Survey Summary: HWDT 10

During the HWDT 10 monitoring expedition aboard Silurian, we travelled a total of 440.8nm and conducted 72hrs total surveying for cetaceans. 100 visual encounters were recorded throughout the survey including: 8 basking sharks, 9 common dolphins, 11 common seals, 9 grey seals, 30 harbour porpoises, 3 minke whales, 1 otter, 2 white-beaked dolphins, 1 unidentified whale, 6 unidentified dolphins and 8 unknown species. 454GB of acoustic data was recorded, which included 368 harbour porpoise detections.

Route surveyed during the monitoring expedition

On Tuesday 15th August we awoke to a stunning rainbow stretching across Tobermory, we departed after introducing the new team of citizen scientists to survey protocol. Heading into the Sound of Mull, the team called out sightings, creels, rubbish and judged distances. Travelling around Ardnamurchan Point, past the small isles of Muck and Eigg, Silurian anchored in Loch Moidart, close to the Castle Tioram, with another lovely rainbow stretching over the castle.

The 'silver lining' of Hebridean weather...lots of rainbows!

On Wednesday 16th, Silurian travelled up through Loch Hourn and Kyle Rhea into Loch Alsh, heading into Loch Duich, where we anchored in the small bay of Ob Aoinidh. The following day, we surveyed through Loch Alsh into the Inner Sound, where we were instructed to keep a one-mile distance from the centre as the MOD were carrying out exercises - we picked up sonar through the hydrophone. Entering the Sound of Raasay, then across the Minch we made our anchorage at Maaruig, on the Isle of Lewis.

Over the next day, we undertook out a series of zig-zags across the Little Minch, using the opportunity to collect data from an area we rarely survey. We had a few encounters of harbour porpoises at the beginning of the day and an encounter of common dolphins in the latter half, we finished at our anchorage in Loch Finsbay, on the Isle of Harris, where we saw a white-tailed eagle soaring high over the hills.

On Saturday 19th we travelled down the east coast of North and South Uist heading for our anchorage on Vatersay, the southernmost inhabited island in the Outer Hebrides.

One of the many beautiful anchorages in the Hebrides, off Vatersay

The next day, Silurian travelled across the Sea of the Hebrides – proving to be the best day of the survey; the sea state flicked between 0 and 1. There was a brilliant diversity of species encountered, including two pods of white-beaked dolphin which both interacted with Silurian, swimming underneath her with their distinct white patterning very visible under the water. Two minke whales were recorded - one staying with us for about twenty minutes, circling the boat allowing us to gather valuable photo-ID data. Eight basking sharks were seen, with a few swimming very close past Silurian apparently motionless on the surface of the water. Plus, a pod of common dolphins which weren’t interested in us so we carried on the survey.  We ended our amazing day at our anchorage at Port Ruadh on the Isle of Tiree in Gunna Sound.

A white beaked dolphin swims alongside Silurian

On Monday 21st we headed through Gunna Sound and past the Treshnish Isles towards our evening anchorage in Bunessan, on the Isle of Mull.  The following day, we headed through the Sound of Iona and surveyed around Colonsay, timing it right we were able to anchor in Kiloran Bay. On Wednesday 23rd we made two long legs of effort before heading into Loch Tuath, anchoring off Ulva.

On the last day of survey, Silurian headed out of Loch Tuadh, around the top of Mull and into the Sound, reaching Tobermory harbour. We all enjoyed our last night together, with a lovely last meal and a lot of reflecting on the amazing journey we’d all had.

A big thank you to all the citizen scientists who took part in HWDT 10, your help was invaluable to us!!

Thanks also to Scottish Natural Heritage who help fund the data collection programme aboard Silurian.

Chris Sharples, HWDT Photo-ID Volunteer 2017

Our wonderful team of volunteer ciziten scientists, without whom we couldn't have undertaken the monitoring expedition!