The Eye of the Survey...

Greetings to all family members, friends and colleagues from our temporary home here aboard the RV Tridens, currently on transect on the Rockall Plateau, which is separated from the European shelf by the more than 2000 metres deep Rockall Trough. This is the furthest we have been out into the Atlantic so far.

 

Rockall itself is a small granite islet (the remains of an extinguished volcano) of less than 800 m², home to gannets and guillemots during the breeding season. International legal arguments concerning overlapping claims on the surrounding shelf have dragged on for decades due to its fish stock, gas, oil and mineral reserves. It was claimed by the United Kingdom in 1955. 

 

So far on this transect, we have not found aggregations of fish that are either of significant size, nor are they at the correct depth for blue whiting. They were more consistent with shoals of pearlsides and mackerel. On the previous transect, the last patch of blue whiting we saw had already been sampled by the other ships on the survey, so we let it be. There was a 12 hour crossing between this and the last transect, so consequently, we haven’t fished in a while.

 

The last one was taken yesterday from a depth of about 500 metres and consisted of mostly blue whiting. There was nothing new or surprising in the bycatch, barracudinas, hatchetfish, dragonfish, squids and yet more lanternfish. With the number of light producing lanternfish we’ve found, you’d wonder if the deep sea was dark at all. 

 

 

 

 

The sea has been spectacularly calm for the last few days as we made our way northwest and it allowed us to spend some time in the bird box on top of the bridge, watching out for seabirds and cetaceans or simply enjoying the sunshine. We saw a beautiful double rainbow that we of course GPSed. We’ll come back and look for the gold when we’ve finished the transect; science must come first. 

 

 

 

 

 

In the afternoon, we were treated to another one of Eric’s famous lectures on acoustics in fisheries. The last one was on the physics of sound waves, this one brought us closer to applying them to live, wild fish by learning about target strength and how it works in practice.

Yesterday we also did a fire drill. The alarm, even though we knew it was coming, startled us into action as we tunneled down corridors and jumbled down stairs to the recreation room, but one of our number was missing. Pre-practised routines were put into action. Four crewmen dressed in layer upon layer of fire fighting equipment, and went to look for the missing person. He came in moments later, propped up by three strong sailors, coughing convincingly. Our colleague (cough, cough, Kees, cough) was treated to a lie down and offered a stretcher, the latter he refused jovially. We can confirm that he had fully recovered by dinner time. 

 

The final part of the drill was “Abandon Ship“. Again, the shrill alarm rang out, and we all set out for our cabins to retrieve two items: a life jacket and survival suit. We then swiftly made our way to our designated life raft and tried on our safety equipment. The life jacket was straight forward enough, the survival suit was more of a challenge. Fortunately ships tend to sink slowly, so we should be fine. At least now we are prepared! 

 

The likelihood of finding fish out here on the Rockall Plateau so far looks slim, so we probably won’t be doing any more hauls for the moment, but we’ll keep you updated. The mild weather has allowed for continuous progress so we anticipate to soon be on our way back towards the continental shelf. We’re all in good spirits and ready for the next haul, whenever it may come!

 

The Good, the Bad and the Scaly...

Since the last post, we’ve been busy.  We’ve taken in seven more hauls of fish and completed our north-south transect.  We’re now further North just past Donegal, joining the other ships on the survey. 

Friday morning did indeed turn out to be stormy, but the presence of a large school of fish below the waves meant we needed to ride it out.  We finally succeeded in fishing that evening, which took us most of the night and following morning to sort.  A second trawl followed on Saturday afternoon, and a third that evening. 

Sunday we woke to the smell of fish.  The Easter Bunny had brought us a large school of blue whiting as you can see in the echogram:

We took in a second trawl just after lunch. 

Since starting our new transect, we’ve trawled twice more, bringing us up to a total of ten. 

The majority of our catch has been blue whiting.

When we take in a new haul of fish, we first sort the fish by species.  All the fish are counted, measured and weighed, but the most attention is given to the blue whiting.   Where we catch a lot of fish, we weigh everything, but take a sub-sample to measure.  For the whiting we also determine what stage of reproduction they are at, whether they’re juvenile, maturing, spawning or spent (released their eggs and sperm already).  Then we collect otoliths, bony structures in the inner ear of bony fishes that are involved in hearing, balance and orientation.  From a scientific standpoint these are used to determine the age of a fish.  As the fish ages, layers are added to the otoliths, similar to the rings in a tree.  It is important to know the age of the fish because when we combine the age and size of the individuals we caught with what we see on the echogram, we can estimate a population profile; how many juveniles there are, how many adults and most importantly, how many more juvenile fish will likely join the population next year.  This is essential to tell us how many fish can be caught without damaging the stock.  We also collect a tissue sample and store it for later genetic analysis by colleagues who determine the relationship between whiting caught in different seas, whether they interbreed, or if they are genetically isolated.  This is important for stock management, but more about that another day.

Anything that is not the target species (i.e. blue whiting) is called bycatch, and we’ve found some exciting things.  This angler fish hasn’t been found on this survey before. 

This was a live barbeled dragonfish (Melanostomias bartonbeani), which flipped around and gave us the stink-eye when we tried to sort it.

A welcome addition to our catch were these snipe eels, Nemichthys scolopaceus, with their long whippy tails and sharp pointed snout, they’re very distinctive.  The tail also possesses considerable grip when wrapped around an object as we found.

We also caught half of whatever this was.  Personally I’m hoping for giant squid, but the characteristics don’t quite match.  It was probably the remains of an octopus.  Whatever it was, it was huge.  Yes, that’s its eye.  

 

We also found this very handsome cephalopod, a jewelled squid (Histioteuthis spec.).

And to go with all the jellyfish we’ve found, a Cornish blackfish, Schedophilus medusophagus (it eats jellyfish).  

After blue whiting, the most numerous fish we’ve found are fishes of the family Myctophidae, which are small, torpedo shaped fishes with luminous spots – photophores.  They tend to be badly damaged by the trawl net, and all look quite similar.  Last we posted we had one species, now we’re up to about eight. 

Two hatchet fish (Argyropelecus spec.), one of which is typically less than 5 cm...

And some Sloane’s viper fish (Chauliodus sloani).  

These are attractively known as stareaters (Astronesthes spec.).  These possess a light-producing barbel which they bob around in front of their mouths, attracting prey into striking distance.  We have two species at present, those with red and black tipped barbels, and those with pink ones.  Certainly wouldn’t want to meet these down any dark alleys. 

 

We’re hoping to fish some more in the next few days, stay tuned.

  

Speaking of the Devil...

A few minutes after posting our first blog entry on Tuesday we observed a welcome sight on the echograms: a dense layer appeared in a depth of around 600 metres, hinting at the occurrence of a large school of Blue Whiting. With excitement we anticipated our first haul. The whole process of setting out the net, fishing through the school and hauling in the net usually takes more than two hours, but we were rewarded with a haul consisting of about 1.6 tons of Blue Whiting, accompanied by some myctophids (Notoscopelus kroyeri) and among others a really nice large flying squid (Todarodes sagittatus).

 A couple of Blue Whiting (Micromesistius poutassou) sorted by size

The myctophid catch, thankfully consisting of only one species this time (Notoscopelus kroyeri)

A nice specimen of Todarodes sagittatus

We followed that up with a second haul at a lesser depth of about 350 metres, catching another 1.5 tons of Blue Whiting with small amounts of bycatch (Argentina silus, hake, various squids).

 The afterdeck of RV Tridens at night during a haul with the pelagic trawl net

On Wednesday, we spent most of the time transitioning between transects north of the Porcupine Bank. The steady clouds of the previous days had given way to actual sunshine, and though there were a lot of white caps on the waves, the sea was rather calm. The weather took a turn for the worse over the course of the day, but it was nevertheless possible to work. In the afternoon, layers of fish were again visible on the echograms during the first north-south transect, so the net was set out. However, while trawling, the net scraped against the seafloor, causing a tear that would prove costly. When it was time to haul in the net, a system failure caused the two winches to operate asynchronously, resulting in a large part of the net getting ripped open completely.


So while the fish lab team was sorting the catch, the replacement trawl net was quickly prepared and tested to ensure that we wouldn’t miss any potential hauls. The species composition was somewhat different from the first two hauls due to getting so close to the seafloor. Although Blue Whiting (2.5 tons) still made up the majority of the catch, we also had about 550 kg of bycatch. A number of large hake (Merluccius merluccius), haddock (Melanogrammus aeglefinus), horse mackerel (Trachurus trachurus) and two yearclasses of mackerel (Scomber scombrus) accounted for most of that. 

 Buckets upon buckets of mackerel (Scomber scombrus)

 Heavy lifting for the fish lab team: Buckets of hake, haddock and mackerel

The rest of the day was spent with a cozy small whiskey tasting while we were steaming westwards towards our next transect.
Thursday brought us even more of the middling weather with a wind speed mostly around 30 knots. The reverbations of the ship hitting the waves can be problematic for the acoustic monitoring especially when heading against the swell, but we were mostly off transect. We started on offshore part of the closely spaced north-south transects in the early evening and are now hoping to find some fish again as we work our way back towards the shelf. Heavy weather is anticipated in the morning hours on Friday, but that won't dissuade us from enjoying the beauty of an evening at sea on the North Atlantic.

 The bow of RV Tridens hitting the waves