Showing papers on "Fish migration published in 2015"

Large reservoirs as ecological barriers to downstream movements of Neotropical migratory fish

Abstract: Most large rivers in South America are fragmented by large dams, and a common management strategy to mitigate impacts has been construction of fish passes. Recent studies, however, indicate that downstream passage of adults and young fish is nil or minimal. Better understanding of this phenomenon is needed if fishways are to provide any tangible conservation value in South America. We propose, in this article, that large reservoirs impose a different kind of barrier to migrating fish: impoundments create a diffuse gradient of hydraulic/limnological conditions that affects fish behaviour and functions as an extensive environmental filter that discourages downstream movements. To develop this idea, we characterize the barriers created by dams and reservoirs by describing their distinct nature, the effects on fish migration and potential solutions. We show, for example, that dams generally prevent upstream movements, whereas reservoirs impede mainly downstream movements. In this context, we explain how fish passes, in some instances, can partially mitigate fragmentation caused by dams, but there is no technical solution to solve the barrier effect of reservoirs. In addition, we present a body of empirical evidence that supports the theory that large reservoirs are important barriers to fish migration in South America, we offer an overview of the size of reservoirs to show that impoundments typically have large dimensions, and we discuss the significance of this theory for other regions. Based on current and proposed river regulation scenarios, we conclude that conservation of Neotropical migratory fish will be much more complicated than previously believed.

Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

Abstract: Oncorhynchus mykiss form partially migratory populations with anadromous fish that undergo marine migrations and residents that complete their life cycle in fresh water. Many populations’ anadromou...

Potential effects of dam cascade on fish: lessons from the Yangtze River

Abstract: Construction of hydroelectric dams affect river ecosystems, fish diversity, and fisheries yields. However, there are no studies assessing the combined effects on fish caused by several adjacent dams and their reservoirs, as in a 'dam cascade'. This study predicts the potential effects that a cascade of ten dams currently under construction in the upper Yangtze River in China will have on local fishes, and uses such predictions to assess the effectiveness of possible fish conservation measures. We found that the dam cascade will have serious combined effects on fishes mainly due to impoundment, habitat fragmentation and blocking, flow regime modification, and hypolimnetic discharges. The impoundments will cause loss of critical habitats for 46 endemic species. The dams will fragment the populations of 134 species and will block migration routes for 35 potamodromous fishes. Corieus guichenoti will have a high risk of extinction due to the combined effects of impoundment and blocking. Modification of the flow regime will adversely affect the recruitment of 26 species that produce drifting eggs. The start of annual spawning for 13 fishes will be postponed by more than 1 month, and fish spawning and growth opportunities will be reduced due to low water temperatures associated with hypolimnetic discharges. Combined dam effects will further reduce the likelihood of successful recruitment of some endangered species, such as Acipenser dabryanus and Psephurus gladius. Three countermeasures hold promise to mitigate the near-term effects of the dam cascade, including preservation and rehabilitation of critical habitat, restoration of a semi-natural flow regime, and stock enhancement that respects genetic integrity. These conclusions can guide the development of protection plans for fishes in the upper Yangtze River. The approach undertaken in this study-by which the known and likely effects of present and future dams were simultaneously considered in light of the biology of the species-highlights the usefulness of ichthyology for fish conservation.

Temporal patterns in adult salmon migration timing across southeast Alaska

Abstract: Pacific salmon migration timing can drive population productivity, ecosystem dynamics, and human harvest. Nevertheless, little is known about long-term variation in salmon migration timing for multiple species across broad regions. We used long-term data for five Pacific salmon species throughout rapidly warming southeast Alaska to describe long-term changes in salmon migration timing, interannual phenological synchrony, relationships between climatic variation and migratory timing, and to test whether long-term changes in migration timing are related to glaciation in headwater streams. Temporal changes in the median date of salmon migration timing varied widely across species. Most sockeye populations are migrating later over time (11 of 14), but pink, chum, and especially coho populations are migrating earlier than they did historically (16 of 19 combined). Temporal trends in duration and interannual variation in migration timing were highly variable across species and populations. The greatest temporal shifts in the median date of migration timing were correlated with decreases in the duration of migration timing, suggestive of a loss of phenotypic variation due to natural selection. Pairwise interannual correlations in migration timing varied widely but were generally positive, providing evidence for weak region-wide phenological synchrony. This synchrony is likely a function of climatic variation, as interannual variation in migration timing was related to climatic phenomenon operating at large- (Pacific decadal oscillation), moderate- (sea surface temperature), and local-scales (precipitation). Surprisingly, the presence or the absence of glaciers within a watershed was unrelated to long-term shifts in phenology. Overall, there was extensive heterogeneity in long-term patterns of migration timing throughout this climatically and geographically complex region, highlighting that future climatic change will likely have widely divergent impacts on salmon migration timing. Although salmon phenological diversity will complicate future predictions of migration timing, this variation likely acts as a major contributor to population and ecosystem resiliency in southeast Alaska.

Increasing hydrologic variability threatens depleted anadromous fish populations

Abstract: Predicting effects of climate change on species and ecosystems depend on understanding responses to shifts in means (such as trends in global temperatures), but also shifts in climate variability. To evaluate potential responses of anadromous fish populations to an increasingly variable environment, we performed a hierarchical analysis of 21 Chinook salmon populations from the Pacific Northwest, examining support for changes in river flows and flow variability on population growth. More than half of the rivers analyzed have already experienced significant increases in flow variability over the last 60 years, and this study shows that this increase in variability in freshwater flows has a more negative effect than any other climate signal included in our model. Climate change models predict that this region will experience warmer winters and more variable flows, which may limit the ability of these populations to recover.

Early human use of anadromous salmon in North America at 11,500 y ago

Abstract: Salmon represented a critical resource for prehistoric foragers along the North Pacific Rim, and continue to be economically and culturally important; however, the origins of salmon exploitation remain unresolved. Here we report 11,500-y-old salmon associated with a cooking hearth and human burials from the Upward Sun River Site, near the modern extreme edge of salmon habitat in central Alaska. This represents the earliest known human use of salmon in North America. Ancient DNA analyses establish the species as Oncorhynchus keta (chum salmon), and stable isotope analyses indicate anadromy, suggesting that salmon runs were established by at least the terminal Pleistocene. The early use of this resource has important implications for Paleoindian land use, economy, and expansions into northwest North America.

An overview of potamodromous fish upstream movements in medium-sized rivers, by means of fish passes monitoring

Abstract: This study aims to investigate the upstream movement patterns of potamodromous fish species using multi-annual monitoring of modern multi-species fish passes in two medium-sized Belgian rivers: the Berwinne and the Ambleve. During a 6-year monitoring period including a frequency of 1–5 times per week, the captured individuals were identified, measured and weighed to determine species abundance, and the periodicity of their seasonal movement patterns was investigated in relation to environmental factors. In the Ambleve, 22 different fish species were monitored (n = 1513 individuals; biomass of 154 kg) and 14 species in the Berwinne (n = 3720; 408 kg). In both fish passes, inter-annual differences were observed, but the first year of monitoring was the best in terms of biomass, indicating the existence of an opening effect just after the fish passes opening, which allowed new migration routes. Salmonids and rheophilic cyprinids were predominant in terms of biomass, while minnow and spirlin were predominant in terms of number of fishes. The diversity in size ranged from 46 to 760 mm demonstrating the importance of movements in various life stages. The capture periodicity showed different mobility patterns between the adult and juvenile stages in most species. Movements occurred frequently during the circum-reproduction period for some species, but many species moved also apart from spawning period. This study highlights the omnipresence of patrimonial holobiotic potamodromous fish at different life stages that reflect their biological needs to move throughout the annual cycle. They must be considered as target species in river continuity restoration programmes and fish-pass design.

Worldwide patterns of fish biodiversity in estuaries: Effect of global vs. local factors

Abstract: The main ecological patterns and the functioning of estuarine ecosystems are difficult to evaluate due to natural and human induced complexity and variability. Broad geographical approaches appear particularly useful. This study tested, at a worldwide scale, the influence of global and local variables in fish species richness in estuaries, aiming to determine the latitudinal pattern of species richness, and patterns which could be driven by local features such as estuary area, estuary mouth width, river flow and intertidal area. Seventy one estuarine systems were considered with data obtained from the literature and geographical information system. Correlation tests and generalized linear models (GLM) were used in data analyses. Species richness varied from 23 to 153 fish species. GLM results showed that estuary area was the most important factor explaining species richness, followed by latitude and mouth width. Species richness increased towards the equator, and higher values were found in larger estuaries and with a wide mouth. All these trends showed a high variability. A larger estuary area probably reflects a higher diversity of habitats and/or productivity, which are key features for estuarine ecosystem functioning and biota. The mouth width effect is particularly notorious for marine and diadromous fish species, enhancing connectivity between marine and freshwater realms. The effects of river flow and intertidal area on the fish species richness appear to be less evident. These two factors may have a marked influence in the trophic structure of fish assemblages.

Climatic and anthropogenic factors changing spawning pattern and production zone of Hilsa fishery in the Bay of Bengal

Abstract: Hilsa (Tenualosa ilisha Hamilton) as a single species accounts 12% for more than half of the total marine catches. About 2% of the entire population of the country is directly or indirectly engaged with Hilsa fishing. Hilsa has a wide geographical distribution in Asia from the Persian Gulf to the South China Sea. Particularly large stocks are found in Upper Bay of Bengal (BoB) region sustained by the large river systems. The global Hilsa catch is reported 75% from Bangladesh water, 15% from Myanmar, 5% from India and 5% from other countries such as Thailand and Iran. Hilsa is a highly migratory and anadromous fish with the same migratory and same breeding behavior as that of Atlantic Salmon fish (Salmo sp.). Due to various anthropogenic activities, climate change effect, increased siltation and rising of the river basins, the migratory routes as well as spawning grounds of Hilsa are disturbed, displaced or even destroyed. During last two decades hilsa production from inland water declined about 20%, whereas marine water yield increased about 3 times. Major Hilsa to catch has been gradually shifted from inland to marine water. Hilsa fish ascend for spawning migration from sea into estuaries. It has been found that the major spawning areas have been shifted to the lower estuarine regions of Hatia, Sandwip and Bhola. At the spawning ground of Hilsa, the fishing level F=1.36 yr−1, where in the river Meghna the Fmsy=0.6 yr−1 and exploitation rate E=0.70 is (Emsy>0.5). Oceanographic changes viz. high turbidity increased flooding, more tidal action and changes of salinity etc. have accelerated the change of migration patterns of spawning, growth and its production. Hilsa fecundity ranges from 1.5 to 2.0 million eggs for fish ranging in length from 35 to 50 cm. Hilsa fecundity is declining in different areas due to climate change and the declining fecundity impacting greatly on Hilsa production. Due to shifting of the spawning ground at the lower zone, the survival rate of juvenile Hilsa is seriously affected.

Importance of Reservoir Tributaries to Spawning of Migratory Fish in the Upper Paraná River

Abstract: Regulation of rivers by dams transforms previously lotic reaches above the dam into lentic ones and limits or prevents longitudinal connectivity, which impairs access to suitable habitats for the reproduction of many migratory fish species. Frequently, unregulated tributaries can provide important habitat heterogeneity to a regulated river and may mitigate the influence of impoundments on the mainstem river. We evaluated the importance of tributaries to spawning of migratory fish species over three spawning seasons, by comparing several abiotic conditions and larval fish distributions in four rivers that are tributaries to an impounded reach of the Upper Parana River, Brazil. Our study confirmed reproduction of at least 8 long-distance migrators, likely nine, out of a total of 19 occurring in the Upper Parana River. Total larval densities and percentage species composition differed among tributaries, but the differences were not consistent among spawning seasons and unexpectedly were not strongly related to annual differences in temperature and hydrology. We hypothesize that under present conditions, densities of larvae of migratory species may be better related to efficiency of fish passage facilities than to temperature and hydrology. Our study indicates that adult fish are finding suitable habitat for spawning in tributaries, fish eggs are developing into larvae, and larvae are finding suitable rearing space in lagoons adjacent to the tributaries. Our findings also suggest the need for establishment of protected areas in unregulated and lightly regulated tributaries to preserve essential spawning and nursery habitats. Copyright © 2014 John Wiley & Sons, Ltd.

Recovery of a mining-damaged stream ecosystem

Abstract: This paper presents a 30+ year record of changes in benthic macroinvertebrate communities and fish populations associated with improving water quality in mining-influenced streams. Panther Creek, a tributary to the Salmon River in central Idaho, USA suffered intensive damage from mining and milling operations at the Blackbird Mine that released copper (Cu), arsenic (As), and cobalt (Co) into tributaries. From the 1960s through the 1980s, no fish and few aquatic invertebrates could be found in 40 km of mine-affected reaches of Panther Creek downstream of the metals contaminated tributaries, Blackbird and Big Deer Creeks. Efforts to restore water quality began in 1995, and by 2002 Cu levels had been reduced by about 90%, with incremental declines since. Rainbow Trout (Oncorhynchus mykiss) were early colonizers, quickly expanding their range as areas became habitable when Cu concentrations dropped below about 3X the U.S. Environmental Protection Agency’s biotic ligand model (BLM) based chronic aquatic life criterion. Anadromous Chinook Salmon (O. tshawytscha) and steelhead (O. mykiss) have also reoccupied Panther Creek. Full recovery of salmonid populations occurred within about 12-years after the onset of restoration efforts and about 4-years after the Cu chronic criteria had mostly been met, with recovery interpreted as similarity in densities, biomass, year class strength, and condition factors between reference sites and mining-influenced sites. Shorthead Sculpin (Cottus confusus) were slower than salmonids to disperse and colonize. While benthic macroinvertebrate biomass has increased, species richness has plateaued at about 70 to 90% of reference despite the Cu criterion having been met for several years. Different invertebrate taxa had distinctly different recovery trajectories. Among the slowest taxa to recover were Ephemerella, Cinygmula and Rhithrogena mayflies, Enchytraeidae oligochaetes, and Heterlimnius aquatic beetles. Potential reasons for the failure of some invertebrate taxa to recover include competition, and high sensitivity to Co and Cu.

Assessing the passage of obstacles by fish. Concepts, design and application

Abstract: 6 Biodiversity is currently undergoing one of the most intense and rapid crises of mass extinction that the planet Earth has ever known and humanity is, without any doubt, the essential cause of the drastic losses. Among the many factors are chemical pressures in the form of water, soil and air pollution as well as in the form of climate change, excessive use of natural resources (hunting, fishing, cutting of forests, etc.), and physical pressures such as the destruction or loss of access to the habitats required by numerous species for their survival. The impact of physical pressures and in particular the fragmentation of habitats is today better understood and has been amply demonstrated. The international community has progressively acknowledged this issue and responded with a number of legal texts. In the European Union, the Water framework directive (WFD) is a prime example. The objective of the texts is generally to preserve and to restore ecological continuity and ecological corridors in order to slow or to stop at least part of the loss of biodiversity now taking place. Before taking action in favour of ecological continuity, it is necessary to assess the degree to which natural areas have been modified and to identify the situations creating the greatest problems. In aquatic ecosystems, hydraulic structures are one of the main causes of degraded ecological continuity, particularly for fish whose survival depends on their freedom of movement. An assessment of the impact of structures on the movement of fish is a prerequisite to determining the seriousness of problems in the field and identifying the priorities for action. To date, these assessments have generally been carried out by a small number of highly specialised experts. However, the massive (yet often unsuspected) numbers of transverse obstacles on rivers (over 70 000 obstacles have already been inventoried in France thanks to the characterisation reports for the WFD) created a pressing need for a simple, robust and standardised method for assessments that could be used by a large number of persons active in the environmental and territorial-planning fields. Onema responded to the challenge and coordinated the development of a protocol to assess the impact of obstacles to flow on the movement of the main fish species in continental France.

Juvenile salmon usage of the Skeena River estuary.

Abstract: Migratory salmon transit estuary habitats on their way out to the ocean but this phase of their life cycle is more poorly understood than other phases. The estuaries of large river systems in particular may support many populations and several species of salmon that originate from throughout the upstream river. The Skeena River of British Columbia, Canada, is a large river system with high salmon population- and species-level diversity. The estuary of the Skeena River is under pressure from industrial development, with two gas liquefaction terminals and a potash loading facility in various stages of environmental review processes, providing motivation for understanding the usage of the estuary by juvenile salmon. We conducted a juvenile salmonid sampling program throughout the Skeena River estuary in 2007 and 2013 to investigate the spatial and temporal distribution of different species and populations of salmon. We captured six species of juvenile anadromous salmonids throughout the estuary in both years, and found that areas proposed for development support some of the highest abundances of some species of salmon. Specifically, the highest abundances of sockeye (both years), Chinook in 2007, and coho salmon in 2013 were captured in areas proposed for development. For example, juvenile sockeye salmon were 2–8 times more abundant in the proposed development areas. Genetic stock assignment demonstrated that the Chinook salmon and most of the sockeye salmon that were captured originated from throughout the Skeena watershed, while some sockeye salmon came from the Nass, Stikine, Southeast Alaska, and coastal systems on the northern and central coasts of British Columbia. These fish support extensive commercial, recreational, and First Nations fisheries throughout the Skeena River and beyond. Our results demonstrate that estuary habitats integrate species and population diversity of salmon, and that if proposed development negatively affects the salmon populations that use the estuary, then numerous fisheries would also be negatively affected.

Environmental Influences on Fish Migration in a Hydropeaking River

Abstract: Fish have evolved traits and life history characteristics that enable them to survive, exploit and depend on the flow regime of rivers, particularly the timing and predictability of flows for spawning and rearing their young. It is unclear to what degree pulsed flows from hydropower facilities and other environmental variables influence migratory behaviours. We used Dual Frequency Identification Sonar in the Michipicoten River, Canada, to address the relationship between fish migration and environmental factors with a focus on flow magnitude and fluctuation. In both 2007 and 2009, the peak of the Chinook (Oncorhynchus tshawytscha) and pink salmon (Oncorhynchus gorbuscha) migration occurred on 8 September. Mean water temperature on this date was 18 °C and precipitously dropped afterwards. The photoperiod was roughly 12-h long with sunrise at 700 h and sunset at 2000 h. Most fishes moved upstream during the hours of darkness between 2000 and 600 h. The lowest counts of fish occurred from noon to just before sunset, whereas highest counts commonly occurred from 1 to 2 h after sunset. Fish moved upstream during all magnitudes of flow; however, there was a slight preference for larger flows in 2007 but not in 2009. Changes in flow magnitude occurred both during the day and night, with flows typically increasing during the day to meet electrical demand and decreasing at night. Most fishes moved upstream during periods of little to no change in flow. High flows and changing flows may deter salmon from moving up the Michipicoten River but not likely in a significant manner to cause energetic stress or harm. Other adverse effects of pulsed flows, however, must still be considered for spawning, hatching and rearing success. Copyright © 2014 John Wiley & Sons, Ltd.

Fish Community Response to a Small-Stream Dam Removal in a Maine Coastal River Tributary

Abstract: Sedgeunkedunk Stream, a third-order tributary to the Penobscot River in Maine, historically has supported several anadromous fishes including Atlantic Salmon Salmo salar, Alewife Alosa pseudoharengus, and Sea Lamprey Petromyzon marinus. Two small dams constructed in the 1800s reduced or eliminated spawning runs entirely. In 2009, efforts to restore marine–freshwater connectivity in the system culminated in removal of the lowermost dam (Mill Dam) providing access to 4.7 km of lotic habitat and unimpeded passage into the lentic habitat of Fields Pond. In anticipation of these barrier removals, we initiated a modified before-after-control-impact study, and monitored stream fish assemblages in fixed treatment and reference sites. Electrofishing surveys were conducted twice yearly since 2007. Results indicated that density, biomass, and diversity of the fish assemblage increased at all treatment sites upstream of the 2009 dam removal. No distinct changes in these metrics occurred at reference sites. We...

Trophic Ontogeny of Fluvial Bull Trout and Seasonal Predation on Pacific Salmon in a Riverine Food Web

Abstract: Bull Trout Salvelinus confluentus are typically top predators in their host ecosystems. The Skagit River in northwestern Washington State contains Bull Trout and Chinook Salmon Oncorhynchus tshawytscha populations that are among the largest in the Puget Sound region and also contains a regionally large population of steelhead O. mykiss (anadromous Rainbow Trout). All three species are listed as threatened under the Endangered Species Act (ESA). Our objective was to determine the trophic ecology of Bull Trout, especially their role as predators and consumers in the riverine food web. We seasonally sampled distribution, diets, and growth of Bull Trout in main-stem and tributary habitats during 2007 and winter–spring 2008. Consumption rates were estimated with a bioenergetics model to (1) determine the annual and seasonal contributions of different prey types to Bull Trout energy budgets and (2) estimate the potential impacts of Bull Trout predation on juvenile Pacific salmon populations. Salmon carc...

Assessing demographic effects of dams on diadromous fish: a case study for Atlantic salmon in the Penobscot River, Maine

Abstract: Dams are a major contributor to the historic decline and current low abundance of diadromous fish. We developed a population viability analysis to assess demographic effects of dams on diadromous fish within a river system and demonstrated an application of the model with Atlantic salmon in the Penobscot River, Maine. We used abundance and distribution of wild- and hatchery-origin adult salmon throughout the watershed as performance metrics. Salmon abundance, distribution to upper reaches of the Penobscot watershed, and the number and proportion of wild-origin fish in the upper reaches of the Penobscot watershed increased when dams, particularly mainstem dams, were removed or passage efficiency was increased. Salmon abundance decreased as indirect latent mortality per dam was increased. Salmon abundance increased as marine or freshwater survival rates were increased, but the increase in abundance was larger when marine survival was increased than when freshwater survival was increased. Without hatchery supplementation, salmon abundance equalled zero with low marine and freshwater survival but increased when marine and freshwater survival rates were increased. Models, such as this one, that incorporate biological, environmental, and functional parameters can be used to predict ecological responses of fish populations and can help evaluate and prioritize management and restoration actions for diadromous fish.

Between-watershed movements of two anadromous salmonids in the Arctic

Abstract: A long-term study in the River Halselva in the Arctic region of Norway demonstrated that movements between watersheds were considerably higher in anadromous brown trout (Salmo trutta) than anadromous Arctic char (Salvelinus alpinus). Fourteen smolt year classes of both species were captured in a fish trap, individually tagged, and thereafter registered each time they passed the trap during their migration between the sea and fresh water every summer. Annual mean survival (i.e., recovery rate) after the first entry to sea as smolts was estimated as 31.4% in Arctic char and 26.6% in brown trout. Most surviving Arctic char returned to the River Halselva to overwinter after the same summer that they migrated to sea as smolts. However, several brown trout overwintered one to four times in other watersheds, mainly the considerably larger River Altaelva, before most eventually returned to the River Halselva upon maturation. The substantial difference in movement rate between watersheds between Arctic char (2.2%)...

Retrospective examination of habitat use by blueback herring (Alosa aestivalis) using otolith microchemical methods

Abstract: Understanding the location and duration of habitat use by young fish is important for management and restoration efforts, but is largely unknown in anadromous species. We used otolith microchemistry and ambient water concentrations of Ca, Ba, Mn, and Sr to identify habitat use in the first year of growth for 131 returning adult blueback herring (Alosa aestivalis) collected in seven spawning runs along the coast of Maine, USA. Ambient Sr:Ca ratios were correlated with salinity and were used as primary indicators of habitat use. Results revealed variable individual migration histories with several discrete migratory patterns; some fish migrated into seawater well before the end of the first year, while the majority exhibited longer residency in freshwater or low salinity habitat. Total area of available habitats ranged from approximately 213 to 6053 ha fresh water and 204 to 3395 ha estuary. Residency in freshwater or low salinity habitats was positively correlated with extent of freshwater habitat (r = 0.3...

Differential use of salmon by vertebrate consumers: implications for conservation

Abstract: Salmon and other anadromous fish are consumed by vertebrates with distinct life history strategies to capitalize on this ephemeral pulse of resource availability. Depending on the timing of salmon arrival, this resource may be in surplus to the needs of vertebrate consumers if, for instance, their populations are limited by food availability during other times of year. However, the life history of some consumers enables more efficient exploitation of these ephemeral resources. Bears can deposit fat and then hibernate to avoid winter food scarcity, and highly mobile consumers such as eagles, gulls, and other birds can migrate to access asynchronous pulses of salmon availability. We used camera traps on pink, chum, and sockeye salmon spawning grounds with various run times and stream morphologies, and on individual salmon carcasses, to discern potentially different use patterns among consumers. Wildlife use of salmon was highly heterogeneous. Ravens were the only avian consumer that fed heavily on pink salmon in small streams. Eagles and gulls did not feed on early pink salmon runs in streams, and only moderately at early sockeye runs, but were the dominant consumers at late chum salmon runs, particularly on expansive river flats. Brown bears used all salmon resources far more than other terrestrial vertebrates. Notably, black bears were not observed on salmon spawning grounds despite being the most frequently observed vertebrate on roads and trails. From a conservation and management perspective, all salmon species and stream morphologies are used extensively by bears, but salmon spawning late in the year are disproportionately important to eagles and other highly mobile species that are seasonally limited by winter food availability.

The Effects of DAM Removal on River Colonization by Sea Lamprey Petromyzon Marinus

Abstract: Habitat fragmentation is an important cause of biodiversity loss in freshwater systems, as worldwide rivers have been fragmented by dams and other hydraulic structures. To restore freshwater fish populations, some barriers have been removed, but the long-term ecological effects of this removal have been rarely quantified. In the present study, we quantified the effects of barrier removal on river colonization by anadromous sea lamprey (Petromyzon marinus) by analyzing the spatial distribution and nest density in a small coastal river (France) from 1994 to 2011. Our results demonstrated the benefit of dam removal within few years after restoration. Indeed, the spatial distribution of nests shifted significantly upstream and was more uniform throughout the river after removal. Our results also suggest that the spatial patterns of habitat colonization were affected by the density of nests, river flow and connectivity. Finally, although the number of nests was significantly higher after removal, it was not possible to clearly identify the contribution of intrinsic versus external factors involved in this pattern. Further investigations are therefore needed to quantify the potential subsequent effects on juvenile recruitment and the overall population dynamics. Copyright © 2014 John Wiley & Sons, Ltd.

An Assessment of Fish Assemblage Structure in a Large River

Abstract: The Penobscot River drains the largest watershed in Maine and once provided spawning and rearing habitats to 11 species of diadromous fishes. The construction of dams blocked migrations of these fishes and likely changed the structure and function of fish assemblages throughout the river. The proposed removal of two main-stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on a dam obstructing a major tributary is anticipated to increase passage of and improve habitat connectivity for both diadromous and resident fishes. We captured 61 837 fish of 35 species in the Penobscot River and major tributaries, through 114 km of boat electrofishing. Patterns of fish assemblage structure did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability within the main-stem river, including smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and golden shiner Notemigonus crysoleucas. However, distinct fish assemblages were present among river sections bounded by dams. Many diadromous species were restricted to tidal waters downriver of the Veazie Dam; Fundulus species were also abundant within the tidal river section. Smallmouth bass and pumpkinseed were most prevalent within the Veazie Dam impoundment and the free-flowing river section immediately upriver, suggesting the importance of both types of habitat that supports multiple life stages of these species. Further upriver, brown bullhead Ameiurus nebulosus, yellow perch Perca flavescens, chain pickerel Esox niger, and cyprinid species were more prevalent than within any other river section. Our findings describe baseline spatial patterns of fish assemblages in the Penobscot River in relation to dams with which to compare assessments after dam removal occurs. Copyright © 2014 John Wiley & Sons, Ltd.

Coastal Migration and Homing of Roanoke River Striped Bass

Abstract: Anadromy in Roanoke River Striped Bass Morone saxatilis has been documented; however, the specifics of the ocean migration and the degree of homing in this population remain unstudied and would greatly benefit the management of this economically important species. To this end, we telemetered and released 19 large Roanoke River Striped Bass (750‐1,146 mm TL) on their spawning grounds during the springs of 2011 and 2012. Data from a large-scale acoustic telemetry array along the U.S. Atlantic coast (480 total receivers, including the Roanoke River) were used to evaluate the seasonal migration and distribution of telemetered fish, their degree of homing and skipped spawning, their migration speeds, and the environmental drivers of migration timing. We found that large Roanoke River Striped Bass (>900 mm TL) rapidly emigrated (»59 km/d) after spawning to distant (>1,000 km) northern ocean waters (New Jersey to Massachusetts), where they spent their summers. They then migrated southward in the fall to overwintering habitats off Virginia and North Carolina and completed their migration circuit the following spring by returning to the Roanoke River to spawn. Our results showed no evidence of straying or skipped spawning, as all migrants successfully returned (homed) to the Roanoke River the next spring to spawn. Cooler ocean water temperatures in 2013 delayed the spring spawning run by nearly 3 weeks relative to a year of average spring temperatures (2012). Our study provides novel information that aids the management of Striped Bass at both small (e.g., setting of fishing seasons in the Roanoke River) and large spatial scales (e.g., stock identification of Roanoke River fish in the mixed-stock ocean fishery) and more broadly highlights the utility of large-scale cooperative telemetry arrays in studying fish migration.

Balancing Conservation and Harvest Objectives: a Review of Considerations for the Management of Salmon Hatcheries in the U.S. Pacific Northwest

Abstract: The U.S. Pacific Northwest (PNW) has one of the largest suites of hatchery programs for anadromous salmonids in the world, with about 500 programs producing about 325 million juvenile fish. A total of about 0.7 million Pink Salmon Oncorhynchus gorbuscha, 21 million steelhead O. mykiss, 50 million Chum Salmon O. keta, 32 million Sockeye Salmon O. nerka, 41 million Coho Salmon O. kisutch, and 182 million Chinook Salmon O. tshawytscha are released annually from PNW hatcheries. These fish provide for robust, sustainable fisheries, and their production and release are designed to meet legal agreements, international treaties, and treaty trust responsibilities. However, this level of hatchery production is often assumed to have negative effects on the conservation of U.S. Endangered Species Act–listed salmon populations in the region. A review of the development of best management practices to balance the conservation and sustainable fisheries goals for PNW salmon hatcheries indicates that to be success...

Ontogenetic differences in Atlantic salmon phosphorus concentration and its implications for cross ecosystem fluxes

Abstract: Nutrient transport across ecosystem boundaries by migratory animals can regulate trophic and biogeochemical dynamics of recipient ecosystems. The magnitude and direction of net nutrient flow between ecosystems is modulated by life history, abundance and biomass, individual behavior, and body element composition of migrating individuals. We tested common assumptions applied to nutrient transport models regarding homeostasis of species' body element composition across space and ontogenetic stage. We quantified whole body phosphorus (P) concentration of three life stages of wild Atlantic salmon (Salmo salar L.) from three distinct populations in Newfoundland, Canada, to evaluate the importance of river of origin and life stage as predictors of salmon %P. We found that life stage was a more important predictor of salmon %P than river of origin, and that %P of post-spawn adults migrating downstream to the ocean (i.e., kelts) was more similar to %P of juveniles migrating downstream to the ocean (i.e., smolts) than it was to %P of adults migrating upstream to spawn. We then compared nutrient flux for the three rivers over a 20-year period calculated with body composition values extracted from existing literature and our direct measurements to evaluate how assumptions regarding spatial and ontogenetic homogeneity in salmon %P influenced the observed P fluxes. We demonstrate that assuming equality of kelt %P and adult %P results in an overestimate of net nutrient flux to rivers by Atlantic salmon and the erroneous conclusion that Atlantic salmon populations are unconditional sources of nutrients to their natal watersheds. Instead, Newfoundland's salmon populations are conditional sinks of freshwater P, which is the opposite functional role of Pacific salmon. Our results highlight that a better understanding of intraspecific variation in body element composition of fishes is a prerequisite to determining their role in global biogeochemical cycling.

Interpreting nitrogen stable isotopes in the study of migratory fishes in marine ecosystems

Abstract: Stable isotopes have proven effective in the ecological study of terrestrial, freshwater, marine and estuarine systems. However, their utility in the study of large migratory fishes in the dynamic ocean may be more difficult to ascertain. Migration across large areas of ocean in short periods of time may result in a large amount of variability in the nitrogen ratios of large pelagic fishes. High variability was found in nitrogen ratios (δ15N) used to quantify trophic positions of large pelagic fish species and their prey in the southern Gulf of California. Mean δ15N values for eleven large pelagic predators ranged from 14.8 ‰ for blue marlin to 18.7 ‰ for amberjack. Predators typically present in the Gulf during winter months had a higher mean value (18.5 ± 0.7 ‰) than summer predators (15.8 ± 1.5 ‰). Common prey items, including cephalopods, fish and crustaceans, had mean δ15N values ranging from 12.2 to 19.1 ‰ (epipelagic fishes = 17.5 ± 0.7 ‰, cephalopods = 15.6 ± 0.9 ‰, inshore fishes = 14.2 ± 1.6 ‰, crustaceans = 12.2 ± 0.4 ‰), in many cases exceeding their predators by more than one full trophic level. We analyzed potential sources of this variability by examining diets, oceanographic conditions and fish migration. Diet shifts with size do not account for the variability, but the likely source appears to be slow turnover rate of body tissues of migratory pelagic fish as they traverse both highly productive and oligotrophic water masses in the eastern Pacific Ocean. From this study, we advise caution when interpreting results of stable isotope ratios in migratory pelagic fishes, and suggest designing studies that account for sources of variability.

The Spawning Success of Early Maturing Resident Hatchery Chinook Salmon in a Natural River System

Abstract: Hatchery propagation of spring Chinook Salmon Oncorhynchus tshawytscha has been shown to increase the proportion of males maturing as minijacks (age 2) or microjacks (age 1) relative to those proportions in wild populations. However, little is known about the success of early maturing males when they spawn in the wild. A captive broodstock program for spring Chinook Salmon in the White River (a tributary of the Wenatchee River, Washington) has a high rate of early male maturity. We used genetic parentage analysis to evaluate the spawning success of anadromous males in comparison with inferred early maturing resident, hatchery-origin males that spawned naturally. Based on samples of juvenile offspring (n = 1,007–1,368 fish/year) and a nearly complete sample of the potential anadromous parents, we found that during 2006–2009, 26–45% of the progeny did not have a male parent in the anadromous sample. In contrast, 0–23% of the progeny did not have a female parent represented in the sample. Using grand...

An experimental field evaluation of winter carryover effects in semi‐anadromous brown trout (Salmo trutta)

Abstract: For semi-anadromous brown trout, the decision whether or not to smoltify and migrate to the sea is believed to be made at the end of the preceding summer in response to both local environmental conditions and individual physiological status. Stressors experienced during the fall may therefore influence their propensity to migrate as well as carry over into the winter resulting in mortality when fish face challenging environmental conditions. To evaluate this possibility, we artificially elevated cortisol levels in juvenile trout (via intracoelomic injection of cortisol in the fall) and used passive integrated transponder tags to compare their overwinter and spring survival, growth, and migration success relative to a control group. Results suggest that overwinter mortality is high for individuals in this population regardless of treatment. However, survival rates were 2.5 times lower for cortisol-treated fish and they experienced significantly greater loss in mass. In addition, less than half as many cortisol-treated individuals made it downstream to a stationary antenna over the winter and also during the spring migration compared to the control treatment. These results suggest that a fall stressor can reduce overwinter survival of juvenile brown trout, negatively impact growth of individuals that survive, and ultimately result in a reduction in the number of migratory trout. Carryover effects such as those documented here reveal the cryptic manner in which natural and anthropogenic stressors can influence fish populations. J. Exp. Zool. 323A: 645-654, 2015. © 2015 Wiley Periodicals, Inc.