• The paradox of pelagic food webs on the Bering-Chukchi continental shelf

      Springer, Alan M.; McRoy, C. P. (1987)
      Prolific primary production and spectacular populations of marine birds and mammals in the northern Bering Sea were for many years considered to be a paradox of an environment that should have had low production, as is typical of shallow continental shelves elsewhere. However, a "river" of oceanic water, Anadyr Water, originating along the continental slope of the Bering Sea carries a perpetual supply of nutrients and biota onto this northern shelf that transforms part of the region into one that is extremely productive at all trophic levels. Diatoms grow profusely throughout the ice-free season and, together with oceanic zooplankton advected in the Anadyr stream, provide the energy base for rich pelagic and benthic food webs. Contrasting with the highly productive pelagic regime is one associated with Bering Shelf Water and Alaskan Coastal Water. Both of these water masses originate over the shallow shelf of the northern and eastern Bering Sea, and are typically nutrient-poor following the spring phytoplankton bloom. Terriginous nutrients introduced by the Yukon and other rivers are not sufficient to elevate primary production above a low level typical of inner shelf regions. The oceanic zooplankton are excluded from this environment, and populations at higher trophic levels are small. The consequence of these contrasting physical regimes is that discrete oceanic and inner shelf food webs coexist in a small geographic region where only a coastal ecosystem is expected.
    • Influences of abiotic factors on the return, ocean abundance, and maturity of sockeye salmon (Oncorhynchus nerka) in the northern North Pacific Ocean

      Yeh, Shinn-Pyng; Nishiyama, Tsuneo (1987)
      The fluctuations in return, ocean abundance, and maturity of sockeye salmon (O. nerka) were examined and related to wind stress curl, sea suface temperature (SST), sea level pressure, and cloudiness, in the area between 40$\sp\circ$N-60$\sp\circ$N and 160$\sp\circ$E-140$\sp\circ$W. Historical records, during two periods, 1971-76 and 1955-86, were the primary source of data. Spectral analysis of a 360-month period of mean wind stress curl during 1955-85 showed 3.1- and 5.3-year cycles. The 5.3-year cycle was correlated (r =.32 to.44, P $<$.10) with the return of Bristol Bay sockeye salmon mostly at 0- (the year of spawning migration) and 1-year lag (the first year of lake residence). The relative ocean abundance of sockeye salmon in the northwestern Northern Pacific during 1971-76 was lowest during the three periods: 1961-70, 1971-76, and 1977-85. Mature Kamchatka sockeye salmon were 24% more abundant than mature Bristol Bay sockeye salmon during 1971-76. A significant relationship was found between the May-June mean SST and abundance of sockeye salmon (r =.56 to.66, P $<$.01) during 1961-85. In the northern North Pacific, the SST was positively (r =.73 to.86, P $<$.001) related with the gonad weight of sockeye salmon. The results indicated a close relation between the return, ocean abundance, and maturity of sockeye salmon and most of the abiotic factors.
    • Intertidal community development along a distance/age gradient in a tidewater glacial fjord

      Sharman, Lewis Crook (1987-12)
      Glacier Bay has recently undergone rapid deglaciation, exposing new substrates to colonization and biological development. There is a clearly defined increase in marine intertidal community development with substrate age (0-200 y) and distance (0-90 km) from present-day locations of tidewater glacier termini. The objectives of this research were (1) to describe length-of-fjord patterns of intertidal community composition and corresponding gradients of the near-surface marine physical environment and (2) to use this approach to evaluate the relative contributions of substrate age and physical factors to determining the degree of community development. Distance and age were almost perfectly correlated. Intertidal species richness increased linearly with distance/age. Environmental factors can be grouped into those that also varied linearly along this gradient, and those that varied exponentially. Distance from the glaciers and the other linearly correlated marine environmental factors of water temperature, salinity, and suspended particulate nitrogen factors are probably the most important determinants of intertidal community development.
    • The carbon cycle in an anoxic marine sediment: Concentrations, rates, isotope ratios, and diagenetic models

      Alperin, Marc Jon; Reeburgh, W. S. (1988)
      The carbon cycle in the anoxic sediments of Skan Bay, Alaska, was investigated in order to better understand the processes that control biogeochemical transformations in an organic-rich sediment environment. Depth distributions of concentration and $\delta\sp{13}$C were determined for five major carbon reservoirs: methane (CH$\sb4$), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate inorganic carbon (PIC), and particulate organic carbon (POC). In addition, methane oxidation and sulfate reduction rates were measured under quasi-in situ conditions using radio-tracer techniques. Diagenetic models were applied to concentration, reaction rate, and isotope ratio depth distributions and the results were integrated into a comprehensive, depth-dependent model of the Skan Bay carbon cycle that considered advective, diffusive, and biological and chemical reactive fluxes for the five major carbon reservoirs. The Skan Bay carbon cycle is fuelled by POC, which is deposited at the sediment surface at a rate of 2290 $\pm$ 480 umol $\cdot$ cm$\sp{-2}$ $\cdot$ yr$\sp{-1}$. Isotope mass-balance calculations indicate that about 60% of this material is derived from kelp while the remainder originates as phytoplankton. About 60% of the organic matter is consumed in the upper 40 cm of the sediment column. The $\delta\sp{13}$C-POC and $\delta\sp{13}$C-DOC depth distributions suggest that the material derived from kelp is more labile, accounting for greater than 60% of the total POC consumption. The products of anaerobic metabolism of POC accumulate in the DOC reservoir creating a large DOC concentration gradient at the sediment-water interface. Flux and stable carbon isotope mass-balance calculations suggest that a sizable portion (30 to 80%) of the DOC produced by degradation of POC diffuses from the sediment prior to oxidation to dissolved inorganic carbon. Methane production appears to occur primarily at depths greater than 40 cm. The CH$\sb4$ diffuses upward and is almost quantitatively oxidized to DIC in a narrow subsurface zone. Methane oxidation accounts for only 20% of the DIC production, but exerts a profound influence on the $\delta\sp{13}$C-DIC profile, contributing to the distinct mid-depth minimum. Pore waters are supersaturated with respect to calcite at depths greater than 10 cm, but isotope mass-balance considerations indicate that carbonate mineral formation is not occurring in these sediments.
    • Physiological and ecological implications of hemorheological variations in marine and terrestrial mammals

      Wickham, Lori Lee (1988)
      The possible significance of variations in interspecific hemorheological properties related to diving behavior was studied in eight species of marine mammals with humans and pigs as terrestrial controls. Diving duration was positively correlated with elevated blood hemoglobin, oxygen capacity and viscosity among animals of the same class. No acclimatization response to activity was evident from studies of blood drawn from newly-captured northern elephant seals and sea otters and those in captivity for extended periods which justified the use of captive animals for rheological studies. Adaptations of marine mammals to diving were evident from comparisons of phocid seal and pig hemorheology. Seals had increased oxygen storage (six times) with less viscosity-dependent reductions in oxygen transport ($-$22%) when compared to pigs at equal packed cell volume. Phocid seal blood samples were compared with those of pigs and humans for erythrocyte aggregation and blood viscoelasticity to study the mechanics of viscometric variations. Viscous and elastic components of seal blood viscosity were 20 to 73% lower than those of pigs due to decreased aggregation extent and rate (P $<$ 0.05). Lower plasma fibrinogen and increased erythrocyte electrophoretic mobility are believed to contribute to lowered seal blood aggregation. Comparisons of the in vivo effects of blood viscosity on whole body and myocardial oxygen consumption by manipulation of whole body hematocrit in seals and pigs revealed that optimal hematocrit ranges for seals were shifted to the right of those from pigs (SEALS: 25%-55%; PIGS: 25%-45%; P $<$ 0.05). Seals showed significantly less viscosity-dependence in total body oxygen transport and oxygen consumption than did pigs. Myocardial oxygen consumption data were variable and showed no statistically significant differences among seals and pigs. The seals' lower erythrocyte aggregation, decreased low-shear viscosity and a greater ability to compensate for viscosity changes may represent adaptations to reduce the stress necessary to reinitiate flow in stagnant venous sinuses thereby reducing blood-flow resistance during dive-recovery. These adaptations may help maintain circulatory perfusion to vital organs, while flow is restricted to less oxygen-dependent tissues during underwater submergence without sacrificing the advantage of increased blood oxygen storage.
    • On the dynamics of the Alaska coastal current

      Luick, John Leonard; Royer, Thomas C. (1988)
      The Alaska Coastal Current (ACC) in the northern Gulf of Alaska is a wind- and buoyancy-driven near-surface jet primarily maintained by the horizontal salinity gradient due to fresh water entering at the coast. It serves as the major source of fresh water to the North Pacific Ocean. The buoyancy driving force is the major focus of this investigation. The study area is situated just "downstream" of Prince William Sound (PWS), a large estuary whose surface outflow is seen to occupy a narrow inshore band after joining the ACC. The effect of this band appears to be the formation of an occasional double maximum in the ACC. The period focused on in this study was selected on the basis of weak windstress but large fresh water input in order to emphasize the buoyancy forcing. The TS characteristics and a water mass tracing technique are used to separate the thermal and haline signals in the buoyancy forcing and to track the origin and fate of the source waters of the study area. The buoyancy driving force is shown to be primarily haline, with temperature playing a secondary, moderating role. Because of the large topographic variability and sloping density interfaces, and in order to exploit the available data, a diagnostic model retaining the baroclinicity and bottom topography terms was chosen to study the dynamics. Model premises are verified by results from hydrographic surveys, moored current meters, and a profiling current meter. The model predicts a midshelf region of negligible sealevel gradient, with a nearshore ($\approx$70 km wide) band over which the sealevel changes by about 25 cm. The sloping surface drives a strong ($\approx$100 cm/s) surface flow, which decreases to zero and reverses below about 100 m due to the opposing baroclinic pressure gradient. The flow splits around a shoal region. The onshore portion joins the outflow from PWS and accelerates downstream forming a double maximum. The offshore segment forms a large meander before rejoining the rest of the ACC, advecting midshelf water shoreward. The momentum balance is dominated by the JEBAT terms, which primarily determine the flow along and across contours of f/H.
    • Migratory behavior of maturing pink salmon in Gastineau Channel, southeast Alaska

      Thrower, Frank Patrick (1988-05)
      Migration and spawning stream selection of maturing pink salmon in the area of Gastineau Channel was studied with respect to: (1) homing of individuals tagged with coded-wire as emergent fry; (2) intermingling and subsequent spawning locus of adults tagged at stream mouths; (3) migratory pathways into Gastineau Channel of fish tagged at north and south entrances; and (4) effects of stress (capture, handling and tagging) on pre-spawning adults in their natal stream on subsequent homing or straying. (1) wire-tagged adults did not stray from two natal streams; (2) of 681 adults marked at stream mouths, 308 were recovered locally, demonstrating complex stock assemblages at some stream mouths and homogeneity at others; (3) of 949 adults tagged at entrances, 300 were recovered locally demonstrating intermingling of stocks at both entrances and differences in the proportions of each stock at each entrance; (4) stress induced straying (2%) from a natal to another stream one kilometer distant.
    • The influence of rookery terrain on population structure, territorial behavior, and breeding success of Steller sea lions in the Gulf of Alaska

      Smith, Louise N. (1988-05)
      The effect of rookery terrain on population structure, territorial behavior and breeding success of Steller sea lions was assessed at two rookeries, in the northern Gulf of Alaska. The sea lions using Sugar loaf and Marmot Islands differed in age structure, juveniles being absent from Sugar loaf but present on Marmot during the breeding season. Territory boundaries of breeding bulls on Sugarloaf were stable, and were unaffected by tides. Territory boundaries on Marmot were unstable, shifting with the tide. Territorial bulls occupied two types of territories on Sugarloaf Island (landlocked and water-access) and three types on Marmot (landlocked, tidal and semiaquatic). The behavior of territorial bulls on Marmot was influenced by tides and presence of juvenile animals. These factors were not important on Sugarloaf. The breeding success of territorial bulls was unaffected by location of territory on Sugarloaf. Territory location was important in the breeding success of Marmot Island bulls.
    • Effects of elevated sediment levels from placer mining on survival and behavior of immature arctic grayling

      Scannell, Patrick O. (1988-12)
      The effect of placer mining effluents on Arctic grayling (Thymallus arcticus) fingerling and egg survival was tested in mined and unmined streams in interior Alaska. Also the influence of turbidity on Arctic grayling reactive distance and avoidance behavior was tested in a laboratory choice chamber. Arctic grayling fingerlings suffered less than 1% mortality during a 96-hr toxicity test in both clear (mean NTU = 1.4) and mined (mean NTU = 445) streams. Arctic grayling eggs did not show significantly (p > 0.1) higher mortality in mined streams than in unmined streams. In a laboratory choice chamber test, Arctic grayling avoided water with a turbidity above 20 NTU (nephelometric turbidity units). Arctic grayling reactive distance diminished proportional to the natural logarithm of turbidity.
    • Nitrogen flux in the northern Bering Sea

      Hansell, Dennis Arthur; Goering, John J. (1989)
      Much of the primary production occurring over the Bering Sea continental shelf is thought to be associated with both ice edge and spring blooms. The nature of summer production over the shelf is now being addressed. A general model is presented for summer phytoplankton production along the Bering Sea shelf break front and subsequent transport of phytodetritus into the northern Bering Sea. Production associated with the shelf break front is estimated to be 200 g $\cdot$ C $\cdot$ m$\sp{-2}$ over a 120-day growing season and is supported by nutrients from the Bering Slope Current. A portion of the biomass accumulating over the front is advected into the Chirikov Basin, supplying 26% of the daily carbon demand of the benthos. The Bering Slope Current bifurcates at Cape Navarin and one branch, referred to as the Anadyr Current, flows north through Anadyr and Bering Straits. Nutrients in the Anadyr Current support an intense surface bloom over the western Chirikov Basin where total nitrogen uptake rates are $>$6.0 mg-at N $\cdot$ m$\sp{-2} \cdot$ h$\sp{-1}$ and nitrate contributes up to 50% of the total nitrogen uptake. Modified Bering Shelf water contains phytoplankton at two depths: both a surface accumulation and a deep layer. Nitrate contributes $<$35% to total nitrogen uptake rates of 1.80 mg-at N $\cdot$ m$\sp{-2} \cdot$ h$\sp{-1}$ in this water. Nitrogen productivity is lowest in Alaskan Coastal water (1.0 mg-at N $\cdot$ m$\sp{-2} \cdot$ h$\sp{-1}$) where nitrate uptake averages only 15% of the total. A simple nitrogen budget suggests that 29% and 62% of the annual nitrogen productivity in modified Bering Shelf and Anadyr waters, respectively, is exported through Bering Strait into the southern Chukchi Sea for deposition. Improved estimates of the rates of urea production and uptake by phytoplankton in the northern Bering Sea were made after determining the change in $\sp{15}$N-atom % enrichment of urea during incubations. Estimates of uptake rates increased by up to 83% using a $\sp{15}$N accumulation model and by $>$210% using a $\sp{15}$N disappearance model. However, a discrepancy exists between the $\sp{15}$N-urea removed from the aqueous phase and the $\sp{15}$N accumulated in the particulate phase. The ability to find in the particulate fraction the $\sp{15}$N removed from solution as $\sp{15}$N-urea was improved by 72% following removal of the $>$20-$\mu$m particulate fraction.
    • Competition between two aquatic microorganisms for oscillating concentrations of phosphorus

      Braddock, Joan Forshaug; Brown, Edward J. (1989)
      The availability of limiting nutrients is a critical factor regulating growth of aquatic microorganisms. In at least some aquatic systems the frequency of addition rather than the absolute concentration of nutrients controls community structure. Gnotobiotic continuous cultures were used to examine the growth characteristics of a green alga (Selenastrum capricornutum) and a heterotrophic yeast (Rhodotorula rubra) when phosphorus-limited steady-state populations were subjected to varying concentrations of pulsed phosphorus. The responses of these organisms to phosphorus additions were measured both in single and dual species continuous cultures. Both organisms exceeded the maximum transport rates for phosphorus predicted from batch and steady-state continuous cultures. Carbon limitation did not cause a decline in phosphorus accumulation in R. rubra. Carbon-limited yeast cultures perturbed with phosphorus attained the highest phosphorus per cell values seen in these studies. The phosphorus pool was not significantly diminished in these cultures only because the total yeast biomass was limited by carbon. These results suggest that carbon-limitation of heterotrophic populations may be essential to the existence of phytoplankton in low-nutrient aquatic environments.
    • Oxytetracycline tags in pink salmon fry applied by immersion and detected by fluorescence spectrometry

      Page, Timothy Kent (1989-05)
      I investigated the feasibility of using spectrophotofluorescence as a quantitative method of analyzing pink salmon fry otoliths for the presence of oxytetracycline (antibiotic). I exposed twenty-four groups of pink salmon fry (approximately 250 individuals each) to solutions of oxytetracycline ranging in concentration from unexposed to 2000 ppm, and in duration of exposure from one to twelve hours. Otoliths from unexposed fry had the lowest mean fluorescence (log e [mean flu. units] = -1.77). Otoliths from fry exposed to 500 ppm for twelve hours had the highest fluorescence (log e [mean flu. units] = 0.899). Fluorescence increased nonlinearly with duration of exposure. There is a linear increase of fluorescence with exposure up to 500 ppm; above which fluorescence decreases. Pink salmon fry exposed to OTC in solution absorb detectable amounts of OTC in their otoliths. These amounts of OTC can be quantitatively measured by spectrofluorometry.
    • Feeding and growth of seasonal cohorts of larval walleye pollock (Theragra chalcogramma) in Auke Bay, Alaska

      Sterritt, David A. (1989-05)
      Larval walleye pollock, Theragra chalcogramma (Pallas), typically occur in the water column in synchrony with peak densities of prey. A primary objective of this investigation was to examine and compare growth rates of larval pollock. The growth rate of a synchronous cohort (hatched 10-14 May, 1986) was found to be significantly higher (P<0.05) than that of an earlier cohort (hatched 15-19 April, 1986) . Synchronous cohorts are larvae that occur simultaneously with the maximum densities of herbivorous copepods. Growth rates were determined by otolith analysis. Prey densities and water temperature were implicated as causes of the observed differences in growth. Prey densities were approximately 3 times higher for the synchronous cohort than the early cohort. Additionally, the early cohort experienced water temperatures 2-3°C colder than the synchronous cohort. Results suggest that synchronous larval walleye pollock have higher growth rates and may have higher survival rates.
    • Competition between two aquatic microorganisms for oscillating concentrations of phosphorus

      Braddock, Joan Forshaug (1989-05)
      The availability of limiting nutrients is a critical factor regulating growth of aquatic microorganisms. In at least some aquatic systems the frequency of addition rather than the absolute concentration of nutrients controls community structure. Gnotobiotic continuous cultures were used to examine the growth characteristics of a green alga (Selenastrum capricornutum) and a heterotrophic yeast (Rhodotorula rubra) when phosphorus-limited steady-state populations were subjected to varying concentrations of pulsed phosphorus. The responses of these organisms to phosphorus additions were measured both in single and dual species continuous cultures. Both organisms exceeded the maximum transport rates for phosphorus predicted from batch and steady-state continuous cultures. Carbon limitation did not cause a decline in phosphorus accumulation in R. rubra. Carbon-limited yeast cultures perturbed with phosphorus attained the highest phosphorus per cell values seen in these studies. The phosphorus pool was not significantly diminished in these cultures only because the total yeast biomass was limited by carbon. These results suggest that carbon-limitation of heterotrophic populations may be essential to the existence of phytoplankton in low-nutrient aquatic environments.
    • Ichthyoplankton vertical distribution and vertical migration in Auke Bay, Alaska

      Pritchett, Marc S.; Haldorson, Lewis J.; Shirley, Thomas C.; Fagen, Robert; McDowell, Peter (1990-05)
      Vertical distributions of larval fishes were examined in Auke Bay, Alaska using an opening/closing 1.0 m² Tucker trawl horizontally towed, at six depths, every four hours for 24 hours. In daytime, larval fishes concentrated at 5-10 m depths, coincident with highest prey densities. At night, osmerids ascended to the surface, walleye pollock and northern smoothtongue descended, whereas other species simply dispersed. A significant relationship existed between larval walleye pollock length and depth distribution with larger larvae migrating further than smaller larvae. Yolk-sac larvae were randomly distributed vertically. Larval walleye pollock are daytime feeders, primarily on copepod nauplii. Larval pollock approximately 7.0 - 7.5 mm standard length expand their diet to include copepodites.
    • An in-season management system for sockeye salmon returns to Lynn Canal, southeast Alaska

      McPherson, Scott A. (1990-09)
      An in-season management system was developed for four stocks of sockeye salmon (Oncorhynchus nerka) from Chilkoot and Chilkat Lakes in Southeast Alaska, using a total run (catch + escapement) database built from analysis of 132,000 scale samples. Separate management objectives were defined for early and late stocks from each lake. A Ricker model, with nonlinear least squares and a bootstrap procedure, was used to estimate optimal escapement levels, which were lower than previous estimates, and precision bounds. Comparison of several in-season forecasting models based on run timing showed that a model combining a preseason forecast with average proportion forecasts was most accurate. Average proportion forecasts were improved by timing shifts identified by inflection points. Linear regression was used to forecast Chilkat Lake escapement in-season. Accuracy of the best forecasting models for each analysis was ≤ 25% by the first quartile of abundance.
    • Seasonal and ontogenetic changes in meiofauna in the diets of postmetamorphic flatfish

      McGregor, Susan Broad (1990-12)
      The diets of intertidal postmetamorphic (9.0-97.0 mm SL) rock sole, Lepidopsetta bilineata (Ayres 1855), starry flounder, Platichthvs stellatus (Pallas 1811), and yellowfin sole, Limanda aspera Pallas 1811, were investigated over a one year period in Auke Bay, Alaska. Rock sole were collected earliest, followed by starry flounder, and yellowfin sole. Harpacticoid copepods were the primary prey of small (<20.0 mm standard length) fish of all species. Harpacticoids were also numerically important in the diets of medium (20.0-34.5 mm SL) fish, but relatively unimportant in the diets of large (>35 mm SL) fish. Meiofauna was collected concurrently with fish samples. Settlement of flatfish did not occur when the density of harpacticoids was highest. Highest densities of total harpacticoids occurred during May in both 1987 (2.6 X 106 ± 2.5 X 10s) and 1988 (1.4 X 106 ± 3.2 X 104). Other meiofaunal taxa did not have the same seasonal changes in density. Some minor taxa were only present seasonally.
    • Numerical modeling study of the circulation in the Gulf of Alaska

      Bang, Inkweon (1991)
      A series of numerical experiments are performed to simulate the Gulf of Alaska circulation and to examine the dynamical ocean response to the annual mean and seasonal forcing using a primitive equation model (Semtner 1974). The model domain encompasses the North Pacific north of 45$\sp\circ$ N and east of 180$\sp\circ$ and is surrounded by artificial walls in the south and west. Biharmonic diffusion is used in the interior to excite mesoscale eddies. A sponge layer with high Laplacian diffusion is incorporated near the western boundary. Horizontal resolution of 30$\sp\prime$ x 20$\sp\prime$ and 20 vertical levels are used to resolve the mesoscale topography and eddies. Wind stress computed from sea level atmospheric pressure and temperature and salinity data of Levitus (1982) are used. A diagnostic model produces a circulation in the Gulf of Alaska which agrees with observed patterns. In a three-layer flat-bottom baroclinic model, baroclinic Rossby waves propagate at 0.8 cm/sec and it takes a decade for spin-up to be completed. Baroclinic models forced by the annual mean wind and thermohaline forcings show the generation of eddies by baroclinic instability. The eddies in the flat-bottom model have a period of 75 days and are interpreted as barotropic Rossby waves. In the model with topography, the period of dominant eddies is 3-4 years and they are interpreted as baroclinic Rossby waves. Anticyclonic eddies near Sitka show similar characteristics as the Sitka eddy. They propagate westward and cause meanders in the Alaska Stream near Kodiak Island. The abnormal shift of the Alaska gyre in 1981 is probably due to the presence of one of these anticyclonic eddies. A flat-bottom model with seasonal forcing shows a large seasonal variability. When bottom topography is present, however, seasonal response is greatly reduced due to the dissipation of barotropic response by bottom topography. The seasonal baroclinic model shows a similar seasonal variability to the seasonal barotropic model indicating that the seasonal response is mainly barotropic. Eddies are also excited in the seasonal case and are almost identical to those of the annual mean case.
    • The significance of marine-derived biogenic nitrogen in anadromous Pacific salmon freshwater food webs

      Kline, Thomas Clayton, Jr. (1991)
      The natural abundance of the stable isotope ratios $\sp{15}$N/$\sp{14}$N and $\sp{13}$C/$\sp{12}$C expressed as $\delta\sp{15}$N and $\delta\sp{13}$C was used to trace biogenic nutrients delivered by returning adult anadromous Pacific salmon into freshwater systems. These systems were Sashin Creek, a rapidly flushing stream located on Baranof Island, southeastern Alaska and Iliamna Lake, the major sockeye salmon, Oncorhynchus nerka, nursery lake in the Kvichak River watershed, Bristol Bay, southwestern Alaska. Marine-derived nitrogen (MDN) was quantifiable by use of an isotope mixing model based on comparison of biota $\delta\sp{15}$N in areas used for spawning by anadromous salmon with salmon-free controls within the same watershed. Control periphyton (benthic primary producers) $\delta\sp{15}$N values $\sim$0 suggested that the control N pool was derived from N$\sb2$ fixation without significant recycling. In contrast, periphyton abundant in areas of intense spawning activity or carcass aggregation had $\delta\sp{15}$N $\sim$ +7. These two values were the basis for comparison of $\delta\sp{15}$N values of higher trophic level biota. A mixing model relating $\delta\sp{15}$N to MDN with trophic level was used to estimate consumer MDN through incorporation of a priori isotopic trophic enrichment factors established in the literature. Distinctive $\delta\sp{13}$C signatures along the Sashin Creek stream gradient and between Iliamna Lake littoral and limnetic production were used in concert with $\delta\sp{15}$N. Sashin Creek fishes reflected isotopic signatures of periphyton and thus production within the same stream section. Isotopic data suggested an overall importance of limnetic production in Iliamna Lake resident fish and juvenile sockeye salmon diets. Salmon eggs and emergent fry retaining the parental marine isotopic signature were distinguishable from autochthonous production derived from marine N, and appear to be a minor dietary component in both Sashin Creek or Iliamna Lake fishes. The proportion of MDN in resident fish N, including juvenile salmon after turnover of the natal N pool, was proportional to the escapement of spawners. Thus there is now direct evidence for a significant natural fertilization process: the flow of remineralized marine-derived biogenic nutrients from returning anadromous Pacific salmon into freshwater food webs.