Now showing items 2167-2186 of 3496

• #### Pacific herring juvenile winter survival and recruitment in Prince William Sound

Small pelagic fish abundances can vary widely over space and time making them difficult to forecast, partially due to large changes in the number of individuals that annually recruit to the spawning population. Recruitment fluctuations are largely driven by variable early life stage survival, particularly through the first winter for cold temperate fishes. Winter survival may be influenced by juvenile fish size, energy stores, and other factors that are often poorly documented, which may hamper understanding recruitment processes for economically and ecologically important marine species. The goal of this research was to improve understanding of recruitment of Pacific herring (Clupea pallasii) within Prince William Sound (PWS) through recruitment modeling and by identifying factors influencing winter survival of young-of-the-year (YOY) herring. Towards this end, my dissertation addresses three specific objectives: 1) incorporate oceanographic and biological variables into a herring recruitment model, 2) describe patterns in growth and condition of PWS YOY herring and their relationship to winter mortality risks, and 3) compare the growth, condition, swimming performance, and mortality of YOY herring that experience different winter feeding levels. In the recruitment modeling study, annual mean numbers of PWS herring recruits-per-spawner were positively correlated with YOY walleye pollock (Gadus chalcogrammus) abundance in the Gulf of Alaska, hence including a YOY pollock index within a standard Ricker model improved herring recruitment estimates. Synchrony of juvenile herring and pollock survival persisted through the three-decade study period, including the herring stock collapse in the early 1990s. While the specific mechanism determining survival is speculative, size-based tradeoffs in growth and energy storage in PWS YOY herring indicated herring must reach a critical size before winter, presumably to reduce size-dependent predation. Large herring switched from growth to storing energy, and ate more high-quality euphausiid prey, which would delay the depletion of lipid stores that compelled lean herring to forage. Lipid stores were highest in the coldest year of the seven-year field study, rather than the year with the best diets. With diets controlled in a laboratory setting, spring re-feeding following restricted winter diets promoted maintenance of size and swimming ability, but had little effect on mortality rates compared to fish continued on restricted rations. Declines in gut mass, even among fully fed herring, and low growth potential suggest limited benefits to winter feeding. Mortalities due to food restriction compounded by disease were highest among herring that fasted through winter months, and among small herring regardless of feeding level. Taken together, these findings illustrate the importance of achieving a critical size and high lipid stores in the critical period before winter to promote YOY herring winter survival and ultimately recruitment.
• #### Pacific sleeper sharks in the Northeast Pacific Ocean: relative abundance, plausible incidental exploitation rates, trophic ecology, and habitat use

Pacific sleeper shark relative abundance indices in the eastern Bering Sea and Gulf of Alaska were developed from sablefish longline surveys and the sustainability of a plausible range in Pacific sleeper shark incidental exploitation rates in the Gulf of Alaska was evaluated with a risk analysis using Monte Carlo simulation for use in fisheries management. A significant increase in Pacific sleeper shark relative abundance was identified in the Gulf of Alaska during the years 1989-2003. The aggregate risk of ending in an overfished condition in the Gulf of Alaska increased from 0% under a low exploitation rate scenario to 59% under a high exploitation rate scenario. Baseline information about Pacific sleeper shark trophic ecology and habitat utilization in the eastern Bering Sea and Gulf of Alaska was developed for use in ecosystem-based fishery management. Analysis of stable isotope ratios of nitrogen (δ¹⁵N) and lipid normalized carbon (δ¹³C′) identified significant geographic and ontogenetic variability in the trophic ecology of Pacific sleeper sharks in the eastern Bering Sea and Gulf of Alaska and revealed wider variability in the feeding ecology of Pacific sleeper sharks than previously obtained from diet data based on stomach contents alone. Time series analysis of Pacific sleeper shark electronic tag data from the Gulf of Alaska identified a simple autoregressive relationship governing short-term movements (hours) throughout the time series which included substantial variation in longer time period movement patterns (months) and demonstrated that statistical inference about habitat utilization could be drawn from simultaneous analysis of an entire time series depth profile (six months of data) stored on an electronic archival tag.
• #### Pacific walrus use of higher trophic level prey and the relation to sea ice extent, body condition, and trichinellosis

The changing Arctic ecosystem may prompt Pacific walruses (Odobenus rosmarus divergens) to change their usual diet of lower trophic level prey (e.g., benthic invertebrates) by increasing the consumption of higher trophic level prey (HTLP). Prey-switching may have consequences to walrus populations through increased energetic costs, increased stress response, declines in body condition, and exposure to diseases, including the zoonotic parasite Trichinella spp. Trichinella is possibly transmitted to walruses via predation or scavenging on seals. The goal of this study was to quantify reliance on HTLP using stable carbon and nitrogen isotope ratios, and assess potential correlations among consumption of HTLP and sea ice extent, sex, Trichinella infection, body lipid stores, and cortisol concentrations used as an index of the stress response. Walrus diet is comprised of ~1-22% HTLP and reliance on HTLP may be correlated with sea ice extent in a complex way. Trichinella was present in ringed seal (Pusa hispida, 1/57), Arctic fox (Vulpes lagopus, 3-7/32), and polar bear (Ursus maritimus, 1/1), but was not detected in walruses (0/137) regardless of %HTLP in the diet. Walrus blubber and attached skin contained 44.6 ±12.4% lipid wet weight, which was lower than that found for other Arctic marine mammals; however, the inclusion of skin likely decreased our %lipid values. While the absolute value of %lipid from blubber and attached skin was not a suitable substitute for %lipid from blubber only, we were still able to detect the influence of biological factors, with sex-linked variability in walrus lipid stores observed. Cortisol analysis from full-thickness blubber resulted in a wide range of concentrations (2.77 to 34.04 ng/g), but showed that this stress hormone can be extracted from blubber. While neither %lipid nor blubber cortisol was correlated with the proportion of HTLP in walrus diet, they may serve as minimally-invasive methods for health monitoring of walruses. Overall, dietary plasticity of walruses is robust and switching to HTLP is not likely to have immediate adverse effects on the Pacific walrus population.

• #### Paleobiology of ichthyosaurs: using osteohistology to test hypotheses of growth rates and metabolism in a clade of secondarily aquatic marine tetrapods

Ichthyosaurians (Ichthyosauria) are one of the most prominent groups of secondarily aquatic Mesozoic marine reptiles. Over their 160 million years of evolution, the clade evolved a streamlined body plan with paddle-like limbs, convergent with modern cetaceans. Despite the fact that ichthyosaurians have been studied by paleontologists for over a century, very little is known about aspects of their biology, including quantification of their age structure and growth rates. Multiple lines of evidence, including oxygen isotope, swimming modality, and body shape analyses suggest that ichthyosaurians experienced elevated growth rates and likely maintained an elevated body temperature relative to ambient sea water. In this dissertation, I test these hypotheses using osteohistological methods. In the first manuscript, we describe new material of the small-bodied Upper Triassic ichthyosaurian Toretocnemus from the Nehenta Formation and the Hound Island Volcanics (both Norian, Upper Triassic) of Southeast Alaska. During the Upper Triassic, ichthyosaurians experienced their greatest size disparity, with large-bodied species rivaling the size of modern blue whales (Balaenoptera musculus; 20+ m body length) living alongside small-bodied species (1 m body length) like Toretocnemus. Prior to this study, Toretocnemus was known from Carnian deposits of California and possibly Sonora, Mexico. The referred material described here expands its geographic and temporal range. There are very few known ichthyosaurians from the Norian; thus, this material sheds light on the clade's diversity before the end Triassic extinction event. In the second and third manuscripts, we use osteohistological methods to describe the microstructure of various skeletal elements of two species of Stenopterygius from the Posidonia Shale (Lower Jurassic) of Germany. The Posidonia Shale is a Konservat-Lagerstätten that preserves over 3000 ichthyosaurian specimens, approximately 80 percent of which are referable to Stenopterygius. First, we sampled over 40 skeletal elements from one individual specimen referred to Stenopterygius quadriscissus to 1) describe the mineralized tissues across the skeleton, 2) infer relative growth rate, and 3) identify elements with growth marks. Almost all elements described demonstrate fibrolamellar primary bone, indicative of a rapid growth rate. We also identify growth marks in several elements, including the dentary and premaxilla, that will be used in future growth studies. In the third manuscript, we sample a scleral ossicle from Stenopterygius triscissus to describe its microstructure and investigate the use of ossicles for skeletochronology. The use of scleral ossicles for determining age structure has been documented in extant sea turtles as well as dinosaurs. We sectioned one ossicle in three planes and document conspicuous growth banding in the short axis section. Although this method requires further testing, we tentatively determine a minimum age of 7 years at the time of death for this individual. This dissertation lays critical groundwork for future studies of the paleobiology of ichthyosaurians. We are already in the preliminary stages of using these results to 1) quantify age structure and growth rates of an ichthyosaurian (Stenopterygius quadriscissus) for the first time, and 2) test the use of scleral ossicles for skeletochronology of ichthyosaurians. Through addressing these basic aspects of ichthyosaurian biology, we can begin to investigate how ichthyosaurian development and physiology changed over time and space and develop a greater understanding of this clade's 160 million years of evolution.
• #### Paleoceanographic shifts in the Gulf of Alaska over the past 2000 years: A Multi-proxy perspective

The Gulf of Alaska (GOA) is a dynamic region influenced by climate variability on time scales ranging from days to millennia. Recent regime shifts suggest interdecadal GOA primary productivity patterns, yet it is unclear whether such fluctuations extend beyond the instrumental record. This thesis examined the nature of prevalent climatic and oceanographic patterns before the twentieth century using several marine sediment core proxies for paleoproductivity and paleoceanography. Sediment cores were from two locations: Bay of Pillars, Kuiu Island, in southeast Alaska (56.63 ̊N, 134.35 ̊W), and a central midshelf location (GAK4) along the Global Ecosystem Dynamics (GLOBEC) Seward Line (59.25 ̊N, 148.82 ̊ W). Proxy data from these cores include: percentages of organic carbon, nitrogen and biogenic opal; organic carbon-to-nitrogen ratios; stable isotope ratios from sediment organic matter (δ13C and δ15N) and foraminifera tests (δ13C and δ18O); and foraminifera faunal analysis. Bay of Pillars proxy data suggest that the onset of the Little Ice Age (LIA) ca. 1200 AD coincides with pulses of decreased salinity and increased productivity. GAK4 proxy data indicate increased productivity and decreased terrestrial input over the past century; as well as fresher surface water was during the latter portion of the LIA (1716 – 1894) and positive Pacific Decadal Oscillation phases.
• #### Paleoclimate and paleoenvironment of the Prince Creek and Cantwell formations, Alaska: terrestrial evidence of middle Maastrichtian greenhouse event

I studied the paleoclimate and paleoenvironmental conditions of the Prince Creek Formation, North Slope Alaska, and the lower Cantwell Formation in Denali National Park, Alaska. I used data from pollen analysis, clay mineral analysis and stable isotope analysis of clay minerals and organic matter applied to paleosols of the Prince Creek Formation. In the lower Cantwell Formation, I reconstructed the sedimentary environment, produced a terrestrial carbon stable isotope record and obtained a ~ 69.5 Ma radiometric age for the lower Cantwell Formation. Clay analysis in the Prince Creek Formation indicates that the genesis of the paleosols was strongly influenced by the properties of the parent material and that an epiclastic bentonitic source contributed to the development of non-allophanic properties which suggests the presence of Andept-like paleosols. Paleosols formed on the floodplains of the Prince Creek Formation reveal features attributed to wet-dry cycles as a result of seasonal flooding, perhaps due to snow melt in the ancestral Brooks Range. Carbon and oxygen isotope analyses, and the geochemistry of paleosol Bw/Bt horizons indicate mean annual precipitation values between 745.56 and 1426.88 ±221.38 mm/yr and mean annual temperatures of 12 ±4.4 °C. The meteoric water δ¹⁸O value calculated from smectite at a 6.3 °C mean annual temperature is ~-24 ⁰/₀₀. The calculated value is δ¹⁸O-depleted as is expected for high latitudes during the Late Cretaceous. Sedimentary facies analysis suggests that The East Fork measured section of the lower Cantwell Formation was likely deposited in the distal part of an alluvial fan. A new U-Pb age of 69.5 ±0.7 Ma from bentonites and carbon isotope values of bulk sedimentary organic matter and wood fragments indicates that a greenhouse event, known as the mid-Maastrichtian Event (MME), is recorded at the East Fork of the Toklat River Section. A mean annual precipitation value of ~ 517.92 ±134.44 mm/yr was obtained from δ¹⁸O terrestrial organic matter. The coeval nature of the lower Cantwell Formation (~69.5 Ma) and the Prince Creek Formation (~69.2 Ma) suggests that the MME likely affected the Prince Creek Formation as well. In the Prince Creek Formation, the age, precipitation, temperature and meteoric water composition from bentonite smectites are consistent with increased precipitation due to an intensified paleo-arctic hydrological cycle, which may have been the result of increased latent heat transport during the mid-Maastrichtian greenhouse episode.
• #### Paleoecology and ecomorphology of the giant short-faced bear in Eastern Beringia

The short-faced bear (Arctodus simus) was a widespread Tremarctine bear indigenous to North America until its extinction around 11,500 BP. Arctodus inhabited Pleistocene ice-free refugia in Eastern Beringia (the northwestern limit of its range) until at least 20,000 BP. Because of its gracile, long-legged build and extremely large size, most paleontologists believe this bear was a high-speed pursuit predator which had preyed on the largest herbivores of Pleistocene North America. Alternatively, energetic arguments have been used to suggest that Arctodus was too large to be carnivorous and evolved its large size within an herbivorous or omnivorous niche. To test these competing hypotheses, I reconstructed aspects of Arctodus' trophic position and paleodiet by analyzing stable isotope ratios ($\delta\ \sp{13}$C and $\delta\ \sp{15}$N) in bone collagen extracted from east Beringian fossils. Other bears and carnivores from Beringia were analyzed to help interpret the results. Isotopes reveal that Arctodus was highly carnivorous, it fed on herbivores which consumed C3 vegetation, and it did not eat salmon. The herbivore/omnivore hypothesis is thus rejected. Predatory hypotheses predict that we should find certain morphological features in a predatory bear which would enhance one or more of the following skills: top running speed, acceleration, or maneuverability at high speeds. I re-analyzed the postcranial morphology of Arctodus and used data on running speed and bone strength in other large mammals to show that a bear the size of Arctodus with long, gracile limbs would not have been able to endure the extreme dynamic forces incurred during predatory activities. Instead, Arctodus' morphology and body size indicate it had evolved to maximize locomotor efficiency using a pacing gait. I suggest that Arctodus evolved as a specialized scavenger adapted to cover an extremely large home range in order to seek out, procure, and defend large-mammal carcasses from other carnivores. By modeling herbivore populations and their mortality, I show that enough carcass biomass was being produced in Pleistocene Beringia to make this scavenging niche energetically feasible. The model helps show that Arctodus' extinction probably is best tied to a reduction of year-round carcasses on the landscape, a condition which arose in the Holocene when the herbivore fauna became less diverse and began to experience more seasonal mortality.
• #### Paleoecology of Twin Cays: interpretation of palynological, isotopic, and stomatal proxies in a peat core from Belize

Reconstructions of Holocene climate from numerous mid- and high-latitude sites have identified millennial-scale cool and arid intervals at 8,200 and 4,200 yrs. B.P. The global nature of these events can only be established by examination of Holocene climate records from low latitude sites. The Central American island of West Twin Cays was chosen as the study location due to its thick peat deposits, which allow for the reconstruction of Holocene vegetation, sea level, and climate for the Belize coastal region. Rhizophora mangle (red mangrove) dominated the island's vegetation since its formation 8,200 cal. yrs. B.P. Alternating periods dominated by dwarf or tall R. mangle reflect changes in phosphorus and nitrogen availability. Heightened Myrsine-type pollen concentrations between 6,300 and 4,200 cal. yrs. B.P. suggests lower sea levels and drier climates. Regional warming accompanied by increased precipitation in the middle to late Holocene is recorded by an increase in exotic Pinus concentrations. These vegetation shifts correlate with regional Central American climate changes and westem Atlantic sea level shifts at 8,200 and 4,200 cal. yrs. B.P. More importantly, these data link Central American changes to worldwide climate events.
• #### Paleoenvironmental changes at treeline: a 6,500 year long pollen and stable isotope record

Combined pollen, macrofossil and stable-isotope records from two lakes in the sub-alpine zone of the north-central Alaska Range indicate significant changes in vegetation and lake productivity during the past 6̃750 ¹⁴C yrs BP. These changes are associated with neoglacial cooling and climate variations during the Little Ice-Age (LIA). Highest spruce densities occurred during a period from 5,000 ¹⁴C yrs BP and 2,500 ¹⁴C yrs BP and coincided with the onset of cooler and moister climate. The shifts in climate, which resulted in increased effective moisture levels in Central Alaska, possibly shifted the competitive balance towards spruce and against tundra taxa. Lake productivity declined as climate cooled. A brief episode of climate amelioration between 1,500 ¹⁴C yrs BP and 800 ¹⁴C yrs was followed by cooking events of the LIA which resulted in decreased spruce densities in the sub-alpine forest-tundra zone and a possible lowering in treeline at higher elevation.
• #### Paleoethnobotany in Interior Alaska

Vegetation and plant resources can impact forager mobility and subsistence strategies. However, misconceptions about the preservation of organics in subarctic archaeological contexts and underestimations of the importance of plant resources to foraging societies limit paleoethnobotanical research in high-latitude environments. This research draws upon concepts from human behavioral ecology to address questions relating to site seasonality, plant resource use, land use, and deposition and taphonomy. The model developed in this thesis outlines expectations of seasonal archaeobotanical assemblages for Late Pleistocene and Holocene sites in interior Alaska. I consider these expectations in light of plant macroremains found in anthropogenic features from Components 1 and 3 (approximately 13,300 and 11,500 cal yr BP, respectively) at the Upward Sun River site, located in central Alaska. Site-specific methods include bulk sampling of feature matrix in the field and wet-sieving matrix in the laboratory to collect organic remains. Analytical measures of density, diversity, and ubiquity tie together the model expectations and the results from Upward Sun River. The dominance of common bearberry in the Component 1 archaeobotanical assemblage meets the expectations of a late summer or fall occupation. This suggests that site occupants may have focused on mitigating the risk of starvation in winter months by foraging for seasonally predictable and storable resources. The variability in results from the Component 3 features could relate to longer-term occupations that extended from mid-summer to early fall, in which site occupants foraged for locally available and predictable plant resources such as blueberry or low-bush cranberry species. In this thesis, I argue that large mammal resources were a key component in Late Pleistocene and Holocene subsistence strategies. However, foragers were flexible in their behavior and also targeted small mammals, fish, waterfowl, and plant resources in response to environmental conditions and cultural preferences. The results illustrate the long-standing use of culturally and economically important plant resources in interior Alaska and draw attention to aspects of human behavior that are under-conceptualized in northern archaeology, such as the gender division of labor, domestic behavior, and potential impacts of plant resource exploitation on mobility and land use.
• #### Paleohydrology of a catastrophic flood release from Okmok caldera and post-flood eruption history at Okmok Volcano, Umnak Island, Alaska

Okmok caldera, located on the northeastern end of Umnak Island, Alaska, contained a 5.8 x 10⁹m³ lake that catastrophically drained as a result of failure of the 2050 yr. B.P. caldera rim between 1560 and 1010 yr. B.P. Flow competence equations, dam-break models, and the Simplified Dam-Break computer model were used to estimate the paleohydrology of the flood. Models indicate that the peak discharge at the breach in the caldera rim was at least 5.8 x 10⁴ m³/s, and the maximum possible discharge was 1.9 x 10⁶ m³/s. A second smaller flood release occurred 190 yr B.P., coinciding with the 1817 A.D. eruption, and destroyed a small Aleut village at Cape Tanak. Stratigraphic analysis reveals that Okmok Volcano has maintained a high level of volcanic activity following the large flood release. Major eruptive events producing air-fall tephra deposits average 1 every 80 years since 1010 yr. B.P.
• #### Paleomagnetism Of The Wrangellia And Alexander Terranes And The Tectonic History Of Southern Alaska

Wrangellia was the first Alaskan tectonostratigraphic terrane to be widely accepted as allochthonous with respect to North America. There is, however, considerable disagreement as to the age of emplacement of this terrane as well as the hemisphere in which it originated. Some 800 paleomagnetic samples were collected from 24 localities in southern Alaska to elucidate the paleolatitude translation history of Wrangellia and other associated terranes. Data of known polarity from the Skolai Group (Pennsylvanian/Permian) strongly suggest that Wrangellia originated at 10-15 degrees North latitude. The Permian Pybus Dolomite yields a 9 degree S paleolatitude and suggests that the Alexander terrane moved southward in late Paleozoic and Triassic time. Evaluation of geologic data indicates that the Wrangellia and Alexander terranes amalgamated in an oceanic setting in mid to Late Jurassic time. Paleomagnetism of the Brothers Volcanics (Alexander terrane) and MacColl Ridge Formation (Wrangellia) documents a low latitude for both terranes during the Cretaceous, thereby precluding a pre-Tertiary age of emplacement for the amalgamated superterrane. Speculative apparent polar wander paths for Wrangellia and the Alexander terranes, in addition to geologic and biogeographic constraints, allow development of the following hypothetical tectonic model. Both the Alexander and Wrangellia terranes originated in the northern hemisphere adjacent to western North America in mid-paleozoic and late Paleozoic times, respectively. The Alexander terrane moved into the southern hemisphere during the Paleozoic and Wrangellia began moving southward in the Late Triassic or Early Jurassic. These two terranes amalgamated in mid to low southern paleolatitudes in later Jurassic time and formed part of a composite terrane, here termed the Southern Alaska superterrane. This superterrane began northward translation in Late Jurassic time, accreting to North America in Tertiary time.
• #### Paleopedology, palynology, and geochronological interpretation of alluvial paleosols, Cenomanian Dunvegan formation, Alberta, Canada

The Dunvegan Formation is a mid-Cretaceous deltaic deposit exposed in the Rocky Mountain foothills of Alberta and British Columbia along the Peace River Valley. Intrinsic features of Dunvegan Formation paleosols understood through micromorphology, geochemical, and mineralogical analysis provide a paleoclimatic interpretation of warm to cool temperate. Micromorphological and geochemical analysis lead to reconstruction of the depositional and pedogenic histories of the five primary paleosols of this study. Preserved palynomorphs of the paleosols are primarily composed of fern spores with much less abundant conifer and cycad species. The paleoclimate based on the palynomorphs is humid and ranges from cool temperate to subtropical. The overall paleoenvironmental interpretation based on both paleosols and palynology is humid cool to warm temperate. Geochronology using the ⁴⁰Ar/³⁹Ar dating method was implemented in an effort to date pedogenesis. This technique needs further refinement in order to be successful in dating paleosols. The multi-proxy approach of this study lead to a more complete interpretation of the climatic, pedogenic and depositional history and should be used in the future.