Tarajoq for Walther Herwig III, Cruise 488

Time on board passes quickly and we are now almost at the end of the first leg of the survey. Only a few transects to go and we will have covered the dedicated survey area for the first time. So far, we have carried out 71 plankton stations with the “Nackthai” and four fishing hauls.

Working on board with the Greenlandic and Faroese crew goes well and is very pleasant. The working atmosphere is professional, but always friendly and relaxed, which makes it easier to overcome any language barriers. A handwritten language guide on the whiteboard in the mess also helps. The food is good and the chef sometimes serves Greenlandic cuisine - lots of fish and we already had some reindeer. Fitness is taken care of by Martin, the first officer, who organises a fitness session at 9 PM in the evening, which takes place on the bridge or, in good weather, on the foredeck. A fitness room with lots of equipment and weights provides further opportunities to keep fit.

We sort out the fish eggs from the plankton samples on board and identify them. To make sorting easier, we use the so-called “spray method”. This involves transferring the sample into a tall container with a drain. Air is then injected into the liquid containing the sample using a fine water nozzle. This has the effect that fine air bubbles adhere to all extremities of the predominant crustaceans and fish larvae and these particles float to the top, while the smooth fish eggs sink to the bottom and can be drained. If this process is repeated, the fish eggs can be completely separated from the remaining sample.

Once the eggs have been separated, the actual sorting and identification work begins. In a first step, the eggs are sorted according to a simple characteristic: Is one (or more) oil globules visible inside them or not? Some species, including mackerel and horse mackerel, form oil globules in the egg, which are thought to serve as a floating aid. 

Let's take a closer look at the eggs with oil globules. As mackerel and horse mackerel eggs only have one oil globule and no other special characteristics, eggs with several oil globules or a visible stratification of the egg shell can be sorted out immediately. Other characteristics are, for example, the pigmentation of the egg shell, of the oil globule or the emerging larva. However, the primary identification feature of the similar-looking mackerel and horse mackerel eggs is the egg and oil globule diameter as well as the ratio of these two measured values to each other.

The final step is to determine the developmental stage of the mackerel and horse mackerel eggs. This is necessary because only the early stages of development are included in the calculation of egg production. Only after this step a sample is fully processed.

The initial results show that mackerel spawning has begun. While our Irish and Spanish colleagues, who were in the area before us, had not yet found any or only a few mackerel eggs, we can already clearly see a few hotspots along the continental slope at the 200 m depth line. Horse mackerel is later and there are only a few spots with freshly spawned eggs. We will have a closer look how the spawning activity develops during the next part of our survey.

After a short break in Brest we have already started the second leg of our cruise. On the evening of 10 April, we began to cover the area once again heading north from our southernmost transect. We are using routinely the “Nackthai” to collect mackerel and horse mackerel eggs. Up to now, shortly before Easter, we have done 128 plankton hauls and sorted more than 10,000 fish eggs out of the samples.

When we are in the right area where we can expect to catch adult mackerel, we set the fishing net. We are doing that because we also need information about how fertile mackerel are, i.e., how many eggs an average female produces, in order to be able to estimate the biomass of the adult mackerel, the so-called spawning stock biomass, from the egg production. For this purpose, we have carried out 8 fishing hauls to date.

Students from the Bremerhaven University of Applied Sciences and the University of Hamburg are also helping us with the work. Lizzy Draudt and Pauline Wagner describe their impressions of “Tarajoq“ here:

"On our first tour of the “Tarajoq“ on 24 March, we noticed two things: the beautiful photo prints that decorate all the chambers and corridors and the good atmosphere on board. When we want to try out the dartboard in the engine a few days later and ask for permission, the engineer says: ‘You can do anything here’ - and adds with a laugh - ‘almost!!!’. Of course, he wasn't being completely serious, but we felt very welcome here.
Communication during the work is a little bumpy due to the different languages spoken (Faroese, Greenlandic, English and German), but in the end everything has worked out so far. We now understand the announcement ‘Veer in 10 minutes’ in all languages and, thanks to the collective exchange of vocabulary on the notice board, ‘Good morning’ and ‘Cocoa and bread rolls at 7 pm’ are now also understood. We have cocoa and bread rolls every Sunday evening after singing a few Greenlandic and Danish songs together, and now also German, which is still a bit of a challenge.

"Tarajoq“ means “Sea salt” in Greenlandic. Our “Tarajoq“ is a ship with several uses, but it is mainly a fishing research vessel. A complicated conveyor belt system for sorting the catch, a fish tank with a lowerable floor and height-adjustable desks are just a few of the features that make working on board a pleasure. The fantastic crew also help us wherever they can, from taking samples to processing the catch. We have even learnt how to fillet fish.

In addition to the sports lessons already described, we often end the evening with card games and then wake up the next morning to a delicious breakfast, ready for the new day, on which we sort countless fish eggs from plankton samples or process the catch."

On Tuesday we successfully completed the sampling with the 184th “Nackthai” plankton haul. We covered the investigation area assigned to us twice, searching for and finding mackerel and horse mackerel eggs. In addition, we carried out 12 fishing hauls and obtained samples for the fecundity analysis of the adults. The spawning behaviour derived from this seems to indicate a smaller mackerel population for our survey than in previous years. However, we will only be able to finalise this once the results of all participating nations are available in summer 2025 and the results are incorporated into the stock assessments.

The work on the ‘Tarajoq’ with the active support of the Greenlandic and Faroese crew went really well. A big thank you to them. We all really enjoyed the friendly working atmosphere on board the ‘Tarajoq’. Many thanks also to the scientific crew, who never let up, even in adverse weather conditions, and were eagerly involved right up to the last haul.

The next survey will take place in 2028 – farewell until then!

Jens Ulleweit (chief scientist)