Death rate, recapture frequency and changes in size of tagged eels

From 475 eels individually marked with floy tags, of which 180 had an additional spot of alcian blue, 142 tags were recovered during a 2-year release-recapture programme, but alcian blue spots were not detected. The marked population declined by c. 95% per year (either through death or tag loss); tagged eels did not grow but lost weight; no trap avoidance could be detected. It is concluded that these tagged eels in poor condition did not suffer from winter mortality, and that during summer they moved around very actively.