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The majority of Louisiana’s wild crayfish landings are harvested from the Atchafalaya River Basin (ARB) during floodplain inundation from the annual flood pulse. Spatial and temporal heterogeneity in ARB physicochemical characteristics are associated with flood pulse characteristics and floodplain inundation, and extensive areas of the ARB experience environmental hypoxia (dissolved oxygen [DO] < 2.0 mg·L-1) for several weeks to months during the annual flood pulse. The purpose of this research was to evaluate the effects of flood pulse characteristics and physicochemistry on harvested crayfish populations at 14 sites in the ARB that were sampled biweekly during the 2016 and 2017 crayfish seasons. Despite dissimilar 2016 and 2017 flood pulse characteristics, red swamp crawfish Procambarus clarkii and southern white river crawfish P. zonangulus carapace length and CPUE were similar between sample years. Comparisons of P. clarkii populations among physicochemical location groupings indicated that DO concentration, particularly chronically hypoxic water, is the principal abiotic variable influencing P. clarkii population characteristics. Although not significant, normoxic locations produced larger crayfish and yielded higher CPUE values for the majority of both crayfish seasons. Furthermore, hemolymph protein concentrations in P. clarkii from normoxic areas were significantly and consistently higher than individuals from chronically hypoxic locations.

The dopamine hypothesis of aging suggests that a monotonic dopaminergic decline accounts for many of the changes found in cognitive aging. The authors tested 44 older adults with a probabilistic selection task sensitive to dopaminergic function and designed to assess relative biases to learn more from positive or negative feedback. Previous studies demonstrated that low levels of dopamine lead to avoidance of those choices that lead to negative outcomes, whereas high levels of dopamine result in an increased sensitivity to positive outcomes. In the current study, age had a significant effect on the bias to avoid negative outcomes: Older seniors showed an enhanced tendency to learn from negative compared with positive consequences of their decisions. Younger seniors failed to show this negative learning bias. Moreover, the enhanced probabilistic integration of negative outcomes in older seniors was accompanied by a reduction in trial-to-trial learning from positive outcomes, thought to rely on working memory. These findings are consistent with models positing multiple neural mechanisms that support probabilistic integration and trial-to-trial behavior, which may be differentially impacted by older age.