By Kathrine Michalsen
Flocks of grey geese fly southwards in the autumn along set routes. Wild reindeer, red deer and elk also often follow fixed paths. The migration routes of fish, on the other hand, remain a mystery. In the sea we are dependent on new technology to increase our knowledge about the distribution, migration patterns, geographic origin and natural behaviour of fish and marine mammals.
We want to find out why there are such large fluctuations in fisheries from one year to the next, and the reason for variations in fish distribution in time and space. In order to do so, we must obtain information about how environments change over time, and how fish react to changes in their environment.
Of course tagging also provides important information about local distribution, which can be used to look at the impact of oil installations and fish farms, as well as to map the activity of fish along the coast and in the open seas.
The Institute of Marine Research has just concluded a tagging experiment on cod off the coast of Finnmark. The tagging was done on board the “Bjarne Nilsen”, which is based in Hammerfest.
A green strip of plastic
By using a Danish seine to catch the cod, we managed to tag a large number of fish very quickly, and the quality/ survival rate of the fish was also good in comparison to the use of other fishing methods.
Over the course of two hectic days, we managed to measure, clip the fins of and tag almost 1500 cod. The fin clips will later be used to carry out genetic analyses, which in turn will tell us what type of cod the various individuals are.
The tags are green strips of plastic attached to the first dorsal fin of the cod. The tag includes a reference number and a contact address.
Questions relating to the migration patterns, geographic origin, distribution changes and component populations of cod stocks can be answered by performing tagging experiments. Combining tagging, genetic identification methods and the more traditional analyses of the ear bone of fish will allow us to obtain new knowledge about cod and their migration patterns at a time when the environmental conditions in the sea are constantly changing.
This is part of a joint project with Russian scientists, and will help to map the distribution and migration of adult cod over the course of the year.
Recently questions have been raised about the migration patterns, geographic origins, distribution changes and component populations of cod stocks. To find out more about whether there is migration between cod populations, whether fish spend time under the ice and in deep-water channels, whether they return back to specific fjords and so on, the Institute of Marine Research is tagging cod in several places along the Norwegian coast.
The big three
Cod were also tagged in the same area last year. This year a number of large individuals were tagged. Over 140 individuals were over one metre long, and 20 fish were longer than 120 cm. The three largest individuals were over 130 cm long. We named the three of them after famous women who have made an important contribution to life at sea and Finnmark in general. They were named after women because the largest cod are females, capable of spawning over 15 million eggs each. Thus Helga (Pedersen), Oddrun (Petersen) and Hanna (Kvannmo) are helping to produce the cod generations of the future (with a small green tag on their backs).
Tell us if you re-catch them
However, the success of this tagging experiment is completely dependent on everyone who catches a tagged fish sending the tag to the Institute of Marine Research, along with the otholits of the fish and information about its sex and where it was caught.
It is very important for us to get information about all of the tagged cod that are caught. For each fish we would like information about where (position and depth) and when (the date) it was caught. We would also appreciate being told the length of the fish to the nearest centimetre and its sex. It would be great if people also send us the otholits.
To thank them for their assistance, everyone who sends in a tag will receive a finder’s reward (scratch cards and various information about current research projects).
If you catch a tagged cod, please contact:
Postboks 1870 Nordnes