1. Center for Stock Assessment Research, Department of Applied Mathematics and Statistics; University of California; Santa Cruz CA 95064 U.S.A.
2. Dipartimento di Elettronica, Informazione e Bioingegneria; Politecnico di Milano; Via Ponzio 34/5 I-20133 Milan Italy
3. Station Biologique de la Tour du Valat; Le Sambuc F-13200 Arles France
4. Fisheries Ecology Division, Southwest Fisheries Science Center; National Marine Fisheries Service, National Oceanic and Atmospheric Administration; 110 Shaffer Rd Santa Cruz CA 95060 U.S.A.
5. Department of Biology; University of Bergen; Bergen 5020 Norway