Why tag cod with Data Storage Tags?

Conventional tagging with inert plastic tags is used to gather information on the growth rates, distribution, abundance, and migration patterns of cod populations in studies all over the world. However, conventional tags only give information about the behaviour of the fish at two points in time (release and recapture) and can be misleading. Electronic tags that can measure environmental variables such as depth and pressure vastly increase the amount of information about cod behaviour such as migration mechanisms, spawning patterns and feeding behaviour. It also helps to predict the effect of changes in the environment, such as global warming. Since 1995 about two thousand cod have been tagged with electronic Data Storage Tags and released by researchers working in Iceland, the Faeroes, Norway, Scotland and England.

How are cod tagged?

Electronic tags can be placed internally or externally. For internal placement, cod are anaesthetised and tags are surgically inserted into their bellies. Small 'flag' or 'Howitt' tags are placed behind the dorsal fin of each internally tagged cod to indicate that there is a tag inside. External tagging is used less, and involves attaching the DST by means of sutures to the dorsal musculature of each fish. All tagging is undertaken by fully trained and certified personnel who operate under strict national Governmental regulations concerning animal welfare.

Are all tags the same?

A number of different types of electronic tag will be used to study cod tagged within the CODYSSEY project. The type of tag used depends on the type of environment the fish are caught and released in, and the requirements of the particular tagging experiment. Each tag is uniquely numbered and carries a return address for returning the tag. When the fish is recaptured, often months or years later, and the tag is returned to the release lab, scientists can look up the tag number in the tagging database. This allows the scientist to determine when and where it was tagged and what length the fish was when it was tagged.

If fishers provide other details such as fish length and location of capture, growth rates and movement patterns can be determined. If the ear stones (otoliths) of the fish can also be returned, scientists can age the fish, determine seasonal growth rates and reconstruct the life of the fish even more accurately.

What do I do if I find a cod with a tag in it?

Try to get as much information as you can about where and when the fish was captured, its length, what sort of condition it was in, and any other information that you think is important (e.g. maybe the fish's gut contents). It is very important to do this as soon as possible after capture because if you wait too long, you may forget some of the details. Typically we would like to know the following information:

Date of capture (year, month and day)
Location (either Latitude and Longitude, or a general description)
Gear type used, including mesh size for gill net
Length of fish (from tip of snout to fork of tail)
Condition of fish
Depth fished

It is very important that you do not guess about some of the recapture information. If you do not know the details leave them blank; you will still receive the reward.

Ideally, we'd like to receive the fish and tag together, plus the information about the capture, rather than just the tag and the capture information. The best way to do this is by dealing with your local fisheries office. You will be paid a generous market value for the fish, in addition to the reward for the tag return. If you'd prefer to keep the fish to sell yourself, then please consider sending us (either direct or through your local fisheries office) the ear-stones (otoliths) if possible.

The addresses for tag returns are as follows:

CEFAS, Pakefield Road, Lowestoft, SUFFOLK, NR33 0HT, UK

Institute of Marine Research, P.O. Box 1870 Nordnes, Norway

DIFRES, Charlottenlund Castle, DK-2920 Charlottenlund

FRS Marine Laboratory, PO Box 101, Victoria Road, Aberdeen, Scotland, UK

Marine Research Institute, Skulagata 4, P.O. BOX 1390, 121 Reykjavik,Iceland IS.

Fiskirannsóknarstovan, PO Box 3051, Nóatún, Tórshavn, Faroe Islands

National Board of Fisheries, Institute of Marine Research, Box 4, S-453 21, Lysekil, Sweden.

What will happen when I send back a tag?

Individuals who return a tag will receive a reward and information letter from the appropriate fisheries laboratory. The letter provides them with details about where and when the fish was tagged, the recapture information provided by the fisher and an opportunity to verify that the information is correct. Any errors can then be submitted by the fisher and corrected in the tagging database. You will also be sent a cash reward.

Do I have to be a commercial fisherman to claim a cod tag reward?

No, anyone who catches a tagged cod can claim a cod tag reward. You must send the tag back to one of the participating laboratories. No reward can be issued until we have received the tag.

What are the rewards for returning a tag?

Anyone who returns a DST released as part of the CODYSSEY project will receive a reward of approximately 40Euros (£25UK). A generous market value will also be paid if the carcass of the tagged fish is returned. In addition, a limited number of tags are 'Golden tags' and will receive a higher reward (200Euro or £150UK). Only the tag program administrators know which tags are 'Golden' ('Gold' status has been conferred on certain, randomly identified, tags at the start of CODYSSEY). In addition, individuals returning tags originally released by the CEFAS or FRS laboratories will be entered into a lottery (drawn annually), with prize money of £1000 (approx 1500Euro). So if you do return a tag, it could turn out to be very worth your while!

The rewards are used as an incentive to encourage people to return the tags. Rewards will be paid for returning the tag even without any recapture information, but obviously much more will be learned if accurate recapture information is provided.

Where can I get more information about the results of the CODYSSEY project?

Get in touch with the scientists working on the CODYSSEY project through the contact addresses detailed above, or email: codyssey@cefas.co.uk