animals. The first group consisted of 6 loosely associated animals spread over an area of 5 miles. Interestingly, they were all mature males. It is unusual to see so many large males associated together. Mature males tend to be solitary, moving between groups that include receptive females while in tropical water. The second group comprised smaller animals of both sexes and mature females - a matriarchal group.

We left the sperm whales and resumed our coastal survey. Bob Pitman was keen to find killer whales and we continued to search for the elusive Longman's beaked whale. Deciding to leave the east coast, we sailed through the One and a Half Degree channel between Huvadu and Huddummati atolls, to the west side of the archipelago. Bowriding spinner and spotted dolphins accompanied the boat periodically.

The next morning, Bob called down from observation watch. He spotted a large blow off the port beam about half a mile away. The tall, stately column of vapor belonged to a baleen whale, but we could not identify the species from this distance? Mark changed course until the blow was off the bow with the distance between us closing rapidly. The crew scanned in all directions, straining to see over the whitecaps. The whale blew again 300 meters off our stern and we realized she wasn't alone. It was a Bryde's whale (Balaenoptera edeni) mother and calf pair. The calf looked to be a few months old - scientists do not yet know exactly how long Bryde's whales nurse for. The cow was skinny, about as skinny as they get, demonstrating the difficulties inherent in being a resident rorqual in the tropics. All other species of baleen whale migrate twice a year from their polar feeding grounds to their tropical calving grounds and back. Bryde's whales are the exception, living permanently in the less productive tropical waters and feeding primarily on Euphausiids - small crustaceans. We were pleased to see her defecate, indicating she is feeding, while her calf appeared fat and healthy, readily approaching Odyssey and swimming across our bow. Several remoras attached themselves to the back of the calf. Remoras are merely 'hitchhikers' causing their host no harm. They have a specially adapted sucker on top of their head they use to attach themselves, letting go whenever food scraps are available. There are different species of remora that specialize in attaching themselves to a number of marine creatures ranging from whales and dolphins to sharks, manta rays and fish.

LatestPhoto
A mature male sperm whale raises its enormous flukes and 'tail slaps' off the bow of Odyssey.
Photo : Chris Johnson

With less than a week remaining of this research leg, there is still no sign of any Longman's beaked whales or the elusive killer whales that inhabit the lower latitudes of the tropics. However, we all hope to find them before we return to port.

Links:

Log written by Genevieve Johnson.

Links:

Log written by Roger Payne.

 
 
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