The expansion of Arapaima cf. gigas (Osteoglossiformes: Arapaimidae) in the Bolivian Amazon as informed by citizen and formal science

Abstract

The giant osteoglossomorph fish Arapaima cf. gigas was introduced to the northern Bolivian Amazon over a half century ago and now contributes significantly to commercial fisheries. Despite this, little is known regarding its current distribution and invasion potential. Here, we address this knowledge gap using two complementary methods: interviewing key informants and examining fisheries landing records in the principal landing site (Riberalta). Both interviews and landing data revealed that the species represents approximately 50% of the total commercial catches, and that it now occupies approximately 340 km 2 of floodplain lakes in the Beni, Orthon and Madre de Dios River basins. The annual yield is estimated at 258 t, equivalent to 0.76 kg/ha/year. The current geographic distribution represents approximately one-quarter (24%) of floodplain lakes in the lower Bolivian Amazon, suggesting high fisheries potential of the species if it would also colonize the remaining Mamore and Itenez River basins. The potential for negative ecosystem impacts of the A. cf. gigas invasion seems likely, considering the large body size, life history and feeding ecology of this species, but has not yet been clearly demonstrated. Factors that might limit further expansion are natural barriers (waterfalls) in the lower Mamore, and periodic cold temperature conditions in the Mamore and Itenez River basins.