Cefas crab tagging programme in the English Channel, 2007 – 2010

Results from major tagging studies carried out in the 1970s indicated that mature female crabs generally moved from east to west through the English Channel and in a more southerly direction further west (see illustration). Male crabs tended to move less far and with a less discernable pattern. Return movements of adult females were not observed. Studies of planktonic crab larvae distributions have indicated offshore spawning grounds to the south of Devon and Cornwall from which larvae drift in a north-easterly direction back into the Channel. However, the rate of larval drift is thought to be insufficient to return larvae to fishing grounds in the eastern Channel, which suggests the possibility of separate stocks in the eastern and western Channel.

In 40 years since the last tagging programme much has changed including warming seas, increased fishing effort and the expansion of the fishery to the south of Devon and Cornwall. Over the next 3 years Cefas will carry out a new crab tagging programme, using double T-bar tags (retained through the moult) and electronic data storage tags (DSTs).

This project aims to release up to 5,000 double T-bar tagged crabs each year for the next 3 years. These tags are retained through moulting and cause less injury than suture tags used in previous studies. Tagging will be carried out from commercial vessels in various locations throughout the English Channel from 2007 - 2009. Tags will vary in colour, but will all be the same design and bear the tag number followed by "WWW.CEFAS.CO.UK PLEASE RECORD TAG NO. DATE. LAT & LONG, WIDTH, SEX" (upper inset).

In 2008 and 2009 up to 100 crabs will also be tagged using electronic data storage tags (DSTs). These provide continuous records of depth and temperature for periods of up to a year and the data can be used to determine the location of the crabs during the period between release and capture. DST recoveries will provide detailed information on crab movements and behaviour, which may help us to identify migration routes and spawning grounds and will complement the double T-bar tagging study.

To maximise the information obtained from the programme, rewards (£6 for T-bars, £50 for DST’s) are payable for the return of the full recapture details: tag colour, tag number, date, latitude, longitude, sex, carapace width in millimetres (lower inset). Don’t forget your own contact details. There is the opportunity to win up to £1000 in tag number raffles. On each anniversary of the project in 2008, 2009 and 2010 a lottery draw for a £500 prize will take place using those tags returned during the previous year. An additional final grand draw with a prize of £500 will also be made in 2011 in which all T-bar tags returned during the project will be entered. Returned DSTs will be entered into a separate draw with a prize of £1000.

For information on returning tags see: What to do if you find a Cefas tagged fish