Geology topics

Research about Maine

Source-linked reports with geographic coverage including Maine.

At least 73 records · Page 4Linked to original sources

USGS2020

River channel response to dam removals on the lower Penobscot River, Maine, United States

Most geomorphology studies of dam removals have focused on sites with appreciable quantities of stored sediments. There is great interest in channel responses to sediment releases because of potential effects on aquatic and riparian habitats and human uses of these areas. Yet, behind many dams in the Northeast U.S. and other regions of the world only minor accumulations of sediment are present because of small impoundments, run‐of‐river dam design and management (inflow ≈ outflow), low watershed sediment yield, and/or channel beds dominated by coarse sediment and/or bedrock. The two lowermost dams on the Penobscot River in Maine, United States, removed in 2012–2013, exemplified those conditions. Great Works and Veazie dams were about 6 and 10 m high, respectively. Pre‐project geophysical surveys showed coarse substrates dominated the reservoir beds and little sediment was stored in either impoundment—functions of reach geology, late Quaternary history, and upstream dams. Repeat cross‐section surveys in each impoundment, as well as the upstream and downstream reaches, were completed from 2009 to 2015 to evaluate channel morphology responses to the removals. Bed‐sediment grain size and turbidity were also measured to characterize changes in bed texture and suspended sediment. Pre‐ and post‐removal survey comparisons confirmed the expectation that bed elevations, channel shapes, and channel positions would not change substantially. Changes were often within, or close to, our estimated random measurement error. Our study shows that large‐scale physical changes are likely to be minimal when impoundments storing relatively little sediment are removed from erosion‐resistant streambeds. Many dams eligible for removal have these characteristics, making these observations an important case study that is largely unrepresented in the dam removal literature.

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USGS2020

Methods of collection and quality assessment of arsenic data in well-water supplies in Maine, 2001–2 and 2006–7

The U.S. Geological Survey, in cooperation with the U.S. Centers for Disease Control and Prevention and the Maine Center for Disease Control and Prevention, assessed the chemical characteristics and the occurrence, distribution, and oxidation state of inorganic arsenic in drinking water from selected domestic well-water supplies in Maine in 2001–2 and 2006–7. The data collected provide support for evaluating arsenic-removal efficiencies of household water-purification systems and provide information to State and local officials that can be used in determining a water-treatment approach for the removal of arsenic from drinking water.

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USGS2020

Science in action or science inaction? Evaluating the implementation of "best available science" in hydropower relicensing

Over the next two decades, half of all hydropower projects in the USA will require relicensing by the Federal Regulatory Commission (FERC). Relicensing proceedings invoke a range of informational sources and agency regulators are tasked with using the “best available science” (BAS) to make informed decisions about hydropower operations and management. Although embraced as the standard, BAS is not well-defined. The Kennebec and Penobscot River watersheds in Maine provide an ideal opportunity for studying BAS in the relicensing process. Using citation analysis and an online survey, we identified informational sources used in relicensing decisions for dams in this system and assessed agency perceptions of BAS. Analysis of relicensing documents (n=62) demonstrates that FERC and licensee documents are highly similar in citation composition. National Oceanic and Atmospheric Administration (NOAA) documents typically cite more sources and are three times more likely to cite peer-reviewed sources than FERC and licensee documents. Survey data reveals that federal and state agency respondents (n=49) rate peer-reviewed literature highly as BAS, followed by university, agency, and expert sources while industry and community sources rate poorly. Federal respondents report using peer-reviewed/academic sources more frequently and expert sources less frequently than state respondents. Overall, the agreement between individuals with respect to the valuation of sources is low. The reported differences in information use may be linked to disparities in the access to certain sources of information, particularly peer-reviewed literature. Enhanced understanding of information use may aid in identifying pathways for better informed relicensing decisions.

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USGS2020

Balancing fish-energy-cost tradeoffs through strategic basin-wide dam management

Dam management often involves tradeoffs among hydropower generation capacity, environmental impacts, and project costs. However, our understandings of such tradeoffs under a full range of dam management options remain limited, which hinders our ability to make sound and scientifically defensible dam management decisions. In order to assess the scope for theoretical tradeoffs, a dynamic model of hydropower production, important fish populations, and project costs was developed using the system dynamics modeling technique. Three dam management options investigated the likely outcomes from: dam removal, fishway installation (e.g., pool-and-weir, Denil, and fish lift), and no action. The model was applied to the Penobscot River located in Maine, United States as a proof of concept, where recent actions (i.e., dam removal and fishway construction) have been undertaken. We modeled theoretical influence of these actions on four significant sea-run fish (alewife Alosa pseudoharengus , American shad Alosa sapidissima , Atlantic salmon Salmo salar , and sea lamprey Petromyzon marinus ) by developing an index of spawner population potential based on population models for each species. Optimal dam management solutions may maximize spawner population potential and energy production to 60-62% of maximum achievable values while limiting the project cost to US$17 million (44% of the maximum value). Our results demonstrate that basin-scale management strategies may increase the migratory fish restoration while preserving hydropower generation capacity. Diversification of management options (e.g., combination of fishway installations, dam removals, and generation capacity) may increase the efficacy of strategic fish-energy-cost tradeoffs.

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USGS2019

Groundwater recharge estimates for Maine using a Soil-Water-Balance model—25-year average, range, and uncertainty, 1991 to 2015

To address the lack of information on the spatial and temporal variability of recharge to groundwater systems in Maine, a study was initiated in cooperation with the Maine Geological Survey to use the U.S. Geological Survey Soil-Water-Balance model to evaluate annual average potential recharge across the State over a 25-year period from 1991 to 2015. The Maine Soil-Water-Balance model was calibrated using annual observations of recharge, runoff, and evapotranspiration for 32 calibration watersheds in the State during 2001–12 (902 total observations). Observations of recharge, runoff, and evapotranspiration were developed for each watershed to reduce the possibility of nonunique combinations of model parameters during the calibration. The Maine Soil-Water-Balance model was run using an optional evapotranspiration calculation method that provides more control for calibration than the standard method. The model was calibrated using the Parameter ESTimation software suite. The overall mean model error (average of all annual residuals for recharge, runoff, and precipitation) was 0.39 inch. The mean of the absolute value of the residuals, or the mean absolute error, was 2.32 inches. The root mean squared error for the calibrated model overall was 3.14 inches. Statistical tests indicated that the model residuals are normally distributed. To determine the potential uncertainty in the median annual potential recharge that results from uncertainty in the parameters as they relate to information contained in the observations, 300 alternate model realizations were run, and the standard deviation of the median potential recharge value at every pixel was calculated. Simulated 25-year median potential recharge across the State is widely variable; this variability closely follows patterns of precipitation, with additional variability contributed by the patchwork nature of the combinations of land-use class and hydrologic soil group inputs, and distribution of available water capacity in the soil across the State. Overall, the 25-year median annual potential recharge across the State is 7.5 inches, ranging from a low of about 5 inches to over 30 inches. The statewide range in the 25-year minimum values is from just over 2 inches to just over 20 inches. The statewide range in the 25-year maximum potential recharge is between 15 and 48 inches per year. The model areas with the highest simulated median potential recharge include areas underlain by type A soils (sandy and well drained), particularly those that also have land uses with low or little vegetation (blueberry barrens, developed, open space, scrub/shrub, and cropland, for example). The potential recharge values for these areas are similar to previously published values for comparable soil types. The 25-year average potential recharge grids were compared to recharge evaluated through groundwater-flow models or other methods in four hydrogeologic settings at six study areas in the State. A key factor in the ability of the Soil-Water-Balance model to reproduce the earlier study results was whether the available water-capacity data were an appropriate match for the hydrologic soil groups. The Maine Soil-Water-Balance model does a good job in representing an accurate potential recharge under circumstances where the surficial mapped soils extend below the surface to the water-table aquifer and where the available water-capacity data are in an appropriate range for the hydrologic soil group. One hydrogeologic setting that was challenging for the model was where a silt and clay layer was below a shallow soil unit that did not have available water-capacity data that were appropriate for the hydrologic soil group. In these cases, typically the available water-capacity data were very low, not accounting for the impedance of water flow provided by the underlying soil. The model also does not simulate well areas where bedrock surfaces are above the water table but below the plant rooting zone. The data products accompanying this report are intended to be used to provide first-cut estimates of recharge for geographic areas no smaller than the smallest watersheds used in the calibration of the model—or about 1.5 square miles. It is recommended that the grids are used to calculate an area-wide average potential recharge for any given area of study, and an uncertainty around the mean should be calculated from the standard deviation grid at the same time.

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USGS2019

Avian influenza virus prevalence in marine birds is dependent on ocean temperatures

Waterfowl and shorebirds are the primary hosts of influenza A virus (IAV), however, in most surveillance efforts, large populations of birds are not routinely examined; specifically marine ducks and other birds that reside predominately on or near the ocean. We conducted a long-term study sampling sea ducks and gulls in coastal Maine for IAV and found a virus prevalence (1.7%) much lower than is typically found in freshwater duck populations. We found wide year-to-year variation in virus detection in sea ducks and that the ocean water temperature was an important factor affecting IAV prevalence. In particular, the ocean temperature that occurred 11 d prior to collecting virus positive samples was important while water temperature measured concurrently with host sampling had no explanatory power for viral detection. We also experimentally showed that IAV is relatively unstable in sea water at temperatures typically found during our sampling. This represents the first report of virus prevalence and actual environmental data that help explain the variation in marine IAV transmission dynamics.

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USGS2019

Observations of American Shad Alosa sapidissima approaching and using a vertical slot fishway at the head-of-tide Brunswick Dam on the Androscoggin River, Maine

American Shad Alosa sapidissima have historically supported an important fishery along the Atlantic coastal waters of North America. However, the construction of dams reduced populations and restricted landings. Fishways are intended to mitigate obstacles to anadromous fish migrations, but a thorough evaluation of their efficiency is warranted. We analyzed data collected from video recordings, hydropower turbine operations, and telemetry conducted by the Maine Department of Marine Resources to evaluate American Shad behavior while approaching and using a vertical slot fishway at the head-of-tide Brunswick Dam on the Androscoggin River in Maine. American Shad passage at the dam has been poor, ranging from 0 to 1,100 fish per year, relative to passage at other facilities in the region. Additionally, our observations indicate that there are relatively high numbers of American Shad present downstream in the river (averaging 50,000) compared with the entrance of the fishway or its pools (<8,000). On average, the rates of observed American Shad on the side of the river near the fishway entrance were significantly higher (6.5–8.6 individuals/min) when the turbine closest to the entrance of the fishway was not operating compared with when it was operating (4.1 individuals/min). Most of the radio-tagged American Shad remained in the river below the dam or went undetected. Eleven of 57 tagged fish were detected at the fishway entrance and of those only five were detected in the lower fishway. Individuals that were detected were observed making multiple attempts at entering the fishway, but movements were restricted to the lower pools. Our results suggest that this fishway is not conducive to the passage of American Shad. Examining the relationship between hydropower operations and other environmental variables on the behavior and passage of migrating anadromous fish remain an area for further study.

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USGS2019

Replicated landscape genomics identifies evidence of local adaptation to urbanization in wood frogs

Native species that persist in urban environments may benefit from local adaptation to novel selection factors. We used double-digest restriction-side associated DNA (RAD) sequencing to evaluate shifts in genome-wide genetic diversity and investigate the presence of parallel evolution associated with urban-specific selection factors in wood frogs ( Lithobates sylvaticus ). Our replicated paired study design involved 12 individuals from each of 4 rural and urban populations to improve our confidence that detected signals of selection are indeed associated with urbanization. Genetic diversity measures were less for urban populations; however, the effect size was small, suggesting little biological consequence. Using an F ST outlier approach, we identified 37 of 8344 genotyped single nucleotide polymorphisms with consistent evidence of directional selection across replicates. A genome-wide association study analysis detected modest support for an association between environment type and 12 of the 37 F ST outlier loci. Discriminant analysis of principal components using the 37 F ST outlier loci produced correct reassignment for 87.5% of rural samples and 93.8% of urban samples. Eighteen of the 37 F ST outlier loci mapped to the American bullfrog ( Rana [Lithobates] catesbeiana ) genome, although none were in coding regions. This evidence of parallel evolution to urban environments provides a powerful example of the ability of urban landscapes to direct evolutionary processes.

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USGS2019

It’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem

The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of 1) key seasonal processes, patterns, and events; 2) direct evidence for shifts in timing; 3) implications of phenological responses for linked ecological-human systems; and 4) potential phenology-focused adaptation strategies and actions. Twenty studies demonstrated shifts in timing of regional marine organisms and seasonal environmental events. The most common response was earlier timing, observed in spring onset, spring and winter hydrology, zooplankton abundance, and diadromous fish migrations. Later timing was documented for fall onset, reproduction and fledging in Atlantic puffins, spring and fall phytoplankton blooms, and occurrence of some larval fishes. Changes in event duration generally increased and were detected in zooplankton peak abundance, early life history periods of macro-invertebrates, and lobster fishery landings. Reduced duration was observed in winter-spring ice-affected stream flows. Two studies projected phenological changes, both finding diapause duration would decrease in zooplankton under future climate scenarios. Phenological responses were species-specific and varied depending on the environmental driver, spatial, and temporal scales evaluated. Overall, a wide range of baseline phenology and relevant modeling studies exist, yet surprisingly few document long-term shifts. Results reveal a need for increased emphasis on phenological shifts in the Gulf of Maine, identify opportunities for future research and consideration of phenological changes in adaptation efforts.

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USGS2019

Landscape genetics reveals unique and shared effects of urbanization for two sympatric pool-breeding amphibians

Metapopulation-structured species can be negatively affected when landscape fragmentation impairs connectivity. We investigated the effects of urbanization on genetic diversity and gene flow for two sympatric amphibian species, spotted salamanders ( Ambystoma maculatum ) and wood frogs ( Lithobates sylvaticus ), across a large (>35,000 km 2 ) landscape in Maine, USA, containing numerous natural and anthropogenic gradients. Isolation-by-distance (IBD) patterns differed between the species. Spotted salamanders showed a linear and relatively high variance relationship between genetic and geographic distances ( r = .057, p < .001), whereas wood frogs exhibited a strongly nonlinear and lower variance relationship ( r = 0.429, p < .001). Scale dependence analysis of IBD found gene flow has its most predictable influence (strongest IBD correlations) at distances up to 9 km for spotted salamanders and up to 6 km for wood frogs. Estimated effective migration surfaces revealed contrasting patterns of high and low genetic diversity and gene flow between the two species. Population isolation, quantified as the mean IBD residuals for each population, was associated with local urbanization and less genetic diversity in both species. The influence of geographic proximity and urbanization on population connectivity was further supported by distance-based redundancy analysis and multiple matrix regression with randomization. Resistance surface modeling found interpopulation connectivity to be influenced by developed land cover, light roads, interstates, and topography for both species, plus secondary roads and rivers for wood frogs. Our results highlight the influence of anthropogenic landscape features within the context of natural features and broad spatial genetic patterns, in turn supporting the premise that while urbanization significantly restricts interpopulation connectivity for wood frogs and spotted salamanders, specific landscape elements have unique effects on these two sympatric species.

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USGS2019

Satellite-detected forest disturbance forecasts American marten population decline: The case for supportive space-based monitoring

Limited monitoring resources often constrain rigorous monitoring practices to species or populations of conservation concern. Insufficient monitoring can induce a tautology as lack of monitoring resources makes it difficult to determine whether a species or population deserves additional monitoring resources. When in-situ monitoring resources are limited, remote habitat monitoring could be a useful supplementary tool, as linking parameterized species distribution models to spatially explicit time-series of environmental correlates allows iterative prediction of population change. Yet the performance of predictive forecasts or hindcasts has been difficult to evaluate. We paired contemporary field data, historic population estimates, and a remotely-sensed archive of landscape change to evaluate predictions of American marten ( Martes americana ) population decline owing to habitat loss in Maine, USA. We estimated contemporary spatial patterns in marten density relative to landscape disturbance with spatial capture-recapture models. We compared current density estimates to historical density calculations to evaluate population decline, and compared historical calculations to habitat-based model predictions to evaluate the efficacy of habitat monitoring as a proxy for direct monitoring. Marten density was negatively associated with the proportion of surrounding regenerating forest, and point estimates within focal townships were 50–80% lower than historical calculations. Habitat-based hindcasts of marten density across our entire focal area interest suggested a smaller population decline (roughly 50%) within our focal area. Thus, although habitat-based predictions underpredicted marten decline, they provided correct directional inference. Habitat monitoring and predictions from species distribution models may provide useful inference about population changes given trends in habitat at limited expense when in-situ information is lacking.

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USGS2019

Evidence for conservative transport of dissolved organic carbon in major river basins in the Gulf of Maine Watershed

Transport and fate of dissolved organic carbon (DOC) in rivers are important aspects of the carbon cycle and the critical linkage between terrestrial, aquatic, and marine systems. Recent studies have quantified fluvial export to the marine environment in many systems, but in-stream losses of DOC are poorly constrained. This study compares DOC yields (kg C/ha) between the area-weighted averages of several tributaries within larger watersheds with the DOC yields of the larger watersheds to gain insight on in-stream losses in larger river systems. Four large watersheds, 22 tributaries to those watersheds, and 5 additional main stem locations in Maine were studied during 1 April to 15 November in 2011 through 2013. There were no significant differences in the area-weighted average DOC yield of the tributaries and the larger watersheds indicating little net in-stream loss in the main stems of the larger rivers. It is unlikely that inputs of DOC from un-gauged areas compensated for losses from gauged tributaries based on similarity in DOC yield longitudinally along the main stems of two of the rivers. In addition, wetland abundance, which is associated with higher DOC yield in this environment, did not consistently increase from tributaries to the larger watershed or longitudinally along the main stems. This geographic distribution of wetlands therefore also indicates that it is unlikely that inputs of DOC from un-gauged areas compensated for losses from gauged tributaries. These findings suggest that in-stream losses of DOC in these larger river systems are minimal and that the vast majority of DOC in major rivers in Maine is transported conservatively to the coastal ocean.

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USGS2019

Managing dams for energy and fish tradeoffs: What does a win-win solution take?

Management activities to restore endangered fish species, such as dam removals, fishway installations, and periodic turbine shutdowns, usually decrease hydropower generation capacities at dams. Quantitative analysis of the tradeoffs between energy production and fish population recovery related to dam decision-making is still lacking. In this study, an integrated hydropower generation and age-structured fish population model was developed using a system dynamics modeling method to assess basin-scale energy-fish tradeoffs under eight dam management scenarios. This model ran across 150 years on a daily time step, applied to five hydroelectric dams located in the main stem of the Penobscot River, Maine. We used alewife ( Alosa pseudoharengus ) to be representative of the local diadromous fish populations to link projected hydropower production with theoretical influences on migratory fish populations on the model river system. Our results show that while the five dams can produce around 427 GWh/year of energy, without fishway installations they would contribute to a 90% reduction in the alewife spawner abundance. The effectiveness of fishway installations is largely influenced by the size of reopened habitat areas and the actual passage rate of the fishways. Homing to natal habitat has an insignificant effect on the growth of the simulated spawner abundance. Operating turbine shutdowns during alewives' peak downstream migration periods, in addition to other dam management strategies, can effectively increase the spawner abundance by 480–550% while also preserving 65% of the hydropower generation capacity. These data demonstrate that in a river system where active hydropower dams operate, a combination of dam management strategies at the basin scale can best balance the tradeoff between energy production and the potential for migratory fish population recovery.

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USGS2019

A dam passage performance standard model for American shad

Objectives for recovery of alosines commonly involve improving fish passage at dams during migration. However, a quantitative basis for dam passage performance standards is largely absent. We describe development of a stochastic life-history-based simulation model for American shad, Alosa sapidissima , to estimate effects of dam passage and migratory delay on abundance, spatial distribution of spawning adults, and demographic structuring in space and time. We used the Penobscot River, Maine, USA, as a case study to examine sensitivity of modeled population metrics and probability of achieving specific management goals to inputs. Spawner abundance and percentage of repeat spawners were most sensitive to survival and migration delay at dams, marine survival, and temperature cues for migratory events. Recovery objectives related to abundance and spatial distribution of spawners were achievable under multiple scenarios, but high rates of upstream and downstream passage were necessary. The simulation indicated trade-offs between upstream and downstream passage efficacy whereby increased downstream passage was required to maintain or increase population abundance in conjunction with increased upstream passage. This model provides a quantitative support tool for managers to inform ecologically based decisions about a suite of management scenarios to facilitate recovery and sustainability of diadromous fish populations.

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USGS2019

Adult survival of common eiders in Maine

Although most species of sea ducks are poorly studied, much is known about the population dynamics of the American race of Somateria mollissma dresseri (Common Eider). Although Common Eiders typically have high adult survival and low recruitment rates, their populations in Maine have declined since the early 1990s. Wildlife managers hypothesized this decline was due to reduced adult survival; therefore, they decreased daily bag limits in Maine in 1999 and 2009 to increase local populations. The goals of this project were to assess (a) whether survival rates of adult females captured while nesting varied between historical estimates (1943–1993) and recent estimates (2000–2012), (b) whether survival rates increased from 2000–2009 after the initial harvest restrictions were implemented in 1999, and (c) determine if estimates of survival rates of adult males and females captured while molting differed from estimates of adult females captured while nesting. We used mark–recapture models to estimate survival rates of Common Eiders we banded in Maine (nesting females [ n = 2340] from 2000 to 2012; molting males [ n = 4366] and molting females [ n = 4952] from 2000 to 2009). We found no difference in survival of nesting females based on historical (mean ± SE = 0.9003 ± 0.0841) and recent estimates (0.90 ± 0.015). Although we observed annual fluctuations in survival, survival rates did not increase following the implementation of harvest restrictions. Mean annual survival rates were similarly high for molting females (0.894 ± 0.0205) and nesting females, but lower for molting males (0.855 ± 0.0128). Lower survival rates of adult males may reflect the preference by US hunters to selectively harvest adult males. Overall mean recovery rates of banded birds were low (females: 0.037 ± 0.00043, males: 0.0226 ± 0.0006). We hypothesize that current harvest rates may be influencing decreased survival of adult males to some extent.

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USGS2019

Role of recovering river herring population on smallmouth bass diet and growth

Fish assemblages in Atlantic coastal rivers have undergone extensive ecological change in the last two and a half centuries due to human influence, including extirpation of many migratory fish species, such as river herring (Alosa spp.) and introduction of nonnative piscivores, notably Smallmouth Bass Micropterus dolomieu. Recently, dam removals and fish passage improvements in the Penobscot River, Maine, have allowed river herring to return to reaches of the river that have been inaccessible since the late 19th century. Alosine populations have increased and this trend is anticipated to continue. This may increase forage in the system which could potentially increase growth for Smallmouth Bass, the dominant piscivore. We examined the diet and growth of Smallmouth Bass collected from areas of the Penobscot River watershed with and without access to river herring as prey. We collected 765 Smallmouth Bass throughout 2015, examined the stomach contents of 573 individuals, and found notable differences in diet among three river reaches with common seasonal trends. Juvenile river herring composed an average of 19% (SE = ±6%) of stomach contents by mass from Smallmouth Bass collected in the freshwater tidal area but were rarely observed in the diets upstream. We used estimates from von Bertalanffy growth models to examine differences in growth among reaches and found that asymptotic length was the longest (425 mm TL) in the Tidal reach where access to river herring was unrestricted. We then used these data to predict changes to growth associated with increased access to juvenile river herring prey with bioenergetics models. Results indicated that substituting juvenile river herring for less energy-dense prey (e.g.,invertebrates) may lead to increases in seasonal growth throughout the watershed as river herring populations continue to rebound in response to dam removal. Our results provide insight into the diet and growth of Smallmouth Bass in a large New England river, and provide a foundation for future work investigating unfolding changes to these characteristics following recent dam removals.

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USGS2018

Modeling White Sucker (Catostomus commersonii) populations to assess commercial harvest influence on age structure

Commercial harvest of White Suckers Catostomus commersonii for bait in the American Lobster Homarus americanus industry is minimally regulated in Maine and there are concerns as to the influence of increasing harvest. We built a population model using parameters (i.e. age-specific mortality, age at maturity, and size-specific fecundity) from literature and field studies to investigate the theoretical effects of harvest mortality on age structure. Because stock-recruitment relations are poorly characterized for this species, we explored the influence of both Beverton-Holt and Ricker recruitment processes. Our base model closely resembled the empirical age structures reported from three unfished lakes in Maine, with four percent of fish in the modeled spawning run being age-10 or older. We assessed the additive effects of harvest mortality on age structure using the full range of possible mortalities. As expected, increased harvest mortality in the model resulted in a decline and disappearance of older age-classes such that few fish greater than age-10 remained in the population under a realistic harvest mortality scenario. This age-truncation was qualitatively comparable to data from aggregate age distributions reported from three commercially harvested lakes in Maine. Because the loss of older fish may compromise population viability, this model is a valuable guidance tool for managers to craft regulation of this growing fishery.

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USGS2018

Movement and mortality of Atlantic salmonkelts (Salmo salar) released into thePenobscot River, Maine

The Penobscot River is home to the last major run of Atlantic salmon (Salmo salar) in the United States. For over one century, the river has been stocked intensively. Since the late 1970s, most kelts are released to the Penobscot River estuary following spawning in a hatchery. Over that time, the proportion of the run made up of iteroparous individuals has declined to < 1%. These fish may make a disproportionate contribution to the spawning population because they are typically large and produce more eggs than virgin spawners. We radio-tagged 55 kelts that were artificially spawned at the Craig Brook National Fish Hatchery in 2015 and released them in two different locations in the river (head of tide and ~50 km upstream) to assess 1) when hatchery-spawned kelts leave the river, 2) whether release location influences river exit timing, and 3) if kelts from the upper river could successfully outmigrate through the lower Penobscot River’s hydroelectric complex. The kelts were tracked from November 2015 to July 2016. Although some fish from both release groups were documented leaving the system within one month, the majority of fish (84%) overwintered in freshwater habitat. Many (71%) of those kelts that overwintered in the Penobscot River made directed, upstream movements in November and December. However, there was no difference in upstream movement rates, timing of outmigration, or survival between the release groups. Survival to outmigration was 23.6%, which is considerably lower than kelt survival documented in Canadian and European rivers. Low survival to outmigration may have contributed to the disappearance of iteroparous individuals from the Penobscot River run of Atlantic salmon over the last four decades.

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