• Biotic and abiotic influences on the use of Arctic lakes by fish and loons

      Haynes, Trevor B.; Lindberg, Mark; Rosenberger, Amanda; Lopez, Andrés; Titus, Kimberly (2014-12)
      The particularly severe effects of climate change anticipated in the Arctic, accompanied by ongoing anthropogenic activities, necessitate proactive and knowledge-based management of the region's aquatic ecosystems. However, the paucity of information on the Arctic's aquatic environments hinders strategic or spatially-explicit management. In this dissertation, I examine the habitat use of poorly studied taxa of the Arctic Coastal Plain (ACP) of Alaska, including freshwater fishes and yellow-billed loons (Gavia adamsii). Distribution studies can be biased by false absences; therefore, I began by determining the detection probabilities of six fish species common to Arctic lakes for five gear types (Chapter 2). Variation in gear- and species-specific detection probability was considerable, suggesting a multi-method approach may be most effective for whole-assemblage sampling. Adjusting for detection probability, I then examine how occupancy probabilities of the six fish species were related to lake and landscape scale covariates (Chapter 3). Three large-bodied salmonid species were influenced by factors associated with the probability of fish colonizing lakes, including whether the lakes had a stream connection. Models for small-bodied fish indicated different strategies for persistence among species. Ninespine stickleback (Pungitius pungitius) were widespread and captured in lakes that freeze to the bottom, suggesting rapid dispersal after spring freshet (when snow and ice had melted rapidly and caused widespread flooding) and colonization of sink habitats. In contrast, Alaska blackfish (Dallia pectoralis) distributions reflect tolerance to harsh conditions, while the slimy sculpin's (Cottus cognatus) was indicative of its marine origin. Based on these patterns, I propose a model of primary controls on the distribution of fishes in ACP lakes. Severe winter conditions limit occupancy through extinction events, while lake occupancy in spring and summer is driven by directional migration (large-bodied species) and undirected dispersal (small-bodied species). To provide insight to the relevance of species-specific distributions of prey fish to yellow-billed loons (Gavia adamsii), I investigated loon diet on their breeding grounds using quantitative fatty acid signature analysis (Chapter 4). Tissues were collected from 26 yellow-billed loons (shortly after they had moved from coastal staging areas), nine fish species and two invertebrate groups. Results suggest that yellow-billed loons are eating high proportions of Alaska blackfish, broad whitefish (Coregonus nasus) and three-spined stickleback (Gasterosteus aculeatus). The prominence of blackfish in diets highlights the importance of this species' tolerance to winter conditions that permits its widespread availability during the early stages of loon nesting. Broad whitefish and three-spined stickleback are more likely to be encountered in coastal regions at this time, and their importance may reflect pre-nesting period diet, when loons are staging in coastal and brackish waters before lakes are ice free. Finally, I use the prior chapters to inform an investigation into lake occupancy dynamics of nesting yellowbilled loons and loon chicks (Chapter 5). From a total of four years of data (collected over nine years for nests and seven years for chicks), I examine landscape features that influence the distribution and breeding success of breeding loons on ACP lakes (>7 ha in area), including landscape and lake features, and fish prey occupancy. Over this time, nesting yellow-billed loons exhibited a relatively low (< 30%), but stable to increasing, lake occupancy. Local extinction and colonization rates were also relatively stable, suggesting the nesting population in this region may be near equilibrium. A decreasing rate of change in chick occupancy associated with concomitant increases in nesting occupancy implies density-dependence in chick production. The occupancy probability of a prey fish, least cisco (Coregonus sardinella), had a positive influence on the probability of colonization of unoccupied lakes by nesting loons. I confirm that lake size and lake depth were not only positively associated with nesting occupancy, but also with chick production. Large lakes had occupancy probabilities near one for nesting loons and chicks; this, along with the near equilibrium in breeding loon occupancy and the relative rarity of these large lakes over the landscape, suggests breeding habitat is limiting loon populations in this part of their range. Given the lack of data from the ACP on fish distributions and yellow-billed loons, my findings inform current management practices and provide foundation for future research.
    • Blasting Bridges And Culverts: Water Overpressure And Vibration Effects On Fish And Habitat

      Dunlap, Kristen N.; Smoker, William; Timothy, Jackie; Kelley, John; Quinn, Terrance II (2009)
      Water overpressures and ground vibrations from blasting may injure or kill salmonid fish in streams and embryos in streambeds. Explosives are used to remove failing structures in remote areas of the Tongass National Forest that impair watershed function. The State of Alaska Department of Fish and Game standards limit blast induced water overpressures to 2.7 lb/in 2 (18.6 kPa) and streambed vibrations to 0.5 in/s (13 mm/s) when embryos are present. Researchers, however, have reported salmonid mortality from pressures only as low as 12.3 and 19.3 lbs/in2 (85 and 133 kPa) and embryo mortality from vibrations as low as 5.75 in/s (146 mm/s). I recorded in-stream overpressures and streambed vibrations with hydrophones and geophones at various distances from log bridge, log culvert, and metal culvert blasts. Peak water pressures (lb/in2) were directly related to cube-root scaled distances with an attenuation rate of -1.51. Peak particle velocities in gravel were directly related to square-root scaled distances (SRSD, ft/lb 1/2) with an attenuation rate of -0.75. Water pressures were less than 7.1 lb/in2 (49.0 kPa) in all but one blast, and streambed vibrations did not exceed 5.5 in/s in gravel streambeds. State standards should be revised to reflect reported mortality and these observations of blasts in streams.
    • Blubber and beyond: the role of lipids in thermoregulation and energy reserves of phocid seals

      Pearson, Linnea E.; Burns, Jennifer M.; Horstmann-Dehn, Larissa-A.; Pfeiffer, David C.; Mellish, JoAnn E.; Buck, C. Loren (2015-08)
      Phocid seals rely on lipids in the form of a blubber layer as insulation and lipids as energy sources in blubber and muscle. The amount and lipid composition of blubber and other lipid stores vary throughout life within and among species of phocid seals. I hypothesized that this variation in regulation, allocation, and interactions among lipid stores is influenced by species, ontogeny, and tissue-specific thermal regimes in polar phocids: harp (Pagophilus groenlandicus), hooded (Cystophora cristata), and Weddell (Leptonychotes weddellii) seals. I investigated the thermoregulatory strategy of neonatal harp, hooded, and Weddell seals, and throughout the transition to an aquatic environment in harp seals. All three species had similar thermal resistance, though it was achieved differently using either lanugo or blubber. While there was variation in the main thermoregulatory strategy among species, no species possessed all thermal adaptations of adults. Harp and Weddell seals had higher surface area to volume ratios (SA:V), thus higher potential heat loss, though compensatory mechanisms for heat production were different between species. Harp seals were the only species with the potential for nonshivering thermogenesis (NST) in brown adipose tissue (BAT), whereas Weddell seals had the highest potential for shivering thermogenesis (ST) in their skeletal muscle. Hooded seals relied on blubber, and had a significantly lower SA:V than the other two species. As harp seal pups develop, their potential for NST declines and they shift to a reliance on blubber for insulation. By late weaning, harp seal pups have similar insulative capabilities as adults, and can likely meet the thermoregulatory challenges associated with living in water. In neonatal and young seals that have little blubber, other lipid stores such as BAT and skeletal muscle lipids provide heat-generating mechanisms (NST or ST) to offset potentially high rates of heat loss. The potential for NST declines with age, as the blubber layer develops in harp seals, and weaned pups look to have similar insulative capabilities as adults. While phocid adults rely on blubber for insulation and maintain a thermal gradient across the tissue, otariids (fur seals and sea lions) instead maintain an external gradient across a thick fur layer. This has implications for the underlying lipid composition of blubber, as the fatty acids (FA) that make up this lipid respond differently to temperature. In phocid blubber, latitude (a proxy for environmental temperature) had a positive correlation with the proportion of polyunsaturated fatty acids, but a negative correlation with saturated fatty acids. In otariids, these trends were reversed. This suggests interactions between blubber and the ambient environment play a role in the overall relative proportions of FA classes in blubber. Unlike in blubber, the FA class composition of harp, hooded, and Weddell seal skeletal muscle was similar among species. In adult female Weddell seals, the relative proportions of individual FA in blubber and muscle were significantly different between tissues; these differences persisted across seasons, and were independent of female reproductive state. It appears that the FA in blubber and muscle reflect the tissues' roles within the body. Blubber contained a greater proportion of monounsaturated FA, which remain fluid at lower temperatures, while the muscle contains a larger proportion of SFA, which produce the greatest amounts of ATP per mole oxidized to support metabolism. In adult phocids, the FA composition of the blubber layer appears to be influenced by environmental interactions with latitude (temperature), in accordance with the location of and steepness of the thermal gradient through the blubber layer. Finally, environment looks to have little influence on the FA stores in skeletal muscle, and seasonally persistent tissue differences between blubber and muscle highlight how lipid is dynamically modulated within the body of phocid seals. How and what lipids are allocated to blubber is a mixture of abiotic and biotic cues throughout life, linked to thermodynamics, ambient environment, and energy dynamics.
    • Body composition (carbon, nitrogen and calories) and energetics of immature walleye pollock, Theragra chalcogramma (Pallas), in the southeast Bering Sea

      Harris, Robert K. (1985-05)
      The body composition (carbon, nitrogen and calories) of Bering Sea and Resurrection Bay (Alaska) immature walleye pollock (9-360 g wet weight) were related to dry weight and Fulton's condition factor index by regression models. The condition factor was a better predictor of body composition than dry weight. As condition improved from a minimum starvation level of 0.42 to a maximum of 1.16, body caloric, percent carbon, and the carbon-nitrogen ratio increased, while percent nitrogen and percent ash decreased. The body composition measurements allowed energy budget terms (assimilation coefficient, growth, and metabolism) to be expressed in common units. The assimilation coefficient and growth terms were estimated from literature sources. Oxygen consumption measurements at 3-10°C yielded the metabolic term. The daily food requirement for 0-3 year old walleye pollock, at their annual average Bering Sea habitat temperature of 3.8°C, was 1.0 - 1.5% of the body weight.
    • Breeding performance of kittiwakes and murres in relation to oceanographic and meteorologic conditions across the shelf of the southeastern Bering Sea

      Lloyd, Denby S. (1985-12)
      Contrary to expected results, black-legged and red-legged kittiwakes on St. George Island exhibited more variability in annual breeding performance than black-legged kittiwakes at Cape Peirce. Thick-billed and common murres at St. George also showed more annual variability than common murres at Cape Peirce. Kittiwakes at St. George exhibited improved breeding performance during years with colder water temperatures and lower summer wind speeds. Correlations between breeding performance in kittiwakes and murres and environmental conditions at Cape Peirce were inconclusive. A general decline in the annual breeding success of kittiwakes and murres at St. George between 1976 and 1984 coincided with reduced abundance of juvenile walleye pollock. Consistently low breeding success of kittiwakes and murres at Cape Peirce varied little among six years observed between 1970 and 1984. These results challenge previous considerations of pelagic food webs on the outer shelf as being more stable than those in the coastal domain.
    • Carbon and nitrogen assimilation in the Bering Sea clams Nuculana radiata and Macoma moesta

      Weems, Jared; Iken, Katrin; Gradinger, Rolf; Wooller, Matthew (Elsevier, 2012-06)
      We analyzed bulk carbon and nitrogen stable isotope values (delta C-13 and delta N-15) of the benthic clams Nuculana radiata and Macoma moesta from the Bering Sea during controlled feeding experiments (spring of 2009 and 2010) using isotopically labeled sea ice algae. The aim was to determine the ability of these clam species to assimilate carbon and nitrogen from sea ice algae. Specimens were collected in the Bering Sea and placed into jars without sediment (2009, N. radiata only) or into natural sediment cores (2010, both species). The clams were offered isotopically enriched (both C and N) or non-enriched algal feeds for time periods of 42 (2009) and 18 d (2010). Isotopic assimilation rates for carbon and nitrogen were calculated using the change in the isotope ratios of the clams over the experimental time. N. radiata in the jar experiments had slow isotopic assimilation rates (0.01 to 0.23 parts per thousand d(-1)), with solvent-extractable organic matter/lipids taking up both of the isotope markers fastest and muscle tissue the slowest. Lipids may thus be particularly suitable to track the immediate ingestion of sea ice algal production in benthic consumers. M. moesta showed 30% higher isotopic assimilation compared to N. radiata in sediment cores, likely reflecting the different feeding behaviors of these two species. Based on our results, N. radiata is likely better able to utilize food sources buried in the sediment and may be more competitive over the sediment surface feeding M. moesta under conditions of reduced ice algal production in the northern Bering Sea. (C) 2012 Elsevier B.V. All rights reserved.

      Weems, Jared; Iken, Katrin; Gradinger, Rolf; Wooller, Matthew (University of Alaska Fairbanks, 2011-08)
      The predicted climate-induced reduction in sea ice presence in the Bering Sea could impact benthic trophic interactions; however, species-specific consumer dependence on ice algal production is largely unknown. My objective was to track feeding in the benthic clams, Nuculana radiata and Macoma moesta, using stable carbon and nitrogen isotopes. Nuculana radiata had slow isotopic assimilation rates, with lipids taking up isotope markers fastest and muscle tissue the slowest. Lipids may thus be particularly suitable to track the immediate ingestion of sea ice algal export in benthic consumers. When isotopically enriched food was added to natural sediment cores, N. radiata assimilated 60% less of the isotope markers than when feeding on algal food in isolation. Possibly, this difference is related to the ingestion of other, naturally present food sources in the sediment. Macoma moesta showed 30% higher isotopic assimilation compared to N. radiata in sediment cores. I suggest that differing feeding behaviors between the species provide differential access to the sedimented algal food. Based on these results, N. radiata is likely better able to utilize food sources buried in the sediment and may be more competitive over M. moesta under conditions of reduced ice algal production in the northern Bering Sea.
    • Carbon biogeochemistry of the eastern Bering Sea shelf

      Cross, Jessica; Mathis, Jeremy; Feely, Richard; Stockwell, Dean; Weingartner, Thomas; Whitledge, Terry (2013-12)
      The uptake of anthropogenic carbon dioxide (CO₂) has caused perturbations to marine biogeochemistry in recent years, including decreasing ocean pH and carbonate mineral saturation states (Ω). Collectively termed ocean acidification (OA), these conditions hinder the growth of calcium carbonate shells and effectively reduce habitat for some marine calcifiers. Given that the Bering Sea is one of the world's most productive marine ecosystems and supports both commercial fishing industries and subsistence communities, it is integral to understand its susceptibility to OA. Here, new observations of the organic and inorganic carbon systems are used to identify mechanisms leading to CO₂ accumulation and sub-regional enhancement of vulnerability to OA processes. Chapter 1 describes the state of knowledge of OA in this area, highlighting two regions where low Ω conditions are consistently observed: near the coast, and over the northern shelf. Chapter 2 describes net heterotrophic processes near the coast, in conjunction with low bottom water Ω. Chapter 3 examines this heterotrophy in more detail, showing that focused deposition of organic matter and its subsequent respiration. Chapters 4 and 5 focus on very low Ω values observed over the northern shelf. In combination with natural respiration processes, anthropogenic CO₂ was shown to cause low Ω and seasonal dissolution of carbonate minerals in Chapter 4. Chapter 5 illustrates how sea ice cover inhibits the flux of CO₂ from the surface ocean to the atmosphere, which raises the inventory of CO₂ in the water column. These results are synthesized in Chapter 6. Low-Ω conditions and areas of carbonate mineral dissolution will continue to expand as anthropogenic CO₂ accumulates in shelf waters in the coming decades, further reducing viable habitat for key calcifiers. Model projections of future surface water conditions indicate that average Ω over the Bering Sea shelf will drop below the observed natural variability by 2100, with average conditions favoring carbonate mineral dissolution in surface waters by 2150. Presently, episodic events will cause regions of the Bering Sea to be undersaturated in Ω, which could have significant and cascading impacts throughout the Pacific-Arctic region.
    • Carbon flux and particle-associated microbial remineralization rates in the northern Bering and southern Chukchi seas

      O'Daly, Stephanie Hicks; McDonnell, Andrew M. P.; Hardy, Sarah M.; Johnson, Mark A. (2019-12)
      It has been hypothesized that climate change will reduce the strength and episodic nature of vernal phytoplankton blooms, increase heterotrophy of microbes and zooplankton, and weaken the tight coupling between pelagic and benthic production that is characteristic of Arctic continental shelves. As a part of the Arctic Shelf Growth, Advection, Respiration, and Deposition rates measurement (ASGARD) project, I quantified sinking particle fluxes and incubated sinking particles to measure the rate of microbial respiration associated with those particles. These measurements were used to characterize the strength of the pelagic-benthic connection. After a record-breaking year of warm temperatures and low-ice conditions in the northern Bering and southern Chukchi Seas, we observed massive vernal fluxes of sinking particulate organic carbon, ranking amongst the highest observed in the global oceans. Moreover, low rates of particle-associated microbial respiration indicate negligible recycling of sinking organic matter within the water column. These results suggest that the strength of the biological carbon pump may be maintained or enhanced in a warming Arctic, supporting strong benthic and upper trophic level productivity and carbon export.
    • Carbon isotopic composition of polycyclic aromatic hydrocarbons and their weathering in Kachemak Bay sediment

      Borland, Tara Ann (2004-05)
      Identification of sources of polycyclic aromatic hydrocarbons (PAH) in sediments is an important step in reducing anthropogenic contamination. Identifications based solely on the composition of PAH can be confounded by compositional changes during weathering and biodegradation. Stable isotopic composition of individual PAH offer a source marker that may be less susceptible to alteration. The [alpha]¹³C values of PAH in major potential sources to the Kachemak Bay area were analyzed. To determine the stability of the [alpha]¹³C values of PAH in crude and diesel oil, microbial degradation experiments using sediment from the Kachemak Bay, Alaska, area were conducted over a one-year period. The impact of weathering on the isotopic composition of North Slope crude oil and diesel oil was also examined over a five-week period in aquaria with Macoma balthica, an intertidal bivalve. For both degradation experiments, PAH concentrations decreased and their composition changed, but the [alpha]¹³C values of individual PAHs remained stable. Hence, [alpha]¹³C values of individual PAHs have excellent potential as a relatively stable indicator of their sources. Based on isotopic and compositional data, the PAH in Kachemak Bay sediments appear to have several sources.
    • Carbon sources and trophic connectivity in seafloor food webs in the Alaska Arctic and sub-Arctic

      Oxtoby, Laura Elizabeth; Wooller, Matthew; O'Brien, Diane; Iken, Katrin; Horstmann, Larissa; Budge, Suzanne (2016-05)
      Stable isotope analysis offers critical insight into organic matter pathways that sustain and link consumers in a food web. Indirect examination of organic matter sources and consumer diets using stable isotope analysis is especially valuable in the Alaska Arctic and sub-Arctic marine realm, where organisms of interest are difficult to observe given their remote habitat and elusive behavior. The research objective of this body of work was to use novel applications of stable isotope analysis to extend our understanding of organic matter sources, trophic pathways, and resource competition among benthic consumers. Microphytobenthos, a community of photosynthesizing unicellular microscopic algal cells on the seafloor sediment, has not been included in stable isotope food web models in the Alaska Arctic and sub-Arctic due to challenges associated with sample collection and analysis. I constrained the isotopic composition of this potential algal source by integrating field measurements, physiological relationships previously established by laboratory studies, and a range of algal growth rates specific to high latitude primary production. Relative to other sources of primary production in the Arctic, sub-Arctic, and lower latitude ecosystems, estimates for stable carbon isotope values of total organic carbon from microphytobenthos in the Beaufort and Chukchi seas were higher than those for Arctic riverine organic matter, but lower than ice algal sources and microphytobenthos measurements from lower latitudes. To further elucidate trophic pathways and resource partitioning among benthic invertebrate consumers, I combined compound-specific stable isotope analysis, a relatively new analytical tool, with fatty acid analysis to estimate proportional contributions of algal sources from ice, open ocean, and surface sediments to common polychaete and bivalve consumers in the Bering Sea. Benthic invertebrates were collected in 2009-2010 and represented a diverse range of feeding strategies, including the suspension/surface deposit-feeding bivalves Macoma calcarea and Ennucula tenuis, the subsurface deposit-feeding bivalve, Nuculana radiata, the head down deposit-feeding polychaete Leitoscoloplos pugettensis, and the predator/scavenger Nephtys spp. Differences in dominant algal sources to these invertebrate consumers corresponded, for the most part, to feeding strategy. Bivalves primarily obtained fatty acids from surface sediments, whereas L. pugettensis obtained fatty acids from a microbially altered phytodetrital fatty acid pool, and Nephtys spp. from ice algal fatty acids acquired indirectly through predation. This multi-proxy compound-specific stable isotope approach was then applied to examine dietary overlap between Pacific walruses (Odobenus rosmarus divergens) and bearded seals (Erignathus barbatus) in 2009-2011 who feed primarily on benthic invertebrate prey. Differences in the relative proportions of fatty acids produced exclusively by benthic prey (non-methylene interrupted fatty acids) indicated that walruses and bearded seals had divergent diets. Proportional contributions of algal sources from ice, open ocean, and surface sediments to the prey consumed by walruses and bearded seals also varied. Walruses consumed prey that relied primarily on benthic and pelagic carbon sources (i.e., suspension/surface and subsurface deposit-feeding bivalves). In contrast, bearded seals consumed prey that relied on benthic and ice algal carbon sources (i.e., omnivorous and predatory benthic invertebrates). In conclusion, this research revealed that, in the recent study years, benthic food webs in the Alaska Arctic and sub-Arctic contained several trophic pathways linking consumers to distinct organic matter sources. Consequently, projected changes in algal production with future climate warming may elicit species-specific responses among benthic organisms.
    • Changes in embryonic development, hatching, and zoeae of snow crab with variation in incubation temperature

      Webb, Joel Benjamin (2005-08)
      The effect of incubation temperature on duration of embryonic development and morphology, weight and energetic content of post-hatch zoeae was described for snow crab, Chionoecetes opilio, from the eastern Bering Sea held at -1, 0, 1, 3, and 6° C in the laboratory from collection to hatch. The mean incubation time increased with decreasing temperature by 32% (113 d) between 6 and -1° C. Extrusion success of females at 6° C was lower versus 0 or 3° C, but the duration of hatching did not vary significantly with incubation temperature. A one-year cycle of embryo incubation was observed, indicating that switching from one to two-year duration of embryo incubation may occur early in development. The energy content and individual weights of post-hatch zoeae were not significantly affected by temperature, indicating that longer incubation periods may not have an energetic cost. The rostro-dorsal length of zoeae incubated at 6° C was smaller than those from cooler temperatures. Conversely, the length of the 3rd abdominal somite increased significantly with decreasing temperature, perhaps serving as an indicator of incubation temperature in field collected zoeae. The consequences of varying incubation temperature appear on post-hatch zoeae appear to be limited between -1° and 6° C.
    • Changes in the spring sea ice concentration in the Bering Sea from 1972-2000 in relation to spotted seal (Phoca largha) pregnancy rates

      Picco, Candace M. (2005-08)
      Spotted seals are most dependent on the seasonal sea ice in the Bering Sea during the spring pupping and mating season. Changes in sea ice characteristics, as related to recent documented changes in climate, may have an effect on spotted seal reproduction. This study investigates the relation between changes in the spatial and temporal patterns of the spring sea ice concentration in the Bering Sea from 1972-2000 to changes in the pregnancy rates of the spotted seal (Phoca largha). Multinomial time-series regressions were used to determine the influence of different climatic variables on the sea ice concentration. Different statistical methods were used to compare the ice conditions of defined regions in the Bering Sea and spotted seal pregnancy rates among 20 years from 1964- 2003. The results showed no definitive patterns relating the monthly climatic variables and sea ice concentration averages; however, noticeable trends in sea ice were found. The variability of the seal pregnancy rates coincided with changes in the Bering Sea ecosystem and ice concentration. This study demonstrated that seal pregnancy rates and sea ice concentration varied temporally and spatially, the direct causality of these variations was uncertain.
    • Characteristics of the Sulukna River spawning population of inconnu, Yukon River drainage, Alaska

      Esse, David Andrews; Margraf, F. Joseph; Sutton, Trent M.; Brown, Randy J. (2011-12)
      Inconnu Stenodus leucichthys are large migratory whitefish harvested in subsistence and sport fisheries in Alaska. Research on the Sulukna River spawning population of inconnu was conducted in September and early October from 2007 to 2009. Samples were collected to verify maturity and spawning readiness, and to determine age distributions of mature males and females. Spawning abundance was estimated and post-spawning migration timing was identified. Otoliths were analyzed optically to determine age and chemically to determine amphidromy. Maturity sampling indicated that all sampled fish were in spawning condition or had recently spawned. Abundance estimates were 2,079 and 3,531 inconnu in 2008 and 2009, respectively. Post-spawning downstream migration timing was nearly identical between years, with the majority of fish moving downstream between September 30 and October 9. In both years, migrating inconnu displayed a nocturnal migration pattern, with 96% migrating between 10:00 pm and 9:00 am hours daily. Age estimates ranged between 6 and 26 years. Chemical analysis indicated that some Sulukna River inconnu were amphidromous, making migrations of over 1,300 km to the sea. This information indicates that the Sulukna River spawning population of inconnu has a large and variable abundance, in which amphidromy is facultative.
    • Characterizing glucocorticoid levels in five species of sea ducks occurring in Alaska

      Nilsson, Peter B. (2004-12)
      Stress hormone analysis, used in conjunction with other physiological parameters, may help identify factors affecting sea duck populations in their natural environment. Corticosterone, the primary 'stress hormone' in birds, is secreted in response to a stressor and enhances an individual's chance of survival by inducing physiological and behavioral changes. Establishing a valid method for evaluating stress hormone levels in sea ducks and gaining basic information on baseline concentrations and stress response in these birds are important first steps to identify factors that may negatively affect sea duck populations. This study validated a radioimmunoassay (RIA) procedure to measure corticosterone concentrations in harlequin duck serum and feces and in Steller's, spectacled, common, and king eider serum. Other objectives included characterization of baseline corticosterone concentrations, investigation of stress response, and the relationship between corticosterone and other variables in captive and wild sea ducks. The results indicate that fecal samples can be used to non-invasively measure corticosterone in harlequin ducks. Captive birds exhibited overall lower baseline levels of corticosterone than wild birds. The stress response observed in harlequin ducks was similar to other avian species. Rapid post-capture blood sampling is critical for evaluation of baseline corticosterone levels.
    • 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.