• Identification of spawning areas and the influence of environmental variation on freshwater migration timing and in-river movements of adult coho salmon in the Buskin River, Alaska

      Stratton, Michelle Eileen; Westley, Peter; Finkle, Heather; Falke, Jeff (2019-08)
      The timing of freshwater entry by anadromous salmonids varies markedly among species and populations within species and is frequently used as an indicator of local adaptation to sitespecific patterns of selection. Although complex stock structure is most often associated with large watersheds that have extensive habitat diversity, even small drainages can produce multiple co-occurring stocks that differ in migratory timing. In addition, migration timing can be influenced by within-year environmental conditions experienced by migrating individuals en route to spawning sites, staging near the river mouth in the ocean, or within the river itself. Each stage of migration through both freshwater and saltwater could be altered based on climatic drivers and how each individual fish reacts to these stressors. The objective of this thesis was to assess the potential for stock structure in Coho Salmon within a small coastal watershed on Kodiak Island, Alaska by 1) identifying important differences in spawning and holding locations associated with run timing, length, and stream life between main stem and tributary spawners, 2) quantifying the influence of large-, intermediate-, and local-scale climate variables on freshwater entrance timing and in-river movements. To address the first objective, fish were tracked to their spawning locations using acoustic telemetry in three spawning seasons (2015-2017). I detected no statistically or biologically meaningful differences in body size (length, mm) or migration timing into the river between main stem and tributary spawning fish. Unexpectedly, I found that a large portion of fish (80%) utilize the lake during their in-river migration suggesting the lake may represent critical staging habitat for adult Coho Salmon prior to spawning. I also identified holding habitat throughout the river that both spawning groups consistently used across years that also appears to be important to premature migrating Coho Salmon. In Chapter Two, I analyzed 33 years of freshwater entrance timing data and utilized radio tags to track in-river movement to quantify the influence of precipitation and temperature on total distance moved and probability of moving. Despite marked variation among years, I found no evidence of a temporal trend in entrance timing based on escapement counts, which contrasts with other recent examples throughout Alaska reporting changes in run timing. The strongest influence on timing of freshwater entry was ocean sea surface temperature, where cold temperatures delayed entry up to 11 days. Within-river movements were positively related to precipitation and temperature, confirming local traditional knowledge in this system, and consistent with life history patterns of Coho Salmon. The primary messages of this thesis are that i) any within-watershed stock structure is unlikely to be differentially affected by harvest or management given overlapping run timing, body size, and use of main stem holding areas; future population genetics analyses would be an obvious and illuminating next step to assess the extent to which main stem and tributary spawners are reproductively isolated groups; ii) both main stem and tributary spawners use Buskin Lake as holding habitat prior to spawning, and thus assumptions that fish that enter the upper watershed are destined to spawn in headwater tributaries are invalid, which in turn limits the utility of enumerating adult passage into the lake for escapement-based management, iii) adult freshwater entrance timing is highly variable but not changing systematically through time, though the extent to which the variation in timing reflects environmental response vs. uncertainty in the counts at the weir is unknown, and iv) low precipitation and warm temperatures suppress movement and result in protracted use of main stem and lake habitats for holding, which may put some individuals at risk to angler harvest or, in extreme events, potentially low dissolved oxygen environments. Spatial management that restricts fishing in locations of known primary holding habitats may be an option to reduce probability of mortality and stress in years of low adult abundance.
    • Impacts of a top predator (Esox lucius) on salmonids in Southcentral Alaska: genetics, connectivity, and vulnerability

      Jalbert, Chase S.; Falke, Jeffrey; Westley, Peter; López, J. Andrés; Dunker, Kristine (2018-12)
      Worldwide invasion and range expansion of northern pike (pike; Esox lucius) have been linked to the decline of native fishes and new techniques are needed to assess the effects of invasion over broad geographic scales. In Alaska, pike are native north and west of the Alaska Mountain Range but were introduced into Southcentral Alaska in the 1950s and again in the 1970s. To investigate the history of the invasion into Southcentral Alaska, I identified 7,889 single nucleotide polymorphisms (SNPs) from three native and seven introduced populations in Alaska and examined genetic diversity, structure, and affinities of native and invasive pike. Pike exhibited low genetic variability in native populations (mean heterozygosity = 0.0360 and mean π = 0.000241) and further reductions in introduced populations (mean heterozygosity = 0.0227 and mean π = 0.000131), which suggests a bottleneck following introduction. Population differentiation was high among some populations (global FST = 0.424; max FST = 0.668) when compared to other freshwater fishes. I identified five genetically distinct clusters of populations, consisting of three native groups, a single Susitna River basin invasive group, and a Kenai Peninsula group, with little evidence of admixture among groups. The extremely reduced genetic diversity observed in invasive northern pike populations does not appear to affect their invasion success as the species range Southcentral Alaska continues to expand. To assess the vulnerability of five species of Pacific salmon (Oncorhynchus spp.) to the invasion, I combined intrinsic potential habitat modeling, connectivity estimates, and Bayesian networks across 22,875km of stream reaches in the Matanuska-Susitna basin, Alaska, USA. Pink salmon were the most vulnerable species, with 15.2% (2,458 km) of their range identified as "highly" vulnerable. They were followed closely by chum salmon (14.8%) and coho salmon (14.7%). Finally, analysis of the intersection of vulnerable salmon habitats revealed 1,001 km of streams that were highly vulnerable for all five Pacific salmon. This framework is easy to implement, adaptable to any species or region, and cost effective. With increasing threats of species introductions, fishery managers need new tools like those described here to efficiently identify critical areas shared by multiple species, where management actions can have the greatest impact.
    • Impacts of sea otter predation on commercially important sea cucumbers (Parastichopus californicus) in Southeast Alaska

      Larson, Sean D.; Eckert, Ginny L.; Woodby, Douglas A.; Kruse, Gordon H. (2012-12)
      Consequences from management actions, particularly those regarding species reintroductions, are not always immediately apparent. After sea otters were extirpated from Southeast Alaska in the 18th and 19th century fur trade, it is presumed that marine invertebrate stocks grew in the absence of sea otter predation. Since reintroduction in the 1960s, the Southeast Alaska sea otter population has grown, with great potential to deplete the commercially important sea cucumber, Parastichopus californicus. This study evaluates the interaction with and impacts of sea otters on sea cucumbers using foraging observations and sea cucumber density data collected for fishery management. Sea otter diets, in terms of edible biomass, include about only 5% cucumbers, and yet sea otters are depleting sea cucumbers; declines in sea cucumber density at sea otter affected transects ranged from 26 to 100%. Sea otter predation should be included in sea cucumber fishery management, possibly as an additional form of mortality in the surplus production model, as a step toward ecosystem based management.
    • Incorporating stakeholder input in research priorities for the Aleutian Islands

      Wadsworth, Rachael Margaret; Criddle, Keith R.; Muse, Ben; Kruse, Gordon H. (2012-12)
      Federal law requires that resource management agencies consider stakeholder input in the selection of preferred alternatives for proposed actions. Not only do stakeholders contribute unique perspectives on the impact of alternative actions and the desirability of various policy objectives, including stakeholders in the decision process adds to the perceived legitimacy of those decisions. Incorporating stakeholder input is legally required and advantageous to sustainable governance of the oceans and implementation of a National Ocean Policy such as ecosystem-based management. Agencies use a variety of formal and informal mechanisms to solicit and incorporate stakeholder input. In this study, we compare expert panel and stakeholder rankings of research and information needs in the Aleutian Islands region to see if stakeholder preferences are consistent with those of resource managers and experts when the analytical hierarchy process is used to prioritize those research and information needs. Normalized individual ratings were averaged across interest groups and compared to ratings averaged across all respondents. Spearman rank-order correlations were used to test the statistical significance of differences between groups and against the overall mean. Sensitivity analyses were used to check the robustness of the rankings across groups. We found a high level of association between rankings by an expert panel and rankings by stakeholders and little sensitivity to the make-up of stakeholders. These results suggest that the analytical hierarchy process can serve as a useful mechanism for organizing stakeholder input for environmental planning and resource management.
    • The influence of glaciers on coastal marine ecosystems in the Gulf of Alaska

      Arimitsu, Mayumi L.; Mueter, Franz; Beaudreau, Anne; Hood, Eran; Hobson, Keith; Piatt, John (2016-08)
      Glacier runoff (i.e., meltwater and rainwater discharged at the glacier terminus) provides about half of the freshwater discharge into coastal margins of the Gulf of Alaska, where contemporary glacier melting rates are among the highest in the world. Roughly 410 billion metric tons of glacier runoff enter the Gulf of Alaska each year. With freshwater discharge volumes of that magnitude, I hypothesized that glacier runoff has both direct and indirect effects on the receiving coastal marine ecosystems that support rich food webs, abundant and diverse marine communities, commercial fisheries and tourism industries. To examine the influence of glacier runoff on coastal marine ecosystems, I focused on three questions: 1) How does the marine food web respond to physical and biological gradients induced by glacier runoff? 2) What is the contribution of riverine organic matter (OM) and ancient carbon resources in glacier runoff to marine food webs from plankton to seabirds? and 3) How does the influence of glaciers on coastal marine ecosystems differ at small to large spatial and temporal scales? I measured physical, chemical and biological indices within four fjord systems along the eastern Gulf of Alaska coast. In chapter one I used geostatistics as well as parametric and non-parametric models to demonstrate a strong influence of glacier runoff on ocean conditions and coastal food webs across all the fjord systems. In chapter two I used isotopes (δ2H, δ13C, δ15N, and Δ14C) to trace riverine OM and ancient carbon resources into the marine food web. This work included the development of a novel multi-trophic level 3-isotope Bayesian mixing model to estimate the proportion of allochthonous resources in animal tissues. Mean estimates from 14 species groups spanning copepods to seabirds ranged from 12 – 45 % riverine OM source assimilation in coastal fjords, but ancient carbon use by marine food webs was low. In the third chapter I synthesized information on the scale-dependent influence of glaciers on lower-trophic level productivity, predator-prey interactions and ways that humans may be affected by anticipated changes in glacier coverage. This contemporary understanding of glacier influence on coastal ecosystems aligns with paleoenvironmental evidence suggesting that over geological time scales glaciers have and will continue to shape marine ecosystems in the Gulf of Alaska.
    • Influence of hydrological processes on the spatial and temporal variation in spawning habitat quality for two chum salmon stocks in interior Alaska

      Maclean, Scott H. (2003-05)
      I investigated the hydrological mechanisms that influence spatial and temporal variability in incubation habitat quality for summer- and fall-run chum salmon. The intragravel habitat was characterized by measuring water velocity, temperature, and dissolved oxygen (DO). Habitat quality was characterized by determining the survival of eggs in gravel filled baskets. Summer-run egg survival was greatest in a zone of upwelling produced by hydraulic gradients between the main Chena River and a slough. Water took approximately one month to make this trip and microbial activity likely reduced the concentration of DO considerably. As a consequence of these processes, there was considerable spatial and temporal variability in upwelling velocity, DO, and temperature. Most variability in egg-to-fry survival was explained by DO, and, to a lesser extent, by water velocity. Fall-run fish used an area of groundwater upwelling on the south side of the Tanana River. Here physical habitat characteristics were spatially and temporally uniform compared to the summer-run site, a consequence of the larger spatial scale of processes generating the upwelling. Egg-to-fry survival was low despite high DO and favorable temperature. This was probably the consequence of glacial silt invading egg baskets and reducing intragravel flow related to falling groundwater tables.
    • Influence of physical and biological oceanography on the structure of the seabird community in the northeastern Chukchi Sea

      Gall, Adrian E.; Blanchard, Amy L.; Weingartner, Thomas J.; Mathis, Jeremy T.; Hopcroft, Russell R.; Day, Robert H. (2015-12)
      The Chukchi Sea is losing seasonal ice cover as global temperatures rise, facilitating human access to the region for activities such as oil and gas exploration, shipping, and tourism. Processes and responses to environmental change by marine ecosystems are often challenging to quantify because they are hidden under water. Seabirds, however, offer visible evidence of the health and status of marine ecosystems. I studied the community structure, variability in abundance and distribution, and habitat associations of seabirds in the eastern Chukchi Sea. My results provide insights into the influence of climate change on seabirds and a benchmark against which to evaluate possible impacts of anthropogenic activity. Repeated sampling of systematic transects in the northeastern Chukchi Sea during the ice-free seasons of 2008-2012 showed that the community consisted of ~40 species and was dominated numerically by planktivorous seabirds, particularly Crested Auklets (Aethia cristatella) and Short-tailed Shearwaters (Puffinus tenuirostris). In contrast, benthic-feeding birds were rare. The abundance of seabirds in the offshore northeastern Chukchi Sea varied by up to two orders of magnitude among years and birds generally were more abundant in September than August. Despite these seasonal and interannual variations in abundance, the species composition was similar among years, with anomalies occurring only in years of persistent ice cover. I compared data from this recent period (2008-2012) with data from historical surveys (1975-1981) to evaluate decadal trends in seabird abundance and composition and related those changes to reductions in seasonal ice cover. The seabird community shifted from one consisting primarily of piscivorous seabirds to one consisting primarily of planktivorous seabirds. This shift suggests that zooplankton prey are more accessible now to avian predators as seasonal ice cover has declined. I explored the relationships between seabirds, hydrography, and zooplankton abundance with spatially explicit generalized additive models. The associations of seabirds with habitat characteristics varied with foraging method and preferred prey. Species that fed primarily by pursuit diving were more abundant in warm, weakly stratified water, whereas surface-feeding species were more abundant in cold, strongly stratified water. Planktivorous seabirds (auklets, shearwaters, and phalaropes) were more abundant within 20 km of thermal surface fronts and in contrast, omnivores (gulls and murres) were more abundant far from thermal fronts. For 5 of the 8 seabird species, information about prey biomass improved predictions of seabird abundance, although the relationships were not as clear as they were for the physical habitat characteristics indicative of processes that aggregate prey. Advective processes that transport oceanic species of zooplankton from the Bering Sea to the Chukchi Sea, together with the local influence of sea ice on physical and biological processes, strongly influence the distribution of seabirds, particularly the planktivorous species. Scientists and decision-makers can use the results of this multi-species and multi-disciplinary study as a benchmark to assess the ecological consequences of anthropogenic activity against the backdrop of climate change that is affecting the Chukchi Sea.
    • The influence of rookery terrain on population structure, territorial behavior, and breeding success of Steller sea lions in the Gulf of Alaska

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

      Bell, Lauren; Iken, Katrin; Okkonen, Steve; Wooller, Matthew; Bluhm, Bodil (2015-05)
      Terrestrial organic matter (OMterr) can function as a food source for Arctic marine consumers, though the relative contribution of OMterr to the structure and efficiency of marine food webs compared to marine production is unclear. Forecasted increases in OMterr inputs to the Arctic Beaufort Sea necessitate a better understanding of the proportional contribution of this organic matter source to the trophic structure of marine communities. This study investigated the relative ecological importance of OMterr across the Beaufort Sea shelf and slope by examining differences in community trophic structure concurrent with variation in terrestrial versus marine organic matter influence. Hydrogen stable isotope ratios (δD) of surface water, surface sediment particulate organic matter (sPOM), and selected benthic consumers were used as an exploratory assessment of freshwater and OMterr distribution in the Beaufort Sea. δD values of surface water confirmed the widespread influence of Canada's Mackenzie River plume across the Beaufort Sea; however, δD values of terrestrial and marine production were not sufficiently distinguishable to differentiate organic matter sources in consumers. Carbon stable isotope ratios (δ¹³C values) of pelagic particulate organic matter (pPOM) and marine consumers confirmed a significant decrease in OMterr presence and utilization by consumers with increasing distance from the Mackenzie River outflow. Food web length, based on the nitrogen stable isotope ratios (δ¹⁵N values) of marine consumers, was longer closer to the Mackenzie River outflow both in shelf and slope locations due to relatively higher δ¹⁵N values of pelagic and benthic primary consumers. The absence of macrofaunal consumers at the lowest trophic levels of OMterr-influenced food webs was interpreted to result from the prior metabolic turnover of OMterr by the microbial loop, which was not sampled in this study. The inferred presence of strong microbial processing of OMterr in the eastern regions of the Beaufort Sea resulted in a higher proportion of relative epifaunal biomass occupying higher trophic levels, suggesting that OMterr as a basal food source can provide substantial energetic support for higher marine trophic levels. These findings challenge the current conception of low terrestrial matter contributions to the Arctic marine food web, and compel a more specific understanding of energy transfer through the OMterr-associated microbial loop.
    • Insight into the diet history of ice seals using isotopic signatures of muscle tissue and claws

      Carroll, Sara Shanae; Norcross, Brenda; Horstmann-Dehn, Larissa; Quakenbush, Lori; Wooller, Matthew (2012-05)
      Climate change and sea ice reduction in the Arctic may impact foraging of ice-associated predators. The goal of my thesis work was to examine interannual differences in the diet of ringed, bearded, spotted, and ribbon seals as described by stable nitrogen and carbon isotope ratios of muscle tissue and claws to assess foraging plasticity. Isotopic mixing models from muscle data were used to describe the proportional contribution of prey groups during 2003, 2008-2010. Results showed a higher proportional contribution of smelt (Osmeridae) and benthic prey to ringed and bearded seal diets in 2003 compared to 2008-2010. Seasonal keratin layers deposited in claws can document trophic history up to about 10 years. During 2007 (record ice minimum), proportionally more ringed seals fed at a lower trophic level, while spotted seal adults and young-of-the-year fed at a lower trophic level during 2006. Bearded seals may have been foraging more pelagically from 2008 to 2010. Ice seals may be taking advantage of more abundant pelagic crustaceans as the Arctic ecosystem changes to a pelagic-dominated food web. Interannual variations and high variability among species and individual diets illustrate the opportunistic nature and flexibility of ice seals to changes in prey composition.
    • Integrating local and traditional knowledge and historical sources to characterize run timing and abundance of eulachon in the Chilkat and Chilkoot rivers

      Olds, Allyson Leigh; McPhee, Megan; Beaudreau, Anne; Carothers, Courtney; Ryan, Brad (2016-08)
      Eulachon smelt Thaleichthys pacificus are anadromous forage fish of the North Pacific Ocean that annually spawn in coastal rivers of North America in late winter and early spring. These spawning runs range from northern California to southwestern Alaska and provide important resources to nearby communities, indigenous cultures, and wildlife predators. However, eulachon life history is not well understood or documented throughout their range. In recent years, concerns for eulachon population abundances in the southern portions of their range have led to federal protection. Though there are no federal listings in Alaska, there have been local concerns documented for eulachon runs of the Chilkat and Chilkoot rivers since approximately 1990. However, eulachon run timing and abundance trends are difficult to detect due to limited available data and variability in eulachon runs. To document baseline information and explore patterns of eulachon runs of the Chilkat and Chilkoot rivers, we sought local and traditional knowledge from residents of nearby communities to document information about local uses, run timing, abundance, and wildlife observations related to eulachon runs. Observations of eulachon runs were integrated with historical records from newspaper articles and scientific reports to construct temporal trends in eulachon run timing and abundance. Based on the findings of this study, annual eulachon runs of the Chilkat and Chilkoot rivers generally occur for about a week or two between mid-April and mid-May. The arrival dates of eulachon runs often vary from year to year, but the timing appears to have shifted earlier, from mid-May to mid-April, over the past couple of decades. Abundance records were not sufficient to quantify trends. However, qualitative information regarding abundance did not suggest any clear trends in eulachon abundances of the Chilkat and Chilkoot rivers over the years, nor did there appear to be prominent local concerns about abundance declines. Many respondents suggested that eulachon populations were naturally too variable to be able to describe trends in abundance. Interviews also provided insight into local perspectives on eulachon life history and ecology. These results suggest that variability in eulachon run timing and abundance could be related to environmental conditions, including tidal height, river habitat, and water temperature. For a data-limited species like eulachon, integrating local observations and historical records offers a promising approach to documenting baseline information and improving the scientific understanding of eulachon runs and other environmental phenomena.
    • Inter-decadal change in sablefish, Anoplopoma fimbria, growth and maturity in the Northeast Pacific Ocean

      Howard, Katy B.; Adkison, Milo D.; Hillgruber, Nicola; Sigler, Michael F. (2008-08)
      Errors in growth and maturity estimates can drastically affect the spawner-per-recruit threshold used to recommend commercial fish catch quotas. Growth and maturity parameters for Alaskan sablefish, Anoplopoma fimbria, have not been updated for stock assessment purposes for 20 years, even though sablefish aging has continued. In this study, the old length-stratified data set (1981-1993) was updated and corrected for bias. In addition, newer, randomly collected samples (1996-2004) were analyzed, and new length-at-age, weight-at-age, and maturity-at-age and length parameters were estimated. A comparison of the two datasets showed that in recent years, sablefish are growing larger and maturing later and that growth and maturity differ somewhat among regions. The updated growth information improves data fits in the sablefish stock assessment model. It also provides results that are biologically reasonable. These updated and improved estimates of sablefish growth and maturity help ensure the continued proper management of this commercially important species in Alaskan waters.
    • Interannual and spatial variation in the population genetic composition of young-of-the-year Pacific Ocean Perch (Sebastes alutus) in Alaskan waters

      Kamin, Lisa M.; Gharrett, Anthony J.; Heifetz, Jonathan; Tallmon, David (2010-05)
      We know little about the population structure of Gulf of Alaska (GOA) and Bering Sea rockfish, including Pacific ocean perch (POP, Sebastes alutus), and early life history information is sparse for many rockfish species. Young-of-the-year (YOY) POP were collected with surface trawls during surveys of juvenile salmon in the GOA and Bering Sea. These samples presented a unique opportunity to study POP genetics and life history. Fourteen microsatellite loci were used to characterize the genetic variation in POP collected in a total of 45 hauls over five years. The coincidence in timing and location of several collections between years allowed examination of both fine- and broad-scale geographic variation (within cohorts) as well as interannual (between cohorts) genetic variation. The geographic genetic structure of these collections was also compared to geographic structure of adult POP described in a previous study (Palof, 2008). As in the adult study, significant broad-scale geographic divergence was observed in YOY POP in the GOA. Fine-scale geographic divergence was also observed and may be the result of variable current regimes and oceanographic features at several locations. The limited amount of temporal variation observed seems to be the result of variable oceanography and fine-scale population structure rather than the influence of a sweepstakes effect. The relationship between genetic divergence and geographic separation is virtually identical in YOY and adult POP, which confirms that dispersal of POP is limited in all life stages and also demonstrates that most YOY are produced by adults that are located nearby.
    • Interannual variability of epibenthic communities in the Chukchi Sea, Alaska

      Powell, Kimberly Keeler; Konar, Brenda; Coyle, Ken; Winsor, Peter (2015-08)
      Epibenthic communities contain a wide range of organisms and serve an important role in marine ecosystems. They are involved in carbon remineralization, benthic production, and are important prey items for higher trophic levels. Arctic epibenthic communities may be experiencing significant changes in species composition, abundance, and biomass at both short and long term time scales. While epibenthic communities may be responding to long term shifts in the environment, differentiating long term trends from short term interannual variation can be problematic. The present study examined interannual differences of epibenthic communities and potential environmental drivers of their variability in the Chukchi Sea. For this, a plumb-staff beam trawl was used to sample epibenthic species composition, abundance, and biomass of the dominant invertebrate taxa at 71 stations around the Chukchi Sea during the ice free seasons of 2009, 2010, 2012, and 2013. Over the entire study area and within a smaller area with the most temporal coverage, the largest separation was between 2009 and 2013, with more difference between 2009 to 2010 than between 2012 and 2013. Crustaceans were the most significant contributors to community composition, based on abundance, and biomass. The important environmental drivers that varied along with the epibenthic community in some but not all years included bottom water temperature, salinity, dissolved oxygen, mean sediment chlorophyll a, and sediment organic matter. In contrast, sediment grain size was important in all years and, therefore, was the least likely to contribute to the biological variability among years. While these data provide a benchmark on interannual variability of epibenthic communities in the Chukchi Sea, more monitoring is essential to determine long term trends.
    • Interannual variations in the carbon to chlorophyll a ratios during the spring bloom in Prince William Sound, Alaska

      Tamburello, Kathereen Rachel (2005-05)
      The carbon to chlorophyll a ratio of phytoplankton during the spring bloom in Prince William Sound, Alaska was investigated for 3 seasons and related to major physical and chemical variables. Carbon to chlorophyll a ratios (C:Chl) were determined by two methods, based on particulate organic carbon to chlorophyll (POC:Chl) and phytoplankton cell carbon to chlorophyll (PCC:Chl). These ratios were compared to a more commonly used estimate, a fixed ratio of C:Chl, taken from literature, for the spring phytoplankton community. The hypothesis that the C:Chl ratios were significantly different between years was proven false. This research indicates that the C:Chl ratio is primarily determined by species composition of the phytoplankton community rather than external factors such as nutrients, temperature or salinity. In addition, this research indicates that the identification and enumeration method, although rarely used because it is the most time and labor intensive method, provides the best estimate of phytoplankton carbon. The mean PCC:Chl ratio for all three years was 18, and is the best fixed ratio to estimate spring phytoplankton carbon in Prince William Sound when an EI Niño is not present.
    • Interdisciplinary assessment of the skate fishery in the Gulf of Alaska

      Farrugia, Thomas J.; Seitz, Andrew C.; Kruse, Gordon H.; Criddle, Keith R.; Goldman, Kenneth J.; Tribuzio, Cindy A. (2017-12)
      Skates are common bottom-dwelling fishes and valuable non-target species in Gulf of Alaska fisheries. Although there is little demand for skates in the United States, markets in Europe and Asia are fueling desires for additional fishing opportunities on skates in Alaska. Management agencies, however, have been hesitant to allow increased harvests due to the lack of information on the ecology and population dynamics of skates, and the bioeconomics of skate fisheries. Specifically focusing on the two most commonly landedskate species in the Gulf of Alaska (GOA), the big skate (Beringraja binoculata) and the longnose skate (Raja rhina), I conducted an interdisciplinary project to address these knowledge gaps. First, I advanced our understanding of the movement patterns and habitat use of skates by satellite tagging big skates in the GOA. The results show that big skates can, and likely frequently do, travel long distances, cross management boundaries within the GOA, and spend more time in deeper waters than previously thought. Second, I used the insights from the movement study to develop the first stock assessment models for skates in the GOA. This represents an important improvement in modeling, laying the groundwork for the North Pacific Fishery Management Council to move from Tier 5 (more data limited) to Tier 3 (less data limited) harvest control rules, which should lead to increased confidence with which the total allowable catch (TAC) for skates is set. Finally, I used the sustainable harvest estimates from the stock assessment models to develop a model that examined the impacts of management decisions on the profitability of skate fishing. My research provides essential information about these understudied fishes, helping to improve the sustainability and profitability of skate harvests. Incorporation of best available science regarding skate ecology, population dynamics, and bioeconomics into fishery management fosters more responsible development of skate fisheries, sustainable fishery revenues, and employment, and reduces the risk of overfishing, stock collapse, and prolonged fishery closures. It is my hope that fishery management agencies and the fishing industry make use of the new information and insights presented in this dissertation to work collaboratively towards the responsible development of skate fisheries.
    • Interrelationship among temperature, metabolism, swimming performance and recovery in Pacific cod (Gadus macrocephalus): implications of a changing climate

      Hanna, Shannon K. (2006-12)
      Physiological constraints are suggested to contribute to the observed changes in relative abundance of Pacific cod (Gadus macrocephalus) seen in association with interdecadal changes in sea surface temperatures. To examine this concept, two experiments were conducted to determine critical swimming speed (Ucrit), rates of oxygen consumption and recovery post-exhaustion of adult cod acclimated to different temperatures. In addition, hematocrit and plasma concentrations of cortisol, metabolites and ions from resting and exhausted fish were measured to assess the impact of swim trials on fish condition. In experiment one, fish acclimated to 4°C had similar mean Ucrit (1.07 BL/s) and resting metabolic rates (35.34 mg O₂/kg⁰⁸/hr) compared to fish acclimated to 11°C fish (1.07 BL/s; 49.43 mg O₂/kg⁰⁸/hr). Similarly, concentrations of blood constituents differed little between temperature treatments; each exhibited increases in plasma cortisol and metabolites from pre- to post-swim. Experiment two illustrated few differences in rates of recovery between temperature groups (2 and 7°C). After four hours of recovery there was no evidence of plasma cortisol or metabolites returning to pre-swim concentrations in either temperature group. It seems unlikely that physiological constraints on the metabolic performance of adult Pacific cod contribute to changes in their relative abundance.
    • Interrelationships of Pacific herring, Clupea pallasi, populations and their relation to large-scale environmental and oceanographic variables

      Williams, Erik Hamilton; Quinn, T. II (1999)
      Recruitment estimates for Pacific herring, Clupea pallasi, populations in the Bering Sea and Northeast Pacific Ocean are highly variable, difficult to forecast, and crucial for determining optimum harvest levels. Age-structured population models for annual stock assessments of the sac-roe fisheries rely on fishery and survey age composition data tuned to an auxiliary survey of total biomass. In Chapter 1, the first age-structured model for Norton Sound herring was developed similarly to existing models. Estimates of variability from age-structured stock assessment models for Pacific herring are often not calculated. In Chapter 2, a parametric bootstrap procedure using a fit of the Dirichlet distribution to observed age composition data was developed as a quick and easy method for computing error estimates of model estimates. This bootstrap technique was able to capture variability beyond that of the multinomial distribution. This technique can provide estimates of variability for existing population models with age composition data requiring little change to the original model structure. Recruitment time series from Pacific herring stock assessment models for 14 populations in the Bering Sea and Northeast Pacific Ocean were analyzed for links to the environment. For some populations, recruitment series were extended backward in time using cohort analysis. In chapter 3, correlation and multivariate cluster analyses were applied to determine herring population associations. There appear to be four major herring groups: Bering Sea, outer Gulf of Alaska, coastal SE Alaska, and British Columbia. These associations were combined with an exploratory correlation analysis of environmental data in chapter 4. Appropriate time periods for environmental variables were determined for use in Ricker type environmentally dependent spawner-recruit forecasting models. Global and local scale environmental variables were examined in forecasting models, resulting in improvements in recruitment forecasts compared to models without environmental data. The exploratory correlation analysis and best fit models, determined by jackknife error prediction, indicated temperature data corresponding to the year of spawning resulted in the best forecasting models. The Norton Sound age-structured model, parametric bootstrap procedure, and recruitment forecasting models serve as enhancements to the decision process of managing Pacific herring fisheries.
    • Intertidal community development along a distance/age gradient in a tidewater glacial fjord

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

      Turner, Jessica S.; McDonnell, Andrew; Johnson, Mark; Islas, Ana Aguilar (2015-12)
      The Gulf of Alaska is a seasonally productive ecosystem surrounded by glaciated coastal mountains with high precipitation. With a combination of high biological production, inputs of suspended sediments from glacial runoff, and contrasting nutrient regimes in offshore and shelf environments, there is a great need to study particle cycling in this region. I measured the concentrations and size distributions of large marine particles (0.06-27 mm) during four cruises in 2014 and 2015 using the Underwater Vision Profiler (UVP). The UVP produces high resolution depth profiles of particle concentrations and size distributions throughout the water column, while generating individual images of objects >500 μm including marine snow particles and mesozooplankton. The objectives of this study were to 1) describe spatial variability in particle concentrations and size distributions, and 2) use that variability to identify driving processes. I hypothesized that UVP particle concentrations and size distributions would follow patterns in chlorophyll a concentrations. Results did not support this hypothesis. Instead, a major contrast between shelf and offshore particle concentrations and sizes was observed. Total concentrations of particles increased with proximity to glacial and fluvial inputs. Over the shelf, particle concentrations on the order of 1000-10,000/L were 1-2 orders of magnitude greater than offshore concentrations on the order of 100/L. Driving processes over the shelf included terrigenous inputs from land, resuspension of bottom sediments, and advective transport of those inputs along and across the shelf. Offshore, biological processes were drivers of spatial variability in particle concentration and size. High quantities of terrigenous sediments could have implications for enhanced particle flux due to ballasting effects and for offshore transport of particulate phase iron to the central iron-limited gyre. The dominance of resuspended material in shelf processes will inform the location of future studies of the biological pump in the coastal Gulf of Alaska. This work highlights the importance of continental margins in global biogeochemical processes.