• Back to the future: Pacific walrus stress response and reproductive status in a changing Arctic

      Charapata, Patrick Maron; Horstmann, Larissa; Misarti, Nicole; Wooller, Matthew (2016-08)
      The Pacific walrus (Odobenus rosmarus divergens) is an iconic Arctic marine mammal that Alaska Natives rely on as a subsistence, economic, and cultural resource. A decrease in critical sea ice habitat and uncertain population numbers have led to walruses being listed as a candidate for the Endangered Species Act. However, there is no clear understanding of how walruses might be affected by climate change. The first objective of this study was to describe how bone steroid hormone concentrations relate to commonly used blubber and serum steroid hormone concentrations (i.e., cortisol, estradiol, progesterone and testosterone), because steroid hormones have not been extracted from marine mammal bone until now. Bone, blubber, and serum were collected from individual adult walruses (n = 34) harvested by Native Alaskan subsistence hunters during 2014 and 2015. Complete turnover of cortical bone in a walrus skeleton was estimated as ~33 years, approximately the lifetime of a walrus. Results showed bone and blubber steroid hormone concentrations were similar (P = 0.96, 0.51, 0.27 for cortisol, estradiol, and progesterone (males only), respectively), but not testosterone (males and females, P = 0.003) nor progesterone in blubber of female walruses (P = 0.007). Progesterone concentrations in males were significantly correlated between bone and blubber (R² = 0.51, P < 0.001). Estradiol measured in bone had high interannual variability (P < 0.001), indicating a shorter reservoir time in cortical bone compared with other hormones in this study, possibly due to local production of estradiol in walrus bone. Overall, bone serves as a long-term reservoir of steroid hormone concentrations compared with circulating serum concentrations. Progesterone measured in blubber can be compared with bone progesterone, but local production of estradiol in bone should be taken into account when interpreting these concentrations in cortical bone. The second objective of this study was to understand the physiological resiliency of walruses to the current warming in the Arctic. Steroid hormone concentrations were measured in walrus bone collected from archaeological (n = 38, > 200 calendar years before present (BP)), historical (n =135, 200 – 20 BP), and modern (n = 47, 2014 – 2015) time periods, but were also analyzed at a finer decadal (1830s – 2010s) scale. Walrus bone cortisol concentrations measured in modern-day walruses were similar to other time periods (P = 0.38, 0.07, for archaeological and historical time periods, respectively) indicating no increase in the stress response of walruses as a result of current sea ice conditions in the Arctic. Estradiol (females only), progesterone, and testosterone were significantly negatively correlated with walrus population estimates (P = 0.008, 0.003, <0.001, respectively). A negative correlation indicates that walrus population numbers are low when reproductive hormone concentrations are high, and population numbers are high, possibly at carrying capacity, when hormone concentrations are low. Data from the current decade (2014–2015) show that the current walrus population has lower reproductive hormone concentrations compared to times of rapid population increase. These data indicate the present-day walrus population may not be increasing, but is either experiencing low calf production and / or is near its carrying capacity. Overall, these data provide walrus management with insights into the physiological resiliency of walruses in response to arctic warming, and validate bone as a valuable tissue for monitoring long-term physiological changes in the walrus population.
    • Bacteria associated with paralytic shellfish toxin-producing strains of Anabaena circinalis

      Raudonis, Renee Alaine (2007-12)
      Paralytic shellfish toxins (PSTs) are produced by dinoflagellates and cyanobacteria. There is growing evidence that bacteria associated with dinoflagellates play a role in the production of PSTs, however, no studies have examined the type of bacteria associated with toxic cyanobacteria or the role these bacteria could play in PST-production or metabolism. Further, there are no known axenic cultures of PST-producing cyanobacteria, suggesting that cyanobacteria are dependent on one or more bacteria for growth/survival. The research reported here examined the bacterial community associated with six Australian freshwater cyanobacterial strains of Anabaena circinalis obtained from the CSIRO, three toxic and three non-toxic. The goal was to identify bacteria that could be essential for cyanobacterial growth/survival and/or PST production/metabolism. Confirmation of cyanobacterial species identification was confirmed by molecular techniques; one species was found to be more closely related to Anabaena flos-aquae. PST-production by the three toxic strains was confirmed using HPLC. Bacterial communities associated with the cyanobacteria were dominated by the [alpha]-Proteobacteria, of which the Rhizobiales group was dominant. Two bacterial ribotypes were associated with only the toxic cyanobacteria, and could be important in PST-remineralization.
    • Balancing life: perceptions and practices of health among young adult Yup'ik women

      Ebsen, Cecilie R.; Plattet, Patrick; Schweitzer, Peter; Rasmus, Stacey (2014-08)
      Ten years ago CANHR (Center for Alaska Native Health Research) asked Yup'ik men and women of all ages how they would define health and wellness; that is, what it means to be well and happy. The answers were largely centered on living a subsistence lifestyle, eating subsistence foods and respecting natural spirits and lands. Today a new generation of young Yup'ik women has emerged. A generation that has grown up in villages and cities with storebought food available next to subsistence food, TV, and Internet. In this study young adult Yup'ik women's perceptions of health and their use of dancing as a practice of health are investigated. This study looks at how this new generation of young adult Yup'ik women understand health. Young adult Yup'ik women's perceptions and practices of health, such as dancing, are examined to determine what these women consider important to stay healthy and how the notion of health itself can be understood. Ideas of what it means to the subjects comprising the study population to be healthy are crucial to understand before conducting any kind of health research. How people interpret, navigate and understand the very notion of health must be uncovered in order to work with them on any and all health issues. As such the notion of health cannot and should not be conceptionalized as the mere presence or absence of disease but includes instead a wide network of social, spiritual, physical, mental, and emotional factors. Consequently, this study approaches health from a holistic perspective implementing a wide network of factors in the investigation of young, adult, Yup'ik women's perceptions and practices of health.
    • Bald eagle (Haliaeetus leucocephalus alaskanus) nesting related to forestry in southeastern Alaska

      Corr, Patrick O. (1974-05)
      There were 136 nests located by aerial survey along 225 miles of beach in six logged plots and six virgin plots. Nest densities during the three years were 0.20, 0.23, and 0.20 active nests per beach mile. Islets present within 2 miles of a logged main shore provided nesting territories for eagles not able to find suitable nest sites along the logged shore. Spatial distribution of active nests indicated a 1.25 mile territory radius per nesting pair. Statistical comparison (Mann and Whitney U test) of mean territory size found in logged versus virgin plots showed no significant difference in territory size between the two plot types. Nests located in beach fringe timber remaining after harvesting were utilized frequently because of the lack of alternate nest sites in the immediate vicinity; these nest sites were highly susceptible to wind throw. Storm damage resulted in the loss of 20 per cent of the known nests during winter 1968-1969. It is recommended that buffer zones (10 chain radius - 660 feet) around eagle nests be maintained during harvesting, and that logging activity in the vicinity of nesting eagles be curtailed during April and May. Also, smaller, scattered timber sales should be promoted to ensure that extensive beach strip logging does not remove potential nest sites along miles of shoreline.
    • Barents Sea hydrographic variability (1975-1991)

      Zimmermann, Sarah Lukens (2003-12)
      Barents Sea temperature and salinity anomalies and their connection to the Arctic Oscillation (AO) are analyzed using a 16-year time-series of hydrographic data (1975-1991). Seasonal and inter-annual variations are investigated along two sections spanning the meridional and zonal length of the Barents Sea over two depth layers, 0 to 50m and 50 to 200m. Depending on location, mean seasonal differences in the deeper layer are as large as 3°C in temperature and 0.2 in salinity, whereas the upper layer differences are 6°C and 1.4. Inter-annual anomalies are 0.6°C and 0.07 in the deeper layer and 0.8⁰C and 1.2 in the upper layer. Temperature and salinity anomalies' leading EOFs explain 49% and 34% of the total variance, and are in-phase from 1975-1985 but out-of-phase for 1985-1991. Examination of the surface heat-flux suggests the temperature anomaly is advective before 1985 and locally formed after 1985. This is supported by the temperature anomaly's changing propagation pattern through the Barents Sea after 1985. The salinity anomaly's source appears to be advective throughout the period. The AO correlates with the temperature EOF suggesting the AO's influence on the temperature anomaly is stronger over the Norwegian Sea before 1985 and stronger over the Barents Sea after 1985.
    • A Bark Thickness Model for White Spruce in Alaska Northern Forests

      Malone, Thomas; Liang, Jingjing (Department of Forest Sciences, University of Alaska Fairbanks, 2009)
      Here we developed a simple linear model to estimate white spruce bark thickness in the northern forests of Alaska. Data were collected from six areas throughout interior and southcentral Alaska. Geographic variation of bark thickness was tested between the Alaska statewide model and for each geographic area. The results show that the Alaska statewide model is accurate, simple, and robust, and has no practical geographic variation over the six areas. The model provides accurate estimates of the bark thickness for white spruce trees in Alaska for a wide array of future studies, and it is in demand by landowners and forest managers to support their management decisions.
    • Barley Production in the Delta-Clearwater Area of Interior Alaska

      Lewis, Carol E.; Wooding, Frank J. (School of Agriculture and Land Resources Management, Agricultural and Forestry Experiment Station, 1978-04)
      When oil from Prudhoe Bay on the northern coast of Alaska began to flow in the fall of 1977, it marked the beginning of another flow of perhaps equal significance. Eighty per cent of the revenue received by the State of Alaska in the foreseeable future will come from the oil industry. This prompts concern that long-term growth of the Alaskan economy is based on revenue from a single nonrenewable resource. Historically, nonrenewable resources have exhibited a boom-bust development pattern. Diversifying the economy of the state could contribute to economic stability. Of particular interest, when the development of renewable resources is considered, is the potential for agriculture. A half century ago, the Tanana Valley in interior Alaska produced a higher per-capita quantity of agricultural products for Fairbanks consumers than it does today. Now, more than 95 per cent of the food consumed in the area is imported from areas outside the state. Additionally, there is a growing worldwide concern abut increasing populations and the need for increased food production. This has created a new awareness of agriculture in Alaska as well as across the nation.
    • Barriers To Ahtna Athabascans Becoming Public School Educators

      Johnson, Michael A.; Jacobsen, Gary; Barnhardt, Ray; Elliott, James W.; Richey, Jean A. (2012)
      Using a mixed-method phenomenological approach, this cross-cultural study utilizes a non-formalized survey and interviews. Data was gathered and presented in a manner consistent with Ahtna cultural norms and values. Survey data set was analyzed by statistical description. Interview transcripts were analyzed thematically through axial coding. The review of literature and data gathered from Ahtna Athabascan participants identified barriers common to other minorities groups evidenced in Ahtna-specific ways. Through a thematic analysis, the data showed barriers, consequences, benefits, and solutions to Ahtna Athabascans becoming public school educators. Through this study, Ahtna Athabascans expressed an overwhelming desire to see more Ahtna Athabascans teachers in public schools. Among the policy and practical implications identified in the study are the need to improve the quality of K-12 educational experiences for Ahtna youth and improved guidance counseling services. The analysis of the data set provides pathways for future Ahtna-specific research and Ahtna-specific solutions for increasing the number of Ahtna Athabascan teachers in local public schools.
    • Barriers to graduation: an examination of first-generation college students

      Smith, Sarah M. (2012-08)
      The college experience of first- generation college students is unique in comparison to their peers. Many students do not have the support from their family and require help in the navigation of college life. Student Support Services, a federally funded TRIO program helps students successfully graduate with a bachelor's degree. Qualitative interviews were conducted on ten undergraduate students at UAF who were labeled as first-generation college students. All ten students were active participants in Student Support Services at the University of Alaska Fairbanks during the time of the interview. A thematic analysis produced six emergent themes. It was found that students utilized communicative strategies based on Orbe's co-cultural communication theory. First-generation college students, a non-dominant part of society, tried to negotiate through the University system, the dominant section of society. Through this negotiation, a co-cultural group was formed.
    • Basal shear strength inversions for ice sheets with an application to Jakobshavn Isbræ, Greenland

      Habermann, Marijke; Truffer, Martin; Maxwell, David; Freymueller, Jeff; Pettit, Erin; Tape, Carl (2013-12)
      Satellite and in situ observations of ice sheet outlet glaciers around the turn of the 21st century showed that rapid changes in ice dynamics are possible and important for the evolution of ice sheets. When attempting to model these dynamic changes the conditions at the ice-bed interface are crucial. Inverse methods can be used to infer basal properties, such as the basal yield stress, from abundant surface velocity observations by using a physical model of ice flow. Inverse methods are very powerful, but they need to be applied with care, otherwise errors can dominate the solution. In this study we investigate the potentials and caveats of inverse methods. Synthetic experiments can be designed where basal conditions are assumed and an ice flow model is used to produce a set of 'synthetic' surface velocities. These can then be used to examine and evaluate inverse methods. We find that in iterative inverse methods it is essential to use a stopping criterion that will prevent overfitting the data. We introduce a new and rapidly-converging iterative inverse method called Incomplete Gauss Newton method, where the linearized problem is partly minimized in each step.In a practical application of inverse methods to the terminus region of Jakobshavn Isbræ, Greenland we investigate changes in basal conditions over time by performing inversions for different years of available surface velocity data. We find a decrease in basal yield stress in the lower areas of the glacier that agrees with effective pressure changes due to the changes in ice geometry. This supports an ocean and terminus driven system. The difference between the modeled and observed velocity fields, called residual, contains information about the ability to reproduce the velocities when only adjustment of the basal condition is allowed. With a properly regularized inversion the residual patterns can be used to investigate sources of error in the system. We find that the ice geometry and the model simplifications influence the ability to reproduce observed velocity fields more than the error in observed velocity does. This indicates that further progress must come from model improvements and improved capabilities to measure bedrock geometry.
    • Baseline data of bird populations in the Sierra Gorda Biosphere Reserve, Mexico: a citizen science approach

      Anderson, Teresa S.; Fix, Peter J.; Carsten-Conner, Laura D.; Dalle-Molle, Lois K. (2017-12)
      This project tested the viability of converting a local environmental education group, "Eco Chavos" into a team of citizen scientists. In rural biosphere reserves in Mexico, with few resources and large resident populations, community-based biological inventory and monitoring has the potential to increase the impact of Mexican biosphere reserves by generating scientific information and engaging local residents in hands-on environmental education. To test this, I formed a citizen science birding group and trained them in bird identification, survey techniques, data collection, and data management. The project began in January 2016 and in December 2016 I stopped mentoring the program and let it continue under its own leadership. Our team was composed of an Eco Chavos group and a resident ornithologist who conducted land and water-based surveys multiple times a month. As of August 2017, 160 bird species have been registered, including three species endemic to Mexico; the Crimson-collared Grosbeak (Rhodothraupis celaeno), Blue Mockingbird (Melanotis caerulescens), and Spotted Wren (Campylorhynchus gularis). The survey provided an inventory of bird diversity in the reservoir, and could serve as a starting point to measure occurrence and abundance over time. The data were published in the updated management plan of the Sierra Gorda Biosphere Reserve as well as in a new bird book, Guía de Aves de la Presa Jalpan. A new community group, "Aves de la Presa Jalpan" was formed and contributed information via an online public database. The database may be used by the international network of bird monitors to analyze population trends in both local Mexican bird populations and in international bird migrations. In addition, participants showed increased bird identification skills, leadership, increased interest in birds, and engagement in project tasks and planning. Infrastructure was built to encourage birdwatching tourism in the Biosphere Reserve and the foundation was set to continue this research in the future.
    • Baseline geochemical studies for resource evaluation of D-2 Lands - geophysical and geochemical investigations at the Red Dog and Drenchwater Creek mineral occurrences

      Metz, P.A., Robinson, M.S., and Lueck, L. (University of Alaska Mineral Industry Research Laboratory, 1979)
      Major zinc, lead and barite mineralization has been discovered at Red Dog and Drenchwater Creeks in the DeLong Mountains of north-western Alaska. The host rocks for the mineral occurrences are carbonates, cherts, shales, and dacitic volcanic rocks of the Mississippian Lisburne Group. The host rocks are deformed in a narrow belt of imbricate thrust sheets that extend from the Canadian border to the Chukchi Sea. The rocks strike generally east-west and dip to the south. The sulfide minerals occur as stratiform mineralization parallel to bedding planes, as breccia fillings and vein replacements, and as disseminations in the various host rocks. The primary ore minerals are sphalerite, pyrite, pyrrhotite, and galena. Barite occurs as massive beds up to 90 meters (300 feet) thick at Red Dog Creek and as nodules, veinlets, and disseminations at Drenchwater Creek. Close spaced soil sampling, mercury vapor sampling, and magnetic and radiometric surveys were conducted over the areas of exposed sulfide mineralization to test the response of these techniques to these types of deposits in northern Alaska. There is potential for additional deposits of this type in the Lisburne Group of the entire northern Brooks Range. These techniques provide a rapid low cost method for the discovery and preliminary evaluation of these types of mineral occurrences in northern Alaska.
    • Basic Science Poster Design: A Short Guide

      Agricultural and Forestry Experiment Station, School of Natural Resources and Agricultural Sciences, University of Alaska Fairbanks, 2004
    • Bathymetric and spatial distribution of echinoderms on seamounts in the Gulf of Alaska

      Underwood, Danielle Parker (2006-12)
      The bathymetric and spatial distribution of echinoderms was examined on five seamounts in the Kodiak-Bowie seamount chain in the northern Gulf of Alaska from video transects of 200 or 500 m length, conducted at approximately 700, 1700 and 2700 m depths with the DSV Alvin in August, 2004. Temperature and salinity varied significantly with depth, but not between seamounts; an oxygen minimum zone encompassed the shallowest depth sampled. Holothuroid (Pannychia and Psolus) and asteroid density for the shallower depth category was 19.94·100 m⁻² and 2.07·100 m⁻², significantly higher than at the deeper depths. Asteroid density generally decreased northwesterly along the seamount chain. Density of three ophiuroid genera (Asteronyx, Amphigyptis, and Ophiomoeris) was 139.6·100 m⁻² on Dickens Seamount, and was significantly less on the other three seamounts to a low of 31.19·100 m⁻² on Pratt Seamount. Ophiuroid density was significantly higher at the intermediate depth (141.07·100 m⁻²), and lower at the other two depths. Density of Pentametrocrinus and Guillecrinus crinoids was not significantly affected by seamount or depth, but was highest (3.15·100 mm⁻²) at the deepest depths. No echinoids were found on transects, but were observed on three of the seamounts. Many brittle stars and asteroids were found associated with paragorgid and primnoid corals.
    • Bathymetry of Alaskan arctic lakes: a key to resource inventory with remote-sensing methods

      Mellor, Jack C. (1982-05)
      Water depth is a major factor in predicting resources associated with tens-of-thousands of uninventoried Alaskan arctic lakes. Lakes were studied for physical, chemical, and biological resources related to water depth in 3 specific areas along a north/south transect extending from Pt. Barrow on the Arctic Ocean to the foothills of the Brooks Range. Side-Looking Airborne Radar (SLAR) imagery was acquired over the same study transect to investigate its application for determining lake depth. Ice thicknesses, necessary for the interpretation of depth contours from SLAR imagery, were measured along with other parameters in the study lakes throughout the winter 1978-79. This ice-thickness data and sequential SLAR images are used to illustrate a method of contouring water depths in arctic lakes. This is based on changes in intensity of SLAR signal return which define the zone at which ice cover contacts the bottom. This intensity is a function of physical and dielectric properties of the snow, ice, water, bottom substrates, and ice inclusions within these lakes. A computer program was developed to manipulate Landsat satellite digital data and compile a master file of lakes and their computer-calculated surface features (i.e. area, perimeter, crenulation, and centroid). The master file uniquely identifies each computer catalogued lake by latitude and longitude and stores the calculated features in a data base that can be retrieved for a specified geographic ABSTRACT area. Each lake record also provides storage space for resource data collected outside the computer generated data. The application of these remote-sensing tools and the knowledge of aquatic resources associated with bathymetry add to our ability for regional inventory, classification, and management of arctic lake resources.
    • Bayesian methods in glaciology

      Brinkerhoff, Douglas; Truffer, Martin; Aschwanden, Andy; Tape, Carl; Bueler, Ed (2017-12)
      The problem of inferring the value of unobservable model parameters given a set of observations is ubiquitous in glaciology, as are large measurement errors. Bayes' theorem provides a unified framework for addressing such problems in a rigorous and robust way through Monte Carlo sampling of posterior distributions, which provides not only the optimal solution for a given inverse problem, but also the uncertainty. We apply these methods to three glaciological problems. First, we use Markov Chain Monte Carlo sampling to infer the importance of different glacier hydrological processes from observations of terminus water flux and surface speed. We find that the opening of sub-glacial cavities due to sliding over asperities at the glacier bed is of a similar magnitude to the opening of channels due to turbulent melt during periods of large input flux, but also that the processes of turbulent melting is the greatest source of uncertainty in hydrological modelling. Storage of water in both englacial void spaces and exchange of water between the englacial and subglacial systems are both necessary to explain observations. We next use Markov Chain Monte Carlo sampling to determine distributed glacier thickness from dense observations of surface velocity and mass balance coupled with sparse direct observations of thickness. These three variables are related through the principle of mass conservation. We develop a new framework for modelling observational uncertainty, then apply the method to three test cases. We find a strong relationship between measurement uncertainty, measurement spacing, and the resulting uncertainty in thickness estimates. We also find that in order to minimize uncertainty, measurement spacing should be 1-2 times the characteristic length scale of variations in subglacial topography. Finally, we apply the method of particle filtering to compute robust estimates of ice surface velocity and uncertainty from oblique time-lapse photos for the rapidly retreating Columbia Glacier. The resulting velocity fields, when averaged over suitable time scales, agree well with velocity measurements derived from satellites. At higher temporal resolution, our results suggest that seasonal evolution of the subglacial drainage system is responsible for observed changes in ice velocity at seasonal scales, and that this changing configuration produces varying degrees of glacier flow sensitivity to changes in external water input.
    • Bayesian predictive process models for historical precipitation data of Alaska and southwestern Canada

      Vanney, Peter; Short, Margaret; Goddard, Scott; Barry, Ronald (2016-05)
      In this paper we apply hierarchical Bayesian predictive process models to historical precipitation data using the spBayes R package. Classical and hierarchical Bayesian techniques for spatial analysis and modeling require large matrix inversions and decompositions, which can take prohibitive amounts of time to run (n observations take time on the order of n3). Bayesian predictive process models have the same spatial framework as hierarchical Bayesian models but fit a subset of points (called knots) to the sample which allows for large scale dimension reduction and results in much smaller matrix inversions and faster computing times. These computationally less expensive models allow average desktop computers to analyze spatially related datasets in excess of 20,000 observations in an acceptable amount of time.
    • Beach ridge geomorphology of Kotzebue Sound: Implications for paleoclimatology and archaeology

      Mason, Owen Kenneth (1990)
      Beach ridges occur on all continents and record the horizontal addition of shoreface beyond the reach of storms. Improved cartographic methods in the nineteenth century allowed British historians to link shoreline changes with abandoned villages. This scientific trajectory was paralleled in the Bering Strait region from the 1880's to the 1930's. In the 1950's J. L. Giddings formalized "beach ridge archaeology" as a survey strategem using relative position to infer relative cultural chronology in northwest Alaska. Modern researchers use archaeological dates and data to document past climates or environments. At Cape Espenberg, on Seward Peninsula, my use of archaeological, stratigraphic, pedological, granulometric and photogrammetric data allows the delineation of 4000 years of coastal evolution. Four chronostratigraphic units are distinguished, using archaeological dates as minimum age assignments. Dune ridges formed in discrete intervals: 3300 to 2000 BP and from 1200 BP to the present; while low, berm ridges are predominant 4000-3300 and from 2000-1200 BP. The two different types of ridges correspond to variable climatic conditions: dune ridges formed after higher storm surges and winter winds while the lower berm ridges are related to less intense storm surges. Coastal dunes at Cape Espenberg are soon altered by plant succession processes with distance from the beach. As primary dunes are eroded, a complex blowout topography results. Erosional processes in blowouts were monitored during 1987-1989, revealing substantial vertical changes, up to 10 cm of erosion per yr. These rapid changes have considerable influence on archaeological site stability. Studies of the gravel ridge systems confirm the proxy storm record apparent in the coastal dunes atop the beach ridges on the Seward Peninsula. The geoarchaeological methodology allows correlations between depositional units within nine of the principal beach ridge and chenier complexes of northwest Alaska. The onset of deposition was at 4000-3500 BP. The complexes at Cape Espenberg and Choris Peninsula contain elevated, broader transgressive ridge sets 3300-2000 BP and from 1100-200 BP, connected with increased storm activity in the North Pacific. Erosional disconformities between successive sets of beach ridges occur at Cape Krusenstern at ca. 3000 BP and before 2000 BP. Between 2000-1000 BP extensive progradation occurred at nearly all complexes, indicating that less stormy conditions predominated.
    • Beaver population ecology in interior Alaska

      Boyce, Mark S. (1974-05)
      The ecology of beaver (Castor canadensis Kuhl) populations along two streams in interior Alaska was studied in 1972 and 1973. The two study areas were similar in most respects, except for the history of human trapping intensity. The heavily trapped population exhibited the following contrasts to the essentially unexploited population: (1) higher mortality among adult age classes, (2) higher survivorship of the prereproductives, (3) a sex ratio with a preponderance of females, (4) decreased age at first breeding and consequently, (5) a smaller average size at maturity. Males appear to expend lower effort for parental activities than do females, and consequently exhibit higher survivorship than their mates. Population regulating mechanisms, management implications, and the evolution of an optimal life history strategy are discussed. The distribution and abundance of beaver colonies were related to habitat types and characteristics of the physical environment by multiple linear regression analysis.