The fish congregate, making it easier for fisheries biologist to go out to sea and survey the extent and size of these fish stocks. Therefore, for us fish biologists working with cod, saithe and haddock, winter is the season when it is easiest to survey the entire extent of the fish stocks.
This is why I currently find myself on board the RV Johan Hjort, IMR’s research vessel, at 76 degrees N in the Barents sea, one-and-a-half days steaming north of Nordkapp, the northernmost point on mainland Europe. Up here in 2-4 degrees C at depths typically of 250 m, we systematically survey the sea for fish using a bottom trawl that we tow for 15 minutes at preselected locations. After the survey is finished, we and two other vessels (one of them Russian) will have surveyed over 1,5 million square kilometers of the Barents sea, sampling fish at over 350 trawl stations. Measurements of the temperature and salinity of the sea water, as well as acoustic measurements of fish in the water column (using an advanced version of a fish-finder), will together with the trawl catches be used by my colleagues in the assessment of the sizes of the various fish stocks. This in turn is the basis for projecting how much fish there will be in the sea next year, and hence setting a sustainable quota for the various fisheries in the Barents Sea.
So the winter survey in the Barents Sea is the best survey to measure how much fish there is, making it tremendously important for the multi-million-dollar fisheries operating here. The fishing-boats operating in these waters mainly come from Russia and Norway who share the Barents Sea 50-50, but there is also a small quota to third-party EU countries. Therefore, our scientific surveys here are of great importance to the fishing-sector of several countries, and all of us who are on the RV Johan Hjort and the other research vessels feel that responsibility and strive to deliver.
Much has changed on the survey since the last millennium
This time I am participating in the survey as an experienced scientist in the role as scientific cruise leader. But I've participated before, back in 1999 when I was an inexperienced student looking for a job. The last time I was on the winter survey I was working in the fish lab, sorting and measuring fish.Much has changed since then, although the reasons for carrying out the survey remain essentially the same. In the '90s we didn't have a permanent satellite uplink, which we have now - and allows me (among other things) to make blog-posts and tweet. Back in 1998 there was no data transfer, and if you needed to contact the mainland, a satellite phone charging $5 per hour was your only option. Also, there was not TV or radio, so in the evenings we all got together and played games or talked, now we mostly spend our free time watching TV or surfing the net... Back in 1999 we still used paper and pencil for recording our measurements. All fish were measured manually and their lengths tallied on a sheet of paper which was later entered into a data-base. This was a time-consuming process prone to typos and errors. Today this task is computerized using electronic length-measuring boards and scales connected to a computer that records the data automatically, quickly and without typos.
New technology has definitely made the way we work in the fish lab more efficient, and the time that has been freed up is put to good use. While we in the '90s only had time to focus on the 8-10 commercially most important fish, lumping the rest of the catch in an 'other' group. Since the early 2000's we've classified, measured and recorded everything we get on deck. All the non-commercial fish and shrimps are classified to species, measured and weighed. While we in the previous millennium could get by with a limited taxonomic knowledge, now our technicians are highly trained in species identification of the 250 or so fish species that live in the Barents Sea. They are able to tell them apart based on minute differences in traits like the eye-size, size of the snout, or angle of spikes. This makes the data from the survey valuable in a wider context than just for stock assessment of the commercially most important species. Now we can get better insights into the ecology and species communities in the different regions of the Barents Sea. Such detailed fish data has allowed for our scientists to analyze how climate change has impacted the species distribution in the Barents Sea in the past decades.
The trawl-catches are central to the monitoring and stock assessment, but they only give us information on the fish species composition and density at the bottom in the exact location we were trawling. Using echo sounders that continuously send out sound pulses that reflect from plankton and fish in the water column, we are able to "see" what is below the research vessel at any given time. This allows us to interpret what species of fish and how much there are at various depths, and in the areas between the trawl stations. Interpreting the acoustic recordings requires skill and experience, where we rely on both the echo strength, form, location and depth to deduce what is the most species most likely "seen"