Effectiveness of releasing gilthead sea bream (Sparus aurata, L.) for stock enhancement in the bay of Cadiz

This paper reports a program of gilthead sea bream releasing in the bay of Cadiz, the effectiveness of which has been determined according to fish size, release site and water quality. Between 1993 and 1998, a total of 18,253 marked specimens of gilthead sea bream of two average weight classes (15 and 100 g) were released into this bay. Recapture rate was 0.03 +/- 0.05 for specimens of 15 g and 3.52 +/- 1.71 for specimens of 100 g; therefore, stocking with fish of 100 g is recommended. Of the total recaptures, 40.4% were concentrated in a sector of the bay where molluscs were abundant, indicating attraction of these fish to food. Places with no recaptures were associated with low water quality, mainly oxygen depletion by organic pollution (4.0 +/- 1.6 ppm) and freshwater influence (23.13 +/- 9.01 ppt). It is necessary to avoid polluted habitats for devising a feasible stocking program for gilthead sea bream. (C) 2004 Elsevier B.V. All rights reserved.