The Dolphins of Little Loch Broom

 

Our two transects around the North of Rockall Plateau didn’t yield any more fishing opportunities, just the occasional pause for CTD casts (Conductivity, Temperature and Depth measurements).  When we eventually found fish, the weather had worsened, making it dangerous to put out the net.

 

Neptune decided to bless us with some southerly winds of force 8 to 9 on the Beaufort scale (about 50 knots wind speed), so we set course for the Isle of Lewis. 

The Isle of Lewis with its northernmost lighthouse, the 'Butt of Lewis'

 While hiding from the weather, we’re using our time in Little Loch Broom near the Scottish mainland to calibrate the echosounders. The purpose of calibrating the echosounders is so that we can interpret the results from wild fish by comparing them to the signal from an object of known acoustic properties, to ensure the biomass volumes we’re seeing are accurate. This is done using a small tungsten carbide sphere suspended from four winches under the boat. Essentially we tied a copper weight to a metal ball and keel-hauled it with luminous fishing wire.

The Scottish mainland appearing in the distance

Entering Little Loch Broom

  

 

Preparations for the echo sounder calibration

 

 

How many scientists does it take to solve a knot?

 

 

But something odd happened when we turned on the echosounding equipment.  A large shape appeared in the echogram and disappeared again. We thought it was a blip until it happened again. We all peered at the screens, checked the connections, scratched our heads… It wasn’t until we heard laughing outside that we figured out what it was. We came out on deck and found two dolphins circling the Tridens. It seems they had followed us in from the sea, probably thinking the same thing we were, that it was safer in the sheltered bay than in the North Atlantic at the moment. They stayed for about half an hour, clicking into the recorder, playing with the tungsten carbide ball, generally being an entertainment but also a nuisance, as we couldn’t continue the calibration until they’d gotten bored of us. 

On the plus side, we now have some wonderful echograms of dolphins. 

Monitoring the calibration

When we’re finished, we’re planning a harbour stop for Saturday evening at Stornoway. After that we'll head back out into the North Atlantic, north of the Hebrides to complete our last two transects for this year. Fingers crossed for more fish.

 

Cue Calibration and Dolphins

Saturday 28^th 2015

Rough seas today with 6 meter swell. Making slow progress on western transect, average speed a steady 4 knots. Estimated time to complete this leg of the survey was 30 hours. With little option we decided to shorten the next two transects to ensure we are not out when the force 10 hits the next evening. 

Waves crashing over the bow of the Tridens.

.... meanwhile somewhere below deck, I (Helen) spot a common dolphin outside my cabin window. In quick(ish) response I grab my camera and make for the bridge. Unfortunately I was too slow to even see them again, let alone get any photographic evidence (three flights of steep stairs is a real challenge in rough seas). Will have to try harder next time! However, the local seabirds (mostly gannets and fulmars) are always keeping us company on our voyage and always look far more content with the waves than some of us on board look in these conditions.

A gannet named Janet floating above the waves

As for fish there were very few marks seen on the echosounders throughout the day and therefore no fishing was carried out.  

Sunday 29^th March 2015

After an uneventful night on acoustic watch, the morning offered a stunning dolphin display....at least for those who were awake. A pod of around 100 common dolphins (Delphinus spp) surrounded the boat and swam with us for about half an hour – something which is always nice to see.

Common dolphins jumping in the Tridens wake.

As the weather is predicted to get much worse over the next few days we headed for Loch Duich on the west coast of Scotland to do a calibration of the acoustic equipment. The conditions in the Loch are ideal for calibration of the EK60 echosounders. Deep water (50 – 105 m), small swell, little to no tidal current, relatively sheltered from the wind and very few fish below us (fish can interfere with the calibration as they often swim across the place in the beam we are interested in).

Once successfully calibrated, we will stay at anchor and spend the night in Loch Duich. We will head to either Kyle (132 km west of Inverness or 20 km from the Tridens) or Stornoway (Isle of Lewis) tomorrow morning and wait out the bad weather. We’ve already researched the local pubs in the area.

 

Flying the Scottish flag as we enter Loch Duich for calibration. 

The crew are hard at work erecting the calibration booms.

Will we fit? It’s a narrow passage en route to the calibration site further down the loch.

Being chased by rain and snow down the loch

Everyone settling in for a night of calibration.