• Characterizing the diet and population structure of lampreys Lethenteron spp. using molecular techniques

      Shink, Katie G.; López, Andrés; Murphy, James M. (2017-08)
      Lampreys contribute to the health of aquatic ecosystems and are targeted in both subsistence and commercial fisheries. Despite their ecological and commercial importance, the management and conservation of native lampreys have been largely overlooked. The goal of this study was to close current knowledge gaps of lamprey biology through the examination of Lethenteron spp. in Alaska. This study applied two molecular techniques, DNA metabarcoding and microsatellite genotyping, to (1) characterize the diet of marine-phase Arctic lamprey Lethenteron camtschaticum (N = 250) in the eastern Bering Sea and (2) investigate the population structure of larval lampreys Lethenteron spp. (N = 120) within and among three Yukon River tributaries. A combination of visual observations and DNA metabarcoding revealed the presence of diagnostic structures/tissues (i.e., eggs, fin[s], internal organs, otoliths, and vertebrae) and detected DNA sequences of ten ray-finned fishes in the diets of L. camtschaticum. The most frequent prey taxa were Pacific sand lance Ammodytes hexapterus, Pacific herring Clupea pallasii, gadids, and capelin Mallotus villosus. Five of the ten taxa identified in this study were reported for the first time as prey for L. camtschaticum. To investigate the genetic diversity of larval lampreys, a recognized knowledge gap for populations in Alaska, a total of 81 larval lampreys were successfully genotyped at all loci. Global FST of larvae was 0.074 (95% CI: 0.042 - 0.110), while pairwise FST values among the three localities examined ranged from 0.066 - 0.081. Hierarchical model-based Bayesian clustering analyses detected three genetic clusters (K = 3) among all larval lampreys and two genetic clusters (K = 2) among Chena River larvae; no further genetic clustering was identified within the remaining two tributaries. Estimates of contemporary gene flow indicated reciprocal migration among sites. The diet analyses indicated anadromous L. camtschaticum function as flesh-feeding predators that prey upon pelagic fishes in the eastern Bering Sea, while genetic analyses suggested that larval lamprey aggregations within three Yukon River tributaries exhibited higher levels of genetic diversity than are typically found among broad-ranging populations of anadromous lamprey species. Ultimately, this study highlighted the value of molecular techniques to improve our understanding of the biology of a poorly studied fish species in Alaska.
    • Characterizing the fish community in turbid Alaskan rivers to assess potential interactions with hydrokinetic devices

      Bradley, Parker T.; Seitz, Andrew; Sutton, Trent; McPhee, Megan; Burr, John (2012-12)
      The Yukon and Tanana rivers are two large, glacially turbid rivers in Alaska, where hydrokinetic projects are being explored for feasibility of electricity production. Downstream migration behavior of fishes in these rivers is poorly understood; as a result, the potential impacts of hydrokinetic devices, which will be placed in the deepest and fastest part of the river, on fishes are unknown. Downstream migrating fishes were sampled during the ice-free season along the river margins of the Yukon River in 2010 and the river margins and mid-channel of the Tanana River in 2011. Results suggest that the river margins in the Yukon and Tanana rivers are primarily utilized by resident freshwater species, the mid-channel is utilized by Pacific salmon (Oncorhynchus spp.) smolts, and only chum salmon (Oncorhynchus keta) smolts utilize both of these areas. Some species exhibited distinct peaks and trends in downstream migration timing including longnose suckers (Catostomus catostomus), whitefishes (Coregonine), Arctic grayling (Thymallus arcticus), lake chub (Couesius plumbeus), Chinook salmon (O. tshawytscha), coho salmon (O. kisutch), and chum salmon. As a result of these fishes' downstream migration behavior, hydrokinetic devices installed in surface waters of the middle of the river channel will have the most potential interactions with Pacific salmon smolts during their downstream migration to the ocean from May through July.
    • Chemosensory responses and foraging behavior of Pycnopodia helianthoides: predator or scavenger?

      Brewer, Reid; Norcross, Brenda; Highsmith, Raymond; Iken, Katrin (2003-08)
      Chemical cues released by damaged or dead organisms can affect how and where benthic scavengers feed, whether damage or mortality is natural or fishery-related. These cues may also cause predators to act as facultative scavengers. Experiments were performed to determine the role that the seastar Pycnopodia helianthoides plays in the presence of scavengable prey. The results of these experiments suggest that P. helianthoides preferentially scavenge in lieu of its normal predatory role. When given a choice, P. helianthoides choose damaged or decaying food over live prey even when live prey is encountered en route to the damaged animal. The densities and activities of P. helianthoides were compared between areas where food was continually introduced and areas where food was not introduced. Adding scavengable food to areas with P. helianthoides caused a spatial redistribution of the seastar population, a change in the foraging dynamics of the seastars, and in some cases, a change in the densities of the prey that P. helianthoides normally consume. The effects of introducing food appeared to result in a change in the role that P. helianthoides plays in the benthic community. This change in modes could have significant effects on the equilibrium of the benthic community.
    • Circulation and dynamics on the Northeastern Chukchi Sea Shelf

      Fang, Ying-Chih; Weingartner, Thomas J.; Winsor, Peter; Kowalik, Zygmunt; McDonnell, Andrew; Williams, William J. (2017-12)
      The circulation on the northeastern Chukchi Sea shelf is controlled by the poleward pressure gradient between the Pacific and Arctic Oceans. Local winds modulate the upper ocean and can rapidly alter the flow field. Present understanding of the circulation is largely based on subsurface measurements, but the response of near-surface currents to the slowly-varying secular pressure gradient and rapidly-varying local winds has not been addressed. I analyzed surface current data, extending more ~150 km offshore in the northeastern Chukchi Sea, collected from shore-based high-frequency radar systems (HFR) during the open water season. I find three wind-induced circulation regimes. Two of these are related to strong northeasterly winds when wind speeds approach or exceed 6 m s⁻¹ and the third results from infrequent northwesterly winds at >~6 m s⁻¹ . I find two dynamically different regions separated along ~71.5°N associated with hydrographic changes. North of 71.5°N the water column is strongly stratified due to cold and dilute ice meltwaters, whereas the water column to the south is much less stratified. These differences are reflected in the current response to the winds. I also adapted and refined an HFR data processing technique and developed an economical way to assess HFR-derived data quality, which is beneficial when using HFR data collected from networks having suboptimal coverage. I investigated the poorly understood circulation around Hanna Shoal. North of the Shoal there is a zonal gradient in the thermohaline and flow fields. The eastern side of the Shoal is strongly stratified year-round and vertically sheared unlike the western side, where the flow is steadily northeastward over the water column. Dense bottom waters flow clockwise around Hanna Shoal, but zonal convergence is implied in the upper water column north of the Shoal. The circulation is influenced by the distribution of late summer sea ice and by clockwise-propagating topographic waves.
    • Climate, embryonic development, and potential for adaptation to warming water temperatures by Bristol Bay sockeye salmon

      Sparks, Morgan McKenzie; Falke, Jeffrey; Westley, Peter; Adkison, Milo; Quinn, Thomas (2016-08)
      Rapidly warming water temperatures associated with climate change represent a substantial disturbance to the habitat of aquatic ectothermic organisms. For salmonid fishes (family Salmonidae), early life history survival and timing of reproduction and development are closely tied to temperature, such that altered thermal regimes could alter patterns of survival or shift phenology into a mismatch with the environment. Because temperature is the dominant driver of developmental rates, empirical statistical models have been developed to predict the timing of hatching and fry emergence based on incubation temperature. In this thesis I explored how the timing of hatching and emergence may shift in response to warming temperatures and how spawning timing across an Alaskan landscape is shaped by incubation temperatures experienced by sockeye salmon (Oncorhynchus nerka) embryos and alevin. Additionally, I quantified the relative roles of genetics and environmentally induced plasticity on the timing of hatching in two populations of sockeye salmon from the Iliamna Lake system, Alaska by rearing them in common garden conditions in the laboratory. To meet these goals I reformulated a widely cited developmental model to incorporate variability in natural regimes and use it to predict hatching timing over the course of the spawning duration for 25 populations of Bristol Bay sockeye salmon. Additionally, I hind- and forecasted lake temperature based off historical and predicted air temperatures to estimate and predict hatching for a single population. I found that predicted hatching timing for wild populations varied between 58 and 260 days, and was largely variable as a result of habitat thermal heterogeneity and parental spawn time. I also predicted a three-week decrease in hatching timing over the course of the next century for a single beach spawning population, which was just beyond historic variability. Counter to expectations, for a subset of populations hatching and emergence timing variability exceeded that of spawning timing, indicating the relationship between spawning timing and incubation temperature may be weaker than expected. The results of the common garden experiment revealed indistinguishable differences between populations in hatching timing across five temperature scenarios, but strong plasticity as timing differed between 74 and 189 days in the warmest to coolest treatment. Furthermore, I detected family-specific differences in hatching timing both within and among treatments consistent with heritable developmental rates and gene by environment interactions in days to hatch, where the interaction between treatment and family was as high as 10 days difference in hatching. Population or family-specific survival in this experiment did not differ in response to temperature suggesting a lack of thermal adaptation in this regard during this life stage in these populations. Alevin mass and length upon hatching varied little among treatments (<10%), but did significantly decrease with cooling temperatures. Taken as a whole this study indicates that the effects of climate change during the early life history stages may be buffered by phenotypic plasticity and variability in populations and habitats will be important for maintaining diversity in the face of climate change.
    • Commercial fishing livelihoods, permit loss, and the next generation in Bristol Bay, Alaska

      Coleman, Jesse M.; Carothers, Courtney; Donkersloot, Rachel; Adkison, Milo; Greenberg, Joshua (2019-08)
      Fishing people across the globe have experienced a fundamental restructuring of their livelihoods, communities, and economies as the result of shifts to rights-based fisheries management in the past halfcentury. The ideological underpinnings of this movement are based in neoliberalism, which is a belief system that values individualism, competition, private property, and governance by the free market. I examine some of the long-term and latent effects of this and other significant historical transitions in the fishery-dependent Bristol Bay region of Alaska. Relationships between humans and salmon in Bristol Bay evolved over thousands of years and inform the way that many fishing livelihoods are pursued today. In addition to these foundational relationships, many significant changes have occurred that have shocked and stressed the livelihood "fabric" woven many interlocking threads (i.e., the sociocultural, economic, knowledge/skill, political, natural, physical building blocks needed to construct a fishing livelihood in the region). Informed by literature review and ethnography, I describe in detail four such changes: colonization of Bristol Bay's Indigenous peoples, industrialization of the commercial fishery, implementation of a rights-based access regime (i.e., limited entry permit program), and the sockeye salmon price crash of the early 2000s. These effects linger today and raise questions for the future of the Bay and its fisheries, with respect to two particular issues: the uncertainty around the next generation of fishermen, and the severe loss of locally held permits in the Bay. To address the former, I conducted a survey of local students to measure their perceptions of the fishing industry and of community life. The results of this survey suggest that familial fishing ties, experience in the fishery, subsistence fishing activity, and household economic dependence on commercial fishing income are strong predictors of a student's desire to be engaged in commercial fishing as an adult. I examine the second issue--the loss of locally held fishing rights since the implementation of limited entry--through the combined analysis of qualitative ethnographic data and quantitative data on commercial fishery permit holdings, subsistence activity, permit holder age, and new entry trends by community and residence category. The immense loss of limited entry permits continues to challenge livelihoods because access to local fisheries is the foundation of not only the region's economy, but also of the shared identity, history, and culture of local people, family and social networks, and the mechanism by which fishing knowledge, skills, values, and ethics are transferred to the next generation. I suggest that policymakers and fishery managers dispense with neoliberal panaceas, and design fisheries policies that reflect the multiplicity of worldviews held by the policy's target populations by diversifying their own means and methods for understanding fishery systems.
    • Comparing the nutritional quality of Steller sea lion (Eumetopias jubatus) diets

      Bando, Monica Kaho Herkules (2002-12)
      Though the primary cause(s) of the Steller sea lion decline remains unknown, one hypothesis is nutritional stress, possibly the result of climatic regime shifts reducing prey availability and/or quality. Researchers at the Alaska SeaLife Center formulated three feeding regimes representative of Steller sea lion diets: prior to and during their population decline and from a stable population. The purpose of this project was to compare the nutritional quality of these diets using proximate composition and bomb calorimetry. The pre-decline and stable diets are composed of more high-fat prey, like herring, with resulting energy densities being significantly higher than the decline diet, comprising more low-fat prey, like octopus. Assumining the feeding regimes analyzed represent Steller sea lion diets prior to and during their population decline and in stable populations, results from this study are consistent with the possibility that nutritional stress is a cause of the Steller sea lion decline.
    • Comparing the Performance of Two Commercial Salmon Management Strategies Using Run Reconstruction and Model Simulations

      Carney, Justin Monroe; Adkison, Milo; Baker, Tim.; McPhee, Megan; Quinn, Terrance II (2013-05)
      Two commercial salmon management strategies currently being used in Alaska are management by emergency order opening ("active management") and, to the extent practical, a fixed fishing schedule. Active management is more expensive than a fixed fishing schedule. The objective of this thesis is to compare the performance of the two management strategies on the Egegik and Togiak fisheries in Bristol Bay, Alaska. To accomplish this, we reconstructed the sockeye salmon (Oncorhynchus nerka) runs to Egegik and Togiak and then simulated the management strategies on each fishery. Active management resulted in higher yearly catches, a higher percentage of the run caught, less yearly variation in escapement, and less years of escapement below the goal range. A fixed fishing schedule resulted in less yearly variation in catch and a more even harvest rate. Potential benefits of active management are that maximum sustained yield is more likely to be achieved, under escapement is less likely, and the productive capacity of the fishery is better protected. Potential benefits of a fixed fishing schedule are lower management costs, better maintenance of the genetic and phenotypic diversity and sex ratio, and more predictability for fishermen and processors.
    • A comparison of sockeye salmon (Oncorhynchus nerka) in two climate regimes in the north Pacific Ocean using stable carbon and nitrogren isotope ratios

      Satterfield, Franklin Robert (2000-12)
      This study explores how the climate shift in the late 1970's impacted sockeye salmon feeding. Stable isotope ratios (¹³C and ¹⁵N) of recent muscle and scale tissues from five mature salmon species are highly correlated (R²=0.96 and 0.91, respectively), validating the use of archived scales for retrospective analysis. These data suggest a trophic separation by species with chinook occupying the highest level, followed by coho with some degree of overlap among sockeye, pink and chum at the lowest level. Archived scales from four different sockeye stocks from Kodiak Island and Southeast region were analyzed over the last 34 years to investigate changes relative to the 1976-1977 Climate Regime Shift. Most stocks show no statistical differences before and after the regime shift in either isotope. Despite recorded differences in sockeye abundance and size between these two regimes, these data suggest only minor changes in prey items.
    • A comparison of the food habits of juvenile Pacific cod and walleye pollock in the southeast Bering Sea

      Lee, Sang Suh (1985-05)
      The food habits of juvenile Pacific cod, Gadus macrocephalus, and walleye pollock, Theragra chalcogramma, collected in July and August in 1981 through 1983 in the eastern Bering Sea, were compared in relation to some morphological characteristics. The fishes' gill rakers were counted, the distances between gill rakers were measured, and the stomach tissue weight was measured. The stomach contents were analysed by occurrence, number and volume. It was found that the fishes' gill structures were related to size-selective predation in both fishes. Pollock utilized small zooplankton and cod large zooplankton. Food competition was expected when fishes are smaller than 40 mm TL as indicated by high values in proportional similarity. However, food competition decreases as the fishes grow and develop distinct size-selective predation habits. Prey composition in the stomachs reflected the regional differences of local oceanographic environments.
    • Comparisons of Arctic Cod, Arctic Staghorn Sculpin, and Shorthorn Sculpin diets throughout the northeastern Chukchi and western Beaufort Seas

      Gray, Benjamin P.; Norcross, Brenda; Seitz, Andrew; Beaudreau, Anne; Blanchard, Arny (2015-05)
      Diet information for Arctic Cod (Boreogadus saida), Arctic Staghorn Sculpin (Gymnocanthus tricuspis), and Shorthorn Sculpin (Myoxocephalus scorpius) in the northeastern Chukchi and western Beaufort seas is mostly descriptive. In this study, I examined diet variability due to region, depth, and body size by quantitatively comparing these fishes' diet compositions. To accomplish this, I analyzed the stomach contents of 1,620 fishes collected over three summers in the northeastern Chukchi Sea (2010-2012) and one summer in the western Beaufort Sea (2011). In general, body size and region accounted for most differences in diets. As body size increased, each species consumed a more varied diet composed of larger prey. Additionally, each species consumed more benthic prey taxa in the northeastern Chukchi Sea than in the western Beaufort Sea. These findings indicate that a combination of both body size and region-specific oceanographic processes are likely driving the observed variability in these species' diets. Documenting this variability provides a better insight into the present relationships between these fishes and their prey over a large area and offers a benchmark for future diet analyses in the western Arctic.
    • Compensatory growth following winter food deprivation in hatchery produced coho and chinook salmon smolts

      Triebenbach, Stan P. (2007-08)
      This study investigated whether coho and Chinook smolts that experienced food deprivation during the winter would increase growth rates in the spring and attain the same physiological attributes as smolts fed to satiation twice per week during the winter. The treatment groups were deprived of food for 10 and 16 weeks, centered on the winter solstice. All groups were returned to daily satiation feeding at the end of the respective food reduction periods. Treatment fish were smaller than control fish after food deprivation but had higher growth rates after feeding resumed and the 10 week fish were not significantly different in size from the control fish at the end of the study. Protein and lipid content decreased during deprivation, while moisture and ash content increased, but all groups were not different by the end of the study. Gill ATPase activity was unaffected by deprivation. Hematocrit levels declined in response to deprivation but a consistent response was not observed after feeding resumed. Coho and Chinook smolts subjected to winter food deprivation grew faster in the spring, restored body composition, and did not lose osmoregulation ability but the long-term effects on body size are unknown.
    • Competition And Recruitment In Southeast Alaskan Subtidal Kelp Communities

      Okamoto, Daniel Kenji (2009)
      Shallow subtidal rocky reefs in the Northeast Pacific host frequent physical and biological disturbances as well as multiple competing algal species, including kelps and algal crusts. Kelps serve a critical role in local ecosystems by generating primary productivity and essential fish habitat. While kelp forests rank among the best understood ecosystems in the marine environment, protected and subarctic systems remain largely ignored. Because of the importance of kelp habitat in Southeast Alaska, and the susceptibility of kelps to both disturbance and competition, I estimated the variability in kelp community structure of subtidal, kelp dominated reefs in the Lynn Canal and quantified kelp recruitment in response to both competing algae and bare space which included clearings, artificial reefs, and settlement tiles installed at different periods. Surveyed communities varied most within rather than among reefs. Kelps exhibited strong, rapid, variable and apparent taxa specific colonization potential to clearings, artificial reefs and settlement tiles installed from summer to late fall. Algal crusts imposed a near 100% inhibition of kelp recruits in the field and lab; however the strong colonization potential of kelps facilitated recruitment in the face of strong inhibition by algal crusts.
    • Condition and food availability to Pacific sand lance (Ammodytes hexapterus) in Prince William Sound, Alaska

      Mabry, Julia (2000-05)
      Pacific sand lance (Ammodytes hexapterus) is a common forage fish for seabirds in Prince William Sound, Alaska (PWS). The objectives of this study were to determine if condition of young-of-the-year (YOY) sand lance varies within PWS, and if variation in condition is related to temperature and food availability. Fish were collected in 1996, 1997, and 1998 and assayed for energy content. Zooplankton samples were collected concurrently. SeaWiFS ocean color satellite images and AVHRR temperature images were analyzed for chlorophyll biomass and temperature history. Standard lengths of YOY sand lance ranged from 47 to 97 mm, and their energy content ranged from 4490 to 5670 cal/g, with significant differences among stations. Sand lance in southern PWS were in better condition than those in other areas. Surface chlorophyll concentration and zooplankton abundance were not related to energy content; however, there was a positive and significant relationship between energy content and SST.
    • Contemporary evolution in threespine stickleback from uplifted islands in Alaska

      Lescak, Emily; von Hippel, Frank; Lopez, Andres; Mcphee, Megan; Harrison, Benjamin; Cresko, William (2015-08)
      How rapidly can evolution occur in the wild? Threespine stickleback (Gasterosteus aculeatus) fish are a prime model organism to address this question because we can study post-glacial populations that are only about 13,000 years old. During this relatively short period of time, oceanic stickleback have repeatedly and independently colonized newly available freshwater habitat, giving rise to resident freshwater populations that exhibit repeated patterns of phenotypic and genetic divergence. However, it is currently unknown whether it actually takes thousands of years for resident freshwater populations to diverge from the ancestral form. To address this question, we have identified phenotypically variable stickleback populations in freshwater sites formed on islands in Prince William Sound and the Gulf of Alaska as a result of uplift from the 1964 Alaska Earthquake. Population genomics analyses support the hypothesis of ongoing independent colonization of freshwater habitats by oceanic ancestors. Despite recurrent gene flow between oceanic and freshwater stickleback, we find that the magnitude of phenotypic and genetic divergence between the ancestral and derived populations is comparable to what has been observed in populations that were founded thousands of years ago. Our data implicate natural selection as the major driver of phenotypic diversification and support the hypothesis that the metapopulation organization of this species helps maintain a large pool of standing genetic variation available for selection when oceanic stickleback colonize fresh water. We propose that the greatest amount of phenotypic evolution occurs within the first few decades after stickleback colonize novel freshwater environments.
    • Contemporary mesozooplankton communities of the Beaufort Sea

      Smoot, Caitlin A.; Hopcroft, Russell; Winsor, Peter; Coyle, Kenneth (2015-08)
      Zooplankton are critical trophic links and important modifiers of organic carbon cycles, yet are poorly characterized for much of the Arctic's Beaufort Sea, particularly in mesopelagic (> 200 m) waters. Zooplankton were sampled with 150 and 505 μm mesh nets in the upper 200 m in sections of the Beaufort Sea between Barrow Canyon and the Mackenzie River during August and September 2010-2013 to characterize the species composition, abundance, and biomass of epipelagic Beaufort Sea zooplankton communities. I observed 106 taxonomic zooplankton categories during four field seasons across both mesh sizes; copepods exhibited the highest species richness (38 species), followed by cnidarians (16 species) and amphipods (14 species). Average holozooplankton abundance ranged from 1110-3880 ind. m⁻³ in the 150-μm net and 47-215 ind. m⁻³ in the 505-μm net. Average holozooplankton biomass ranged from 23.8-76.9 mg dry-weight (DW) m⁻³ and 13.9-57.6 mg DW m⁻³ in the 150-μm and 505-μm nets, respectively. Spatial structure of zooplankton communities reflected a blending of across- and along-shelf temperature and salinity gradients that were driven by relative contributions of different water mass types. To characterize mesopelagic zooplankton communities of the Beaufort Sea, I collected stratified zooplankton samples and physical oceanographic data at stations along the Beaufort Sea slope during August 2013. I documented 93 taxonomic categories; greatest diversity was observed in the copepods (48 species), followed by the cnidarians (10 species) and amphipods (8 species). Distinct zooplankton communities were associated with the three main water masses in the study region: the Polar Mixed Layer (PML), Arctic Halocline Water (AHW), and Atlantic Water (AW). Average abundance and biomass were highest (1150 ind. m⁻³ and 27.1 mg DW m⁻³ , respectively) in the PML (0-50 m) and declined with depth, to a minimum in the 500-1000 m layer of AW (15 ind. m⁻³ and 0.6 mg DW m⁻³). Conversely, species richness increased with depth. Community structure was highly correlated with salinity and depth, both in terms of abundance (Spearman correlation (ρ) = 0.84, p < 0.01) and biomass (ρ = 0.81, p < 0.01). Zooplankton communities in the Beaufort Sea exhibit structure along three axes: alongshore, across-shore, and depth-related. Community structure along these axes reflects hydrographic gradients created by different water masses and physical factors in the study region. This work provides a contemporary benchmark for Beaufort Sea zooplankton community species composition, abundance, and biomass from which future change may be assessed.
    • Contribution of muskeg channel habitats to juvenile coho salmon production in the Situk River, Alaska

      Schaberg, Kevin L. (2006-12)
      This study examines seasonal patters of habitat use by juvenile coho salmon in the Situk River and the importance of muskeg channels. To determine seasonal patterns I trapped fish from a range of habitats every two weeks during the summer of 2005. Analysis of the length-frequency data these samples provided showed most fry emerged in gravel bedded channels and that a substantial number of these fish then moved into muskeg channels during their first summer, rearing there until smolting at age 1 + or 2+. To estimate the number of coho salmon using muskeg channels, I established a relationship between channel width and fish density and scaled this up to the entire drainage using GIS analysis. This demonstrated that muskeg channels provide important rearing habitat. Comparison with published data suggests that muskegs are responsible for between 14% and 80% of total coho salmon smolt production in the Situk River.
    • Counting seals: estimating the unseen fraction using a covariate and capture-recapture model

      Moran, John R. (2003-08)
      We evaluated the influences of environmental covariates on the proportion of harbor seals (Phoca vitulina richardsi) ashore on Tugidak Island using a series of photographic capture-recapture experiments and ground based counts. We used general linear models to examine the significance of combinations of covariates including quadratics terms. Time of day, tide height, rate of tide change, surf, and wind speed significantly influenced the number of seals ashore during the molting period. The model including all significant covariates best explained the probability of seals being hauled out. We observed a decline in the local population using the haulout suggesting that seasonal migration affects the number of seals ashore. The relationship between covariates and the number of seals hauled out on Tugidak Island differ in some respects from those reported at other sites in Alaska, implying that a region wide application of a single correction factor to counts of hauled out harbor seals may not adequately account for seals at sea.
    • Current Primary Production Rates Of The Western Arctic Ocean Estimated By Stable Carbon And Nitrogen Isotope Tracers

      Lee, Sang Heon; Whitledge, Terry E. (2005)
      Currently, the environments in the Arctic are rapidly changing. These changes of climate and ice conditions may alter the quantity, quality, and timing of production of ice algae and phytoplankton in the Arctic Ocean. The objectives in this study were to detect any change in the carbon production between current and previous studies and lay the groundwork for the future monitoring of ecosystem response to climate change in the different regions of the western Arctic Ocean. As an Arctic ocean mostly covered by multi or first-year ice, the deep Canada Basin had generally low photosynthetic rates and the maximum rates were found between 50 and 60 m in the basin. Based on the percentage of ice cover, the annual production ranged from 3 to 7.5 g C m-2 Z in the basin. Nutrients appear to be a main limiting factor at surface, whereas the phytoplankton activity might be limited by the low light in the Chl a-max layer. At the surface below the ice, photosynthetic activity might be controlled by both low light and nutrients. Studies of ice algae and phytoplankton at the first-year sea ice of Barrow in Alaska showed that bottom sea ice algae and phytoplankton are limited mainly by light. Therefore, the current downward trend of sea ice thickness and extent in Arctic Oceans might cause an increase in primary production or/and change in timing of the production. In addition, the composition in macromolecules of primary producers might be changed under the current ice conditions and thus nutritional status of higher trophic levels might be altered. As shallow shelf regions, Bering Strait/Chukchi Sea showed that the range of nitrate in the central Chukchi Sea was rather higher whereas the biomass of phytoplankton was lower in this study than in previous studies. Consistently, the mean carbon and nitrogen productivities from this study were almost half of values from previous studies. In conclusion, it appears that lower phytoplankton biomass in Bering Strait and the Chukchi Sea resulted in the lower carbon and nitrogen uptake rates and consequently more unused nitrate in the regions.