Homeward bound!

We finished our last transect yesterday around 10 a.m. and set course for Cork due to arrive in port in the early hours of Thursday the 7th. The survey might be coming to a close, but life on the ship still holds its little surprises and treats for us.

A view of the Scottish coast from afar

During the final transect, we were hoping to find a dense layer of blue whiting and finish with one last fishing haul but the schools on the echograms were too small and patchy to target with our pelagic trawl net. Hour upon hour passed as we closed in on the end of the transect, growing more impatient by the minute. We knew that we might not get the opportunity for one more haul…

An echogram from shortly before our last haul

Right as we made our way up to the shelf slope, a strong signal appeared at a depth of about 300 metres: this was our chance! Soon afterwards, the net was shot and we trawled through the whiting school, which now showed up as an extensive layer on the echograms. After a tow time of only 15 minutes, the net was hauled back in.

 

 

 

 

 

Handling the trawl doors

 

 

All hands on deck for the common goal

Gannets diving for fish near the codend of the net

 

The school had been more dense than expected. The net contained about 3.5 tons of blue whiting, making it one of the largest hauls of the cruise. There was a high proportion of larger size classes of blue whiting (> 30 cm) and compared to other hauls, these fish were quite young, with many not older than 4-6 years. We also caught some larger bycatch species; mostly hake, mackerel, argentines and horse mackerel. Due to the shallower depth of this haul compared to the others, the mesopelagic species were absent except for a single lanternfish and a snipe eel.

A small subsample from the bycatch

Blue whiting otoliths

Two large saithe (Pollachius virens) that found their way into our net

We promised a deep sea haul, but unfortunately we ran out of time. At the end of transect, we headed down passed the Isle of Lewis, through the Scottish Islands and down the Irish Sea. The wind picked up again on Wednesday, making for a rougher sea than the last few days. Steaming at about 15 knots, we are on schedule to arrive in Cork in the morning. While everyone on board is busy cleaning up and packing for the trip home, we are finishing the blog. For some of us, this will be the last night on board, so we are sending you our best wishes once more as we are passing through St. George’s Channel into the Celtic Sea.

Slán abhaile, agus go n’éirigh on bothar libh.

Safe home, and may the road rise with you. 

Stornoway: There and back again!

Hello again from the RV Tridens, where we are nearing the end of this year’s Dutch contribution to the Blue Whiting Survey.

Sunrise at Little Loch Broom

After enjoying a calm night on Little Loch Broom, we finished the calibration of our echo sounders on Saturday morning, so we headed for Stornoway on the Isle of Lewis. As luck would have it, we were greeted with summery weather - a bright blue sky and sunshine provided a warm welcome as we arrived in Stornoway harbour during the early afternoon.

 

Taking down the calibration equipment

 

Upon docking at the pier, everyone on board quickly scattered into town for a well earned evening off. We all found our way back to the Tridens (more specifically its bar) that night to celebrate together.

Arrival at Stornoway

 

The dock at Stornoway harbour

We set off at 10 am on Sunday.  The sunshine had been replaced by solid clouds and light rain, but the winds remained gentle. A light drizzle and overcast skies greeted us as we set off to our final two transects. Soon, the acoustics room was busy again and we started recording on the last westward transect.

Leaving Stornoway behind

It took about two hours to find dense aggregations of fish. After 5 days without fishing, the net was finally shot again. But disaster struck! Some cables on the net had become tangled, and we had to haul it back in again. Our seasoned crew replaced those parts after another two hours and we were back in business. Unfortunately by the time the net went back in the water, the fish had scarpered. Another two hours later and the net was back on deck, fortunately it still contained a large amount of blue whiting. Interestingly, the size distribution of the individual fish was different from earlier hauls in that it consisted of a larger proportion of very small and large fish. The bycatch was dominated by almost 400 kg of hake and a lot of large argentines with a small number of mackerel, horse mackerel and gurnards. There were also some barracudinas, hatchet fish and of course, lanternfish.

Dirk with a sample of blue whiting

Finally, there's work to be done in the fish lab

A large hake (Merluccius merluccius) eyeing the camera

Grey gurnard (Eutrigla gurnardus)

Mackerel (Scomber scombrus) and horse mackerel (Trachurus trachurus)

We have just started our final transect for this year and will hopefully fish again for Blue whiting this evening. Tomorrow we hope to do a deep sea trawl (around 1000 metres depth) as our last task for this year in the North Atlantic. If all goes to plan, we’ll have another super post presenting you the fishes of the deep sea, so stay tuned.

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.