• Distribution, Growth And Egg Production Of Euphausiids In The Northern Gulf Of Alaska

      Pinchuk, Alexei I.; Hopcroft, Russell (2006)
      The euphausiids Thysanoessa inermis, Thysanoessa spinifera and Euphausia pacifica are key pelagic grazers and important prey for many vertebrates in the Gulf of Alaska (GOA). This thesis provides the first account of distribution, egg production, growth, development, and temporal variability in abundance of the euphausiids in relation to environmental variations in the northern GOA. T. inermis and T spinifera were abundant on the shelf within 120-130 km from the coast, while E. pacifica originated from offshore and was advected onto the shelf during summer. E. pacifica produced multiple broods with brood size strongly related to ambient chlorophyll a concentrations. In contrast, T. inermis released eggs once in the season and its brood size did not depend on chlorophyll content. Early development of these species showed a remarkably similar response to changes in temperature. The highest molting increments were observed during the spring phytoplankton bloom for T. inermis, and in summer for T. spinifera and E. pacifica, suggesting coupling with food availability. The molting rates were strongly influenced by temperature. Growth rates depended on euphausiid size, and were close to 0 in early spring, reaching maximum values in May (0.123 mm d-1 or 0.023 d -1 for T. inermis) and July (0.091 mm d-1 or 0.031 d-1 for T. spinifera). The growth rates for E. pacifica remained below 0.07 mm d -1 (0.016 d-1) throughout the season. The relationship between T. inermis weight specific growth rate (adjusted to 5�C) and ambient chlorophyll-a concentration fit a Michaelis-Menten curve (r2=0.48), but such relationships were not significant for T. spinifera or E. pacifica. Reproduction of T. inermis occurred during April in 1998 and 2003, and was extended through May in 1999-2002. The spawning of T. inermis and T. spinifera was related to the spring diatom bloom on the inner shelf, while the spawning of E. pacifica occurred later in season, when the water temperature increased. A strong increase in abundance of T. inermis, associated with the extended colder phase in the North Pacific, indicates that progressive cooling in 1999-2002 may have resulted in greater reproductive success of early spawning T. inermis on the inner shelf.
    • Diversity and community structure of eukaryotic phototrophs in the Bering and Chukchi seas

      Lekanoff, Rachel M.; Collins, R. Eric; McDonnell, Andrew M.P.; Danielson, Seth L. (2020-05)
      The phytoplankton of the Bering and Chukchi seas support highly productive ecosystems characterized by tight benthic-pelagic coupling. In this study, we focus on the northern Bering and Chukchi seas, considering them as one ecosystem. This community has historically been dominated by diatoms; however, climate change and accompanying warming ocean temperatures may alter primary producer communities. Using metabarcoding, we present the first synoptic, high-throughput molecular phylogenetic investigation of phytoplankton diversity in the Bering and Chukchi seas based on hundreds of samples collected from June to September in 2017. We identify the major and minor taxonomic groups of diatoms and picophytoplankton, relative abundances of genera, exact sequence variants (201 for diatoms and 227 for picophytoplankton), and describe their biogeography. These phylogenetic insights and environmental data are used to characterize preferred temperature ranges, offering insight into which specific phytoplankton (Chaetoceros, Pseudo−nitzschia, Micromonas, Phaeocystis) may be most affected as the region warms. Finally, we investigated the likelihood of using shipboard CTD data alone as predictive variables for which members of phytoplankton communities may be present. We found that the suite of environmental data collected from a shipboard CTD is a poor predictor of community composition, explaining only 12.6% of variability within diatom genera and 14.2% variability within picophytoplankton genera. Clustering these communities by similarity of samples did improve predictability (43.6% for diatoms and 32.5% for picophytoplankton). However, our analyses succeeded in identifying temperature as a key driver for certain taxa found commonly throughout the region, offering a key insight into which common phytoplankton community members may be affected first as the Alaskan Arctic continues to warm.
    • Diversity, abundance and fate of ice algae and phytoplankton in the Bering Sea

      Szymanski, Anna; Gradinger, Rolf; Iken, Katrin; Collins, R. Eric (2014-12)
      Sea ice algae are an essential part of Arctic and subarctic ecosystems. They significantly contribute to total algal primary production, serve as an early spring food source for both pelagic and benthic biota, and can seed the spring phytoplankton bloom during periods of ice melt. In the subarctic Bering Sea, virtually nothing has been known about the composition of the ice algal community, its magnitude, and its connection to pelagic and benthic ecosystems. This study, therefore, focused on the diversity, abundance, and ultimate fate of ice algae in the Bering Sea using sea ice, water and sub-ice sediment trap samples collected during two spring periods: ice growth (March to mid-April) and ice melt (mid-April to May) in 2008 and 2009. Ice algal species composition was comparable to those in Arctic regions. The phytoplankton species inventory was similar to that found in the overlying ice, suggesting that the spring phytoplankton were seeded from the ice algae. Algal abundance in the ice was on average three orders of magnitude higher than in the water column throughout both periods, as the extensive Bering Sea ice cover in 2008-2009 delayed the phytoplankton bloom. There was a substantial increase in the vertical flux of algal cells beneath the ice during the period of ice melt, but measurable amounts appeared as early as mid-March. The majority of this flux was composed of healthy algal cells, making it a rich food source for benthic organisms. Differences in the relative species composition between ice and trap samples indicate that algal fate was influenced by the species specific sinking rate of algal cells, among other factors, in the water column. In conclusion, ice algae in the Bering Sea are diverse and abundant, and contribute to both pelagic and benthic systems.
    • Diving physiology of the ringed seal: adaptations, capability and implications

      Ferren, Howard Jennings (1980-08)
      Adaptations that influence duration of diving in the ringed seal, Phoaa (Pusa) hispida were examined. Mean blood volume was 234 ml/kg lean body mass (LBM) and oxygen capacity was 30.7 ml O2/100 ml of whole blood, yielding a total blood oxygen capacity of 70 ml O2/kg LBM. Abrupt and prolonged bradycardia occurred upon submersion. Experimental dives indicated submersion durations of up to 18 minutes before the onset of physiological dysfunction. The percentage of LBM represented by the brain is least in the relatively large Weddell seal (0.2%), greater in the harbor seal (0.7%) (the compared species) and greatest in the ringed seal (1.4%); this sets the requirement for minimum obligatory oxygen consumption. The differences observed in diving durations between the three species is considered to be mainly the consequence of brain/body size relationship.
    • Dungeness crab depth distribution: effects of sea otters

      Scheding, Karen A. (2004-05)
      The distribution and abundance of Dungeness crabs in the Glacier Bay area were observed with a submersible in five bays with and three bays without sea otters. A matrix design was used with three levels of sea otter occupation and three depth categories. Goals of this study were to determine: 1) the depth distribution of crabs; 2) if depth was a refuge from sea otter predation; and, 3) the habitat of ovigerous female aggregations. Scuba was used to calibrate submersible counts and collect substrate samples; crab pots were used to confirm submersible sightings. Abiotic and biotic variables were analyzed to interpret distribution data and aggregation sites. A regional, long-term crab survey dataset was also examined. Sea otters may have decreased crab abundance in shallow waters. Two aggregations of ovigerous Dungeness crabs were observed in shallow water with sand substrate. However, only 1% of the 33 km of transects were classified as sand, suggesting that sand may be a limiting resource. No conclusions could be made about the independent effects of sea otter presence or depth due to strong interaction. Submersible observations, crab pot surveys, and marine topography together however, point towards a shift in crab depth distribution with sea otter presence
    • Dynamics of a migratory fish population with applications to the management of sablefish in the Northeast Pacific Ocean

      Heifetz, Jonathan; Quinn, Terrance J. II (1996)
      Quantitative models are developed to describe the dynamics of an age-structured migratory fish population subject to exploitation. Migration rates are quantified, alternative ways of apportioning harvest among areas are examined, and the dynamics of a migratory population is described within the general theoretical framework of a projection matrix model. Application of these modeling efforts is within the context of the sablefish (Anoplopoma fimbria) fishery in the North Pacific Ocean. A Markov model that includes natural and fishing mortality, tag reporting and shedding rates, and migration is used to quantify migration rates of tagged sablefish among fishery regulatory areas. Estimates of annual migration rates out of an area are in the range 19-69% for small (<57 cm fork length (FL)), 25-72% for medium (57-66 cm FL), and 27-71% for large (>66 cm FL) sablefish. The predominant direction of migration along the continental slope is eastward for large sablefish and westward for small sablefish. Most estimates of migration are precise, unconfounded, and robust to perturbations of input constants. An age-structured model that includes migration is constructed to examine harvest policies for sablefish. Areal estimates of yield-per-recruit depends on the geographic distribution of recruitment. In general, when evaluated under the current annual exploitation rate of 10%, apportioning harvest among areas based on areal estimates of biomass and apportionment based on the steady-state distribution of biomass give similar results. A policy of apportionment based on a weighted moving average of areal estimates of available biomass is preferred to others. This policy adapts to current information about geographic distribution of biomass, reduces the effects of measurement error, and does not require estimates of migration probabilities for implementation. The reproduction, mortality and migration of an age-structured fish population are incorporated into a projection matrix model. The model is parameterized to include areal specificity in the stock-recruitment relationship and events such as larval dispersion that is decoupled from local reproduction. For the sablefish fishery where direction of movement is age dependent, fishing at a common rate among areas may be detrimental to the population in a given area. Area-specific fishing strategies can be devised to meet management objectives such as maintenance of areal spawning potential.
    • Early Life History Dynamics Of Lake Sturgeon

      Caroffino, David C. (2009)
      Populations of lake sturgeon Acipenser fulvescens in the Laurentian Great Lakes have not recovered after dramatic declines in the late 1800s despite the implementation of numerous recovery plans. Although extensive lake sturgeon research has and continues to occur, critical knowledge gaps remain. Recruitment of lake sturgeon is variable, but the extent of that variation, its limiting factors, and mortality rates experienced by early life stages are unclear. The purpose of this study was to increase our understanding of lake sturgeon early life stages by examining characteristics of a remnant population in the Peshtigo River, Wisconsin. Specifically, this research sought to empirically estimate rates of early life stage mortality, describe the vertical distribution of drifting larvae, evaluate the impacts of predation on recruitment, and describe patterns in movement and abundance of age-0 juveniles. Extensive sampling of lake sturgeon eggs, larvae, age-0 juveniles, and potential predators occurred during 2006 and 2007. Although drifting lake sturgeon larvae were captured in all parts of the water column, more were found near the surface than the substrate. After drifting to nursery areas, individuals exhibited variable movement patterns. Some fish were never recaptured more than 10 m from the initial capture site, while other individuals moved more than 9 km. Even though absolute abundance of juveniles differed by an order of magnitude between 2006 and 2007, a pattern of steady decline during the summer months was similar during both years. This downstream movement may have resulted in emigration from the Peshtigo River, as there was no evidence of predation on this life stage. Overall mortality from the egg to age-0 juvenile life stage exceeded 99.9% in both study years. Predation on eggs was extensive by both crayfish and fish (white sucker Catostomus commersonii ), but was minimal on other life stages. These results suggest that recruitment can vary significantly, and predation is likely only limiting at the egg life stage. These results will allow more effective monitoring and management of lake sturgeon early life stages, thereby promoting population recovery.
    • Early marine growth patterns of Situk River steelhead, Oncorhynchus mykiss

      Catterson, Matthew R.; McPhee, Megan; Love, David; Sutton, Trent (2017-08)
      Steelhead Oncorhynchus mykiss exhibit complex life-history patterns described by variable freshwater and marine residency periods, maturation patterns, and reproductive characteristics. Over 300 small populations of Steelhead are present in Southeast Alaska, and similar trends in abundance among these populations suggest the influence of population-regulating forces operating on a regional scale. The Situk River, near Yakutat, Alaska, supports the largest known population of Steelhead in Alaska. Stock assessment studies on this river have collected the longest set of biological data and scale samples for Steelhead in the state. For this study, retrospective scale pattern analysis of samples from Situk River Steelhead was synthesized with regional abundance information to investigate patterns in early marine growth among different life-history and demographic groups, as well as to explore linkages between growth, abundance, and marine environmental variables. Positive correlations were identified between freshwater growth, first ocean-year growth, and adult length, while first ocean-year growth was negatively correlated with second ocean-year growth. Early maturing Steelhead were found to have increased first ocean-year growth and reduced adult length relative to later maturing Steelhead, confirming connections between growth and maturation. Correlations in abundance among Southeast Alaska Steelhead populations suggest that marine and climatic drivers may impact these populations in a regionally coherent manner. Correlations among patterns in abundance also varied along a distance gradient: populations located closer to the Situk River were more correlated with the Situk River than more distant populations. Positive relationships between Gulf of Alaska sea surface temperature, North Pacific Gyre Oscillation, and Situk River Steelhead abundance further supported the importance of climate-driven marine conditions to Steelhead productivity. While conservation concerns for Steelhead in Southeast Alaska are currently minimal, proactive investigations into life-history diversity and population linkages may become more relevant with increased marine ecosystem variability related to climate change.
    • Ecological factors influencing fish distribution in a large subarctic lake system

      Plumb, Miranda Paige (2006-05)
      The coastal climate and frequent wind storms in southwest Alaska create an atypical thermal environment (non-stratified in summer) in the remote Ugashik lakes. This study documents the distribution of lake trout 'Salvelinus namaycush, ' arctic char 'S. alpinus', Dolly Varden 'S. malma, ' arctic grayling 'Thymallus arcticus, ' round whitefish 'Prosopium cylindraceum, ' and pygmy whitefish 'P. coulterii' relative to depth, substrate particle size, food habits, length, and age in the absence of strong thermal structure. Sample sites were randomly chosen within sampling strata and gill nets were set at each site. Lake trout and round whitefish were most abundant and had the oldest individuals in the catch. In more typical thermally stratified lake systems lake trout and Arctic char usually move to colder, deeper water in summer. In the Ugashik lakes, however, both species were abundant in shallow water all summer. Prior to this study pygmy whitefish were undocumented in this system. The fish examined in the Ugashik lakes were opportunistic feeders, consuming organisms such as isopods and amphipods. Fish in the Ugashik lakes were found in locations different from what one would expect from predominant literature. Fisheries managers may need to take this into account in their fisheries management.
    • Ecological interactions among important groundfishes in the Gulf of Alaska

      Barnes, Cheryl L.; Beaudrea, Anne H.; Dorn, Martin W.; Holsman, Kirstin K.; Hunsicker, Mary E.; Mueter, Franz J. (2019-12)
      Complex ecological interactions such as predation and competition play an important role in shaping the structure and function of marine communities. In fact, these processes can have greater impacts than those related to fishing. We assessed ecological interactions among economically important fishes in the Gulf of Alaska - a large marine ecosystem that has recently undergone considerable shifts in community composition. Specifically, we developed an index of predation for Walleye Pollock (Gadus chalcogrammus) to examine spatiotemporal changes in consumption, quantify portfolio effects, and better understand diversity-stability relationships within the demersal food web. We also evaluated the potential for competition between two important pollock predators, Arrowtooth Flounder (Atheresthes stomias) and Pacific Halibut (Hippoglossus stenolepis). We found highly variable predation intensity on Gulf of Alaska pollock. The combination of a single dominant predator and synchronous consumption dynamics indicated strong top-down control in the region. Spatial heterogeneity, however, may offset trophic instability at the basin scale. Assessments of resource partitioning provided little indication for competition between Arrowtooth Flounder and Pacific Halibut of similar lengths. Morphological differences between the two flatfish predators prompted an exploration into whether our conclusions about resource partitioning were dependent upon the size metric used. From this study, we found a relatively early onset of piscivory for Arrowtooth Flounder. Relationships between predator size and prey size also suggested gape limitation among Pacific Halibut sampled. Trophic niche separation was more pronounced for fishes with larger gapes, indicating greater potential for competition among smaller Arrowtooth Flounder and Pacific Halibut in Southeast Alaska. Reexamining basin-scale relationships between spatial and dietary overlap according to gape size would further elucidate the effects an increasing Arrowtooth Flounder population has had on changes in Pacific Halibut size-at-age. Results from this dissertation improve our understanding about the impacts of complex ecological interactions on population and community dynamics, and how those interactions may change in time, space, and under different environmental conditions.
    • Ecology and energetics of early life stages of walleye pollock in the eastern Bering Sea: the role of spatial variability across climatic regimes

      Siddon, Elizabeth Calvert; Mueter, Franz J.; Duffy, Janet T.; Heinz, Ron A.; Hillgruber, Nicola; Norcross, Brenda L. (2013-08)
      Understanding mechanisms behind variability in early life survival of marine fishes can improve predictive capabilities for recruitment success under changing climate conditions. Ecosystem changes in response to climate variability in the eastern Bering Sea affect commercial species including walleye pollock (Theragra chalcogramma), which represent an ecologically important component of the ecosystem and support the largest commercial fishery in the United States. The goal of my dissertation was to better understand spatial and temporal dynamics in the ecology of early life stages of walleye pollock in the eastern Bering Sea through: (1) an examination of shifts in larval fish community composition in response to environmental variability across both warm and cold conditions; (2) a quantification of the seasonal progression in energy content of age-0 walleye pollock which provides critical information for predicting overwinter survival and recruitment to age-1 because age-0 walleye pollock rely on sufficient energy reserves to survive their first winter; and (3) a modeling approach to better understand the role of prey quality, prey composition, and water temperature on spatial and temporal patterns of juvenile walleye pollock growth with implications for year-class survival and recruitment success. In the community analysis, I identified a strong cross-shelf gradient delineating slope and shelf assemblages, an influence of water masses from the Gulf of Alaska on species composition, and the importance of nearshore areas for larval fish. Species assemblages differed between warm and cold periods, and larval abundances, including that of walleye pollock, were generally greater in warm years. I identified different energy allocation strategies indicating that distinct ontogenetic stages face different survival constraints. Larval walleye pollock favored allocation to somatic growth, presumably to escape size-dependent predation, while juveniles allocated energy to lipid storage in late summer. Finally, I provide evidence that a spatial mismatch between juvenile walleye pollock and growth 'hot spots' in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. I highlight the importance of climate-driven spatial patterns in community structure, prey dynamics, and environmental conditions that influence the growth and survival of an important gadoid population in a sub-arctic marine ecosystem.
    • The ecology of age-1 copper rockfish (Sebastes caurinus) in vegetated habitats of Sitka Sound, Alaska

      Byerly, Michael M. (2001-12)
      Variables that may indicate habitat quality were measured to assess the relative value of shallow subtidal vegetated habitats to age-1 copper rockfish (Sebastes caurinus). All habitats studied appeared beneficial to fish with respect to the particular variable measured. Relative growth rate was significantly higher in kelp than in other habitats while energy content was highest in eelgrass. Though fish in eelgrass had lower growth rates, they were significantly larger, and had high densities. Mixed kelp and eelgrass habitat was suboptimal with respect to growth and energy content but also had high densities. Fish in mixed habitat moved the least both within and to other habitats while the opposite occurred in eelgrass. Diets were similar for fish in kelp and eelgrass habitats and daily ration did not differ significantly between habitats. Thus, observed differences in the variables measured were not related to food but may instead be dependent on non-exploitative interactions.
    • The ecology of eulachon (Thaleichthys pacificus) in Twentymile river, Alaska

      Spangler, Elizabeth Ann Kitto (2002-12)
      The ecology of eulachon (Thaleichthys pacificus) was studied at Twentymile River, a tributory of Turnagain Arm located in southcentral Alaska. In 2000 and 2001, we investigated the environmental factors associated with the migration of adult eulachon and downstream drift of larval eulachon. We assessed run timing, freshwater duration, length, weight, age, presence or absence of teeth, fecundity, and gear selectivity for dip and gill nets. Catch per unit effort of migrating adult fish were correlated with water temperature, tide height, river discharge, light intensity, and the density of bald eagles (Haliaeetus leucocephalus). Water temperature, river discharge, tide height, and light intensity were related to downstream drift intensity of larvae. Radio telemetry was used successfully to study the migratrion movements of adult eulachon. Clusters of the upstream limits of migration identified four common spawning areas in both years.
    • Ecology Of Juvenile Pink Salmon In The North Gulf Of Alaska And Prince William Sound

      Boldt, Jennifer Lynn; Haldorson, Lewis J. (2001)
      Increased production of salmon in Alaska has been accompanied by a decrease in average body size and decreased wild stocks, indicating a possible density-dependent response to increases in salmon populations and hatchery releases. Pink salmon have a short two-year life cycle and most post-hatch mortality is thought to occur during their first months at sea; therefore, processes in the early marine residence period may determine abundance. Geographic and seasonal patterns in distribution, growth, and condition of juvenile pink salmon during their first months at sea were examined in Chapter 1. The migration of pink salmon from Prince William Sound (PWS) occurred over several months. Fish lengths, weights, and energy contents varied geographically and seasonally. Pink salmon energy content was highest on the Gulf of Alaska (GOA) shelf in July and August and lowest in PWS in July, indicating that growth conditions were better on the GOA shelf. Spatial and temporal variation in growth and condition is indicative of disparate feeding opportunities for juvenile pink salmon. An unusual aspect of this study was the concurrent collection of zooplankton and fish in PWS and on the GOA shelf. Geographic and seasonal changes in juvenile pink salmon diets were examined during their first six months at sea in Chapter 2. Pink salmon diets varied geographically and seasonally, and prey size increased as fish grew. A unique opportunity existed to compare the energy content of thermally marked hatchery pink salmon to their wild counterparts in PWS (Chapter 3). Fish condition varied geographically, however, there were no differences among hatchery groups and/or wild pink salmon at any one location. This indicates that fish were staying together as a group. In Chapter 4, pink salmon consumption was estimated to represent a small fraction of the production but potentially a large proportion of the available standing stock of zooplankton in PWS. Geographic variations in fish condition, diet, and zooplankton densities were observed in this study. This supports the hypothesis that local processes, including food depletion and/or zooplankton availability are important to juvenile pink salmon.
    • The ecology of the Arctic char and the dolly varden in the Becharof Lake drainage, Alaska

      Scanlon, Brendan P. (2000-12)
      Becharof Lake is home to both Arctic char (Salvelinus alpinus) and the closely related Dolly Varden (Salvelinus malma), two species known not only to be similar in appearance but also to exhibit similar life histories. The body morphometry, otolith microchemistry, and stomach contents of both species were studied in fish collected from May to September 1998. Morphometric and meristic analysis revealed clear separation in body structure between the two species, as well as potential sub-populations within each species. Otolith microchemistry revealed incidences of anadromy and non-anadromy in both species. Stomach content analysis revealed a broad feeding niche but smaller ranges in food types in individual Arctic char with little seasonal preference, whereas Dolly Varden showed seasonality in food choices. Data suggest that both species can move in and out of the lake system, and that little competition for food or habitat occurs between the two species in the summer months.
    • The effect of temperature on circulating levels of methyl farnesoate and ecdysteroid hormones in female snow crab Chionoecetes opilio, from the Bering Sea

      Mitchell, Jacqueline Loretta (2007-12)
      Methyl farnesoate, a reproductive hormone in crustaceans, was detected for the first time in the hemolymph of female Chionoecetes opilio. Ovigerous crabs were maintained at -1,0, 1, and 3° C to represent near bottom temperatures of the Bering Sea, throughout a reproductive cycle to assess changes, and temperature effects, in hormone levels associated with ovarian maturation, hatching and subsequent extrusion of the next clutch. Methyl farnesoate (MF) levels did not change significantly in any treatment throughout the duration of egg incubation. Levels of MF significantly decreased in crabs exposed to -1 and 0° C when initial versus post extrusion levels were compared. Ecdysteroid levels remained low throughout the egg incubation period but increased significantly after extrusion in all treatments except the 0° C treatment. Decrease in temperature significantly prolonged time to extrusion between all temperature groups except 3 and 1 ° C. Extrusion was delayed in the 0 and -1 ° C treatments when compared to the 3 and 1 ° C treatments. The duration of extrusion increased by as much as 77% (between -1 and 0° C) as temperature decreased, suggesting changes in temperature can have a significant effect on the reproductive timing in C. opilio.
    • The effect of under ice crude oil spills on sympagic biota of the Arctic: a mesocosm approach

      Dilliplaine, Kyle B.; Gradinger, Rolf; Bluhm, Bodil; Collins, Eric; Eicken, Hajo (2017-05)
      The Arctic marine environment is facing increasing risks of oil spills due to growing maritime activities such as tourism and resource exploration. Encapsulation and migration of spilled oil through the brine channel system in sea ice poses significant risk to ice-associated biological communities. The first objective of this study was to establish mesocosms that allow the growth of artificial sea ice leading to sea ice physical properties similar to young natural sea ice. In addition, the mesocosms should be capable of growing and maintaining a sea ice community. Six sea water tanks with 360 l capacity each were inoculated with biological cultures collected from landfast sea ice near Utqiaġvik AK in April 2014 (year 1) and March 2015 (year 2). The two experiments lasted 24 and 27 days, and final ice thickness reached a mean value of 33 cm. The light conditions under the ice mimicked natural spring irradiances of 15 umol photons m² s⁻¹. Different inoculation approaches for ice biota were used. In year 1 we did not observe any algal growth. In year 2, biological characteristics in the ice prior to oil release (chlorophyll a, Extracellular Polymeric Substance (EPS) concentrations and algal and bacterial abundances) were similar to natural concentrations from early spring first year ice. The second objective was to evaluate the impact of Alaska North Slope crude oil on sea ice biota. Two different oil spill scenarios were tested in the mesocosms: discrete oil lenses and dispersed emulsions. Tanks were sampled prior to oil release and 13 or 10 days post-release in year 1 and year 2, respectively. In year 1, bacterial abundances increased after oil release, while establishment of algal populations was unsuccessful. In year 2, algal growth rates and EPS production increased over time in the control tanks, while they did not change in the oil exposed tanks. Differential response of bacteria and algae between year 1 and 2 not only point to the potential of nutrient competition, but also to the need of measuring several biological properties to detect effects of oil exposure in the event of a spill. Future studies can build upon the developed experimental framework including biological responses to low, sub-lethal oil dosing.
    • Effects Of Adult Salmon Carcasses On The Energy Allocation Strategies Of Juvenile Salmonids

      Heintz, Ron A. (2009)
      When adult salmon return to their natal streams to spawn they deliver energy in the form of carcass tissues and eggs. Currently, the effect of this marine-derived energy on the growth and energy allocation strategies of juvenile salmonids is unknown. This thesis examined the effects of marine-derived energy on the growth and energy allocation strategies of juvenile coho salmon and resident Dolly Varden. Fatty acid analysis was developed as a tool for monitoring the flow of marine-derived lipids and hence energy from carcass tissues to consumers in laboratory and field settings. Fish in these settings were examined before and after the arrival of adult salmon carcasses in their respective habitats. The allocation of protein and lipid was monitored in concert with the fatty acid analysis. In addition, the effect of different diets on fasting of wild coho salmon was studied to determine how marine-derived diets might influence over winter survival. Marine-derived energy was acquired by juvenile salmonids through both direct and indirect processes. Direct acquisition entailed consumption of marine-derived lipids or short trophic linkages between carcass tissues and consumers. Indirect acquisition was typified by long trophic linkages between consumers and carcass tissues in which marine lipids were incorporated by consumers after marine-derived lipids permeated food webs. The benefits of consuming marine-derived lipids depended on the method of acquisition. Fish that directly acquired marine-derived lipids altered their energy allocation strategies by storing greater amounts of lipid; allowing them to maintain elevated metabolic rates over winter and start spring in a high nutritional state. In contrast, indirect acquisition of marine-derived lipids afforded fish few benefits. These fish survive winter by down regulating metabolic rates and start spring in a low nutritional state. The ubiquity of direct acquisition by coho salmon and variable routes of acquisition in Dolly Varden suggest that the presence of carcass tissues may serve to reinforce anadromy among juvenile salmonids rearing in streams.
    • Effects of areas closed to bottom trawling on fish and invertebrate species in the eastern Bering Sea

      Frazier, Christine Ann; Norcross, Brenda; Hills, Sue; Norcorss, Brenda; Witherell, David (2003-12)
      The Bering Sea is a productive ecosystem with some of the most important fisheries in the United States. Constant commercial fishing for groundfish has occurred since the 1960s. The implementation of areas closed to bottom trawling to protect critical habitat for fish or crabs resulted in successful management of these fisheries. The efficacy of these closures on non-target species is unknown. This study determined if differences in abundance, biomass, diversity and evenness of dominant fish and invertebrate species occur among areas open and closed to bottom trawling in the eastern Bering Sea between 1996 and 2000. This study represented four areas: two within Bristol Bay closed areas and two within comparable fished areas. Total abundance and biomass were not significantly different among fished and closed areas or between pre-closure (1990-1994) and post-closure (1996-2000) years. Diversity and evenness were greater in fished areas than closed areas. The biomass of some functional feeding groups (i.e. piscivores, detritivores) of species decreased when compared among areas and in pre-closure versus post-closure years while others increased. These results support the need for continued research and monitoring of eastern Bering Sea closed areas to determine recovery time and the efficacy of closures as a management tool.