• Habitat use by migrating and breeding shorebirds on the eastern Copper River delta, Alaska

      Murphy, Stephen M. (1981-05)
      This study examines the phenology, species composition, relative abundance, patterns of habitat use, and resource partitioning by migrating and breeding shorebirds on the eastern Copper River Delta. The peak of spring migration in 1978 occurred on 11 May, several days later than normal. Interspecific competition for foraging space on intertidal mudflats was minimized by temporal differences in the peaks of migration of the most abundant species and by spatial segregation during feeding. Fall migration differed from spring migration in several ways: 1) different species composition, 2) lower densities of staging birds, 3) different patterns of habitat use, and 4) less habitat segregation between species. Forty-five nests of six species of shorebirds were located along 52 km of transects. The peak of nest initiation was between 25 May and 31 May. Over 75% of the nests occurred in three habitat types, all of which were dominated by varying degrees of sedge, grass, and moss.
    • Headwater stream invertebrate communities: a comparison across ecoregions and logging histories

      Medhurst, R. Bruce (2007-08)
      Monitoring stream condition is not always conducted with understanding how climate may influence anthropogenic disturbances. Stream monitoring has traditionally been accomplished through sampling benthic invertebrates, while sampling drifting invertebrates as a potential monitoring tool has received little attention, in spite of drift often being easier and less expensive to sample. The objectives of this study were to understand how logging influences headwater stream invertebrate communities (benthic and drift) across two ecoregions in the Cascade Range, central Washington, and to determine whether drift samples might serve as a replacement for benthic samples in assessing headwater stream condition. Benthic and drifting invertebrates were sampled from 24 headwater streams in logged and unlogged watersheds within two ecoregions (wet and dry), and community metrics contrasted. Invertebrate community responses to logging varied with ecoregion (e.g., higher shredder densities in logged watersheds of wet ecoregion only). Differences in benthic community structure were not reflected in the drift, and relationships between benthos and drift were highly variable. Although both sampling types (benthic, drift) revealed ecoregional and land-use (logging) differences in invertebrate communities, lack of consistent relationships between the sampling types suggests drift sampling does not provide more reliable information about stream benthos or headwater stream condition.
    • Health and condition of juvenile chinook and chum salmon near the Chena River Dam, Alaska

      Daigneault, Michael Joseph (1997-05)
      During May-June, 1995 and 1996, outmigrating chum salmon, Oncorhynchus keta, and chinook salmon, O. tschawytscha, were captured in the Chena River near the Chena River Lakes Flood Control Project. Fish condition was determined through the investigation of physical injury and scale loss. Except for one sample, the proportion of injured fish was never greater than 7% for chum or chinook salmon. Few injuries were severe. The proportion of chinook salmon with scale loss ranged from 1-33%, most of which were only partially descaled. When significant length differences existed, injured, descaled, and partially descaled fish were always larger than non-injured and non-descaled fish. Arctic grayling (Thymallus arcticus) diet by weight consisted of chum salmon (2%), invertebrates (89%), other fish (3%), and miscellaneous material (6%). Plasma cortisol levels were used as an indicator of the primary stress response of chinook salmon and did not indicate any unusual physiological stress level.
    • Heterogeneity and bias in abundance estimates of outmigrating chinook salmon in the Chena River, Alaska

      Lambert, Ted M. (1998-12)
      The objective was to examine bias due to heterogeneity in capture probability (p) in an abundance estimate for chinook salmon (Oncorhynchus tschawytscha) outmigrants in the Chena River, Alaska. A higher proportion of day-marked fish (21 / 636 = 0.0330) compared to night-marked fish (17 / 1724 = 0.0098; p<0.0001, α=0.05) was recaptured at the lower site in a Cormack-Jolly-Seber experiment with upper, middle and lower sites. Heterogeneity was also likely at the middle site between upper site-marked and unmarked fish. Simulations with heterogeneity confined to the middle and lower sites (i.e., due to inadequate mixing) caused small bias (<2.5%) in the upper site abundance estimate. With heterogeneity at all three sites (a subpopulation effect), the upper site estimate had 22.9% to 29.3% negative bias. Because heterogeneity observed in the Chena was probably due to inadequate mixing (related to daytime trap evasion), bias in the upper site estimate was probably small.
    • Home range, habitat selection, and movements of lynx (Lynx canadensis) in eastern interior Alaska

      Perham, Craig J.; Follmann, Erich H.; Rextad, Eric A.; Cook, Joseph; Jenkins, K. (1995-12)
      Lynx home ranges, habitat selection, and daily track deposition rates were determined in interior Alaska. Male home ranges averaged 167 km2 in 1991-92 and 127 km2 in 1992-93, but varied (14-270 km2); females averaged 33 km2 in 1991-92 and 48 km2 in 1992-93. Nomadic lynx displayed erratic movements and large ranges, whereas others dispersed from the study area. Lynx with small home ranges may use snowshoe hare refugia whereas other lynx may range over expanded areas to acquire food. Lynx preferred broadleaf and mixed forests and avoided dwarf shrub/tundra. Lynx used a 1959 burn more than expected; more recent burns (<11 years) were used less than expected. Track deposition was significantly related to snowfall, temperature and barometric pressure change (P< 0.001), the overall model, however, explained only 16% of the variation in deposition (R2 = 0.162). Temperature was most related to track deposition; as temperature increased, track deposition became more variable.
    • Identification and characterization of inconnu spawning habitat in the Sulukna River, Alaska

      Gerken, Jonathon D.; Margraf, Joseph; Zimmerman, Christian; Verbyla, David; Brown, Randy (2009-12)
      Inconnu (Stenodus leucichthys) is present throughout much of the Yukon River drainage in Alaska, but only five spawning areas have been identified. Spawning habitat requirements are therefore thought to be very specific; however, the physical qualities of these habitats have only been characterized in general terms. The Sulukna River is one of five identified inconnu spawning areas within the Yukon River drainage. A systematic sampling design was used in September and October of 2007-2008 to define Sulukna River spawning locations. Presence of inconnu was identified using hook and line sampling methods and spawning was verified by catching broadcast eggs in plankton nets. Small-scale, large-scale, and chemical habitat variables were sampled at transects located every 1.8 river kilometer (rkm). Project results indicate that spawning habitat was confined to a narrow reach of approximately 20 rkm. Spawning habitat occurred significantly more often in transects characterized with substrate between 6 and 12 cm, a width to depth ratio between 15 - 36, and water conductivity between 266 - 298 microsiemens per centimeter. Similar studies on other known spawning habitats would reveal whether these qualities are common to all inconnu spawning populations or unique to the Sulukna River.
    • Infection rates, parasitemia levels, and genetic diversity of hematozoa in New World waterfowl

      Smith, Matthew M.; Lindberg, Mark; McCracken, Kevin; Winker, Kevin; Pearce, John (2014-12)
      Blood parasites can limit the productivity of birds and increase the vulnerability of isolated and naïve populations to extinction. I examined 804 blood samples collected from 11 species of South American waterfowl to assess infection by Haemoproteus, Plasmodium and/or Leucocytozoon parasites. In addition, I strove to develop a new molecular tool to quickly and accurately determine relative parasitemia rates of Leucocytozoon parasites in avian blood. I used samples collected from waterfowl in interior Alaska (n = 105) to develop and optimize a real-time, quantitative PCR methodology using TaqMan fluorogenic probes. Molecular screening produced an apparent prevalence rate of 3.1% for hematozoa infections in South American waterfowl samples, and analysis of hematozoa mitochondrial DNA produced 12 distinct hematozoa haplotypes, four of which were identical to hematozoa lineages previously found infecting waterfowl in North America. Phylogenetic analyses of hematozoa DNA revealed close relationships between parasite lineages infecting waterfowl on both continents. Our qPCR assay showed high levels of sensitivity (91%) and specificity (100%) in detecting Leucocytozoon DNA from host blood when compared to results from a well-used nested-PCR protocol. Additionally, statistical results of a linear regression supported correlation between relative parasitemia estimates from our qPCR assay and greater numbers of parasites observed on blood smears (R2 = 0.67, P = 0.003).
    • Influence of weather on movements and migrations of caribou

      Eastland, Warren George (1991)
      Caribou (Rangifer tarandus granti) are typified by use of calving grounds and by making twice-annual migrations between summer and winter ranges. This study used satellite technology to examine the influence of weather on calving site selection, autumn and spring movements, and timing and directionality of migrations of the Porcupine Caribou Herd (PCH) that calves in northeast Alaska and northwestern Canada adjacent to the Beaufort Sea. The reigning hypothesis that females select areas that become free of snow early for calving sites was rejected because females selected areas of $>$75% snowcover ($P=0.02$) preferentially for calving. Benefits from use of mottled snow for calving were access to vegetation in its early phenological stages and protection for their calves from predators. Access to nutritious forage and predator avoidance appeared to be the main reasons for calving site selection. Multiple linear regression models were used to examine rate and direction of autumn and spring migrations using weather data from U.S. and Canadian sources. Weather was found to be both an ultimate and an approximate influence on the rate and direction of autumn migration ($P<0.05$). Explanatory power of the equations was low ($R\sb{a}\sp2<0.41$). Proximal causes of movement were best explained by caribou tracking of vegetation phenology. Pre-rut movements in September lacked concurrence between rate and direction whereas rate and direction were related in October. Models of spring migration of parturient females indicated a common timing among years, late April and early May, and movements were significantly affected by weather ($P<0.02$), in particular snow depths and conditions that would affect foraging and traveling conditions. This study suggests that: (1) females preferentially use areas of delayed snow melt for calving, and (2) weather influences both spring and autumn migration of caribou, although the effect of weather may be more indirect than direct.
    • Injury, survival and growth of rainbow trout captured by electrofishing

      Taube, Thomas Theodore (1992-05)
      Electrofishing injury studies in Arizona and Alaska revealed spinal injury rates of over 50% among large (>300 mm long) rainbow trout Oncorhynchus mykiss captured by electrofishing with pulsed direct current (PDC). My goal was to identify an alternative waveform that would efficiently capture large rainbow trout with injury rates less than 15%. Experiments in homogeneous and heterogeneous electrical fields tested six waveforms; lower injury rates resulted with DC (17%), CPS™ (8%), and 20-Hz PDC at 75% duty cycle (25%). In field experiments with these three waveforms, PDC and DC gave higher capture rates than CPS™. However, injury rate was 60% with 20-Hz PDC and highly variable (0-47%) with DC. Long-term mortality of rainbow trout shocked with 60-Hz PDC at 50% duty cycle was 35% after 203 days. I recommend DC as an alternative to PDC waveforms for relatively safe and efficient capture of large rainbow trout.
    • Investigations of patterns of vegetation, distribution and abundance of small mammals and nesting birds, and behavioral ecology of arctic foxes at Demarcation Bay, Alaska

      Burgess, Robert M. (1984-05)
      Analyses of habitat use, activity budget and activity patterns of arctic foxes (Alopex lagopus) at known distribution and abundance of prey are presented. Behavioral data on foxes were collected by direct observation of 2 radio-collared females and their mates in summer 1979. Prey availability was determined through monitoring bird nest success and phenology, mark-recapture studies of small mammals, and analysis of vegetation patterns and distribution of prey in 1978 and 1979. Prey availability fluctuated dramatically within each season and between years. Foxes relied almost exclusively on avian prey in 1979. Small mammal densities were extremely low in 1979 and foxes failed to rear pups in that year. Fluctuating prey availability did not affect fox activity patterns, activity budget or habitat use. The significance of caching in regulating food availability and the relationship between scent-marking and foraging efficiency are discussed.
    • King eider migration and seasonal interactions at the individual level

      Oppel, Steffen; Powell, Abby; Murphy, Edward; Verbyla, Dave; O'Brien, Diane (2008-12)
      Seasonal interactions describe how events during one season of the annual cycle of a migratory bird affect its fitness in subsequent seasons. Understanding the strength and mechanism of seasonal interactions is important to predict how migratory birds will respond to future challenges caused by habitat loss and climate change. This dissertation explores seasonal interactions between different stages of the annual cycle in an arctic-breeding sea duck, the King Eider (Somateria spectabilis). Concerns over recent population declines and potential effects of climate change on marine habitats used by the species highlight the need for a better understanding of its life history. I used satellite telemetry to describe migration routes, timing of migration events, and geographic regions used by King Eiders throughout the year. I found highly variable movement patterns, and wide dispersion of King Eiders to three regions in the Bering Sea during winter. I then developed stable isotope techniques to examine seasonal interactions at the individual level. First, I examined the relative contribution of body reserves to egg production using stable isotope analysis of egg components and blood. I found that most birds use only small proportions of body reserves to produce eggs, but rather rely on nutrients obtained on breeding grounds to form a clutch. Thus, contrary to general expectation, King Eiders use an income strategy to produce eggs, and I hypothesize that they may retain body reserves for incubation. Body reserves may reflect the residual body condition from the previous winter. I further examined whether females wintering in different regions in the Bering Sea had different rates of nest survival. The northern Bering Sea has a higher benthic biomass and is closer to breeding grounds than winter regions farther south. However, nest survival rates of female King Eiders in northern Alaska did not differ between females that had wintered in the northern or southern Bering Sea. Overall, I found large individual variation in movement and breeding strategies, and little evidence for strong seasonal interactions between winter, spring, and summer. This indicates that King Eiders are a very adaptable species that depend on resources acquired on breeding grounds to a larger extent than previously assumed.
    • King eider wing molt: inferences from stable isotope analyses

      Knoche, Michael J. (2004-12)
      The western North American population of the king eider is thought to have declined by over 50% between 1974 and 1996 without an apparent cause. The non-breeding period of king eiders consists of 80-100% of their annual cycle if not impossible by observation. I used stable carbon and nitrogen isotope values of feathers and muscle to examine the wing molt and migration ecology of king eiders in 2003. Eider primary feathers were isotopically homogenous along the length of the feather, implying invariable diets during wing molt. Captive eiders in their hatch-year did not fractionate nitrogen isotopes, potentially indicating preferential protein allocation associated with growth. Six percent of female eiders sampled molted primary feathers on their breeding grounds, which had not been previously substantiated. Tissue samples from both genders corroborated dietary shifts inherent in switching from a marine to terrestrial diet. Carbon isotopes of feathers from satellite-transmittered males were correlated with longitude of their known wing molt locations indicating that the gradient of carbon isotopes can be used to draw inferences about molt location of eiders.
    • Lake Area Change In Alaskan National Wildlife Refuges: Magnitude, Mechanisms, And Heterogeneity

      Roach, Jennifer; Griffith, Brad; Harden, Jennifer; Verbyla, David; Jones, Jeremy (2011)
      The objective of this dissertation was to estimate the magnitude and mechanisms of lake area change in Alaskan National Wildlife Refuges. An efficient and objective approach to classifying lake area from Landsat imagery was developed, tested, and used to estimate lake area trends at multiple spatial and temporal scales for ~23,000 lakes in ten study areas. Seven study areas had long-term declines in lake area and five study areas had recent declines. The mean rate of change across study areas was -1.07% per year for the long-term records and -0.80% per year for the recent records. The presence of net declines in lake area suggests that, while there was substantial among-lake heterogeneity in trends at scales of 3-22 km a dynamic equilibrium in lake area may not be present. Net declines in lake area are consistent with increases in length of the unfrozen season, evapotranspiration, and vegetation expansion. A field comparison of paired decreasing and non-decreasing lakes identified terrestrialization (i.e., expansion of floating mats into open water with a potential trajectory towards peatland development) as the mechanism for lake area reduction in shallow lakes and thermokarst as the mechanism for non-decreasing lake area in deeper lakes. Consistent with this, study areas with non-decreasing trends tended to be associated with fine-grained soils that tend to be more susceptible to thermokarst due to their higher ice content and a larger percentage of lakes in zones with thermokarst features compared to study areas with decreasing trends. Study areas with decreasing trends tended to have a larger percentage of lakes in herbaceous wetlands and a smaller mean lake size which may be indicative of shallower lakes and enhanced susceptibility to terrestrialization. Terrestrialization and thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened the unfrozen season. Future research should characterize the relative habitat qualities of decreasing, increasing, and stable lakes for fish and wildlife populations and the ability of the fine-scale heterogeneity in individual lake trends to provide broad-scale system resiliency. Future work should also clarify the effects of terrestrialization on the global carbon balance and radiative forcing.
    • Land cover change on the Seward Peninsula: the use of remote sensing to evaluate the potential influences of climate change on historical vegetation dynamics

      Silapaswan, Cherie Sumitra (2000-12)
      Vegetation on the Seward Peninsula, Alaska, which is characterized by transitions from tundra to boreal forest, may be sensitive to the influences of climate change on disturbance and species composition. To determine the ability to detect decadal-scale structural changes in vegetation, Change Vector Analysis (CVA) techniques were evaluated for Landsat TM imagery of the Seward Peninsula. Scenes were geographically corrected to sub-pixel accuracy and then radiometrically rectified. The CVA results suggest that shrubbiness is increasing on the Seward Peninsula. The CVA detected vegetation change on more than 50% of the burned region on TM imagery for up to nine years following fire. The use of both CVA and unsupervised classification together provided a more powerful interpretation of change than either method alone. This study indicates that CVA may be a valuable tool for the detection of land-cover change in transitional regions between tundra and boreal forest.
    • Landscape modeling of threespine stickleback occurrence in small Southeast Alaska lakes

      Gregovich, Dave (2007-12)
      Although threespine stickleback (Gasterosteus aculeatus L) are known to inhabit a wide range of habitats, their distribution in lakes across Southeast Alaska is not known. Threespine stickleback are an important prey item for many consumers in freshwater ecosystems. Additionally, isolated populations may be genetically unique and thus important from a conservation perspective. This study focused on identifying' landscape factors and models useful in predicting the presence of threespine stickleback in small (0.5-5 ha) lakes of Southeast Alaska. Stickleback occurrence was assessed via snorkeling and minnow trapping in 54 lakes, which were divided into calibration (n=36) and prediction (n=18) data sets. A number of models representing four methodologies-generalized linear models, generalized additive models, classification trees, and artificial neural networks-were built based on the calibration set, cross-validated, and evaluated by prediction to the test set of lakes. Lake elevation, distance from saltwater, and slope of lake outlet stream were the most useful predictors of stickleback occurrence. Results suggest that the likelihood of stickleback presence is highest in low elevation lakes near the coast. Human development and recreational activity also tends to be common in these areas, and so land-use planning should account for the high potential occurrence of threespine stickleback here
    • Lichen Availability on the Range of an Expanding Caribou (Rangifer tarandus) Population in Alaska

      Fleischman, Steven J.; Klein, David R.; Thompson, Steven K.; Viereck, Leslie A.; White, Robert G.; Regelin, Wayne L. (1990-05)
      Terrestrial lichen abundance, lichen availability as affected by snow, and winter fecal composition were investigated for the Delta Caribou Herd (DCH), which recently quadrupled in size and expanded its early winter range. Mean lichen abundance was relatively low (10-85 g/m2). However, even on heavily-used range, caribou ate only 7% of lichen standing crop annually. Snow affected lichen availability only slightly on peripheral tundra ranges, since lichens predominated on xeric sites with little snow. On traditional ranges, lichens were shorter and rarely found in high-density patches; disproportionate grazing and trampling of exposed lichens had caused reduced lichen availability. This was reflected in lower fecal lichen for caribou on traditional ranges, however DCH population growth or seasonal movements probably were not substantially affected. A model of caribou cratering energetics indicated that loss of potential foraging time may influence energy balance more than does cratering energy expenditure.
    • Life history and management of the grayling in interior Alaska

      Wojcik, Frank J. (1955-04)
      Field work on the Arctic grayling was conducted from September, 1951, to May, 1953; data on movements, spawning, food habits, sex ratios, and population dynamics were obtained. Returns on 1,222 tagged grayling varied from 0 to 20 per cent with areas. No returns were obtained from 165 fin-clipped fish. Fish entered the streams in the spring as soon as water started flowing, the dates varying from March 15 to May 9, 1952. Spawning in the Little Salcha River during 1952 is believed to have occurred between June 12 and June 16, Of 262 grayling checked for maturity, 18.7 per cent were mature in their fourth summer, 45 per cent in their fifth summer, and all by their sixth summer. Sex ratios obtained for adults varied with areas. The average sex ratio found for all areas was 79 males per 100 fem ales. The rate of growth was determined for grayling from six areas. The average increment for class V fish varied from 2.7 to 4.6 cm. per year. Aquatic insects were the main food organisms taken by grayling. Some terrestrial insects, fish, fish eggs and vegetable, matter were also taken. In view of the findings made in this study, overfishing appears to be the major cause of the decline in the sizes of grayling populations along the highways in the Fairbanks area. A twelve-inch minimum size limit is apparently the best management procedure, although an area closure is advisable for overfished spawning runs.
    • The limnology of Lake Clark, Alaska

      Wilkens, Alexander Xanthus (2002-12)
      This study gathered baseline limnological data to investigate the thermal structure, water quality, phytoplankton, and zooplankton of Lake Clark, Alaska. Results indicate Lake Clark is oligotrophic and mixes biannually, but stratification is weak and thermoclines are deep. Longitudinal gradients were seen in measurements of temperature, suspended solids, turbidity, light penetration, algal biomass, and zooplankton density. Wind and tributary inputs determine the thermal regime. Glacially-influenced tributaries drive turbidity and light gradients by introducing suspended solids to the inlet end of the lake. Suspended solids likely create the algal biomass gradient by limiting the light available for photosynthesis in the inlet basin. Algal biomass and turbidity gradients may interact to create an area of high productivity and low predation risk, causing high zooplankton concentrations in the central basin. Oxygen supersaturation was discovered in the hypolimnion but remains unexplained. Because tributaries are glacially influenced, Lake Clark could be sensitive to global warming.
    • Longitudinal distribution patterns and habitat associations of juvenile coho salmon Oncorhynchus kisutch in tributaries of the Little Susitna River, Alaska

      Foley, Kevin Michael; Rosenberger, Amanda E.; Gerkin, Jonathon; Verbyla, David L.; Mueter, Franz J. (2014-05)
      Understanding how headwater streams function as rearing habitats for juvenile coho salmon Oncorhynchus kisutch is essential for effective population management and conservation. To inform habitat restoration activities within the Matanuska-Susitna Valley, Alaska, I determined upstream distribution limits, validated abundance estimates, and established fish habitat relationships in two headwater stream tributaries of the Little Susitna River in 2010-11. Using a low-effort, spatially continuous sampling approach and linear mixed-effects models, I related local- and landscape-scale habitat associations to abundance estimates. All-aged coho salmon composed approximately 98% of all fish sampled and inhabited the entire stream length to their upstream limits. Age-1+ fish resided in 64% and 44% of the stream length for the two sampled streams. The mean upstream elevation limit for all-aged fish in these streams was 278m and 267m. For age- 1+ fish, the upstream elevation limit in the two streams was 275m and 238m. Percent slope at the distribution limit of all-aged fish was consistent across streams at 5%, whereas percent slope for age-1+ fish correspond to 4% and 6%. Elevation and percent slope consistently described upstream distribution limits among age classes. Therefore, we must consider these landscape features when prioritizing restoration projects in headwater streams.
    • Marine-derived nutrients in riverine ecosystems: developing tools for tracking movement and assessing effects in food webs on the Kenai Peninsula, Alaska

      Rinella, Daniel J. (2010-05)
      Marine-derived nutrients (MDN) delivered by spawning Pacific salmon (Oncorhynchus spp.) contribute to the productivity of riverine ecosystems. Optimizing methods for measuring MDN assimilation in food webs will foster the development of ecologically based resource management approaches. This dissertation aims to better understand relationships among spawning salmon abundance, biochemical measures of MDN assimilation, and the fitness of stream-dwelling fishes. The goals of my first research chapter were (1) to understand the factors that influence stable isotope ([delta]¹³C, [delta]¹⁵N, and [delta]³⁴S) and fatty acid measures of MDN assimilation in stream and riparian biota, and (2) to examine the ability of these measures to differentiate among sites that vary in spawning salmon biomass. For all biota studied, stable isotopes and fatty acids indicated that MDN assimilation increased with spawner abundance. Among Dolly Varden (Salvelinus malma), larger individuals assimilated proportionately more MDN. Seasonal effects were detected for aquatic macroinvertebrates and riparian horsetail (Equisetum fluviatile), but not for Dolly Varden. Of all dependent variables, Dolly Varden [delta]¹⁵N had the clearest relationship with spawner abundance, making this a good measure for monitoring MDN assimilation. Expanding on these results, two chapters examined potential fisheries management applications. The first sought to identify spawner levels above which stream-dwelling Dolly Varden and coho salmon (O. kisutch) parr cease to gain physiological benefits associated with MDN. RNA-DNA ratios (an index of recent growth rate) and energy density indicated saturation responses where values increased rapidly with spawner abundance up to approximately 1 kg/m² and then leveled off. In coho salmon parr, energy density and RNA-DNA ratios correlated significantly with [delta]¹⁵N. These results show strong linkages between MDN and fish fitness responses, while the saturation points may indicate spawner densities that balance salmon harvest with the ecological benefits of MDN. The second application tested a quick and inexpensive method for estimating, spawning salmon abundance based on [delta]¹⁵N in stream-dwelling fishes. Estimates made with coho salmon pair were unbiased, tightly correlated with observed values, and had a mean absolute deviation of 1.4 MT spawner biomass/km. Application of this method would allow estimates of annual escapement to be made on a potentially large number of streams.