Live pictures from Tridens!

For the Herring Acoustic Survey this year Daniel Benden connected a GPS and camera to a little raspberry pi computer and let it draw a live map and take a picture more or less every 15 minutes.
Sometimes the pictures get corrupted, due to the unstable internet connection. If this happens try again later.

Rear deck of the Tridens

Survey track

Raspberry Pi  with the camera taped to the window

 

young gadoids in the Moray Firth

On our second transect going back towards the west, we had another clean herring haul yesterday morning. The marks were continuous along the seabed: 

haul 4: 02/07/2014 @ 5:43 UTC (58º09'N 0º07'W)

Hendrik Jan starting to measure the catch

While progressing further west we approached the entry of the Moray Firth. Just after lunch, an interesting looking echogram presented itself to us. There were scattered schools spread throughout the water column. As similar looking echotraces turned out to be sprat in the past, we shot the net to verify that.

haul 5: 02/07/2014 @ 11:14 UTC (58º08'N 1º17'W)

The catch however consisted of young Norway pout and whiting.
Another similar looking scene could be seen this morning over one of the deep trenches in the south-eastern Moray Firth:

haul 6: 03/07/2014 @ 5:44 UTC (57º45'N 2º04'W)

The catch again contained young Norway pout and haddock:

We also examined the sound scattering properties of these species and compared them to the ones of herring. When looking at how strong the young gadoids reflect sound at the different acoustic frequencies used, one can see a distinct pattern, as indicated below.

example echogram of a school of young Norway Pout at 4 frequencies (38, 120, 200, and 333 kHz; top panel) and the corresponding typical frequency response (backscatter at a given frequency in relation to the backscatter at 38 kHz). It is evident that the reflection are progressively weaker (more blue colours) at higher frequencies.

example echogram of a herring school at 4 frequencies (38, 120, 200, and 333 kHz; top panel) and the corresponding typical frequency response (backscatter at a given frequency in relation to the backscatter at 38 kHz). The decrease in sound reflection at higher frequencies is less severe when compared to young Norway Pout.

the first hauls are in

Tridens has started the survey in the afternoon of Monday 30.06. after heading from Aberdeen to the start of the first transect in the northwestern part of our survey area. Below is a map with the transects we are going to cover this week.

On Tuesday we had our first three hauls containing predominantly herring. Find below the echograms of the situation just before the hauls and associated time/location information.

haul 1: 01/07/2014 @ 5:30 UTC (58º20'N 0º25'W)

haul 2: 01/07/2014 @ 12:00 UTC (58º20'N 0º46'E)

haul 3: 01/07/2014 @ 19:43 UTC (58º08'N 1º20'E)

The catches were several tonnes and herring were mostly between 25 and 30cm, with means around 27 & 28cm.

first herring samples

fish sorting at the belt after the catch has come in

average sized herring from the first haul

Hendrik Jan taking the catch samples

Daniel Gallagher from Ireland helping out during the survey to get some practical experience. Here he is preparing the otoliths (fish earbones) for age reading back in the institute

trays containing the preserved and fixed otoliths: one pair per sampled fish

start of HERAS 2014

Tridens left Scheveningen harbour on 23.06.2014 to head up north for the annual North Sea herring acoustic survey. The first week was dedicated to equipment calibration and the actual survey will take place over the following 3 weeks. Before departure, some shocking scenes were seen in Scheveningen however: the freezer trawler "Johanna Maria" was on fire! The emergency operations could be seen at very close distance.

 

Soon after, we were departing from Scheveningen, in rather nice weather conditions.

Arrival in Scapa Flow was on Tuesday night. The following couple of days were used for equipment calibration. For this, we need a sheltered location with 25-30m of water under the transducer of the echosounder.

Tridens at the calibration spot in Scapa Flow, Orkney Islands

The towed body used as a platform to house the transducers is being prepared for calibration

Dirk Burggraaf steering the tungsten carbide calibration spheres through the acoustic beams in order to calibrate the echosounder.

Sprat off Hartlepool and conclusion

Shortly after haul 21 this morning with the disappointing catch, we came across some nice clupeid pillars (= herring schools) off the coast near Hartlepool. We shot the net for haul 22 (54.47N - 0.46W) and managed to catch part of one off these schools.

During the trawl haul we made a full hit at a school. Hence the frequent "stickers" (Dutch: "stekers") in the meshes in front of the codend

The catch was one and a half ton of sprat (57%) and young herring (43%). The trawl sonar indicated that this mixed catch came from one school: apparently sprat and herring swim in mixed aggregations. This information is important for the interpretation of the echograms!

One and a half ton of sprat and herring in the hold of the vessel.

In conclusion we have had a very smooth and successful survey with extremely good weather and much  more herring in the Tridens-area compared to the previous five years. Our preliminary conclusion of this survey is that there is more herring in the area we covered. This does not mean that there is more herring overall in the North Sea. It may indicate that the distribution of herring in the North Sea was different. At home - IMARES in IJmuiden - we will analyse our data. Next January, during an ICES Working Group meeting we will combine our data with those of the other participating countries in this survey in order to make a combined estimate of the abundance and distribution of herring (and sprat) in numbers and biomass.
The last version of the bubble plot showing the acoustic density of herring (up until yesterday evening) can be seen below:

Porbeagle!

Yesterday - another beautiful day - in the morning (6:30 UTC) we shot the net at 55.25N - 1.28E for a few comparatively large schools in an otherwise empty area (haul 19). The schools were not easy to catch but eventually we hit one. When the net was being hauled something big seemed to stick in the codend.

The crew noticed something in the codend

It turned out to be a large specimen of a porbeagle (in Dutch "Haringhaai"). She (yes, it was a she!) was still very much alive and the crew released her as carefully as possible - not easy with a fighting shark of this size!

We estimated the length of the porbeagle at 2.80m!

Apart from this one large predator the catch consisted of 1.3 ton of young herring (Dutch: "toters") , length range17.5 to 22cm.

Also in the catch: squid (Loligo forbesi)

...and two lumpsuckers!

In the evening, we encountered a lot of small schools at the bottom. They were really difficult to catch. In the end, after one and a half hours trying, we hauled the net for a few baskets of young herring (similar to the herring in the haul in the morning) scattered with some adult specimens (haul 20, 54.24N - 0.20E).

Small schools at the bottom (haul 20)

Cannot wait to join spawning: One male specimen of 20.5cm has already a ripening gonad!

This morning, wednesday 17 july, the net is shot at 54.55N - 0.36W for what we judge to be herring that not yet is grouped into schools. The idea is to fish them now instead of waiting till they lump together: schooling herring is more difficult to fish (haul21).

Scattered swimming herring(?) in haul 21.

The catch is very disappointing: 7 specimens of sprat and one whiting...

BBQ and the blues upon the river Tyne

Saturday 13 July, 13:30, we finished the second of the two longest transects of this survey and headed for a stop in Newcastle. While we sail upon the river Tyne towards Newcastle, we meet an old acquaintance: "our" own ferry which we see daily in IJmuiden where our department of IMARES is located.

The DFDS ferry Newcastle - IJmuiden

Kittiwakes in Newcastle build their nests in windows, on bridges, roofs etc. During our stay, we can hear them all the time. The sound these birds make is supposed to be "kittiwake", but I am not sure whether everyone agrees on this.

Nests of Kittiwakes in the ridges of these factory buildings.

Saturday evening part of the scientific crew went to the pub, studying local ales, stout and cider brands: research is deeply settled in our genes! In the pub we met Tim and Jenny from Birmingham and Newcastle respectively (Tim is Dutch!). Immediately they were invited for our barbeque the next day. Fortunately the weather was beautiful!!!

From left to right: Arie (engineer), Dirk (our man from Havana), Sascha, Jenny and Tim

Overview of the barbeque on the front deck of Tridens.

 After the BBQ we went to the Tyne bar, where the yearly blues festival was going on.

The blues festival at the Tyne Bar was attended by some mysterious looking persons (sea uttermost to the right: Che Guevara??)

 Newcastle is relatively bike-friendly. Like in the Netherlands there are special parking lots for bikes. The difference with the Netherlands is that in Britain, a special P-sign with a bike-icon is required in order to let people know what these steel things are meant for!

Parking spot for bikes.

The Lyndon Anderson Band at the Tyne's bar blues festival.

 O yes, fisheries research: Monday morning we left Newcastle to start on the 55.25 N transect in eastern direction. Just east of the Farn Deeps, we shot the net for these interesting mark on the echogram. They were much stronger on the higher freqencies than on the 38 kHz, indicating that this may be something without a swimbladder. The catch revealed large quantities of Northern Krill (Meganyctiphanes norvegicus), some whiting, on specimen of sprat and some very small (2-4cm) norway pout and cod.

 

Northern Krill (Meganyctiphanes norvegicus) and whiting.

Northern Krill is an important food species for a lot of fish species, birds and cetaceans.

Meanwhile on board, in our hydro acoustic room a butterfly was caught in the light of the window. As we are working on our ecological profile continuously, we looked up the species and made a record here: Ringlet (Aphantopus hyperantus), in Dutch "Koevinkje".

Ringlet or (in Dutch) "Koevinkje"

Tomorrow we hope to encounter again some herring.