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 & 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
The Cefas G5 data
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.
Current and recent Cefas tagging programmes:
Edible (brown) crab
porbeagle and common skate bycatch and discard reduction (FSP,
survivability and movement of porbeagle and spurdog bycatch
(2010-11) (PDF, 332 KB)
mortality of commercially caught skates (2010-11) (PDF, 297
- Tagging dogfish, skates and rays on
research vessels (2003-11)
- Spurdog in
the Irish Sea (FSP, 2009) (PDF, 4.18 MB)
- Thames ray
tagging and survival (FSP, 2007-08) (PDF, 1.54 MB)
Tagging blonde, small-eyed and undulate rays off Jersey
- Studying the movements of plaice in the eastern and western
Irish Sea (MEMFISH, 2008-09)