Influence of supraphysiological cortisol manipulation on predator avoidance behaviors and physiological responses to a predation threat in a wild marine teleost fish

The stress axis in teleost fish attempts to maintain internal homeostasis in the face of allostatic loading.However,stress axis induction has been associated with a higher predation rate in fish.To date,the physiological and behavioral factors associated with this outcome are poorly understood.The purpose of the present study was to investigate the impact of experimental cortisol elevation on anti-predator behavior and physiological responses to predator presence.We hypothesized that semi-chronic cortisol elevation would increase susceptibility to predation by increasing stress-induced risk-taking behaviors.To test this hypothesis,schoolmaster snapper were given cocoa butter implants without cortisol(sham)or with cortisol(50 mg/kg body weight)and tethered to cover.Fish were exposed to either a lemon shark or control conditions for 15-min.Space use and activity were recorded throughout and fish were terminally sampled for blood.Cortisol implantation,relative to shams,resulted in higher blood glucose and plasma cortisol concentrations with a lower plasma lactate concentration.Shark exposure,relative to controls,elicited higher blood glucose and lactate concentrations but had no effect on plasma cortisol concentration.No interactions were detected between shark exposure and cortisol treatment for any physiological trait.Behavioral metrics,including shelter use and activity,were unaffected by either cortisol implantation or shark exposure.Physiological responses to cortisol implantation likely resulted from enhanced gluconeogenic activity,whereas alterations under predator exposure may have been the product of catecholamine mobilization.Further work should address context-specific influences of stress in mediating behavioral responses to predation.

Bright spots for inland fish and fisheries to guide future hydropower development

Hydropower production is one of the greatest threats to fluvial ecosystems and freshwater biodiversity.Now that we have entered the Anthropocene,there is an opportunity to reflect on what might constitute a‘sustainable’Anthropocene in the context of hydropower and riverine fish populations.Considering elements of existing practices that promote favorable social-ecological outcomes(i.e.,‘bright spots’)is timely given that there are plans to expand hydropower capacity in previously undammed rivers,intensify dam development in some of the world's largest river systems,and re-license existing facilities.We approach this from a pragmatic perspective:for the foreseeable future,hydropower will likely remain an important source of renewable electricity.To offer support for moving toward a more‘sustainable’Anthropocene,we provide syntheses of best practices during the siting,design,construction,operation,and compensation phases of hydropower development to minimize impacts on inland fish.For each phase,we offer positive examples(or what might be considered‘bright spots’)pertaining to some of the approaches described within our syntheses,acknowledging that these projects may not be viewed as without ecological and(or)societal detriment by all stakeholders.Our findings underscore the importance of protecting critical habitat and free-flowing river reaches through careful site selection and basinscale planning,infrastructure designs that minimize reservoir effects and facilitate safe passage of fish,construction of hydropower plants using best practices that minimize long-term damage,operating guidelines that mimic natural flow conditions,and compensation that is lasting,effective,inclusive,and locally relevant.Learning from these‘bright spots’may require engagement of diverse stakeholders,professionals,and governments at scales that extend well beyond a given site,river,or even basin.Indeed,environmental planning that integrates hydropower development into broader discussions of conserving regional biodiversity and ecosystem services will be of utmost importance.