Bass tagging
Introduction
In 2000, Cefas initiated a study to investigate whether the movement patterns of adult bass in North-west Europe have changed since the 1980s, and to estimate the level of competition for bass between UK inshore fisheries and international offshore fisheries. The exercise is part of a wider study of bass fisheries and their management, which in England and Wales has been supported by Defra. Over 5,000 bass greater that 36 cm total length have been tagged around the coasts of England, Wales, Southern Ireland and the Channel Isles, and offshore in the Western English Channel, in collaboration with BASS (the Bass Anglers' Sportfishing Society), scientists from Ifremer (the Institut Français pour la Recherche et l'Exploration de la Mer, Brest Centre, France), and commercial fishermen.
The chart below shows the numbers of bass tagged and released in each area.
Bass for tagging were carefully selected to ensure that they were in a suitable condition - undamaged and vigorous, with little damage from scale loss. The tags are made of thin, cylindrical yellow nylon, about 4 inches long and are attached to the lower left flank of each bass. The tags are individually numbered and bear a message in English and French asking for the return of the tag plus recapture details.
It is important that anyone catching a bass examines it closely and, if it is tagged, returns the tag to Cefas or a local Fisheries office, giving the tag number, capture location area, date and size of fish. In line with an international agreement, a £6 reward, plus the market value of the fish, if surrendered, will be made for all tags returned. For information on what to do if you find a tagged fish see the section "What to do if you find a Cefas tagged fish"
Up to the end of August 2006, a total of 240 recaptures have been reported, the positions of which are shown on the chart below.
The results show a similar pattern of movement to that seen in the late 1970s and early 1980s in a similar tagging study, with most adult bass (above 40 cm) recaptured between May and October close inshore, whilst many bass caught in January to April had moved considerable distances to their offshore spawning grounds. However, compared to results for the early 1980s, many more fish were recaptured inshore as late as February, and there was less evidence of the pre-spawning migrations from the North Sea to the Western Channel. These migrations appear to be strongly linked to sea temperature, and provide evidence that climate change is affecting marine fish species.
Whilst 88% of the recaptures of bass tagged inshore were taken by UK fisheries inside the UK 12-mile zone and 3 % were reported from the offshore pair-trawl fishery, 59% of the recaptures of bass tagged in the offshore pair-trawl fishery were made inshore along the UK coast, and 32% in the offshore pair trawl fishery. Most of the remaining 9% of recaptures were taken by UK vessels fishing outside 12 miles. Taking into account the likelihood of a tagged bass being available to be recaptured and reported (4-5 times more likely for bass tagged inshore, chiefly because they survive better than even selected pair-trawl caught fish) and the numbers of bass caught in the respective fisheries, an average of 40 fish tagged inshore were recaptured each year from the UK inshore fishery, and 5 fish from the offshore fishery. This indicates that for every 9 bass that could potentially be caught in the inshore fishery around England and Wales in the period 2000 - 2004, one would be available to be caught by another country's vessel (fishing outside 6 miles). This suggests that the effects of management measures implemented in the UK inshore fishery are largely restricted to that fishery.
