Hebridean sightings of Harbour Porpoises rise while Basking Shark sightings fall

    Sailing by St Kilda. Image by Kerry Froud/HWDT
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    Harbour Porpoise sightings off Scotland’s west coast increased by 25 per cent in 2014 compared to the previous year while sightings of Basking Sharks unexpectedly fell by 33 per cent, during marine research expeditions carried out by Hebridean Whale and Dolphin Trust.

    The latest studies were carried out in a research season lasting from May to October last year, and form part of the trust’s unique long-term monitoring of whales, dolphins and porpoises – collectively known as cetaceans – in the Hebrides. The surveys also collect data on Basking Sharks.

    The trust’s teams of marine scientists and volunteers encountered 574 groups of Harbour Porpoises during 2014 – a 25 per cent increase in the rate of sightings compared to 2013. Reasons for this increased sighting rate may include conducive weather and calm seas, making the unobtrusive porpoise easier to detect.

    Hebridean Whale and Dolphin Trust has previously discovered that the Hebrides hosts one of Europe’s highest densities of the Harbour Porpoise, the UK’s smallest cetacean – but Scotland still has no protected area for this species as required under European Union directives.

    Basking Shark sightings fell by 33 per cent from the previous year – showing a trend of decreasing sightings of the world’s second biggest fish in the area over recent years.

    This does not necessarily indicate a reduction in population size – as possible explanations include a shift further offshore in the distribution of plankton, the sharks’ favourite food. The distribution of plankton within the water column will also dictate where basking sharks are feeding – which means they may still be present, but not feeding at the surface.

    Notable highlights during 2014 included two separate encounters with what is believed to be the UK’s only known resident population of Killer Whales – five males and four females known as the West Coast Community. This small, isolated population of Orca has never produced offspring since studies began, raising fears that it faces imminent extinction.

    In total, the surveys recorded more than 1,400 encounters with cetaceans and Basking Sharks, and recorded almost 600 hours of underwater acoustic detections of cetaceans.

    Kerry Froud, Biodiversity Officer at Hebridean Whale and Dolphin Trust, said: “Our findings add to knowledge about cetacean distribution, abundance and habitat use in Scotland’s western seas – and allow us to make informed recommendations to protect these remarkable species.

    “This pioneering research is vital for effectively conserving the world-class biodiversity of these waters – and for securing the long-term future of spectacular cetaceans and iconic Basking Sharks.”

    Hebridean Whale and Dolphin Trust – based in Tobermory on the Isle of Mull – is recruiting volunteers for its 2015 surveys, to live and work as citizen scientists for periods of almost two weeks from April to September. Participation costs cover boat expenses, accommodation, training, food and insurance, and support the trust’s research. For details, contact Morven Russell at volunteercoordinator@hwdt.org, or visit www.hwdt.org.

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