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Population-level effects of male-biased broods in eelpout (Zoarces viviparus)



Effects of environmental pollutants are most obvious when mortality is increased. However, there are other nonlethal factors that may affect population size significantly. Endocrine disruption as a mechanism of action for pollutants recently has received much attention. Observations of effects likely caused by endocrine disruptors in pulp mill effluents have been made on several fish species, e.g., male-biased broods in eelpout (Zoarces viviparus). Fewer females represent a lower fecundity and could have dramatic effects on the population. In this study, a population viability analysis of the effects of skewed primary sex ratios in the eelpout was conducted using a female-based matrix population model. The model is age-structured with one deterministic version and another that incorporates environmental stochasticity. The model showed that the deterministic and stochastic growth rates in an undisturbed population (50% female fry) were 1.172 and 1.075, respectively, compared to 1.097 and 1.007 using the lowest proportion of female fry observed (38.7%). When primary sex ratios were more male-biased, the probability of pseudoextinction increased. Model simulations showed that the probability of a decreased population size to 5% of the initial within a 100-year time horizon was 44.7% with 38.7% female fry compared to only 7.7% for an undisturbed population.

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