It begins: Blue Whiting Survey 2015

Unfortunately I was unable to upload yesterday’s blog, so here it is today:

Yesterday (Monday 23^rd March) we departed sunny Galway harbour and headed towards the first destination on our newly appointed cruise track. ‘New’ because of a last minute swap with the Russian vessel, ‘Fridtjof Nansen’ due to some issues over their entry into British waters. The seas have been rougher than expected during Monday evening/night which meant we arrived at the first transect several hours later than expected. 

New cruise track for the Tridens.

To our destination.

Despite being well prepared and having done a good calibration of (most) transducers during the test weeks prior to the survey, bad weather has meant large(ish) waves have been continually crashing onto the bow of the Tridens, which resonate sound through the hull. This sound is easily picked up by the echosounders. When you stand in the drop keel room you can hear large crashes and bangs - these are seen as hard spikes on the echograms. We tried a few tricks to hopefully reduce the interference; including a range of speeds and depths to which the drop keel was lowered, unfortunately these made little difference. Lowering the bow of the ship did however reduce the interference slightly. 

Teething problems. Newly installed drop keel aboard the Tridens.

Scientists sharing concerns.

Print screen of 38 kHz echosounder showing 'noise' caused by crashing waves on the bow of the Tridens.

All newly installed equipment is prone to teething problems and aboard the Tridens there is no exception. The main resolve will be to hope for better weather before we come across the main aggregations of fish further along the cruise track (fingers crossed!).

First blue whiting, "good" weather and lost satellite

For the past days we couldn’t get our satellite connection to work properly, hence we did not have internet nor phone working on the vessel.

Luckily we managed to get it up and running again now and we are able to communicate with the outside world.

Since the last post the weather improved dramatically and we are now under the influence of a high, which leaves us “mild” North-eastern wind of “only” force 4-5.

During my last post I claimed that we would be calibrating in the Galway Bay prior to moving towards the beginning of the cruise track. Unfortunately, given the very rough weather conditions and the influence of a rather strong underwater current, we didn’t stand the slightest chance of executing a successful calibration, and gave up after a short period of time. As a consequence, we decided that during each CTD (app.  every 60 nm (~ 6 hours steaming)) we are going to check the functioning of the cables connecting the GPTs (General purpose transceivers) with the transducers on the towed body. If an error occurs, at least we might be able to point out exactly where and when troubles happened and could jump into action. At 5.15 (GMT) the next morning, we arrived at the beginning of our transect and started recording acoustic information.

First blue whiting 

Approaching the shelf and the Porcupine Bank, the first blue whiting marks kept showing up and we were able to see some trawlers on the radar. On Wednesday in the early morning we finally saw the first “real” blue whiting school.  The catch revealed it to be a pure blue whiting school (containing one hake, one mesopelagic shark (dogfish) and 5 mesopelagic species . The catch was dominated by 3-4 year old blue whiting. 

First haul

Second haul

Later on, while moving from Porcupine Bank down into deeper waters, we hit the next school and went fishing once more. The catch was very similar to the first one, with very little mesopelagics and a dominance by relatively young blue whiting.

On the echogram below besides a blue whiting school and our fishing exercise, relatively large pearlside schools can be observed above the blue whiting school.  It is striking how one can distinguish different layers on this echogram. A top layer with probably some plankton, followed by the pearlsides layer, under which probalby a mix of pearlsides and zooplankton mixed with various other stuff can be found. A bit further down the mesopelagic, or deep sea layer starts, containing the blue whiting school. Often such layers are indicative for the presence of a change in environmental conditions, like a thermocline, different light conditions, etc..

Further a ghost bottom (a copy of the real bottom, which is located at a greater depth, not visible on our recordings), and the shelf edge are indicated. If such a ghost bo

  

Second haul

Third haul

Later in the evening we passed over a truly massive school of more than 45 nm in length. As we already took 2 hauls early that day we did not intend to fish on it, but suddenly a rather strange picture developed on the echogram. Unsure if it might be blue whiting spreading out, fish predating on blue whiting or just something completely different, we shot the net once more…But once more it was a clean blue whiting catch with a lot of very small blue whiting (probably 2-3 year olds).

On the echogram the length and height are indicated. It should be noted that the start of this echogram coincides with the end of the echogram from haul 2. Hence bleu whiting was visible from the moment we went down the shelf, until we went it back up again.

Haul 3

For the rest we are currently enjoying the rather nice weather after we got shaken a bit at the beginning of the survey and are all happy that internet and telephone are up an running again. For now we like to believe the weather forecast, which predicts calm weather until Monday…which I think we would deserve after the troublesome start of the survey.