Résumé
Patterns of commercial fish catches over the period from 1984 to 2006 were studied in the Loreto region and in Iquitos, which is the most important town of the region and the principal fish marketplace of the Peruvian Amazon. Despite important inter-annual variations, the overall fish landings have significantly increased in the region during this period. The same three species dominated the catches during the whole period (Prochilodus nigricans, Potamorhina altamazonica and Psectrogaster amazonica), making up about 62% of the catches. However, the number of species exploited by commercial fisheries increased considerably during the 22 years of this study (from about 21 species in 1984 to over 65 in 2006), although part of the difference may be accounted for by a better identification of individual species nowadays. At the same time, the large high-valued species, such as Arapaima gigas, Colossoma macropomum and Brachyplatystoma rousseauxii, declined significantly and were replaced by smaller, short-lived and lower-valued species. Catches of the silver Arahuana (Osteoglossum bicirrhosum) also declined significantly during the studied period, strengthening recent warnings about the species' conservation status (Moreau and Coomes, Oryx 40:152-160, 2006). The relative proportions of the trophic groups (detritivores, omnivores and piscivores) remained relatively constant over the study period, but there were significant changes in the relative abundances of the species groups. The proportion of the dominant group, the Characiformes, which averaged about 81% of the catches, increased between 1984 and 2006, whereas the proportion of the Siluriformes and Perciformes remained constant. On the other hand, the proportion of Osteoglossiformes, represented only by two well known species (Arapaima gigas and Osteoglossum bicirrhosum), declined sharply during the same period. Important differences were observed between the landings of Iquitos and the landing of the whole Loreto region, indicating that conclusions drawn from the study of the Iquitos landings cannot be extrapolated to the whole landings of the Loreto region. The most important difference was the decreasing fish landings in Iquitos, whereas the total landings increased in the Loreto region at the same time. Potential causes of this phenomenon are discussed. Decreasing fish abundance around Iquitos (because of a higher fishing pressure) and a behavioural adaptation of fishermen to better law enforcement in Iquitos are likely explanations to be further investigated.