We thank the fishermen Gilberto Lea˜o (Bosque), Zaidir (Torotama), Heli (Passinho), Adilan (Capivaras), Rui (Z3), Jorge (Mangueira) e Anderson (Va ´ rzea), without whom this work would not have been carried out. We are grateful to Prof. P.C.Vieira for his contribution in several stages of