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Abstract: Population recovery targets are a pressing need for the conservation and management of species at risk, and demographic sustainability, expressed as the size of a minimum viable population (MVP), is frequently used to guide conservation efforts. Here, we conduct population viability analyses of stage-structured populations to explore the roles of maximum capacity for increase (r max), density-dependent compensatory reserves, and catastrophes as determinants of MVP in freshwater fishes. Computer simulations of random-walk population trajectories for 31 freshwater fish species listed as threatened and endangered in Canada were repeated at various probabilities of random catastrophes within the range observed in vertebrate populations. MVP increased with r max and decreased with the strength of compensatory reserves; low compensatory reserves are associated with greater variability in population size. Although large-bodied species exhibit lower r max values, their greater compensatory reserves allow them to buffer density-dependent variability in early mortality. Catastrophes have a small influence on MVP sizes of large-bodied freshwater fishes (e.g., sturgeons). Conversely, MVP sizes of small-bodied freshwater fishes are strongly sensitive to catastrophes, in most cases requiring larger MVP sizes than determined for other vertebrate taxa even at moderate catastrophe probabilities. Thus, knowledge of primary catastrophic events and their probabilities are particularly essential for setting population recovery targets of small-bodied species. [Copyright &y& Elsevier]

The Bay of Quinte, a Z-shaped embayment at the northeastern end of Lake Ontario, has a long history of eutrophication problems primarily manifested as spatially extensive algal blooms and predominance of toxic cyanobacteria. The purpose of this study was to identify the structural changes of the phytoplankton community induced by two environmental alterations: point-source phosphorus (P) loading reduction in the late 1970s and establishment of dreissenid mussels in the mid-1990s. A combination of statistical techniques was used to draw inference about compositional shifts of the phytoplankton assemblage, the consistency of the seasonal succession patterns along with the mechanisms underlying the algal biovolume variability in the Bay of Quinte over the past three decades. Based on a number of diversity and similarity indices, the algal assemblages in the upper and middle segments of the Bay are distinctly different from those typically residing in the outer segments. Our analysis also identified significant differences among the phytoplankton communities, representing the pre- and post-P control as well as the pre- and post-dreissenid invasion periods. Recent shifts in phytoplankton community composition were mainly associated with increased frequency of occurrence of toxin-producing Microcystis outbreaks and reduced biovolume of N 2 fixers, such as Aphanizomenon and Anabaena . Bayesian hierarchical models were developed to elucidate the importance of different abiotic factors (light attenuation, water temperature, phosphorus, and ammonium) on total cyanobacteria, Microcystis , Aphanizomenon , and Anabaena relative biovolume. Our modelling exercise suggests that there is significant spatial heterogeneity with respect to the role of the factors examined, and thus total phosphorus alone cannot always explain the year-to-year variability of cyanobacteria succession patterns in the system. The lessons learned from the present analysis will be helpful to the water quality criteria setting process and could influence the management decisions in order to delist the system as an Area of Concern. [ABSTRACT FROM AUTHOR]