Whales and Dolphins of the Hebrides
The Hebridean Whale and Dolphin Trust (HWDT) established this project to assess distribution, relative abundance and habitat preference of whales, dolphins and porpoises in the waters of the Inner and Outer Hebrides on the west coast of Scotland.
Distribution and relative abundance are researched through visual and acoustic surveys on the research vessel Silurian, with both broad-scale coverage across the region and more intensive sampling in high-use habitats. Spatial modelling (whereby the areas used by the species, and what for, i.e. feeding, breeding, are mapped using sightings data) is used to examine environmental factors that influence cetacean distribution. The team are developing predictions about the oceanographic and ecological mechanisms that result in the observed distribution, which will be used to refine a sampling strategy for testing and to develop these relationships. The research provides essential baseline information about cetaceans in areas which have very little data.
Supported by Earthwatch for five years so far, the project objectives are: modelling temporal and spatial patterns of cetacean distribution and habitat preference; investigating cetacean movement patterns and demographics of Hebridean cetaceans; and mapping anthropogenic environmental inputs (human impacts).
A small, wide-ranging group of bottlenose dolphin (Tursiops truncatus) has been identified and is being monitored, comprising of around 50 photo-identified individuals. This very small population is a cause of conservation concern and understanding their movements is vital to conservation management. Knowledge is improving and sightings of the same dolphins are received from the east coast of Scotland.
The largest cetacean population surveyed in the region is minke whale (Balaenoptera acutorostrata), with 108 individuals identified to date. Information on this population could indicate whether east and west populations interact and will greatly increase knowledge of distribution and movements. A marked decline in minke whale sightings in recent years means that this information is particularly important.
Data shows that abundance is highest in the northern and western areas of the Hebrides. The likely cause is changes in the abundance patterns of their prey of small schooling fish, which clearly affects the whales. Other causes cannot yet be ruled out, but this is almost certainly a factor. Variations in availability and distribution of prey are also thought to be the cause of small group sizes of common dolphins (Delphinus delphis) seen in 2008, compared to 2007 when groups of several hundred were encountered.
During acoustic studies, recordings of noises from Acoustic Deterrent Devices (ADDs) at fish farms (designed to prevent seal predation) are being used to map the extent and degree to which cetaceans are exposed to these sounds. These data are being used in a project investigating the effects of ADDs on cetaceans with the University of St Andrews for the Scottish Aquaculture Research Forum.
Minke and humpback whales (Megaptera novaeangliae) entangled in fishing gear have been reported in Scottish waters, with some mortality, but the extent of the problem is unknown. Data on the location of fixed fishing gear is being recorded and protocols developed to obtain photographs to document scarring from entanglement in these whales.
Long-term monitoring of the area to investigate patterns and causes of changes in species distribution and abundance is an ongoing programme. This monitoring has directly addressed actions in local and national Biodiversity Action Plans (BAPs). Of the 20 UK BAP priority cetacean species, 14 have been identified on the west coast by HWDT monitoring, seven of which are sighted regularly.
In 2008, HWDT conducted 12 survey expeditions from April to September. Five of these expeditions were operated using volunteers and support from Earthwatch.
Results of surveys are disseminated locally, directly to those involved in the wildlife watching industry and to the general public via newsletters and local press. This helps to keep both groups informed of what cetacean species are being seen and where, encouraging more people to continue reporting sightings. HWDT also visits local schools, colleges and community groups to give presentations and talks; it also runs an educational visitor centre which is open all year to the general public.
HWDT is an integral part of the community on Mull and the wider Hebridean area; its work in cetacean research, education and conservation is fully integrated into the area's economic and social structure and development.
Dr. Peter Stevick is Science Director of the Hebridean Whale and Dolphin Trust. He was supported on the Earthwatch 2008 project by Susannah Calderan and Cormac Booth.
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