. 2015. Portfolio theory as a management tool to guide conservation and restoration of multi-stock fish populations. Ecosphere 6(12):296. http://dx.doi.org/10.1890/ES15-00237.1Abstract. Habitat degradation and harvest have upset the natural buffering mechanism (i.e., portfolio effects) of many large-scale multi-stock fisheries by reducing spawning stock diversity that is vital for generating population stability and resilience. The application of portfolio theory offers a means to guide management activities by quantifying the importance of multi-stock dynamics and suggesting conservation and restoration strategies to improve naturally occurring portfolio effects. Our application of portfolio theory to Lake Erie Sander vitreus (walleye), a large population that is supported by riverine and open-lake reef spawning stocks, has shown that portfolio effects generated by annual inter-stock larval fish production are currently suboptimal when compared to potential buffering capacity. Reduced production from riverine stocks has resulted in a single open-lake reef stock dominating larval production, and in turn, high inter-annual recruitment variability during recent years. Our analyses have shown (1) a weak average correlation between annual river and reef larval production (q ¼ 0.24), suggesting that a natural buffering capacity exists in the population, and (2) expanded annual production of larvae (potential recruits) from riverine stocks could stabilize the fishery by dampening inter-annual recruitment variation. Ultimately, our results demonstrate how portfolio theory can be used to quantify the importance of spawning stock diversity and guide management on ecologically relevant scales (i.e., spawning stocks) leading to greater stability and resilience of multi-stock populations and fisheries.

Mechanisms associated with habitat selection by fishes are often unknown and require both physical habitat and growth environment considerations. We used spatially explicit prey biomass estimates, predator growth rate potential (GRP), bottom slope, predator distance from shore, and substrate data to predict habitat use of the saugeye (walleye Sander vitreus × sauger S. canadensis), a popular sport fish that is stocked throughout the central United States. We used telemetry to determine saugeye locations, acoustics to estimate prey biomass and distributions, and a bioenergetics model to aid in calculation of GRP. Akaike's information criterion was used to determine which habitat variables were most important in explaining saugeye location. Models that included both physical habitat and either GRP or prey density performed better than models that considered only one of these parameter types. The resulting models provided the data to create location suitability maps. In general, saugeyes favored steep slopes over hard substrates in nearshore areas with high biomass of gizzard shad Dorosoma cepedianum or high GRP. This comprehensive analysis suggests that the consideration of both spatial habitat suitability and temporal prey availability may improve fisheries management and conservation through a quantitative appreciation of available resources.An understanding of habitat selection and use by animals requires an understanding of both physical habitat and the growth environment. Through its effects on population dynamics and community structure, habitat has the ability to shape life his-

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Growth-selective mortality as larvae can influence recruitment in marine fishes. Its importance in freshwater fishes, however, remains speculative. We quantified growth trajectories within annual cohorts (2011–2013) of Lake Erie walleye (Sander vitreus) and their relationship with recruitment. We hypothesized that selection against slow or fast growth would be associated with high mortality and poor recruitment, whereas weak or nonexistent growth-selective mortality co-occurring with fast growth would be associated with good recruitment. We used otoliths to reconstruct growth rates during the first 15 days of life from larvae collected during spring and juvenile recruits (survivors) collected during late summer. We documented growth-selective mortality during 2011 and 2013, which exhibited poor recruitment as expected. During 2012, growth selection was absent, but growth was slow when compared to historical averages, resulting in poor recruitment. Growth was also considered slow in 2011 and 2013, due to multiple interacting conditions. Our study indicates that the relationship among larval growth, mortality, and future recruitment is complex, highlighting the need for continued research into how larval processes affect recruitment dynamics in freshwater fishes.

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