Search

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 [...]

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]

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 [...]

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, [...]

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]

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]