last few miles

The last week end of the survey was spent in Newcastle-upon-Tyne where the Tridens was docked upriver close to the city.

Tridens underway up the river Tyne towards Newcaslte

The final survey week will now cover the remaining transects in the southern part of the survey area covered by the Netherlands:

Soon after restarting again on the survey track, the net was shot at some aggregations below a dense plankton layer on the sea bed:

haul 17: 14/07/2014 @ 18:34 UTC (55º17'N 1º07'W)

The catch consisted of small herring, ranging between 16.5 and 23 cm. The same was true for the following trawl aimed at more dense individual schools further offshore:

haul 18: 15/07/2014 @ 07:29 UTC (55º17'N 0º27'W)

During these trawls, the GoPro camera was again installed in the net to monitor the capture process:

young herring entering the net during haul 18

monitoring of the capture process using a trawl sonar located on top of the net: the square shape represents the outline of the net which is towed just over the sea bed (seen as a straight pink line). One of the herring schools can be observed entering the trawl.

smaller herring of mean length 20 cm seen in the south of the survey area

Hendrik Jan and John sampling the catch

During the hauling process of trawl station 18, a new broadband echosounder was trialled to collect data on herring schools over a wide frequency band. The data will be used as part of a collaborative science-industry project aimed at improving fish species identification:

screenshot showing acoustic broadband backscatter data (95 - 160 kHz) of a herring school

On the 55º17'N transect, another test trawl aimed at mackerel just below the surface was done. Again, the catch after 30 minute trawling contained a few baskets of mackerel:

the caught mackerel ranged from 29-38 cm, mean length: 32 cm

Hendrik Jan as the centre of attention during the biological sampling process

Acoustic detections on the most recent transects showed mostly aggregations of smaller herring (black circles on the map below) with a few hot-spots with more dense schools. No more Norway pout (red circles on the map below) was seen towards the south of the survey area. However, in the survey area covered by Scotland, just north of us, increased amounts of young 0-group Norway pout were also observed.

Only a few more transects to go now before returning back to Scheveningen after a 4 week journey...

herring again

As we are progressing further south in our survey area, it becomes evident that we have left the biggest herring aggregations behind us. We are now at or beyond the southern border of the main distribution area and fish detections become more sparse and less dense. On Wednesday evening we encountered one of these aggregations consisting of, what seemed like, small herring schools along the seabed. We shot the net to take a sample.

haul 15: 09/07/2014 @ 16:14 UTC (56º19'N 0º04'W)

However, the result was again: Norway pout. They were again juveniles with mean lengths between 5-6 cm.

The weather also got increasingly worse and we were getting gale force 7 winds for a 24 hour period.

the wind was picking up

During the night, while standing still for the few hours of darkness when we are not surveying, the winds were unleashing their damaging forces. Unfortunately, our towed body, which is housing our echosounder transducers and is pulled along the side of the ship on a cable, did take quite a beating. In the morning it was evident that the towing cable got torn and the towed body was just hanging on the transducer cables and a Dyneema rope. Every wave was smashing it into the side of the ship. The result was some bent metal and even fractures in the structure. The morning was therefore spent exchanging damaged parts with those of the spare towed body that we are carrying on board, in order to make it survey-fit again.

bent wing of the towed body

despite the bad weather during repairs the spirits were still high!

new stabilising weights were attached to the towed body and welded to the old frame

after a few hours spent for repair work, the towed body was put in the water again and the survey continued

Soon afterwards we were passing the Devil's Holes to the south and came across some impressive marks. The net was again shot to get a sample of the fish.

haul 16: 10/07/2014 @ 10:01 UTC (56º17'N 1º45'E)

the trawl being deployed

The resulting catch contained (finally again) a few tonnes of herring:

the catch contained herring with a wide size distribution, ranging from 21-29cm

herring sample on the conveyor belt

We are now approaching our final survey week and can probably expect a few sprat catches in the southern part of the North Sea.

more Norway pout and mackerel test trawls

The start of the second survey week saw a continuation of the Norway pout observations seen in the previous week already. On the western side of the 5th transect, the net was shot at some marks on the sea bed:

haul 11: 07/07/2014 @ 13:08 UTC (57º18'N 0º29'W)

The catch consisted predominantly of Norway pout, with a few sandeel. The pout was now a bit bigger than in the previous catches.

catch of Norway pout

The observed distributions of Norway pout are mainly located in the western part of the Dutch survey area. So far we have seen them on every transect. Below you can see a map showing the acoustic densities of Norway pout (red circles) and herring (black circles) recorded so far in the survey:

And the Norway pout story continued yesterday at the Devil's holes, when another haul targeted at some larger aggregations revealed a catch dominated by that species:

haul 14: 08/07/2014 @ 13:48 UTC (56º47'N 0º12'E)

Yesterday morning, we were accompanied by a school of white-beaked dolphin (Lagenorhynchus albirostris). There were about 10-20 of them hunting fish in the distance. But 3 of them started to swim along the ship right next to our towed body for a while:

During the survey we also perform a number of test trawls close to the surface to fish for mackerel. Atlantic mackerel are now distributed in surface waters over a vast area stretching from Greenland, to Icelandic waters, and throughout the Norwegian Sea. A dedicated survey conducted by Norway, Iceland and the Faeroe Islands is trying to map the distribution and abundance of mackerel. However, the waters around Britain, Ireland and the North Sea have not been sampled a lot so far. We therefore try to take a few samples in our survey area.

During these surface trawls the net camera was again in action. So far, we have taken two such trawls (each with a standard towing time of 30 minutes), which both caught a few baskets of mackerel:

Hendrik Jan measuring the mackerel catch

mackerel samples coming in over the conveyor belt

the catch contained mackerel with lengths between 28cm and 33cm. The mean length was 30cm.

Images from the trawl camera video showing mackerel entering the trawl during the test surface trawl stations:

first survey week & net camera trials

Towards the end of the first survey week, another 4 hauls were done on the transects going east out of the Moray Firth and back west again towards north east Scotland. Just east of the Halibut Bank, some further herring aggregations were encountered as seen on the echograms just before the different trawl stations:

haul 7: 03/07/2014 @ 14:26 UTC (57º52'N 0º09'E)

haul 8: 03/07/2014 @ 18:45 UTC (57º52'N 0º52'E)

haul 9: 04/07/2014 @ 09:10 UTC (57º40'N 0º28'E)

 These aggregations stretched out continuously along the seabed for several miles

The catches gave again a few tonnes of herring:

Being a bit more south in our survey area, the herring were now a few cm smaller than the previous samples caught further north. Mean lengths were around 25cm:

 

sampling a catch of herring

When entering the shallower waters of the Halibut Bank again on the southern transect going west, we saw some marks again over several miles. These stretched even further west towards the coast. The echograms below give an indication of the situation seen just before and after haul 10:

haul 10: 04/07/2014 @ 14:20 UTC (57º40'N 0º12'W)

The catch turned out to consist of small Norway Pout. There is a lot of them around!!

towards the end of the week, the weather was picking up a bit

During the past few hauls we were trialling a GoPro camera in the net. The aim of this was to get a better picture of "what is entering the net at what depth and time". As the first trials were done without the light source, it was evident that the pictures below 60m depth were too dark. During the last haul, the camera and LED light source was placed within the trawl tunnel. The pictures showed the stream of young Norway Pout continuously entering the net. However, there were also a few mackerel present!:

this mackerel was swimming happily along within the trawl for several minutes! The individual small Norway Pout (~5cm) can only be seen as little light rays shooting through the picture.

The camera/light system will now be tested during herring trawls this week. More to come!

The following bubble plot gives an indication of the distribution and densities of herring observed during the last week:

 

 This week, we will now be covering the following transects: