You are in: Our science Fisheries information Tagging programmes

Caught a tagged fish?

Tagging programmes

Tagged skate

Why scientists tag fish and shellfish

Cefas and other European scientists tag fish in experiments to record migrations, growth and fishing catch rates. Most of the commercial species have been subject to tagging on all of the major fishing grounds at some time, so there is always the chance of finding a tagged fish wherever you're fishing.

An historical review of the development of electronic tags for fish, called Fish & Chips (2011) (PDF, 1.10 MB), covers the need for a sound scientific understanding of fish movement and behaviour. This report also explores the factors that led to the development of new tag technology, together with some of the challenges and unexpected discoveries that our scientists encountered along the way.

More information about the numbers of different fish species released by Cefas can be found in the Cefas Technical Report: A summary of demersal fish tagging data maintained (2006) (PDF, 4.75 MB).

Types of tag - in detail

Cefas uses two types of tags for tagging fish, which can be broadly classified as conventional or electronic.

The principal types of conventional
tags used by Cefas

A wide variety of conventional tags have been used to mark many different species. The tags are often specific to particular types of fish. Simple button "Peterson" discs are used primarily for flatfish, skates and rays, plastic flags (often "Howitt" tags) for roundfish and T-bar type tags for bass and crustaceans (edible crabs and lobsters). Conventional tags are uniquely numbered, prefixed by the letter "E" (which denotes "English"). They may be used in conjunction with electronic tags that are not always numbered uniquely.

Mark and recapture experiments using conventional tags provide a valuable insight into stock structure and mixing, which have important implications for fishery management and fish stock conservation. Rates of exploitation by fishing can also be estimated by appropriately designed tagging studies.

Although conventional tagging experiments provide much information, data points are restricted to the release and recapture times and locations of individual fish. In order to determine what fish do in between release and recapture, the use of electronic data storage tags (DSTs) is required.

The Cefas G5 data storage tag

Electronic data storage tags (DSTs) record and store detailed information, for example the depth, light and temperature experienced by fish between the times of release and recapture.

Electronic tags are either placed internally or attached externally to the fish depending on the species and size of tag. Internal tags are generally flagged using an external marker tag. Some of our recent DST releases have buoyant day-glo orange flotation jackets. The floating tags will eventually wash up on a coastline somewhere - either when the tags detach at a pre-determined time or when the fish dies - where it is hoped that the bright colour registers with beachcombers.

Following recapture, the data from returned tags is downloaded and analysed. The data can be used to interpret the behaviour patterns of individual fish. Often the migration routes of individuals can be reconstructed.

The battery life of electronic tags now allows data to be recorded over periods of a year or more. Longer data records can allow the opportunity to interpret migration routes over one or more spawning seasons.

Satellite and acoustic tags are also used to track fish movements.