• 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.
    • Investigations of the role of lipids in marine mammal diets, health and ecology

      Mau, Tamara Lynn (2004-05)
      Lipids are essential to many aspects of marine mammal biology. I investigated the amount, type and flux of lipids under a variety of natural and controlled nutritional and dietary conditions, in order to increase our knowledge of marine mammal diets, health and ecology. First, I examined the influence of biological and environmental variables on the quantity and quality of blubber, and their importance in establishing condition indices in the bowhead whale. Blubber was heterogeneous in composition, varying by both site and depth. Sex, age-class, season and body length were all significant factors in determining lipid content (quality) of blubber. Blubber thickness (quantity) was highly correlated with body length after?9 m. Blubber lipid content at umbilicus sites and inner depths was most variable and presumably most responsive to nutritional changes. Blubber properties appeared to exceed what was necessary for insulation, further supporting the concept for the need to store energy as a consequence of the large seasonal and annual variability of food availability in the arctic environment. These data establish a baseline for long-term monitoring of bowhead whale health and population condition. Second, I addressed post-mortem changes in blubber composition of a stranded humpback whale. Lipid content decreased due to tissue decomposition by as much as 24%, limiting the ability to accurately assess nutritional status and health. Finally, in response to a growing need for validation of the use of fatty acid profiles as dietary tracers in top marine predators, I investigated the effects of prey switching on fatty acid profiles in plasma and red blood cell membranes (RBCs) of captive harbor seals. In plasma, nine of fifteen fatty acids responded significantly with prey switching, compared to only three plus one ratio in RBCs. Season and total daily lipid intake also affected the level of some plasma fatty acids. Diet was reliably predicted from fatty acid profiles in plasma after two weeks and in RBCs at four months using discriminant function analysis. Plasma and RBC fatty acid profiles provided an integration of dietary history, representing short-term and long-term 'dietary windows, ' respectively.
    • Juvenile Bristol Bay Sockeye Salmon Ecology

      Farley, Edward V., Jr.; Adkison, Milo (2008)
      Predicting annual returns of Bristol Bay sockeye salmon (Oncorhynchus nerka) has been difficult due to large, unexplained variations in return strength. Ocean conditions, particularly during the first few months after salmon leave freshwater, are believed to have a strong influence on their early marine growth and survival. Limited historical and present research suggests that sea temperature can affect juvenile Bristol Bay distribution. During years with cool spring sea temperatures, juvenile sockeye salmon are distributed nearshore along the Alaska Peninsula, whereas they are found further offshore during years with warm spring sea temperatures. Juvenile sockeye salmon are larger, in better condition, and have higher marine stage survival after the first year at sea when they are distributed further offshore than when they are distributed nearshore along the Alaska Peninsula. Juvenile sockeye salmon stomach contents also shift from primarily Pacific sand lance ( Ammodytes hexapterus) and euphausiids to age 0 walleye pollock ( Theragra chalcogramma) when their distribution changes from nearshore to further offshore. Annual averages of juvenile sockeye salmon growth rate potential (GRP) were generally lower among years and regions with cool spring sea temperatures. In addition, juvenile sockeye salmon GRP was generally higher in offshore regions than nearshore regions of the eastern Bering Sea shelf. A sensitivity analysis indicated that juvenile sockeye salmon GRP was more sensitive to changes in observed (August to September) sea surface temperatures during years when prey densities were lower. The results of the dissertation suggest that variability in early marine survival is primarily due to bottom-up control of the trophic structure of the eastern Bering Sea ecosystem.
    • Juvenile Pacific herring (Clupea pallasi) feeding ecology in Prince William Sound, Alaska

      Foy, Robert James; Norcross, Brenda; Cooney, Robert T.; Paul, A. J.; Mason, Doran M.; Stokesbury, Kevin (2000-12)
      Pacific herring (Clupea pallasi) are commercially exploited along the Asiatic and North American Pacific Ocean continental shelves. In Prince William Sound (PWS), Alaska, herring were commercially important until a year class failures in 1993. A noticeable lack of life history information on juveniles was available in PWS to use for studies addressing the failed recruitment. This study describes the seasonal herring feeding ecology in PWS nursery areas from 1996 to 1998. Zooplankton from 535 vertical tows and herring diet data from 3,282 stomach contents were collected from Eaglek, Simpson, Whale and Zaikof Bays. Zooplankton species composition was dominated by small calanoid copepods, cyclopoids, invertebrate eggs, and adult euphausiids in March prior to the spring phytoplankton bloom. Small calanoid copepods, especially Pseudocalanus spp., were dominant during the peak abundance. Oikopleurans were abundant from August to October. The zooplankton density peaked at 1,234 to 5,594 individuals m-3 between June and July 1996. Zooplankton density was significantly lower in 1997 than 1996. Seasonal density and diversity were found to vary among and within the four bays. The abundance of prey in herring diets was correlated to the timing and degree of zooplankton prey availability. Feeding was highest at 1,192 items per fish in July 1996 and decreased until winter (December to March) when the number of empty stomachs ranged from 70 to 90 %. Lower zooplankton densities in 1997 were reflected in significantly lower abundances of prey in 1997 diets. Prey selectivity was negatively correlated with zooplankton densities among months. Diel and ontogenetic feeding trends as well as differences between feeding depths were noted. Assimilation rates of smaller herring were closer to basal metabolic rates and herring less than 3 g had insufficient energy reserves to survive the winters of 1995-1996 and 1996-1997. These patterns suggest that juvenile herring are dependent on an abundance of prey to successfully feed and have enough energy reserves to overwinter. The effects of increased temperatures on zooplankton fluctuations and changes in herring condition may have had population level consequences in PWS. Successful feeding when prey abundance and composition was highly variable reveals herring’s adaptability to multiple environments.
    • Kelp bed variability and fish population dynamics in Kachemak Bay, Alaska

      Hamilton, Judith Ann (2004-08)
      Understanding interactions between kelp beds and fishes is essential because anthropogenic changes and natural variability in these beds (composition, density, and distribution) may affect available habitat for fishes. In Alaska, little is known about the annual and seasonal variability of macroalgal cover in kelp beds and corresponding changes in associated fish populations. This study investigated natural variability using monthly SCUBA surveys in Kachemak Bay, Alaska from May 2002 to September 2003. Ten shallow (approximately 7m water depth) nearshore kelp beds with varying degrees of macroalgal cover were surveyed visually for fishes and kelp, and measurements of environmental variables were collected. These kelp beds had a persistent, perennial-dominated understory with sporadic, sparse populations of annual canopy kelp. Understory and canopy kelps had affinities with greater bottom structure, and annual kelp density was greatest during periods with higher temperatures. Hexagrammids, especially kelp greenlings, existed year-round in the more structurally complex beds and were typically more abundant during periods with higher temperatures, and at sites with denser annual kelp populations. Most other fishes were transient and generally present only during summer months. Monthly changes in kelp and fish communities reflected a strong seasonal component.
    • Kelp beds as fish and invertebrate habitat in southeastern Alaska

      Calvert, Elizabeth L.; Stekoll, Michael; Shirley, Thomas; Hillgruber, Nicola (2005-08)
      Throughout the temperate marine regime, the shallow subtidal is dominated by rocky reefs and algal assemblages. The ecological significance of high-latitude, cold-water kelp systems is poorly understood particularly for Alaska. Two large-scale experiments conducted near Juneau, Alaska were designed to study fish and invertebrate assemblages in regard to (1) canopy forming Nereocystis luetkeana (1500 m² manipulations) and (2) sub-canopy forming Laminaria bongardiana (600 m²). Fish and invertebrates were quantified using Standard Monitoring Units for the Recruitment of Fish (SMURFs), light traps, and visual surveys. The canopy kelp experiment revealed significantly greater abundance (X=0.57 fish/SMURF; X=0.28 fish/SMURF) and biomass (X=0.95 g/SMURF; X =0.23 g/SMURF) of benthic fishes at Nereocystis sites versus sites without canopy kelp. In contrast, a direct negative effect of Nereocystis was observed for schooling fish; significantly more fish were observed at sites without canopy kelp as compared to Nereocystis sites (X=27.3 fish/15 m³; X=4.2 fish/15 m³). Fish assemblages were independent of L. bongardiana, yet invertebrates were twice as abundant at sub-canopy sites. Nereocystis has direct and indirect effects on fish distributions through behavioral and habitat modifications. Overall, canopy kelps with associated sub-canopy kelps promote more abundant and rich fish assemblages in southeastern Alaska, while invertebrate assemblages are greater in sub-canopy areas.
    • Kelp forests and barren grounds: phlorotannin production and holdfast community structure in the Aleutian dragon kelp, Eualaria fistulosa

      Schuster, Martin D.; Konar, Brenda; Iken, Katrin; Coyle, Kenneth (2012-12)
      The canopy forming kelp Eualaria fistulosa inhabits two organizational states throughout the Aleutian archipelago, kelp forests and barren grounds. Urchin abundance and behavior determines which state dominates in any given area. Sporophyll phlorotannin content and holdfast epibiont fauna were investigated at multiple islands along the Aleutian archipelago to determine how the organizational state affects the production of secondary metabolites and the taxon richness, abundance and biomass of holdfast communities. Barren ground sporophylls had higher phlorotannin content than kelp forest sporophylls, although grazing rates on sporophylls from each state did not differ during in situ grazing experiments. The taxon richness, abundance and biomass of holdfast communities were similar between kelp forests and barren grounds at all islands, although these communities varied among islands and were mostly driven by holdfast volume. These results suggest that physical differences such as light and nutrient availability in the kelp forest structure between organizational states may be responsible for differences in phlorotannin content, but that these differences are not reflected in the holdfast community structure. It appears that barren ground holdfast communities are remnants of a once forested area.
    • Lake trout (Salvelinus namaycush) otoliths as indicators of past climate patterns and growth in Arctic lakes

      Torvinen, Eric S.; Falke, Jeffrey; Arp, Christopher; Zimmerman, Christian; Sutton, Trent (2017-05)
    • Landscape modeling of threespine stickleback occurrence in small Southeast Alaska lakes

      Gregovich, Dave (2007-12)
      Although threespine stickleback (Gasterosteus aculeatus L) are known to inhabit a wide range of habitats, their distribution in lakes across Southeast Alaska is not known. Threespine stickleback are an important prey item for many consumers in freshwater ecosystems. Additionally, isolated populations may be genetically unique and thus important from a conservation perspective. This study focused on identifying' landscape factors and models useful in predicting the presence of threespine stickleback in small (0.5-5 ha) lakes of Southeast Alaska. Stickleback occurrence was assessed via snorkeling and minnow trapping in 54 lakes, which were divided into calibration (n=36) and prediction (n=18) data sets. A number of models representing four methodologies-generalized linear models, generalized additive models, classification trees, and artificial neural networks-were built based on the calibration set, cross-validated, and evaluated by prediction to the test set of lakes. Lake elevation, distance from saltwater, and slope of lake outlet stream were the most useful predictors of stickleback occurrence. Results suggest that the likelihood of stickleback presence is highest in low elevation lakes near the coast. Human development and recreational activity also tends to be common in these areas, and so land-use planning should account for the high potential occurrence of threespine stickleback here
    • Length-based models and population analyses for northern shrimp Pandalus borealis Krøyer

      Fu, Caihong (2000-08)
      The lack of basic knowledge on stock dynamics o f northern shrimp Pandalus borealis, a protandric hermaphrodite, has caused difficulty in regulating fishing effort on a scientific basis and in understanding potential causes behind population fluctuations and collapses. Previous length-based population models (LBMs), developed for other species, are undesirable primarily for two reasons: (1) individual cohort dynamics are masked; (2) variations in annual natural mortality (M) are ignored. This research was primarily aimed at developing a more advanced LBM that provides estimates of parameters such as recruitment (R), fishing mortality (F) and especially annual M. Simulation-estimation experiments were conducted to evaluate model performance. Despite model complexity, annual M can be well estimated provided measurement errors in survey biomass estimates are low. The common assumption of constant M created biased parameter estimates. Estimated M of P. borealis in Kachemak Bay, Alaska increased steadily in the 1980s. Retrospective projections showed that the increasing trend in M in the 1980s resulted in the population collapse. The ultimate goal o f stock assessment is to develop sound harvest strategies. With the widely observed abundance fluctuations in shrimp populations, it is impossible to manage solely based on conventional methods, such as maximum sustainable yield (MSY). Thus, harvest strategies were compared under various situations o f M and R. With M increasing over time, it is important to execute threshold management, i.e., closing the fishery at population levels below a threshold value. Simulations indicated that overfishing caused by underestimated M or overestimated R can be greatly alleviated if the population is sampled once every year. Life history aspects of sex change, growth, M, and their seasonal variations were also incorporated into the LBM. Populations with protandrous animals are likely to be subject to recruitment overfishing; merely protecting older females while allowing high exploitation on younger males can lead to population collapse. Fishing after spring egg hatching is superior to fishing after mating and egg extrusion in fall when F is high. In summary, the length-based model developed here provided a convenient framework for understanding population processes and harvest strategies and should be useful for a variety of hard-to-age species.
    • Life history characteristics, management strategies, and environmental and economic factors that contribute to the vulnerability of rockfish stocks off Alaska

      Patt, Jacqueline; Criddle, Keith; Gharrett, Anthony; Love, Milton; Heifetz, Jonathan (2014-12)
      This study explored the extent to which variations in biological characteristics, environmental and economic factors, and management strategies have affected the tendency for rockfish to become overfished. The analysis used data on 5 species of rockfish that account for more than 95% of commercial catch of rockfish in the Gulf of Alaska (GOA) and Bering Sea and Aleutian Island (BSAI) management regions. These species are: Shortraker Rockfish (Sebastes borealis), Pacific Ocean Perch (Sebastes alutus), Northern Rockfish (Sebastes polyspinis), Dusky Rockfish (Sebastes variabilis), and Shortspine Thornyhead (Sebastolobus alascanus). Fishery management models often treat BMSY, the biomass level that maximizes sustainable yield, as a critical reference point; whenever the biomass of a federally managed fish or shellfish stock is estimated at less than 0.5×BMSY, the stock is declared "overfished" and managers are required to develop a recovery plan that will restore stock abundance above BMSY within about one generation length. Because estimates of BMSY are unavailable for some GOA and BSAI rockfish stocks included in this analysis and because we were interested in developing a model that could be applied to data-poor stocks, we explored two proxies for BMSY. The mean of past estimates of exploitable biomass (avgExpB) was used as a proxy for BMSY for the better-studied stocks. The mean of past catch (avgC) was used as a proxy for BMSY for data-poor stocks. These values were used to scale time series estimates of exploitable biomass (ExpBt) or catch (Ct). A systems estimation approach, seemingly unrelated regression (SUR), was used to estimate parameters of linear and nonlinear models that included available numerical and categorical variables (biological, management, environmental, and economic factors) thought to contribute to increases or decreases in ExpBt / avgExpB or Ct / avgC. Goodness-of-fit statistics and tests of individual coefficients and groupings of coefficients were used to guide model refinement. The modeling approach worked well for better-studied stocks but not for data-poor stocks. The preferred 5-stock model (Pacific Ocean Perch in the GOA and BSAI, Northern Rockfish in the GOA and BSAI, and Dusky Rockfish in the GOA) had an excellent fit to the overall system (R² = 0.922, P << 10⁻⁶) and statistically significant coefficient estimates of the variables included. The model indicated that the past values of ExpBt / avgExpB can be accounted for through time and across stocks by nonlinear variation in: spawning biomass, intrinsic growth rates (k), maximum age, exploitation rates, habitat preferences, Pacific Decadal Oscillation, and ex-vessel price. Because some of these factors are subject to management control and others are predictable, it should be possible to take account of anticipated changes in these factors when setting harvest targets and harvest limits, selecting spatial management strategies, or considering changes to harvest control rules or fisheries governance systems.
    • The life history of the intertidal barnacle, Balanus balanoides (L.) in Port Valdez, Alaska

      Rucker, Tami Louise (1983-09)
      The life history of the boreo-arctic barnacle Batanus balanoides was examined at three study sites in Port Valdez. Ovarian tissue development began in early summer. Fertilized eggs, evident by September, were brooded throughout the winter. Larval release was synchronous with the spring phytoplankton bloom. Settlement was observed in April and continued until June. Maximal shell growth occurred immediately subsequent to assimilation of organic material from the spring bloom. Seasonal fluctuations in body weight were noted and reflect feeding, spermatogenesis, and energy transfer to other biological processes (i.e., shell growth and reproduction). Mortality, greater for juveniles than adults, resulted from seasonal stresses (lowered salinity and heightened sedimentation), spatial competition, predation, and pollutants (hydrocarbons). Once life-history events were confirmed for barnacles in Port Valdez, comparisons of trends observed at the three sites were possible. Differences between populations were evident and were attributed to the unique micro-habitats of the study sites.
    • Life History, Demography, And Ecology Of The Spiny Dogfish "Squalus Acanthias" In The Gulf Of Alaska

      Tribuzio, Cindy A.; Kruse, Gordon; Fujioka, Jeff; Gallucci, Vince; Hillgruber, Nicola; Lowe, Chris; Woodby, Doug (2010)
      The spiny dogfish (Squalus acanthias) is a small, cosmopolitan shark species, common in sub-tropical and sub-arctic waters. The species is often targeted commercially in most areas of the world throughout its range, and in some cases it is overfished or the subject of conservation concern. In the Gulf of Alaska, spiny dogfish are not targeted and not generally retained, but incidental catches can be high for this schooling species. Previously, biological parameters for spiny dogfish in the Gulf of Alaska were assumed from estimates for this specie's neighboring areas, including British Columbia and Washington State. The purpose of this study was to examine spiny dogfish in the Gulf of Alaska and estimate important parameters for stock assessment in four stages: (1) general biology, distribution, and life history; (2) modeling age and growth; (3) population demographic modeling; and (4) ecological interactions revealed by diet analysis. Spiny dogfish are similar in length in the Gulf of Alaska to neighboring regions, but mature at larger sizes and have a greater fecundity than reported elsewhere. There is high natural variability in estimated ages for the species, which is reflected in the poor fit of the growth models, possibly owing to measurement error from using the dorsal fin spine as the aging structure. A two-phase growth model provided the statistical best fit. However, questions were raised about the biological interpretation of the model and whether more traditional models (e.g., von Bertalanffy and Gompertz) may be more appropriate. Using the life-history and growth data, Leslie matrix type age- and stage-based demographic models were created to estimate sustainable fishing mortality rates and to examine the risk of harvest scenarios. Female Gulf of Alaska spiny dogfish can support up to a 3% annual harvest rate; fisheries that target juveniles have the greatest risk of population decline below threshold levels. Spiny dogfish are generalist opportunistic feeders that feed on whichever prey is available, however shrimp are the most important prey type, followed by cephalopods. Results of this study will be used in future ecosystem modeling and stock assessments for this species. Taking into account the history of targeted fisheries for the species on the U.S. east coast and in British Columbia and Washington, as well as the susceptibility of the species to overfishing, fishery managers will need to take a cautious approach should a target fishery develop in the Gulf of Alaska.
    • Light adaptations of plants: a model based on seagrass Zostera Marina L.

      Dennison, William (1979-12)
      Adaptations to light by a temperate seagrass, Zostaro: marina L. (eelgrass), were investigated along a depth transect representing a gradient of plant development. Various light adaptive strategies are proposed in a conceptual model and tested along the natural gradient and under in situ light manipulation experiments. The major light capturing strategy which Zostera employs is that of changing leaf area. Chlorophyll a to b ratios and amounts, measures of adaptation to light quality and quantity, demonstrated little or no adaptive trends when integrative samples were used. The altered light experiments did not affect chlorophyll content but did affect leaf production rates. Although the relative vertical distribution of leaf area is constant along the transect, the absolute leaf area varies, as measured by leaf area index (LAI = area of leaves/area of bottom). A measured maximum LAI of 17 is higher than other aquatic and most terrestrial ecosystems.
    • Linking freshwater growth to size-dependent marine survival of sockeye salmon: interactions between processes of climate, density, and natural selection

      Ree, Marta Elizabeth; Westley, Peter; Finkle, Heather; Beaudreau, Anne (2019-05)
      Due to the mediating role of body size in determining fitness, the 'bigger is better' hypothesis still pervades evolutionary ecology despite evidence that natural selection on phenotypic traits varies in time and space. For Pacific salmon (genus Oncorhynchus), the size at which juveniles migrate to sea (i.e., smolts) has been linked to survival during the early marine period, where larger smolts typically survive at a higher rate than their smaller counterparts. However, the relationship of smolt size and survival becomes more ambiguous when considering confounding factors of age, ocean entry timing, and environmental variability. Despite equivocal results, smolt size appears to be a key trait and therefore changes in freshwater conditions may have consequences for population productivity. Furthermore, due to differences in site-specific habitats, trophic dynamics, and population traits the response of specific populations to these changes is likely to be context specific. The objective of this thesis was to 1) quantify the direction and magnitude of natural selection on smolt size for three age classes of sockeye salmon in a small watershed on Kodiak Island, AK and 2) explore stock-specific effects of temperature and conspecific density on smolt size over a multi-decade time-series to understand historic and possible future trends. To address our first objective, we calculated standardized selection differentials by comparing observed size distributions of out-migrating juvenile salmon to back-calculated smolt length from the scales of surviving, returning adults. Results reveal the magnitude of selection on size was very strong and consistent among years. However, the direction of selection on size consistently varied among age classes. The absolute magnitude of selection was negatively correlated to apparent marine survival and positively correlated to late mean ocean entry timing. To address our second objective, we back-calculated smolt size from returning adult scales to reconstruct a time-series of smolt length of two stocks within a small Alaska watershed on Kodiak Island. Using a dynamic linear model framework, we detected evidence that for one stock, temperature was important in explaining smolt length, and density effects influenced both stocks utilizing the same lakes. Furthermore, forecasts of smolt length showed highly variable responses under scenarios of increasing temperature and high and low densities. Collectively, these results demonstrate that interactions between processes of climate, density, and natural selection are highly context-specific in terms of both inter- and intra- population variability.
    • Local herpetological knowledge in the North

      Ream, Joshua Taylor; Toowóo, Xíxch'i; Lopez, Juan Andres; Gerlach, Scott Craig; Schneider, William; Carothers, Courtney (2016-05)
      Amphibians are important components of ecological communities and of human cultures, even in high northern latitudes where species diversity for this group is low. Despite their ecological and cultural value, and their ability to serve as indicators of ecosystem health, information on the biology of amphibians in Alaska and high latitude segments of their geographic range is limited. By combining local knowledge of herpetology and citizen science approaches, it is possible to circumvent some of the logistical constraints of research in a vast, sparsely populated region to enhance scientific understanding of amphibian populations. The first objective of this investigation is to document the nature and extent of local herpetological knowledge within a rural Alaska community, including perceptions of local human-amphibian relationships. Secondly, this study explores various methods of obtaining this knowledge and engaging the public in citizen science programs for the production of herpetological data. Finally, this study examines the species diversity, distribution and population trends of amphibians in the Stikine River region of Alaska. I demonstrate that local herpetological knowledge, when combined with standard biological techniques, can be used to better understand amphibian populations in Alaska. This study documented 3,645 amphibian observations in the state, including 2,320 observations contributed by citizen scientists and members of the public. Six native species and three non-native species were included in these observations. I found that each method of data acquisition resulted in varying degrees of efficiency and resulting contributions, and that members of the public were generally willing to share their knowledge of amphibians on local landscapes. The nature and extent of contributor knowledge varied, though many participants provided detailed information on past observations. Many respondents also perceive amphibians as important to local ecosystems and human groups. Contributor observations, combined with data from historic and contemporary herpetological inventories, substantially increase scientific knowledge of amphibians in the Stikine River region of Alaska, and more generally across the state.
    • Longitudinal distribution patterns and habitat associations of juvenile coho salmon Oncorhynchus kisutch in tributaries of the Little Susitna River, Alaska

      Foley, Kevin Michael; Rosenberger, Amanda E.; Gerkin, Jonathon; Verbyla, David L.; Mueter, Franz J. (2014-05)
      Understanding how headwater streams function as rearing habitats for juvenile coho salmon Oncorhynchus kisutch is essential for effective population management and conservation. To inform habitat restoration activities within the Matanuska-Susitna Valley, Alaska, I determined upstream distribution limits, validated abundance estimates, and established fish habitat relationships in two headwater stream tributaries of the Little Susitna River in 2010-11. Using a low-effort, spatially continuous sampling approach and linear mixed-effects models, I related local- and landscape-scale habitat associations to abundance estimates. All-aged coho salmon composed approximately 98% of all fish sampled and inhabited the entire stream length to their upstream limits. Age-1+ fish resided in 64% and 44% of the stream length for the two sampled streams. The mean upstream elevation limit for all-aged fish in these streams was 278m and 267m. For age- 1+ fish, the upstream elevation limit in the two streams was 275m and 238m. Percent slope at the distribution limit of all-aged fish was consistent across streams at 5%, whereas percent slope for age-1+ fish correspond to 4% and 6%. Elevation and percent slope consistently described upstream distribution limits among age classes. Therefore, we must consider these landscape features when prioritizing restoration projects in headwater streams.