Modeling population dynamics and conservation of arapaima in the Amazon

Abstract

To promote understanding of fish population dynamics in tropical river-floodplains, we have synthesized existing information by developing a largely empirical population model for arapaima (Arapaima sp.). Arapaima are characterized by very large bodies, relatively late sexual maturity, small clutches, and large parental investment per offspring, and their populations are overexploited and even declining due to overfishing. We used unparalleled time series data on growth, reproduction, catch-atage, and size-class abundance estimates for a population that has increased several-fold and undergone drastic changes in fishing practices in the Amazon, Brazil. Model population numbers were close to observed numbers, with generally low mean absolute percentage errors for juveniles (16%), adults (30%), and catch (18%). In using the model to test ecological hypotheses and to investigate management strategies, we found the following: (1) Annual recruitment is directly and positively related to spawner abundance, and it appears to be density-compensatory following a Beverton-Holt relation (R 2 = 0.85).(2) Fishingselectivity of arapaima caused by use of harpoons and gillnets can lower yield potentials dramatically through removal of the faster-growing individuals of the population. That is in part because fewer individuals live long enough to reproduce and survivors take longer to reach reproductive age. (3) Arapaima populations can sustain annual catches of up to 25% of the number of adults in the population the previous year if minimum size (1.5 m) and closed season (December-May) limits are met. (4) When 25% of the number of adults in the population the previous year is harvested under a 1.6 m minimum size limit of catch, catches are slightly smaller but abundance of adults in the population is considerably greater than under a 1.5 m limit. These findings can be used in ongoing management initiatives, but caution is needed because of present biological and ecological uncertainty about these fishes.

Chemical composition of different muscle zones in pirarucu (Arapaima gigas)

“…The fish inhabits the Amazon River Basin in South America (Torres et al, 2008;Currey, 2010). This fish is economically and ecologically important for riverine population, because of its high commercial and nutritional value (Castello, 2008;Castello et al, 2011).…”

Digestibility of animal and vegetable protein ingredients by pirarucu juveniles, Arapaima gigas

“…However, pirarucu fishing is limited and regulated by inspection and environmental agencies to keep the stock from being depleted and to ensure that ecological balance is maintained, as it is a species at the top of its food chain (Castello et al, 2011).…”

Evidence of polygamy in the socially monogamous Amazonian fish Arapaima gigas (Schinz, 1822) (Osteoglossiformes, Arapaimidae)

“…Even though it has been exploited commercially for many years, much basic life history data are still lacking. However, several recent publications have made significant advances of our understanding of growth and reproductive behavior (Arantes et al, 2010), population dynamics (Coutinho et al, 2010;Castello et al, 2011), spatial and temporal distribution and trophic ecology (Watson et al, 2013) as well as population structuring (Hrbek et al, 2005;Hrbek et al, 2007;Araripe et al, 2013).…”