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Royal tagging
When the presidental couple Guðni Jóhannesson og Eliza Reid had tagged a mackerel each, king Harald was in line. The king received skilled help from Jostein Røttingen (to the left) and Eilert Hermansen from the Institute of Marine Research. When the visitors had left, the three mackerels were let back into the sea.    
Photo: Erlend Astad Lorentzen
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King and president joined mackerel-dugnad

Since 2011, over 250,000 mackerels have been electronically tagged and released back into the sea. On Thursday King Harald of Norway and the Icelandic presidential couple sent out another three mackerels to collect data in the name of research.

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.

Presidental tagging

The President of Iceland Guðni Jóhannesson didn't hesitate when he was invited to tag a mackerel. He joked, and said it was a real pleasure to finally fish in Norwegian waters.   

Photo: Erlen Astad Lorentzen

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.

Advanced mathematics

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.


Mark and recapture using RFID tags:

• RFID stands for Radio-Frequency IDentification.
• 253,635 mackerels have been tagged since the start of the project in 2011 – on average 42,272 mackerels each year.
• The record is 6,447 mackerels in a day.
• 300,000 tonnes of mackerel are scanned each year at fish landing facilities using RFID readers.
• There are eight of these facilities along the Norwegian coast and nine in other countries, including one in the Faroe Islands, four in Scotland and three in Iceland.
• Data from the tag is collected and automatically saved to a database at the Institute of Marine Research.
• The RFID tag includes the year, experiment number, release number, date, time, position, weather conditions, quantity of northern gannet, fish length and name of the person who tagged the mackerel.
• The information about the tagged fish that are scanned and recaptured is used help calculate the size of the mackerel population.