Mark McDougall
Tue 24 September 2024
A minke whale (Image: Hebridean Whale and Dolphin Trust)
A new report has revealed 2023 had the highest sighting rates and numbers of minke whales ever recorded in the Hebrides - but it also saw the lowest known numbers for basking sharks.
The report by the Hebridean Whale and Dolphin Trust was published by NatureScot and presents findings collected during the Trust’s marine research expeditions onboard its research vessel Silurian over the past three years, together with sighting rates and numbers for minke whales and basking sharks from the 20 years the programme has been running.
The latest findings suggest changes in sighting rates, as well as a possible association between the two highly-mobile and long-lived species. When sighting rates for basking sharks are high, they are low for minke whales and vice versa.
It remains unknown why this happens and the Hebridean Whale and Dolphin Trust is calling for more work to analyse the trends as well as investigation into potential causes such as climate change.
Dr Lauren Harny-Mills, the science and conservation manager for the trust, believes it highlights the importance of monitoring the species – particularly in the face of climate emergencies.
Sightings of Basking Sharks have been much lower (Image: Rob Pickering)
She said: “Scotland’s west coast seas are a global hotspot for cetaceans and basking sharks. Our findings highlight the importance of long-term monitoring of these species and the threats facing them.
“In the face of the nature and climate emergencies, gaining new insights and understanding into what is happening in Scotland’s seas is vital, so we can better protect these remarkable animals and this world-class region of marine biodiversity.”
Scotland’s west coast seas are internationally important for whales, dolphins and harbour porpoise – collectively known as cetaceans – and the globally endangered basking shark.
Since 2002, the Isle of Mull-based trust has been monitoring marine life by running expeditions, with members of the public joining its research vessel to survey Hebridean seas.
Sighting rates of minke whale rose to 1.57 per 100 kilometres last year, with numbers reaching a record 167.
In contrast, rates of basking shark fell to 0.07 sightings per 100 kilometres in 2022 and 2023. That is the lowest ever recorded by the trust since monitoring began with just seven basking sharks recorded in each summer.
Scotland’s seas become home to minke whales when they migrates to the west of the country each summer to feed in the rich waters. Despite the encouraging increase in sightings, rates fluctuate over time and there are serious issues affecting the vulnerable species.
Human activities, climate change, entanglement, pollution, underwater noise and habitat degradation are all putting marine life at risk, according to the Trust who say ongoing, long-term research is crucial to understanding the impacts and how best to protect and restore biodiversity.
Rona Sinclair, Marine Mobile Species Monitoring Advisor at NatureScot, said: “This valuable research is allowing us to track how whales and basking sharks are faring over the long-term in the Hebrides. Without collaboration with organisations like the Hebridean Whale and Dolphin Trust, it would be much more difficult to assess the health of these species, why changes are happening, and what’s necessary for future research and conservation, including within Marine Protected Areas.
“The decrease in basking shark sightings is worrying, and there could be many reasons for this, likely linked to availability of their food, zooplankton. However, they may also still be there at depth and just not visible. Continued collaboration with researchers is vital, helping us to know how these giant beasts – the world’s second largest fish – are faring, so we can respond appropriately.”
The new report, ‘Hebridean Cetacean Research Programme 2021-24’, documents data gathered during the Trust’s research expeditions carried out from April 2021-March 2024 on Silurian.
During this time, 49 surveys covered a total of 22,645 km, with 10 species of mammal recorded in more than 3,000 sightings. Almost 300 volunteers conducted visual surveys and monitoring with underwater microphones, and identified individual animals through photography.
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