Close encounter with an ocean giant leaves volunteers spellboundEarthwatch scientists and volunteers in Scotland enjoyed a rare encounter with a humpback whale (Megaptera novaeangliae) this summer.

The Earthwatch team on board the research vessel Silurian were conducting a research survey on 29 June between South Uist and Coll when one of the volunteers spotted a large, bushy blow in the distance. As Silurian approached, the engines were turned off and a humpback whale surfaced within a few hundred metres of the vessel, to the great delight of all onboard.

Relief Science Officer Sarah Barry of the Hebridean Whale and Dophin Trust (HWDT) said: "The whale surfaced three or four times in a row and then dived for about five minutes, so it was most likely feeding below the surface, which is an encouraging sign for the area."

The animal, approximately 10 metres in length, seemed content surfacing alongside Silurian for about an hour and a half. Photographs were taken of the humpback's tail flukes, which have a distinctive pattern, and will be compared with other organisations' photo-identification catalogues to try to identify the individual.

Humpback whale sightings are rare off the west coast of Scotland but not unheard of. In June of this year, a humpback was spotted off Gairloch and in recent years sightings have numbered one or two a year. The species is widely distributed in all oceans, making extensive migrations and ranging from its tropical wintering grounds to the edges of the polar ice zones.

Unmistakable in appearance, the humpback whale's pectoral (side) fins are long and narrow (Megaptera means "great wing") and may measure as much as a third of the body length. When fully grown, humpback whales can measure up to 17 metres and weigh 40,000 kg; the female is normally slightly larger than the male. The tail fluke can measure up to five metres across, has a serrated trailing edge, and is black with distinct patterns of white on the underside; this pattern is unique to each animal and is used for identifying individuals.

Earthwatch scientists from HWDT, with the help of Earthwatch volunteers, conduct research surveys onboard Silurian throughout the spring, summer and autumn months. Volunteers are welcomed onboard to assist with vital data collection which will be analysed by the scientists to provide a better understanding of cetacean distribution and abundance off the west coast of Scotland.

Encounters like these are a reminder that the waters off the west coast of Scotland are exceptional, playing host to a great variety of cetacean species. Reporting sightings to HWDT will contribute to the knowledge of cetacean distribution and abundance within the area. If you are lucky enough to encounter a cetacean, please report your sighting at http://www.whaledolphintrust.co.uk/ or contact the office on 01688 302620.

Find out more about the Earthwatch expedition Whales and Dolphins of the Hebrides.

Editor's Notes

• The Hebridean Whale and Dolphin Trust (HWDT) is dedicated to enhancing knowledge and understanding of Scotland's whales, dolphins and porpoises (cetaceans) and the Hebridean marine environment through education, research and working within local communities as a basis for the lasting conservation of local species and habitats.