In conjunction with the Icelandic state visit to Norway, King Harald, the President of Iceland Guðni Jóhannesson and his wife Eliza Reid were shown how mackerel are given an RFID tag at the Norwegian Ocean Laboratory at Marineholmen. See more photos from the visit here.
The “old” way of estimating fish populations
RFID stands for Radio-Frequency IDentification. The mark and recapture method with RFID technology was developed by the Institute of Marine Research and has been in use since 2011. As of this year, data from these time series are being included in the population estimates that inform the quota advice for the mackerel stock.
– The mark and recapture method is often considered a way of measuring migration, rather than populations, but actually it is one of the oldest techniques used to estimate populations. In the past steel tags were used, which had to be taken off the fish. Now the fish pass under an RFID reader which collects data from the tags and automatically transfers it to a database at the Institute of Marine Research, explains Aril Slotte, who heads the Institute of Marine Research’s pelagic fish research group, and has played a key role in developing the RFID methodology.
It isn’t easy to explain the advanced calculations involved in estimating populations for the purpose of quota advice. The data from the RFID tags also needs adjusting before it can be included in the calculations.
– We assume that after an initial mortality rate caused by the tagging, the fish that have been tagged survive just as well as untagged fish. Basically, that means we can use the number of fish tagged, scanned and recaptured to estimate the size of the population in the release year, explains Aril Slotte.
In a better position to provide advice
The mackerel occupies a key ecological niche in various parts of the North-east Atlantic, both along the coast and out at sea, and financially it is considered the most valuable stock in the Atlantic Ocean. Previously, the data and advice relating to mackerel stocks was described as deficient. In recent years, Norway in particular has put a lot of effort into major research projects and the development of new methods that will improve our population estimates. As well as the mark and recapture method, the Institute of Marine Research has spearheaded the development of a trawl index for the Norwegian Sea, working with scientists from Iceland and the Faroe Islands.
– Now that both of these data series have been included in our population estimates, we are in a better position to estimate the population and provide sustainable advice on mackerel. The methods and technology that we have developed may also be of interest to other countries and other fish stocks. For example, we have now started tagging Norwegian spring-spawning herring, says Aril Slotte.