Evaluating recreational fisheries for an endangered species: A case study of taimen, Hucho taimen, in Mongolia

Understanding the tradeoff between exploitation and conservation is difficult in data-poor situations, which are typical for most recreational fisheries, even in developed countries. In a developing country where the target species is en-dangered, the stakes are higher and the management resources are fewer. We combined a mark-recapture experiment, life history invariants, and meta-analysis to parameterize a delay-difference model for a population of the endangered giant Eurasian trout (taimen, Hucho taimen) in northern Mongolia. The model allowed us to evaluate the impacts of a recreational fishery for taimen based on a suite of population characteristics including equilibrium abundance, biomass, and mean weight. The Bayesian framework and Monte Carlo simulations combine disparate sources of information while keeping track of uncertainty as it propagates through the model. In the case of taimen in the Eg-Uur watershed, the existing catch-release recreational fishery has likely reduced taimen abundance, biomass, and mean weight by less than 10% compared with levels predicted in the absence of recreational fishing. In comparison, if all taimen caught in this fishery were retained (as they are elsewhere in Mongolia), there is a 57% chance that such harvest levels, if maintained, would lead to the eventual extirpation of the population.