Abstract
Arapaima occur primarily in the Amazon and Essequibo River basins and are among the largest freshwater fishes in the world. Their enormous size coupled with the need to come to the surface to breathe makes them vulnerable to intense harvesting and many populations are now over-exploited. Unregulated commercial harvesting of Arapaima in Guyana began in the early 1960's, and by 2001, there were only about 800 individuals over 1 m total length remaining in the Essequibo basin. Population ecological and genetic information is critical for effective conservation and management. In the first chapter, I evaluated the genetic structure of Arapaima from the Essequibo and Branco River basins and discovered the presence of two Evolutionarily Significant Units (one in each basin) and four management units (one in Branco and three in Essequibo). All studied populations exhibited reduced genetic diversity and two populations showed signs of inbreeding. In the second chapter, I estimated growth and mortality rates through analysis of growth ring deposition on scales. I estimated a theoretical maximum length of 192 cm and an annual mortality rate of 72% for ages two to five. Projection of length-weight relations suggests they may attain much greater weights than Amazonian Arapaima. The third chapter investigated the trophic ecology and sources of energy for Arapaima using stable nitrogen and carbon isotopes. I found that Arapaima was supported by prey consisting primarily of detritivorous/algivorous and omnivorous fishes. Diets and trophic structures suggest they are secondary consumers that might be considered omnivores. In the final chapter, I assessed the state of recovery of the population, investigated the influence of environmental factors on Arapaima abundance, and determined relationship between numbers of spawners and recruits. The most recent census in October, 2011, indicated a 7-fold increase in overall abundance over the last 10 years. The stock-recruitment data reveal 1:1 adult to juvenile ratios, which suggest ongoing illegal harvest of juveniles that could slow population recovery. Arapaima in the Essequibo appeared to favor larger lakes with aquatic macrophytes and low conductivity.