thousands of snapshots of humpback whales from families in the western part of the North Atlantic.

Each of the whales has his or her own name and can be distinguished by the tail markings which, Dr. Katona says, are like fingerprints, making it possible to track the mammals' movements.

Dr. Katona, who teaches at the College of the Atlantic in Bar Harbour, Maine, is on the Island to lead the whale watching expeditions along South Shore this month, organised by the Bermuda Biological Station.

He is also giving a lecture on whales during which he will put forward some of his "speculations'' about the "mysterious'' mammals' activities off the Island.

One of his theories is that many years ago when the humpback whale population was considerably larger, Bermuda's waters may have been a breeding ground.

As evidence, Dr. Katona points out the "peculiar fact'' that the male whales sing off Bermuda, where they usually spend a few days before heading north.

Dr. Katona believes that if his theory is correct, Bermuda may again become a breeding ground for the whales when their population swells.

The whales currently inhabit waters off the West Indies, especially the Dominican Republic, for mating and giving birth.

But Dr. Katona points out it is also possible the whales' singing might be to keep them together on their travels or to judge the depth of the waters by the echoes.

One of the mysteries about whales, Dr. Katona says, is how the females use the male's "extraordinary'' songs -- 15-20 minutes long -- to pick their mates.

Each April hundreds of humpback whales pass by Bermuda on their way "home'' after spending winter in the Caribbean.

Dr. Katona says it isn't known for sure how many whales pass by Bermuda because they are only tracked by Biological Station staff at certain times of the day and very rarely at night.

On a good day about 10 to 12 whales are spotted and not all are photographed because their tails are often not exposed.

The whales hail from five regions in the western North Atlantic: Newfoundland, Gulf of St. Lawrence, Gulf of Maine, Greenland and Iceland. The total population of the humpback in those regions is estimated to be roughly 5,000.

On the whale watching trips Dr. Katona hopes to take more photographs of whale tails for his albums, which he will compare and hopefully match.

His collection of photographs is so vast he was able to identify within days a snapshot of a whale tail sent in by Bermudian youngster, Leila Wadson.

The picture of the whale Leila had forwarded after her uncle photographed it off the South Shore, had not been seen in eight years. "We now know it is alive,'' said Dr. Katona.

Tracking the whales enables marine biologists to give fairly accurate estimates of their population which is important as the humpback whale is listed as an endangered species in America.

Dr. Katona's lecture on whales takes place tonight at 8 p.m. in Hanson Hall in the Bermuda Biological Station. Anyone who has photographs of whales' tails is asked to bring them along.

WHALE WATCHING -- A humpback whale (above) is spectacularly photographed leaping out of the Atlantic Ocean. Marine biologists often photograph the tail of a humpback whale (below) for identification and tracking purposes as each one has distinctly different markings.