• 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.
    • Marine-entry timing and growth rates of juvenile chum salmon in Alaskan waters of the Chukchi and northern Bering Seas

      Vega, Stacy L.; Sutton, Trent; Adkison, Milo; Murphy, James (2015-08)
      Recent climate change is most pronounced in the Arctic, with many implications for juvenile salmon life-history patterns, such as altered timing of migrations and/or timing and success of life-history stages. The objectives of this study were to determine the timing of marine entry and early marine growth of juvenile Chum Salmon Oncorhynchus keta in the Chukchi and northern Bering seas. Sagittal otoliths were collected from juvenile Chum Salmon in summers 2007, 2012, and 2013 via surface trawls in the southern Chukchi and northern Bering seas. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to discriminate between freshwater and marine environments, and daily growth increments were counted to determine marine-entry dates and growth rates of juvenile Chum Salmon to make temporal and regional comparisons of juvenile characteristics. Marine-entry dates ranged from mid-June to mid-July, with all region and year combinations exhibiting similar characteristics with respect to entry timing, i.e., larger individuals at the time of capture entered the marine environment earlier in the growing season than smaller individuals. Juvenile growth rates were estimated to be, on average, 4.9 % body weight per day in both regions in summers 2007 and 2012, and 6.8% body weight per day in the Chukchi Sea in 2013. This study shows consistent conditions among regions with respect to juvenile Chum Salmon marine-entry timing, with some variation in growth rates. These results provide a novel and more thorough evaluation of juvenile Chum Salmon early life-history characteristics in the Alaskan Arctic and provide a baseline for comparisons with future climate change studies.
    • Maturation of walleye pollock, Theragra chalcogramma, in the eastern Bering Sea in relation to temporal and spatial factors

      Stahl, Jennifer Paige (2004-12)
      Walleye pollock, Theragra chalcogramma, are both ecologically and commercially important in the eastern Bering Sea (EBS). Maturity is a critical parameter in the stock assessment to set annual total allowable catch. Pollock maturity has not been examined in the EBS since 1976, and possible interannual and geographic variation has not been studied to date. Our goal is to estimate correct maturity schedules for EBS pollock. Maturity data, fish lengths and macroscopic maturity stages were collected aboard pollock trawlers during winter 2002 and 2003 across the EBS from 10,197 pollock. Similar data were collected by NMFS scientists during hydroacoustic surveys from 1989-2002. Histological analysis of ovary tissue confirmed the appropriateness of macroscopic staging. However, some pollock classified macroscopically as 'developing' may mature either in the current or following spawning seasons. Therefore, our analysis was performed with two alternative assumptions: fish classified as 'developing' were either considered immature or mature. Maturity rates were estimated by logistic regression. Geographic variability exists; fish mature at the smallest lengths north of the Pribilof Islands. Size at maturity varies interannually, as well. Temporal and spatial variation in maturity may be due to biological or environmental factors, such as pollock density, water temperature, or prey availability.
    • Maturity, fecundity, growth, and sustained yield of coastal cutthroat trout at Florence Lake, Southeast Alaska

      Foster, M. Birch (2003-08)
      The resident coastal cutthroat trout Oncorhynchus clarki clarki population in Florence Lake, Southeast Alaska was sampled from July through October, 1997 to assess its maturity, fecundity, growth and sustained yield. Maturing female cutthroat have significant gonad development between mid September and late October. A gonadosomatic index threshold was established for female cutthroat trout. A logistic model for maturity estimated asymptotic percentages by age and length: 92% and 100% for males and 86% and 80% for females, indicating presence of skip spawning. Male cutthroat trout matured earlier and at smaller length than females, but females matured more rapidly. An allometric model fitted fecundity data well. Schnute's growth model indicated that growth was relatively slow. An ll-inch (279 mm) minimum size limit allows a high proportion of trout at Florence Lake to spawn at least once. Age-based and length-based per recruit analyses performed comparably and established sustainable fishing mortality estimates.
    • Mercury concentrations and feeding ecology of fishes in Alaska

      Cyr, Andrew Philip; López, Juan Andres; O'Hara, Todd; Wooller, Matthew; Seitz, Andrew (2019-05)
      Mercury (Hg) is a ubiquitous contaminant found in nearly every fish species analyzed. Certain forms of Hg accumulate efficiently in fish tissues, sometimes reaching concentrations of concern for human and wildlife health when consumed. This has motivated considerable research and interventions surrounding fish consumption with Hg concentrations as the underlying cause of over 80% of fish consumption advisories in the United States and Canada. The ecological and physiological drivers that influence the concentrations of Hg in fishes are complex and vary among taxa spatially and temporally. Studying these drivers and their respective influences on Hg concentrations can help elucidate observed differences in Hg concentrations across space and time, which can then be used to improve management and consumption strategies. Here I present a series of studies focused on the chemical feeding ecology of Hg by measuring total Hg (THg) concentrations and ratios of nitrogen and carbon stable isotopes in multiple fish species from three regions in Alaska. In Chapter 2 I described foundational field collection efforts to characterize the fish communities from West Creek and the Taiya River in Klondike Gold Rush National Historical Park, and the Indian River in Sitka Historical National Park, Alaska. This chapter and agency report presents a survey of the fish species assemblage of the rivers and laid the framework for the regional analyses I conducted in the study presented in Chapter 3. In Chapter 3 I report inter- and intra-river comparisons of THg concentrations and associated feeding ecology of riparian Dolly Varden, separated by anadromous barriers in each system. I concluded that resident Dolly Varden that co-habit riverine locations with spawning salmon consume more salmon eggs than resident Dolly Varden from other locations of the same river that do not co-habit with spawning salmon. This is reflected in the isotopic composition of their tissues, and subsequently the THg concentrations of these fish are lower relative to Dolly Varden from parts of the same river above anadromous barriers. In Chapter 4, I describe regional patterns of THg concentrations and stable isotope values of carbon and nitrogen in nine species of fish and invertebrates from the Bering Sea and North Pacific Ocean along the Aleutian Islands, using Steller sea lion management zones as a spatial framework. I determine that most species from the Western Aleutian Islands have greater THg concentrations, and more negative δ¹³C values than those from the Central Aleutian Islands, indicating ecosystem-wide differences in THg concentrations and fish feeding ecology. I also determined that Amchitka Pass, a well-documented oceanographic and ecological divide along the Aleutian Island chain, aligns better with differences in THg concentrations than the boundary between Steller sea lion management zones. In Chapter 5, I report THg and methylmercury concentrations in fishes of Kotzebue Sound, including seven species that are important for subsistence users. I determined that fork length influences Hg concentrations within individual species, and that trophic relationships within a food web, a factor associated with biomagnification, influences Hg concentrations across the entire food web. I also observed that muscle tissues from virtually every individual fish had Hg loads below the State of Alaska's criteria for unlimited consumption. Taken together, the work conducted in this dissertation helps us better understand the ecological dynamics of Hg in aquatic food webs and has contributed to Hg monitoring of fish resources across parts of Alaska.
    • Metabolic hormone levels and immunocompetence of neonatal harbor seals (Phoca vitulina) in rehabilitation settings compared to wild harbor seal pups

      O'Neil, Danielle Renee (2005-08)
      Health of harbor seal pups in rehabilitation and in the wild were compared using two metabolic hormones (cortisol and total thyroxine, TT4), two cellular immunity components (lymphocytes and eosinophils) and morphometric measurements. Neonatal harbor seals in two rehabilitation facilities were compared to wild harbor seal pups. Permanently captive harbor seals housed at the Alaska SeaLife Center were also studied. High levels of cortisol at weaning suggest changes in the stress response may be due to diet adjustments in pups during rehabilitation. The lower cortisol concentrations post-weaning suggest that pups in rehabilitation had overcome the challenge of pre-weaning diet, handling or environment and avoided chronic stress. TT4 concentrations were higher in wild pups, likely attributed to a more energetically demanding life in a dynamic environment. The rehabilitated pups showed lower lymphocyte counts and higher eosinophil counts compared to wild pups. Wild harbor seal pups were heavier and longer than post-weaned pups in rehabilitation. Animals in rehabilitation are possibly compromised at stranding, but it is also possible that current rehabilitation practices do not mimic what a healthy pup would receive from maternal investment, thus pups undergoing rehabilitation likely remain smaller and possibly immunologically compromised despite repeated and constant care in rehabilitation.
    • Microsatellite variation reveals similar population genetic structure for two species of rockfish (Sebastes borealis and Sebastes paucispinis) with different life histories

      Matala, Andrew Paul (2002-12)
      Rockfish belong to the speciose genus Sebastes (72 species described in the Northeast Pacific). Basic biological and life history information for many rockfish species is limited. Little is known about juvenile recruitment, and identification in early life stages is difficult because the larvae of congeners look similar and often occur in spatial and temporal association. Population genetic structure is an important element for characterization of species or populations, and may provide information on productivity and life history. Eight micro satellite loci were evaluated for variability in analyses of genetic structure for two species of rockfish: the deepwater shelf rockfish bocaccio (S. paucispinis) and the demersal shortraker rockfish (S. borealis) of the continental slope. Tests of homogeneity provided evidence of similar geographically based structure in both species, which is consistent with a neighbor model of gene flow. Structure inferred from this study provides information on the sizes of the basic units of productivity, which may aid in management and conservation efforts.
    • The migration and spawning distribution of sockeye salmon within Lake Clark, Alaska

      Young, Daniel B. (2004-08)
      Recent declines in the number of sockeye salmon Onchorynchus nerka returning to Lake Clark, Alaska have caused economic hardship in the region and raised resource concerns among local subsistence users and Federal managers. A lack of information regarding the distribution of spawning habitats in the glacially turbid Lake Clark watershed instigated this research. Radio telemetry was used to 1) determine the in-lake movement patterns of adult sockeye salmon and 2) identify sockeye salmon spawning locations. Sockeye salmon were radio tagged at they entered Lake Clark and tracked to spawning locations. After entering Lake Clark, sockeye salmon usually migrated to a region of the lake that was within 15 km of their spawning location. Tagged fish migrated faster and more directly to spawning locations in tributary rivers and lakes than to Lake Clark beaches. Thirty three spawning locations were identified in the Lake Clark watershed including 18 new spawning locations compared to previous scientific research and ten compared to traditional local knowledge. Most radio tagged sockeye salmon (65%) returned to spawning locations in glacially turbid waters and most spawning locations (75%) were adjacent to privately owned lands. Proactive measures should be taken to conserve both migration corridors and spawning habitats.