Monitoring Response of Diadromous Populations to Fish Passage Improvements on a Massachusetts Coastal Stream

One technical fishway and two innovative nature-like fishways were installed at three dams on the Acushnet River in Acushnet, Massachusetts to facilitate migration of river herring and juvenile American eels （elvers）. Pre-construction and post-construction monitoring of river herring and elver populations used census counting and abundance estimation, respectively. Numbers of adult river herring returning to the upstream spawning grounds during the pre-construction phase were very low; elver counts declined during the pre-construction period and served as baseline levels to determine the effectiveness of the new fishways. Post-construction monitoring of river herring and elvers indicated an increasing trend of spawning adult river herring returning to the spawning grounds, with the total count in the fourth year of post-construction representing an increase of 1,140% over baseline, pre-construction conditions. Results also show increased elver recruitment into the river as well as increased proportions of elvers accessing habitat in the upper watershed that was mostly inaccessible prior to fishway installation. The new fishways at the three dams on the river have improved diadromous fish passage, thereby increasing the probability of restoring healthy populations of river herring and American eels to the Acushnet River system.

Achieving fish passage outcomes at irrigation infrastructure;a case study from the Lower Mekong Basin

Irrigation infrastructure expansion threatens the diversity of freshwater fish worldwide.Irrigation infrastructure creates migration barriers which can block access to important nursery,feeding and spawning habitat.Lao PDR is a landlocked country situated within the Lower Mekong River Basin where there is a substantial dependency on rice and fish for food,income and livelihoods.The country is experiencing an unprecedented boom in irrigation infrastructure investment,with modernisation programs being implemented in every province.Despite significant investment in infrastructure upgrades,and the potential impact on freshwater fish,little consideration has been given to fish passage solutions.In 2008,we commenced a fish passage program in Lao PDR.The intent of this case study is to outline the pivotal elements of the program of knowledge development and transfer,in the context of river connectivity and fisheries management in Lao PDR.We also highlight challenges in international research in development and lessons learned.

Editorial: Global fish passage issues

Dams,culverts,and other water diversion/control structures are the most widespread human alteration to riverine habitat globally.While many of these structures often serve critical services(i.e.,source of agricultural and municipal water,power generation,flood protection,and sensitive ecosystem protection),they cause changes to local ecology by impeding animal movement and altering the adjoining habitat and associated ecological processes(Nilsson et al.,2005;Liermann et al.,2007).The disruption of fish movement by barriers has contributed to the decline of both migratory and non-migratory fish populations around the world.

Effects of plunge pool configuration on downstream passage survival of juvenile blueback herring

Anadromous alosines are widespread throughout the Northern Hemisphere.Juveniles of this clade are notoriously fragile animals that are at high risk of injury and death associated with passage at hydroelectric facilities.Although turbine mortality is a common concern,conditions encountered when bypassed around these routes may also be hazardous.Downstream bypass structures typically discharge into plunge pools,which are highly turbulent and may cause mechanical injury.We subjected live,actively migrating juvenile blueback herring to a suite of realistic plunge pool conditions(3 m drop,pool depth of 60-180 cm,and discharge of 0.28-1.70 m^(3)/s)and monitored them for≥96 h.Survival was generally higher than expected(>80%in all cases).However,both plunge pool volume and total discharge affected survival with elevated discharge and shallow conditions associated with increased mortality.Mortality was often delayed:rates remained elevated throughout the monitoring period,indicating that survival studies based on shorter periods underestimate total mortality.

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.