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Dams challenge Atlantic salmon (Salmo salar) conservation, while hatcheries are a common but poorly evaluated recovery tool. We developed a spatially explicit smolt survival model for the Penobscot River, Maine, USA, population. By partitioning survival through dams (with flow dependency), free-flowing river reaches, and the estuary (with dam dependency), the model quantified how these factors influenced the number of fish entering the ocean. Given historical impounded conditions, 74%-22% of hatchery smolts released entered the ocean annually from 1970 to 2012. Of 19.7 million smolts stocked, 7.7 million entered the ocean (39%). Survival was most variable at dams (range 95% to 63%), followed by in-river (range 98% to 70%) and estuary (range 88% to 82%). Overall, lower-river stocking sites resulted in significantly higher numbers at ocean entry because of fewer dam encounters and shorter migrations. Higher flows also resulted in reduced losses. By reconstructing these freshwater and estuary dynamics, the model provides a more accurate estimate of ocean recruitment annually and can be used for scenario planning of future stocking locations relative to predicted flows while being adaptable to new survival rates. Les barrages constituent un defi pour la conservation du saumon atlantique (Salmo salar), et les alevinieres sont un outil de retablissement repandu, bien que mal evalue. Nous avons developpe un modele de survie des saumoneaux spatialement explicite pour la population du fleuve Penobscot (Maine, Etats-Unis). En partitionnant la survie a travers les barrages (dependant du debit), les troncons a ecoulement libre du fleuve et l'estuaire (dependant des barrages), le modele quantifie l'influence de ces facteurs sur le nombre de poissons entrant dans l'ocean. Etant donne les conditions de retenue historiques, de 74 % a 22 % des saumoneaux d'elevage relaches dans le fleuve sont entres dans l'ocean annuellement de 1970 a 2012. Sur 19,7 millions de saumoneaux d'elevage relaches, 7,7 millions sont entres dans l'ocean (39 %). La survie est la plus variable aux barrages (de 95 % a 63 %), suivis des troncons du fleuve (de 98 % a 70%) et de l'estuaire (de 88 % a 82%). Globalement, les lieux d'ensemencement situes plus bas dans le fleuve se traduisent par des nombres significativement plus grands de saumoneaux entrant dans l'ocean en raison du moins grand nombre de barrages rencontres et des migrations plus courtes. Des debits plus eleves se traduisent egalement par des pertes moins grandes. En reconstituant ces dynamiques en eau douce et dans l'estuaire, le modele fournit une estimation plus exacte du recrutement oceanique annuel et peut etre utilise pour la planification de scenarios de lieux d'ensemencement futurs en fonction des debits prevus, tout en pouvant s'adapter a de nouveaux taux de survie. [Traduit par la Redaction], Introduction Dams impact riverine ecosystem function by interrupting natural physical, chemical, and biological gradients. These impacts increase in systems with multiple dams in a concept called 'serial discontinuity' (Ward and [...]

Timing of ocean entry is critical for marine survival of both hatchery and wild Atlantic salmon (Salmo salar) smolts. Management practices and barriers to migration such as dams may constrain timing of smolt migrations resulting in suboptimal performance at saltwater entry. We modeled influences of stocking location, smolt development, and environmental conditions on (i) initiation of migration by hatchery-reared smolts and (ii) movement rate of hatchery- and wild-reared Atlantic salmon smolts in the Penobscot River, Maine, USA, from 2005 through 2014 using acoustic telemetry data. We also compared movement rates in freeflowing reaches with rates in reaches with hydropower dams and head ponds. We compared movement rates before and after (1) removal of two mainstem dams and (2) construction of new powerhouses. Initiation of movement by hatchery fish was influenced by smolt development, stocking location, and environmental conditions. Smolts with the greatest gill [Na.sup.+], [K.sup.+]-ATPase (NKA) activity initiated migration 24 h sooner than fish with the lowest gill NKA activity. Fish with the greatest cumulative thermal experience initiated migration 5 days earlier than those with lowest cumulative thermal experience. Smolts released furthest from the ocean initiated migration earlier than those released downstream, but movement rate increased by fivefold closer to the ocean, indicating behavioral trade-offs between initiation and movement rate. Dams had a strong effect on movement rate. Movement rate increased from 2.8 to 5.4 km x [h.sup.-1] in reaches where dams were removed, but decreased from 2.1 to 0.1 km x [h.sup.-1] in reaches where new powerhouses were constructed. Movement rate varied throughout the migratory period and was inversely related to temperature. Fish moved slower at extreme high or low discharge. Responses in fish movement rates to dam removal indicate the potential scope of recovery for these activities. Le moment de l'entree en mer joue un role cle dans la survie en mer des saumoneaux de saumon atlantique (Salmo salar) tant sauvages qu'issus d'ecloseries. Les pratiques de gestion et obstacles a la migration, tels que les barrages, peuvent restreindre le moment de la migration des saumoneaux, entrainant une performance moins qu'optimale a l'entree en eau salee. Nous avons modelise les influences du lieu d'empoissonnement, du developpement des saumoneaux et des conditions ambiantes sur (i) le debut de la migration par les saumoneaux eleves en ecloseries et (ii) la vitesse des deplacements de saumoneaux eleves en ecloseries et a l'etat sauvage dans le fleuve Penobscot (Maine, Etats-Unis), de 2005 a 2014, a la lumiere de donnees de telemetrie acoustique. Nous avons egalement compare les vitesses de deplacement dans des troncons non regules et des troncons contenant des barrages hydroelectriques et des reservoirs de barrage. Nous avons compare les vitesses de deplacement avant et apres (1) le retrait de deux barrages sur le bras principal et (2) la construction de nouvelles centrales electriques. Le debut des deplacements par les poissons issus d'ecloseries etait influence par le developpement des saumoneaux, le lieu d'empoissonnement et les conditions ambiantes. Les saumoneaux presentant la plus forte activite de la [Na.sup.+], [K.sup.+]-ATPase (NKA) dans les branchies commencaient leur migration 24 heures plus tot que les poissons avec la plus faible activite de la NKA dans les branchies. Les poissons caracterises par la plus importante experience thermique cumulative commencaient a migrer 5 jours plus tot que ceux avec la plus faible experience thermique cumulative. Les saumoneaux relaches le plus loin de l'ocean commencaient a migrer plus tot que ceux relaches plus en aval, mais la vitesse de deplacement quintuplait plus pres de l'ocean, indiquant des compromis comportementaux entre l'initiation et la vitesse des deplacements. Les barrages exercaient une forte influence sur la vitesse de deplacement, cette derniere augmentant de 2,8 a 5,4 km x [h.sup.-1] dans les troncons dont des barrages ont ete retires, mais diminuant de 2,1 a 0,1 km x [h.sup.-1] dans les troncons ou de nouvelles centrales electriques ont ete construites. La vitesse de deplacement variait tout au long de la periode de migration et etait inversement reliee a la temperature. Les poissons se deplacaient plus lentement a debits extremes forts ou faibles. Les reactions au retrait de barrages refletees dans les vitesses de deplacement des poissons indiquent l'ampleur potentielle du retablissement associee a ces activites. [Traduit par la Redaction], Introduction Seaward migration through freshwater and estuarine habitats to ocean feeding grounds represents a critical transition in the life history of anadromous fishes (Zydlewski and Wilkie 2013). In Atlantic salmon [...]

Objective: Atlantic Salmon Salmo salar in the United States have been the focus of recovery efforts for over 150 years, but long‐term analyses of juvenile demographics are limited. We examined how parr size (fork length [FL]) varied across three Maine drainages (East Machias, Narraguagus, and Sheepscot rivers) during 1980–2014 and was affected by habitat and biological variables using a long‐term electrofishing data set. Methods: We fitted generalized additive mixed models (GAMMs) to determine how parr FL varied with explanatory variables, including mean summer air temperature, elevation, mean channel width, juvenile salmon density, age‐0 parr stocked, a metric for the number of effective fry stocked, and year. When examining model‐averaged GAMM results, we found that parr size varied throughout the 34‐year time period across the three drainages. Result: Between 1980 and 2014, parr FL in the Sheepscot River drainage (mean = 143.9 mm) steadily increased (~5‐mm increase). Parr FL in the Narraguagus River drainage (mean = 124.4 mm) declined from 1980 to about 2005 and then increased from 2006 to 2014. Parr FL in the East Machias River drainage (mean = 127.7 mm) experienced a decrease of approximately 10 mm during the study period. Density dependence was evident across drainages, suggesting that habitats were at capacity or that parr were experiencing competition. Given that the production of parr in Maine is highly reliant on stock enhancement, localized high stocking densities may limit parr growth without further restoration or habitat improvements. Stocking intensities generally decreased in all three drainages after 2000, possibly relaxing density dependence and partially explaining the plateau or increase in FL during recent years in the Sheepscot and Narraguagus rivers. Relationships between FL and summer air temperature were drainage specific, while wide channels and lower elevations were consistently associated with larger parr. Conclusion: Given our results, management should continue to prioritize habitat improvements to improve local carrying capacity and potentially reduce density‐dependent growth so as to increase stock enhancement efficacy within an adaptive management framework at the southern edge of the Atlantic Salmon's range. Impact statement:We examined trends in juvenile Atlantic Salmon size in three Maine, USA, watersheds from 1980 through 2014. Higher densities of juvenile salmon or higher stocking efforts were generally associated with smaller juvenile salmon sizes. Management should continue to prioritize habitat improvements and consider local stocking densities to increase effectiveness of hatchery programs. [ABSTRACT FROM AUTHOR]

The Gulf of Maine Distinct Population Segment of Atlantic Salmon Salmo salar is listed under the U.S. Endangered Species Act, with dams cited as a key threat to the species. Safe, timely, and efficient passage of emigrating smolts is critical for advancing recovery goals. However, climate change and the earlier (and more variable) onset of smolt migration have challenged the effectiveness of measures designed to protect smolts. Therefore, we used data from four long‐term smolt trapping sites in Maine to characterize run duration, identify a standardized smolt run, and develop a predictive model for the initiation of smolt emigration for natural‐ and hatchery‐origin smolts. We combined these data into a basinwide deterministic model that projects the movement of smolts from their point of origin to estuary entry, which we used to (1) evaluate duration and temperature triggers for supplemental spill periods used at hydroelectric dams to protect smolts and (2) investigate how knowledge of smolt emigration dynamics can guide protective measures in rivers where management actions are being developed. Timing of run initiation varied by over 14 d; however, mean air temperature for the first quarter of the year explained over 60% of the variance in the onset of emigration. Initiation temperature was linked with higher‐elevation rearing areas where smolts originated and not with downstream dams where temperature was monitored. The shape of the smolt wave varied considerably; thus, our standardized smolt wave captured average dynamics but not the specific shape. Overall, 14‐d spill windows are too short. To account for the variable timing and shape of the run, a 54–72‐d protection window would be necessary to protect the earliest and latest emigrants in the absence of physical structures (e.g., turbine screens) and preserve the adaptive variation required for populations to respond to climate‐driven changes in temperature and hydrology. [ABSTRACT FROM AUTHOR]

Billions of hatchery salmon smolts are released annually in an attempt to mitigate anthropogenic impacts on freshwater habitats, often with limited success. Mortality of wild and hatchery fish is high during downstream and early ocean migration. To understand changes that occur during migration, we examined physiological and endocrine changes in Atlantic salmon (Salmo salar) smolts during hatchery rearing, downstream migration, and early ocean entry in two successive years. Gill [Na.sup.+]/[K.sup.+]-ATPase activity increased in the hatchery during spring, increased further after river release, and was slightly lower after recapture in the ocean. Plasma growth hormone levels increased in the hatchery, were higher in the river, and increased further in the ocean. Plasma IGF-I remained relatively constant in the hatchery, increased in the river, then decreased in the ocean. Plasma thyroid hormones were variable in the hatchery, but increased in both river- and ocean-captured smolts. Naturally reared fish had lower condition factor, gill NKA activity, and plasma thyroxine than hatchery fish in the river but were similar in the ocean. This novel data set provides a vital first step in understanding the role and norms of endocrine function in smolts and the metrics of successful marine entry. Si des milliards de saumoneaux issus d'ecloseries sont relaches annuellement afin d'attenuer les impacts de l'activite humaine sur les habitats d'eau douce, l'efficacite de ces efforts est souvent limitee. La mortalite des poissons sauvages et provenant d'ecloseries est elevee durant l'avalaison et le debut de la migration en mer. Pour mieux comprendre les changements qui s'operent durant la migration, nous avons examine les changements physiologiques et endocriniens chez des saumoneaux de saumon atlantique (Salmo salar) durant l'alevinage en ecloserie, l'avalaison et le passage en mer pendant deux annees consecutives. L'activite de l'ATPase [Na.sup.+]/[K.sup.+] branchiale a augmente au printemps en ecloserie, puis apres la liberation en riviere et avait legerement diminue apres la recapture en mer. Les teneurs de l'hormone de croissance plasmatique ont augmente en ecloserie, puis davantage en riviere ainsi qu'en mer. L'IGF-I plasmatique est demeure relativement inchange en ecloserie, a augmente en riviere, pour ensuite diminuer en mer. Les teneurs en hormones thyroidiennes plasmatiques etaient variables en ecloserie, mais avaient augmente chez les saumoneaux captures tant en riviere qu'en mer. Si, en riviere, les poissons issus de l'alevinage naturel presentaient des coefficients d'embonpoint, une activite de la NKA branchiale et des teneurs en thyroxine plasmatique plus faibles que ceux des poissons issus d'ecloseries, ces valeurs etaient semblables pour les deux groupes de poissons une fois en mer. Ce nouvel ensemble de donnees constitue un premier pas critique vers la comprehension du role et des normes de la fonction endocrine chez les saumoneaux, ainsi que vers la caracterisation des parametres associes a un passage en mer reussi. [Traduit par la Redaction], Introduction As part of their normal life history, Atlantic salmon migrate as juveniles from freshwater to seawater. Atlantic salmon undergo a transformation that is adaptive for life in the ocean, [...]

North American salmon once ranged from ocean waters near the Arctic Circle southward to southern New England on the Atlantic and Mexico on the Pacific. The colonial and industrial transformation of rivers and oceans have led to extirpation or endangered status of many southern populations. Today, chronic anthropogenic stressors interact with climate change, which means that effective conservation must address changes in transformed ecosystems. Conservation goals are designed to recover both the species and their habitats. While seemingly congruent, habitat and fish management have different timetables due to speed of changes in climate, habitat, and biological processes relative to regulatory processes, habitat restoration, and project implementation. The Resist‐Accept‐Direct (RAD) framework facilitated exploration of ideas and actions to restore suitable conditions for salmon listed under the Endangered Species Act at their southern edge. Creative and big solutions are needed to recover salmon and RAD provided a way to examine conservation options to sustain salmon in an era of change. [ABSTRACT FROM AUTHOR]

2019 is the International Year of the Salmon with events and projects planned across the Northern Hemisphere. Obviously, much of the focus will be on salmon. Yet, we contend in this perspective that salmon recovery, specifically Atlantic Salmon Salmo salar recovery, can inform and be informed by Ecosystem Based Fisheries Management (EBFM). We provide the status of Atlantic Salmon recovery and the definition and objectives of EBFM and then walk through Atlantic Salmon recovery in the context of the definition of EBFM. Our purpose is to provide insight into EBFM in practice. Then we use the principles of EBFM to examine Atlantic Salmon recovery and provide an ecosystem perspective of the recovery efforts. Our intent is to provide a practical approach to considering EBFM and a broader approach for considering Atlantic Salmon recovery. [ABSTRACT FROM AUTHOR]

Diadromous species historically dominated the freshwater fish community in coastal northeastern United States rivers. As these fishes declined in concert with sweeping alterations to the region's waterscapes, so too did their utility, visibility, and relevance to each passing human generation. Due to their historically iconic status, we used endangered Atlantic Salmon Salmo salar as a springboard in our study of attitudes and values about fish in the context of modern human connections to places and the water bodies therein. We surveyed Maine residents about their connections to local water bodies and fish populations. Respondents were generally apathetic toward fish overall, but they valued the water bodies in their home turf as escapes from daily stressors. We explored this finding as it relates to motivating behavior and redefining contemporary baselines of water body health, which may help restore Maine's diadromous fish community to a local and regional treasure and commodity. Understanding the facets of sense of place, including satisfaction and attachment, can ultimately help to reframe how we communicate with the public about acting on behalf of the places they care about that overlap with important fish habitat. [ABSTRACT FROM AUTHOR]

Climate change and decadal variability are impacting marine fish and invertebrate species worldwide and these impacts will continue for the foreseeable future. Quantitative approaches have been developed to examine climate impacts on productivity, abundance, and distribution of various marine fish and invertebrate species. However, it is difficult to apply these approaches to large numbers of species owing to the lack of mechanistic understanding sufficient for quantitative analyses, as well as the lack of scientific infrastructure to support these more detailed studies. Vulnerability assessments provide a framework for evaluating climate impacts over a broad range of species with existing information. These methods combine the exposure of a species to a stressor (climate change and decadal variability) and the sensitivity of species to the stressor. These two components are then combined to estimate an overall vulnerability. Quantitative data are used when available, but qualitative information and expert opinion are used when quantitative data is lacking. Here we conduct a climate vulnerability assessment on 82 fish and invertebrate species in the Northeast U.S. Shelf including exploited, forage, and protected species. We define climate vulnerability as the extent to which abundance or productivity of a species in the region could be impacted by climate change and decadal variability. We find that the overall climate vulnerability is high to very high for approximately half the species assessed; diadromous and benthic invertebrate species exhibit the greatest vulnerability. In addition, the majority of species included in the assessment have a high potential for a change in distribution in response to projected changes in climate. Negative effects of climate change are expected for approximately half of the species assessed, but some species are expected to be positively affected (e.g., increase in productivity or move into the region). These results will inform research and management activities related to understanding and adapting marine fisheries management and conservation to climate change and decadal variability. [ABSTRACT FROM AUTHOR]

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Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon ( Salmo salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater ('parr') stage to the migratory stage where they descend streams and enter salt water ('smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 °C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5 days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes. [ABSTRACT FROM AUTHOR]

Significant differences in growth and prespawning body morphology were detected among three stocks of Atlantic salmon reared in a common marine environment. Smolts originating from river-specific broodstock of the Machias, East Machias, and Dennys populations were reared at two marine net-pen facilities for 25 months. Significant differences in stock-specific growth were observed among two stocks at both sites, suggesting a genetic basis for the observed phenotypic variation. There was a significant stock effect to the total measured phenotypic variation based on collected truss network analyses. Linear discriminant function analysis of a truss network of morphometric distances allowed for 73% accuracy of stock classification. A thin-plate spline procedure characterized the Machias body form as having a shortened narrow caudal peduncle region, a compressed body with an elongated trunk, and a deeper head region relative to the other two stocks. Phenotypic variation may be associated with hydrological characteristics of the Machias watershed. [ABSTRACT FROM AUTHOR]

We evaluated detectability of visual implant elastomer (VIE) tags in individual Atlantic salmon Salmo salar reared from smolts to adults in commercial marine net-pens. A total of 9,000 individual smolts were marked (adipose eye, lower jaw, or both) with colored VIE tags. During the period from March 1998 to December 2000 (2-28 months after tagging) a total of 3,220 fish were visually inspected for VIE tags. Tag detection rates remained high (>90%) for the first 17 months after tagging but then declined sharply, particularly for VIEs in the jaw. Use of a UV light significantly increased detection of both eye and jaw VIE tags. We conclude that VIE tags are optimal for use in Atlantic salmon when recovery of fish occurs within 17 months of tagging. [ABSTRACT FROM AUTHOR]

We investigated habitat use of wild brown trout Salmo trutta in Gilchrist Creek, Michigan, with and without a parallel cohort of introduced steelhead Oncorhynchus mykiss. This stream is typical of the region, having a low-gradient, stable discharge and a high sand bedload. By snorkeling, we evaluated seasonal habitat use in two stream reaches before and after steelhead introduction to one of the reaches. Age-0 brown trout occupied stream margins soon after emergence, using cover provided by aquatic vegetation growing on sand and silt substrates. By summer and fall, brown trout moved into deeper water and used more diverse cover types. From summer to fall, the smaller age-0 steelhead used lower current velocities than did age-0 brown trout. Similar water depth, substrate, and cover were used by the two species. At the densities studied, age-0 brown trout habitat use did not change in response to the presence of age-0 steelhead. We believe that three factors minimized the effect of steelhead: (1) the larger size of the brown trout, which gave them a competitive advantage; (2) vertical habitat segregation with steelhead suspended in the water column and brown trout near or at the bottom; and (3) temporal differences in habitat ontogeny with shifts of older, larger fish to deeper, faster water. These factors may permit these two species to coexist in low-gradient rivers. [ABSTRACT FROM AUTHOR]

We studied the survival and growth of age-0 brown trout Salmo trutta with and without age-0 steelhead Oncorhynchus mykiss, under conditions of equal salmonine density (numbers per unit area), to compare the relative effects of intraspecific and interspecific competition. We conducted these experiments from June through September in an artificial stream with recirculating water and used a replicated, completely randomized design. The experiment was initiated with four allopatric treatments of 14 brown trout each and four sympatric treatments of 7 brown trout and 7 steelhead each. Mortality during the experiment resulted in variable densities among replicates. Interactions with steelhead did not have negative effects on brown trout survival or growth. A model comparing the effects of total salmonine, steelhead, and brown trout densities on brown trout length suggested that intraspecific interactions had the strongest influence. Our results indicate that the steelhead did not influence the brown trout survival or growth during the summer growth period to the same extent as an equivalent number of brown trout. However, we recommend caution in combining these two species until the implications of interactions at other life history stages are examined. [ABSTRACT FROM AUTHOR]

Yearling pink salmon Oncorhynchus gorbuscha were collected from the Lake Huron sports catch from June through August 1985. We documented a northward movement of these fish from the St. Clair River in late spring to the Mackinac Straits area by late August. Pink salmon fed predominately upon rainbow smelt Osmerus mordax (45% by weight) and alewife Alosa psuedoharengus (38%). Other important food items were the adult stages of aquatic and terrestrial insects (5%), primarily of the orders Diptera, Ephemeroptera, and Lepidoptera. Zooplankton, of which primarily Daphnia pulex and Pontoporeia hoyi were eaten, were relatively unimportant (<1%). The diet of pink salmon overlaps those of other salmonids in the Great Lakes, and abundant year classes of pink salmon may adversely affect the growth and abundance of other species in the Great Lakes salmonid complex. [ABSTRACT FROM AUTHOR]