Now showing items 123-142 of 468

• #### Effects of fish wheels on fall chum salmon (Oncorhynchus keta): non-esterified fatty acids and plasma indices of stress

The effect of tagging and capture on plasma concentrations of cortisol, glucose, lactate, chloride, and non-esterified fatty acids (NEFA) in chum salmon was investigated. Adult chum salmon were captured in August-September 2000 and 2001 with a fish wheel on the lower Kantishna River. Tagged and untagged fish were subsequently captured on the lower Toklat River and sampled for blood. Tagged fish (males and females) at the Toklat recovery fish wheels had lower (P <0.04) plasma cortisol concentrations than untagged fish. Glucose concentrations were lower (P = 0.03) in tagged than untagged males but did not differ between tagged and untagged females. Lactate and chloride concentrations did not differ between tagged and untagged fish. Tagged chum salmon captured at the Toklat River recovery wheels had lower concentrations of NEFA (P = 0.02). Taken together, these results suggest there is a metabolic cost from capture and tagging using fish wheels.
• #### Effects Of Glacial Discharge On Kelp Bed Organisms In An Alaskan Subarctic Estuary

Global climate warming is having large-scale, pronounced effects on the physical environment of Arctic and subarctic nearshore marine ecosystems, such as the widespread melting of glaciers. The purpose of this study was to determine how changing environmental conditions due to glacial melting affect subarctic kelp bed community structure and organism fitness. This study compared kelp bed community structure under disparate environmental conditions on a glacially-influenced and an oceanic shore in the same subarctic Alaskan estuary. Laboratory tests assessed the effects of varying salinity and irradiance on growth and physiological competence (as maximum quantum yield ( Fv/Fm)) of the dominant kelp, Saccharina latissima. Reciprocal in situ shore transplant studies examined seasonal growth, Fv/Fm, morphology and storage product levels (mannitol) in S. latissima. This study showed that kelp communities were distinctly different in these two nearshore regions within the same subarctic estuary. In addition, the kelp S. latissima from these two environments, exhibited phenotypic plasticity in terms of growth to varying levels of salinity and light availability, while both populations maintained high physiological competence year-round. However, this phenotypic plasticity was constrained within different seasonal growth patterns in the populations from the two shores, which likely are genetically fixed. This is the first time that phenotypic plasticity within a genetically fixed seasonal growth cycle has been described for macroalgae and especially for two populations in such close proximity. However, the ability to elicit plastic responses and seasonal adaptations in S. latissima may be limited and concerns remain about the long-term persistence of this and other important foundation species and nearshore habitats with continued climate change.
• #### Effects of inbreeding and family origin on size of chinook salmon (Oncorhynchus tshawytscha) fry

We cultured separate lines of chinook salmon fry of Chickamin River, Southeast Alaska, ancestry in seven common garden enclosures. A parentage analysis based on variation of microsatellite alleles showed that within these lines seven brother sister matings created 35 inbred fish from 7 families (F = 0.25) and 37 outbred fish resulted from 10 matings between segregated lines. Outbred and inbred fish did not differ in length (P = 0.42), weight (P = 0.86), or condition factor (P = 0.16). There was significant variation among families for length (P = 0.01) and weight (P <0.01), but not for condition factor (P = 0.48). Because variation among families can be large, it can potentially confound the effects for which a study was designed. To avoid drawing improper conclusions, studies should estimate the amount of variation that can be attributed to family origin, or be certain that many families are sampled.
• #### The effects of intense fire on headwater streams of the Colville National Forest, WA

Forest fires play an important role in shaping ecosystems, and there has been growing concern on the effects of high intensity fires on forest and aquatic ecosystems. Headwater streams are highly connected to riparian and surrounding terrestrial systems, and to downstream aquatic systems, partly through prey and organic matter transfers via aquatic invertebrate drift and emergence. Because of their small size, headwater streams may experience the greatest initial impact from forest fire, but may also return to pre-fire conditions quicker than larger streams. In this study, headwater streams from replicated burned and control watersheds were sampled in the two years following an intense forest fire in northeastern Washington. Benthic, drift and emergence samples of aquatic invertebrates were taken and analyzed for differences in density, biomass and community composition between watershed types. There was significantly higher density of invertebrates in burned sites, but no difference in biomass except in invertebrate emergence which was greater at burned sites. There was lower diversity in the burned watersheds, and the invertebrate community was dominated by chironomids. These changes in invertebrate density and community composition could influence the food resources available to aquatic and riparian consumers.
• #### Effects of jet boats on salmonid reproduction in Alaskan streams

Freshwater angling has increased dramatically in recent years in southwestern Alaska, and jet boat operators serve some of these anglers. Resources agencies are under pressure to regulate use of jet boats in waters that support spawning populations of salmonids, but they need more information regarding these potential effects. This thesis describes the methods and results of experiments to determine the effects of water turbulence from passing boats on embryo mortality and behavior of spawning adults. Field experiments on sockeye salmon were conducted in American Creek (in the Naknek drainage in Katmai National Park and Preserve) in 1992 and 1993. Laboratory experiments on rainbow trout were conducted at Fort Richardson Hatchery. These two species were viewed as surrogates for all species of genus Onorhynchus.
• #### Effects of marine-derived nutrients on population dynamics of sockeye salmon (Oncorhynchus nerka)

The effects of marine-derived nutrients (MDN) on the productivity of sockeye salmon (Oncorhynchus nerka) stocks in Alaska were examined through nitrogen stable isotope analysis of smolts and mathematical models of the sockeye stock-recruit relationship. Smolt 8 [delta]¹⁵N was used to infer the degree to which smolts depend on MDN for their growth. We attempted to identify the characteristics of sockeye nursery lakes and watersheds that affect the availability of MDN to juvenile sockeye using multiple regression. Stock-recruit models incorporating MDN effects were fit to sockeye escapement-return data to test if fluctuations in sockeye stock productivity could be explained by changes in MDN input into nursery lakes. The magnitude of escapement and water residence time were the most important factors affecting the MDN availability to juvenile salmon. Mixing state of lakes and the distance from the coast were also found to significantly affect the MDN availability. We found that regional environmental fluctuations had a large effect on stock productivities in stock-recruit modeling. However, we did not find strong evidence to support our hypothesis that increases in MDN input to nursery lakes will result in increased productivity of sockeye stocks. Stock-recruitment data may be poorly suited to detection of the influence of MDN.
• #### Effects of ocean acidification on development of Alaskan crab larvae

The oceans absorb a large proportion of the carbon dioxide gas (CO₂) emitted into the atmosphere. This CO₂ changes the chemistry of seawater to make it more acidic, a phenomenon termed ocean acidification. Ocean acidification can have negative impacts on marine fauna, especially during early life stages, presenting a risk to ecosystems and fisheries. This research tested the effects of ocean acidification on the larval development of three crab species in Alaska: Tanner crab (Chionoecetes bairdi), rock crab (Glebocarcinus oregonensis), and Dungeness crab (Metacarcinus magister). Experiments were undertaken to assess the effects of exposure to low-pH conditions (decrease of up to 0.6 pH units from current levels, range of pH ~8.1 to 7.5) on survival, growth (morphometrics and mass), and carapace mineral composition of larval Tanner, rock, and Dungeness crabs. Results showed a decrease in survival as well as a small but nonsignificant decrease in size of Tanner crabs. There was a small and complex effect of pH on survival of Dungeness crabs. Rock crabs raised in low-pH conditions (pH 7.5) had higher individual biomass than those raised in ambient conditions (pH 8.1). There was no significant impact of pH on mineralization of any species. Therefore, low pH had a negative effect on development of Tanner crabs, a small effect on Dungeness larval survival and no discernible negative effect on rock crab larvae. Differences in response to ocean acidification may be related to pre-adaptation to variable pH conditions through lifestyle such that species that live in deeper, more stable waters (e.g., Tanner crab) are more vulnerable than species living in shallower, more variable waters (e.g., rock and Dungeness crabs). These observations suggest that ocean acidification will have negative impacts on Tanner and Dungeness crab larval survival with potential implications for recruitment to the adult population and consequently, for their fisheries.
• #### Effects of oil-laden sediments on behavior and growth of juvenile flatfishes

Three species of juvenile Pacific flatfishes: yellowfin sole (Pleuronectes asper), rock sole (P. bilineatus), and Pacific halibut (Hippoglossus stenolepis) were exposed to sediments contaminated with Alaska North Slope crude oil to determine the behavior and growth of juveniles in polluted nursery grounds. Responses were correlated with known biomarkers of toxicant exposure. In the behavior experiments, fish exhibited a strong preference for fine grained sediments ($<$500 microns) when presented with eight different sediment types ranging from mud to pebble. Juvenile yellowfin sole showed a preference for mud and mixed mud substrate, rock sole preferred sand substrates and halibut chose both mud and sand sediments. Flatfishes were able to detect and avoid heavily oiled (1400 $\mu$g/g total petroleum hydrocarbons-TPH) sediments but did not avoid sediments at oil concentrations of 400 $\mu$g/g TPH. Among yellowfin sole and rock sole, sediment preference altered behavioral response to oil whereas halibut did or did not avoid oil irrespective of sediment type. If flatfish do not avoid oil concentrations of 1600 $\mu$g/g and higher on preferred sediment, growth reductions occur. Fish reared on oiled sediment grew slower than controls on non-oiled sediments. Growth reductions in all three species were significant following 30 days of exposure to 1600-1800 $\mu$g/g TPH and became more pronounced over time. As the toxicant concentration or the length of exposure increased, growth per day decreased. By 90 days of exposure, fish exposed to 1600-1800 $\mu$g/g TPH grew 38-57% slower than controls. Halibut had the greatest change in growth rate following oil exposure. Exposure of halibut to sand laden with 4700 $\mu$g/g total hydrocarbons resulted in an 93% reduction in growth in 30 days. Condition factor was also most reduced in halibut. Changes in tissues and parasites indicated a reduction in fish health for all three species. There was an increase in fin erosion, liver lipidosis, gill hyperplasia and hypertrophy, and gill ciliate infestation combined with a decline in macrophage aggregates and gut parasites. Chronic marine oil pollution that results in hydrocarbon concentrations of 1600 $\mu$g/g in nursery sediments has the potential to reduce growth and health of juvenile flatfishes. Recruitment of juveniles to the fishery would be reduced due to increased susceptibility to predation and slower growth to maturity.
• #### Effects of organohalogen contaminants on Steller sea lion survival and female reproduction in the Russian Far East

The presence of persistent organohalogen contaminants (OCs) in the habitats of Steller sea lions, Eumetopias jubatus, may influence reproductive rates and possibly survival. The lack of recovery and the reduction in natality for the western stock has no apparent cause and OCs may be potential contributing factors. Among the most common synthetic OCs measured in marine mammal tissues are polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), polybrominated diphenyl ethers (PBDEs), and hexachlorobenzene (HCB). This project's focus was on the relationship between OCs and the western stock's lack of recovery. A suite of OCs were quantified from 239 hot-branded pups from 2001-2007 at nine Russian Far East rookeries. The use of brand-resighting data provided the opportunity to contrast pup survival, movement, reproductive success, and age at first reproduction between rookeries and among individuals with varying post-natal loads of OCs. Survival and movement were not affected by OC concentrations, but the estimated probability of survival within the first year was lower than expected at some rookeries. The effects of OCs on reproduction were less clear and no consistent pattern of negative effects emerged. Rookery specific differences indicated that location may be an important variable when considering survival, movement, and reproduction.
• #### Effects of outbreeding depression on meristics and bilateral asymmetry in hybrids of spatially separated populations of pink salmon (Oncorhynchus gorbuscha)

Different populations of a species distributed over diverse conditions adapt to their local environments to improve their ability to survive or reproduce. Intraspecific hybridization can alter the locally adapted population, resulting in reduced fitness, causing outbreeding depression. Manifestations of outbreeding depression in Pacific salmon include decreases in survival, fitness, and/or fitness-related traits. Many animals have paired morphological structures, resulting from canalization during development, which promote the animal's fitness; more symmetrical individuals often have faster growth, higher fecundity, or better survival. Meristic traits, such as the number of gill rakers in fish, can be easily determined. This study examined the potential effects of outbreeding depression on morphological meristic characteristics. Variation in fish size and meristic counts of returning F₁ and F₂ hybrids of spatially separated populations of pink salmon was compared to those of controls. There was no evidence for increased fluctuating asymmetry in hybrids. Directional asymmetry was significant for branchiostegals and pectoral fin ray counts. No single character consistently had sire or interaction effects except gill rakers; the few significant effects probably result from maternal environment effects. Canalization of bilateral asymmetry seems to be relatively unaffected by outbreeding depression.
• #### Effects of outbreeding on embryonic development timing of pink salmon (Oncorhynchus gorbuscha)

I studied the effects of outbreeding on embryonic development timing of pink salmon. I used standardized development stages and germ ring opening measurements to compare the variation of development at epiboly for odd- and even-broodyear F₂ hybrids. Analyses of timing of development at epiboly showed no effects of outbreeding depression, but did show a maternal effect for both crosses and backcrosses; and backcross families differed between replicates. These observations suggest that experimental designs lacking consideration of maternal effects or testing for replicate container effects in early salmon development studies may be flawed. I also compared the variation of hatching times for hybrids of two pink salmon populations, Pillar Creek (Kodiak, Alaska) and Auke Creek (Juneau, Alaska), which are separated by about 1,000 km. Analyses of hatching time showed that families with more Pillar Creek genes required more time to hatch at a given temperature. The differences in hatching time between the pink salmon from Auke and Pillar creeks demonstrates that they differed genetically. Both additive and epistatic types of outbreeding depression influenced the differences in hatching time. Prudent resource management requires knowledge of the biogeographical history and the genetic composition of salmon populations with the potential to interbreed.
• #### Effects of rising sea surface temperature and decreasing salinity on kelps and associated macroalgal communities

Kelp forests provide a multitude of vital ecosystems services, such as habitat for commercially and recreationally important species, support of complex food webs, and reduction of coastal erosion. The diversity and resilience of kelp forest communities are threatened as the severity of climate change and other anthropogenic stressors continues to mount. Particularly in the North Pacific, sea surface temperature (SST) is warming and glacier melt is discharging into coastal waters, causing decreases in salinity. This study assesses possible impacts of increasing SST and decreasing salinity on kelp forests by examining the response of key kelp species and their associated macroalgal community to these parameters in a North Pacific estuary, using Kachemak Bay as a model system. This two-part study combines both 1) a retrospective analysis of effects of environmental variables on existing kelp populations (Agarum clathratum, Laminaria yezoensis, and Saccharina latissima) and their associated macroalgal communities at three discreet water depths (5, 10 and 15 m), and 2) a factorial laboratory experiment investigating the effects of rising SST and decreasing salinity on kelp spore settlement and initial gametophyte growth in Eualaria fistulosa, Nereocystis luetkeana, and S. latissima. No strong correlations were observed between adult kelp biomass of any individual species with past SST and salinity changes, with the exception of a negative correlation between SST and L. yezoensis biomass at 10 m. In addition, SST and salinity were insignificant factors in shaping the associated macroalgal community biomass. In contrast to the retrospective analyses, the experimental results indicated that the early life-history stages of all kelp study species experienced decreased settlement and growth at elevated temperatures and decreased salinities. Eualaria fistulosa spores and gametophytes were the most negatively impacted, compared to the more widely distributed N. luetkeana and S. latissima. These results suggest that N. luetkeana and S. latissima are more likely to outperform E. fistulosa under projected conditions. By exploring how both early and late life-history stages of several key kelp species are impacted by dual stressors, this research enhances our understanding of how these species and their associated macroalgal communities will respond to projected changes in SST and salinity.
• #### Effects of sample size and ageing error on estimates of sustained yield

A Monte Carlo simulation model of an exploited age-structured fish population was constructed, to evaluate the effects of sampling and ageing the catch on estimates of population parameters from catch-age analysis with auxiliary information and resultant estimates of sustained yield. A factorial experimental design was used where input parameters were varied among: small (100), medium (300) and large (900) catch sample sizes; high and low levels of ageing precision; and a range of ageing biases. Ageing bias and precision had dramatic effects on estimated sustained yield: positive ageing bias and ageing imprecision generally caused under-estimation of sustained yield, while negative ageing bias caused over-estimation of sustained yield. The multiple reader/reading ageing scenarios designed to mitigate ageing error were able to reduce the affects of ageing imprecision, but were unable to alleviate the problems associated with ageing bias. The simulation model can be modified for a variety of recreational fish populations; a diskette and user manual are available.
• #### Effects of smolt length and emigration timing on marine survival and age at maturity of wild coho salmon (Oncorhynchus kisutch) at Auke Creek, Juneau Alaska

Coho salmon Oncorhynchus kisutch smolt were collected during the 1993-1997 emigrations at Auke Creek near Juneau, Alaska. Each day emigrants were separated into four size categories: small <90 mm), medium (90 - 110 mm), large (111 - 125 mm), and extra large (> 125 mm), tagged with a sequentially coded-wire tag, and released at tidewater. Tags from returning adults and jacks were collected and decoded in 1993-1998. Most survivors originated from the large and extra large categories, 40.5% and 43.1%, respectively. Large smolts contributed 28.9% to smolt-to-jack returns, significantly less than the smolt-to-jack survival contributed by extra large smolts, 67.8%. Smolt year, emigration date, and smolt length were significant in determining the length of returning jacks. In the 1993 and 1997 smolt years, significantly smaller returning adults originated from smolts that migrated later. Larger smolts produced significantly larger returning adults in all smolt years except 1994.
• #### Effects of variable maternal diet conditions on the reproductive success and development of the California sea cucumber (Parastichopus californicus)

Anthropogenic and natural climate change is altering the biology and ecology of marine organisms, which can be reflected in the supply of primary production that provides food for consumers. Primary producers differ in their biochemical composition, and marine food webs are thus based on specific combinations of producers that provide key nutrients such as dietary fatty acids (FA). Some FA cannot be synthesized by marine invertebrates, and must be acquired directly from diets. Reproductive processes in marine invertebrates are often timed to correspond with seasonal patterns in primary production, such that dietary FA and other nutrients can be partitioned to eggs to provide energy for cell division and biomolecules needed for membrane development. My dissertation investigates the consequences of changing patterns in primary production by examining the effects of maternal diet on reproductive fitness of a deposit feeder, and provides information to support the management and continued captive culturing of the commercially harvested Parastichopus californicus (California sea cucumbers). In chapter 1, I describe a novel live-spawning method and quantify basic reproductive parameters for P. californicus. Peak spawning in the Southeast AK population was about two months earlier and three times smaller than previously observed in British Columbia, Canada. Live-spawned captive females produced more viable eggs and strip-spawned females produced higher fecundity rates. These findings are relevant for the management of commercially harvested populations of P. californicus because they more accurately define spawning seasons, and provide a reliable method to spawn captive animals for further aquaculture development. In chapter 2, I present the results of feeding experiments that explore the effects of two mono-specific algal feeds with different FA profiles on female reproductive output and pre-feeding larval fitness. Females fed with the green alga Tetraselmis sp. had higher fecundity, but there was reduced larval survival relative to females that were fed the diatom Thalassiosira sp. Similar rates of larval development were recorded in both feed treatments. Significant differences were observed in the abundance of FA 20:5ɷ3 (EPA), 22:3ɷ6 (DHA), 12:0, 16:0, and 18:0 FAs in eggs and female gonads between the two feed treatments. In chapter 3, I used field collections in Southeast AK to assess temporal patterns feeding behavior and diet, and examined tissue-specific patterns in total lipid and FA storage and utilization, in in situ populations of P. californicus. All tissue ratios (percent of each tissue relative to the total body mass) varied significantly among collection dates. Tissue and gut content total lipid content also varied significantly among collection dates, except for muscle tissue. Shell debris and terrestrial debris were abundant in all guts regardless of collection date. FA composition differed significantly among females with different gonad maturation periods in skin, viscera, and gonads, suggesting the use of lipids stored in skin and viscera for gonad development. These results further the understanding of dietary factors affecting reproductive fitness in deposit feeders by demonstrating the importance of diet and lipid storage to gonad development.
• #### The effects of water temperature on the seasonal distribution and growth of walleye pollock, Theragra chalcogramma (Pallas), in the southeast Bering Sea

The distribution and growth of walleye pollock, Theragva ohalaogvamna (Pallas), were studied in relation to bottom water temperatures, in an area between latitude 54°30'N and 57°30'N and longitude 160°W and 170°W, from the data collected from 1976 to 1980. The annual variations of bottom temperature distribution, including mean temperature, are described. It is found that temperature boundaries regulate spawning aggregation areas and feeding distribution of adult pollock. Young pollock were distributed in a wider temperature range and revealed a clearer feeding migration pattern than the adults. The weight growth for walleye pollock aged 2 to 4 was determined. The growth rate varied with age, sex and year. The relative growth rate was related to the initial weight of the fish and the mean temperature. Additional seasonal variations in the length-weight relationship and condition factor were observed.
• #### The effects of windchill exposure on the snow crab, Chionoecetes opilio

Millions of snow crabs, 'Chionoecetes opilio, ' are aerially exposed during sorting in the annual Bering Sea commercial fishery. A laboratory experiment measured snow crab responses to windchill exposure. Crabs were exposed to 8 to 16 m/s windspeed and air temperatures from -2 to -10 C̊ for 5 minutes. Mortality, autonomy, and righting response were assessed for seven days post-treatment. Crabs experienced 40% to 100% mortality at windchill from -10 to 16 C̊. Reduced exposure time significantly reduced mortality. Autonomy was variable but pronounced below -10 C̊ windchill. The righting response was impaired after all but the least severe treatment. Estimates of mortality of discarded snow crab in 1998 were calculated from deadloss of retained crab, a windchill model, and a temperature/windspeed model. No relationship existed between catch deadloss and the windchill conditions when the crabs were caught. Mortality of non-retained snow crab was estimated at 3.6% by the windchill model and 19.6% by the temperature /windspeed model.
• #### Effects on fitness traits of intercrossing three geographically separate populations of southeast Alaska coho salmon (Oncorhynchus kisutch)

Adaptive differences among three geographically separate populations of coho salmon (Oncorhynchus kisutch) were investigated by forming first generation intercrosses (hybrid lines) and comparing them to parental types (control lines). Survival, development time, size at ponding, and first year growth were measured as indicators of locally adapted fitness traits. Significant differences (p <0.05) were found between mid-hatching times for control and hybrid groups. Effects of intercrossing on development time are consistent with additive genetic variation, indicating that important genetic divergence exists between the populations. Growth studies were broken down into four different experiments; a 'common garden' experiment, containing all possible controls and reciprocal crosses between pairs of populations, and three 'hybrid' experiments which contained one of the three control lines and all reciprocal crosses associated with the control. Effects of intercrossing on growth were more apparent in the hybrid experiments where there were fewer interactions between different lines.
• #### Endocrine And Immune Profiles Of Immature Pinnipeds

There is increasing interest in assessing the health of individuals and populations of pinnipeds found in the North Pacific, primarily due to population declines leading to conservation concerns. This study assessed the "health" of animals by quantifying hormones associated with fat mass (leptin), lipid and water metabolism (cortisol and aldosterone), and growth and metabolism (thyroxine and triiodothyronine) as well as circulating total and differential leukocyte counts and in vitro proliferation of peripheral blood mononuclear cells (PBMC). Body mass and condition are influenced by an individual's disease and nutritional state. Glucocorticoids are known to affect the immune system and may be stimulated by a multitude of factors. I hypothesized that age or body mass would influence leukocyte counts, PBMC proliferation, and hormone concentrations in Steller sea lion (Eumetopias jubatus) pups and that the response of cortisol to an acute stressor would impact immune parameters in juvenile harbor seals (Phoca vitulina ). Further, given the inherent requirements of disturbance and animal handling necessary for sampling pinnipeds, the impact of these activities on endocrine and immune profiles was assessed. Total white blood cell (WBC) counts, neutrophil counts and T cell proliferation decreased with increasing age in Steller sea lion pups. However, no relationship between body condition index and circulating concentration of hormones quantified was detected. Circulating concentrations of cortisol, thyroxine, and triiodothyronine were influenced by the rookery disturbance. However, the variation attributed to the disturbance was low and did not alter total or differential WBC counts or in vitro proliferation of PBMC. In harbor seals, cortisol and aldosterone concentrations increased following an acute stressor which resulted in a stress leukogram. Total WBC decreased driven primarily by the decrease in neutrophil counts with simultaneous increase in lymphocytes leading to an overall decrease in neutrophil to lymphocyte ratio. These findings highlight the endocrine system's influence on the immune system in immature pinnipeds.
• #### Energetics of arctic Alaskan fishes: carbon isotope evidence

The natural abundance of carbon isotopes were used to investigate the energy requirements of arctic aquatic consumer organisms. A mathematical model was developed that describes the relationship between the rate of consumer isotope turnover rates of growth and metabolism, and the utility of the model for calculating energy requirements from seasonal changes in consumer isotopic composition was demonstrated in laboratory experiments and with field data. The energy requirements of anadromous fishes, which were the major consumers studied, could not be determined using the isotopic data. Instead, the requirements were calculated using biochemical data and rates of growth and oxygen consumption, and were about 2.6-6.0 kcal day⁻¹ in the summer and 0.4-1.2 kcal day⁻¹ in the winter. Seasonal changes in lipid and protein contents indicate that anadromous fishes cannot find enough food during the winter to supply their energy requirements, and that about 50% of the energy needed comes from the metabolism of tissues accumulated during the summer. The relative importances of marine and freshwater food webs in supplying the energy requirements were determined by comparing the seasonal isotopic components of anadromous fishes to the isotopic compositions of fish that are permanent residents in each environment. It appears that anadromous fishes that overwinter in the Coleville River (the largest river on the Alaska North Slope) depend almost entirely on the marine environment for their energy, whereas those that overwinter in Canada's Mackenzie River rely on both marine and freshwater habitats.