Onderbreking in Aberdeen langer dan verwacht/Break in Aberdeen longer than anticipated

Op zaterdagmorgen 10:00 NL tijd zijn we binnengelopen in de haven van Aberdeen. On Saturday morning 10:00 Dutch time, we arrived in the port of Aberdeen.

Helaas hebben we ernstige technische problemen gekregen in de nacht van zondag 10 op maandag 11 juni, waardoor we anderhalve dag extra in de haven van Aberdeen zijn gebleven. Er zijn technici ingevlogen om de schade te repareren. Unfortunately in the night from Sunday 10 to Monday 11 July, Tridens suffered from some serious technical problems which caused us to stay another one and a half day in port. Technicians have been flying in on Sunday to solve the trouble.

Inmiddels is de schade herstelt en we nu (14:00 NL tijd) de haven. Meanwhile the damage has been repaired and we presently leave port (14:00 Dutch time;12:00 UTC).

Bram heeft de tijd goed besteed, door visvoer te kopen voor de kleine makrelen in de schacht van de Drop Keel. Bram has spent his time well by buying fishfood for the little mackerels in the shaft of the Drop Keel.

En hier is de beloofde clip die Jan-Kees afgelopen vrijdag heeft gemaakt. And here is the promised clip Jan-Kees made last Friday.

Inside the herring catch by keebock


Bij het verlaten van de haven van Aberdeen, komen we een groepje dolfijnen (tuimelaars) tegen. During departure from the port of Aberdeen there is an encounter with a group of bottlenosed dolphins.

In and out of herring, east of Scotland

Sinds gisteren komen we veel haring tegen op de transecten 57.51N en 57.36N. Alleen in het uiterste westen en in het uiterste oosten van deze raaien zien we geen haring. Hierdoor varen we elke dag "in en uit" de haring. Since yesterday we encounter a lot of herring on the transects 57.51N en 51.36N. Only in the western and eastern outer ends there is no herring. Hence we sail every day "in and out" of the herring.

Veel mensen denken dat haring altijd in dichte grote scholen voorkomt, maar dat is niet altijd zo. De echogrammen van de scholen waarop we de afgelopen twee dagen hebben gevist, laten dat mooi zien. A lot of people think that herring always presents itself in large, dense schools, but that is certainly not always true. The echograms belonging to the schools we fished, are nice examples.

Haul 5, 7-7-2016, 57.51N-0.19W, 800kg herring 21.5 - 29cm

Haul 6, 7-7-2016, 57.51N-0.23E, 11 ton herring 21.5 – 29cm

Haul 7, 8-7-2016, 57.36N-0.28E, 3800 kg herring, 21.5 – 31cm

Haul 8, 8-7-2016, 57.36N-0.20W, 1700 kg herring, 22 – 30cm

Soms gaat het om kleine schooltjes stijf op de bodem, dan weer zijn het kleine schooltjes in een laag boven de bodem en in trek 7 zie je de welbekende, zogenaamde haringpalen. De scholen van trek 7 zitten de hoog in de waterkolom, maar je kunt ze ook op de grond tegenkomen. Sometimes its small schools attached to the bottom, but you may see also small schools as a layer above the bottom. In haul 7 you can see the well-known so called herring pillars. In this case they are in the water column, but you can also find them glued to the bottom.

De vangsten tot nu toe tijdens deze reis, bestonden vrijwel geheel uit haring, met in trek 5 en 8 ongeveer 10% makreel. Toch zitten er altijd een paar verdwaalde vissen van andere soorten tussen. Catches so far this trip, completely consisted of herring with in haul 5 and 8 approximately 10% mackerel. However, in every haul you can find some lost specimens of other species.

Dit vonden we in de trek van vanmiddag (trek 8):

This is what we found in the haul we made this afternoon (haul 8):

Links een paar heel jonge schelvisjes, rechts kever. To the left a few very young haddocks, to the right Norway pout.

Grauwe poon, een soort die eruit ziet alsof hij altijd op de bodem leeft, maar wij komen hem vaak tegen in de waterkolom (pelagisch). Grey gurnard, a species that looks as if it lives alwyas at the bottom, but we see it often in pelagic hauls.

Een wat grotere schelvis, die zwarte vlek wordt wel de "Petrusgreep" genoemd. A bigger haddock. Note the black spot.

Een wijting, een andere kabeljauwachtige, net als kever en schelvis. Whiting, this is another gadoid, just like Norway pout and haddock.

Een kleine zilversmelt (Argentina sphyraena), een kleine zalmachtige die normaalgesproken in dieper water wordt aangetroffen. Argentine (Argentina sphyraena), a small salmoid that is normally found in deeper water.

…en dit zijn de vier manden makreel uit trek 8. … and these are the four baskets of mackerel from haul 8.

Dit is Jan-Kees die een opname met zijn GoPro maakt van haring die vanuit het net in de last valt. De link naar de clip houden jullie nog tegoed! This is Jan-Kees, who makes a recording of herring that falls out of the codend into the hold. The link to his clip follows in a later blog!

otolith pictures





Yesterday 6th July, on our second transect going south, we came across some more herring aggregations stretching for several miles along the seabed. The resulting catch revealed just short of 10 tons of clean herring (22-31 cm).

The schools were scattered all over the seabed, as can be seen on the 3D image from the multibeam data:

after trawl action, it was also possible to collect some broadband acoustic data of these schools using the EK80 echosounder:

During the survey this year we attempt to discriminate the herring by spawning component. The North Sea herring population can be divided into 4 distinct spawning components that use different spawning grounds from the Shetland Islands down to the English Channel (see map giving the different North Sea herring spawning grounds in red).

Those components spawning in the Channel do so in winter and therefore can be identified by the shape of their otoliths, which are distinctly different from the other components. Here a selection of otolith pictures taken so far:

Later on in the night close to the Moray Firth, we encountered some impressive feeding aggregations on our inter-transect going over the trenches in the southeast. The water column was filled with different layers and schools of fish. It was decided to await the start of the next transect in the morning to take a trawl sample... some impressions of the situation:

In order to gain improved insights into what enters the net a GoPro with a custom made housing and 2 external light sources was put into the net. Below some impressions of what the resulting video looks like:

 

Inside the net

Surface herring

In the afternoon of July 5^th we encountered a couple more situations to take a trawl sample. Firstly there were distinct marks very high in the water column between 15-30m depth. Observing the trawl sonar during the targeted surface trawl suggested that nothing entered the net. However, the catch revealed nearly 2 tons of herring, measuring between 23-30 cm.

The echogram shows the surface marks in the upper section of the water column. 

 

 These marks were also nicely visible on the 3D image from the multibeam data:

 
Further towards the east on our northernmost transect, more marks started to appear along the seabed. The following catch consisted of several tons of clean herring:

Some impressions from the trawl activities and subsequent preparations of the first maatjes onboard this year…

 

 

 

Fish in the acoustic dead zone! – Vis boven de transducer!

Departure Monday 4 July at 11:45 UTC, a bit later than planned, due to in and out going traffic in  the port of Aberdeen. We lowered the drop keel with the acoustic equipment till 3.25 m below the vessel. The water enters via the gaps between the keel and the shaft and fills the space above the keel. We are looking from above in the shaft and see the upperside with all the cables disappear under a water layer of about 1.50m. To our surprise, we see fish swimming. Not big, approximately 10 – 15 cm. Where does it come from? Are these fish just swimming in and out of the shaft? In the harbour, when the vessel is at the quay? Or during sailing? That last option seems unlikely to us. It may be possible at night when the survey is interrupted though. Or are these fish prisoners in the shaft? If so, is there enough food? A lot of questions that have nothing to do with the goal of this research campaign. However, they may cause sleepless nights for fishermen and scientists on a research vessel.

Dirk and Sven do not hesitate and lower a camera in the shaft. There appears to be a school with tens of smal mackerel. They look lean. This may mean that this school is trapped. We decide to keep an eye on the shaft during the survey to check whether the same school stays there.

Let us focus on the survey now! This evening we start at 18:00 UTC at 58˚21N-2˚37W.

Vertrek maandag 4 juli om 13:45 NL tijd, iets later in verband met druk scheepsvaartverkeer in en uit de haven van Aberdeen. Drop keel laten zakken tot 3.25m. Het water komt via de kieren tussen de kiel en de schacht en vult de vrijgekomen ruimte boven de kiel op. We kijken vanaf de bovenkant van de schacht en zien de bovenkant met alle kabels onder verdwijnen onder een waterlaag van ongeveer 1.50m. Tot onze niet geringe verbazing, zien we vissen zwemmen. Niet groot, ongeveer tussen de 10 en 15 centimeter. Waar komen die vandaan? Zwemmen deze vissen gewoon in en uit de schacht? In de haven als het schip stilligt? Of tijdens het varen? Dat laatste lijkt ons onwaarschijnlijk. Het is wel voorstelbaar als we ‘s nachts stilliggen. Of zouden ze gevangen zitten in de schacht? Zou er dan wel genoeg eten zijn? Allemaal vragen die natuurlijk niets met ons eigenlijke onderzoek te maken hebben, maar die wetenschappers en vissers op een onderzoeksschip slapeloze nachten bezorgen als ze niet worden beantwoord!

Dirk en Sven aarzelen geen moment en laten een GoPro camera zakken. Het blijkt te gaan om een schooltje kleine makreeltjes. Ze zien er mager uit: zouden de ze dan toch gevangen zitten? We besluiten om in de loop van de survey nog een paar keer te kijken of hetzelfde schooltje er nog zit. Nu eerst concentreren op de survey, die vanavond om 20:00 start op 58˚21N – 2˚37W.

 

Small mackerel found above the drop keel 

Student from Wageningen University

My name is Alessandro, a master student from Wageningen University. I joined this research cruise last Sunday, in Aberdeen. The aim of my MSc project is real-time fish species and size specific discrimination using acoustic backscattering data, which can be quite challenging among species that show similar acoustic responses. In this respect, the new broadband echosounder EK80 uncovers new possibilities, as we become able to study the fish school’s frequency response (intensity of sound reflected at different frequencies) over the complete spectrum 17-460 kHz. To do so, we need clear and consistent data in order to calibrate and validate an identification algorithm in the next months.

When passing through several fish schools and observing a pure catch of a certain species in the net, it is quite reasonable to think that all the aggregations seen on the screen belong to the very one species. Likewise, it can happen to observe a broad variety of species within the same catch, as it happened on Tuesday, July 6^th fishing on several schools around 52 12 N; 00 34 W (Haul 9). 

The catch consisted of mixed Norway Pout, Mackerel, Haddock, Whiting, Grey Gurnard, and Herring, for a total of about one tonne. 

Diverse species on the conveyor belt (Mackerel, Haddock, Norway Pout, Grey Gurnard)

In these circumstances it becomes quite hard to successfully distinguish the different caught species on the echogram!

Which fish school belongs to Herring? Which one to Norway pout?

Thanks to the trawl camera we can attempt to track the history of the fishing session, connecting each school on the echogram to the related species observed with the camera.

A group of 13-16 cm Norway Pout entering the net at GMT 12:19:40 

A mix of Haddock and Whiting caught at GMT 12:30:25

Probable localisation of Norway Pout school after our reconstruction: to do this, we took into account the distance between the transducer and the trawl camera, along with the boat speed

However, for the best performance in species identification we hope for pure catches in the next days. Especially Norway Pout and Herring will be targeted, since it appears to be quite difficult to distinguish them acoustically.

In the meanwhile, I’m helping HendrikJan in sampling catches, taking measurements and collecting otoliths for the Herring survey, to get a more complete insight of the life on a research vessel!