The Pacific walrus inhabits the Bering Sea during winter and the Chukchee Sea in summer, generally in close association with sea ice. The year-round northern limit to this range is marked by the southern edge of the relatively unbroken pack ice which, though not impenetrable, is usually avoided. The southern limit appears to be set by air temperatures, regions with monthly means of 50 F or more being unoccupied. Between these two "barriers," the animals frequent waters of less than 50 fathoms depth in which their preferred food, the pelecypods Mya, Saxicava, Astarte, Macoma, and Clinocardium occur. Seasonal migrations between the Bering and Chukchee Seas appear to be partly in response to changing physical conditions and partly due to an innate or learned behaviour pattern. Females are the most regular migrants; males are more subject to the inconsistencies of ice drift. The bull Pacific walrus reaches sexual maturity at six to eight years of age, the cow at four.to five years of age. Breeding takes place mostly from April to June as the animals are migrating northward , and there is no evidence of any organized polygamy or "harem breeding." Gestation is one full year, and twinning is unknown. An individual cow rarely conceives in successive years, the first three pregnancies generally being at 2-year intervals and later ones three or more years apart. Males become senile at about fifteen years of age. Full adult body size is achieved at four to six years of age by both sexes, though growth continues slowly thereafter. The tusks and other teeth grow at a relatively high rate throughout the life span, and analyses of their structure and size have yielded good techniques for age determination. The population, upwards of 40,000 animals at present, has declined slightly in the past fifteen years, but it has reached or is approaching equilibrium. The birth rate and death rate are about equal, human predation accounting for most of the latter. Since the population is currently too small to satisfy the Alaskan Eskimos' needs, it is recommended that it be permitted to increase by eliminating some of the wasteful hunting practices which are now in effect. / Science, Faculty of / Zoology, Department of / Graduate

This thesis develops and demonstrates an approach for estimating the three-dimensional (3D) location of a vocalizing underwater marine mammal using acoustic arrival time measurements at three spatially separated receivers while providing rigorous location uncertainties. To properly account for uncertainty in the measurements of receiver parameters (e.g., 3D receiver locations and synchronization times) and environmental parameters (water depth and sound speed correction), these quantities are treated as unknowns constrained with prior estimates and prior uncertainties. While previous localization algorithms have solved for an unknown scaling factor on the prior uncertainties as part of the inversion, in this work unknown scaling factors on both the prior and arrival time uncertainties are estimated. Maximum a posteriori estimates for sound source locations and times, receiver parameters, and environmental parameters are calculated simultaneously. Posterior uncertainties for all unknowns are calculated and incorporate both arrival time and prior uncertainties. Simulation results demonstrated that, for the case considered here, linearization errors are generally small and that the lack of an accurate sound speed profile does not necessarily cause large uncertainties or biases in the estimated positions. The primary motivation for this work was to develop an algorithm for locating underwater Pacific walruses in the coastal waters around Alaska. In 2009, an array of approximately 40 underwater acoustic receivers was deployed in the northeastern Chukchi Sea (northwest of Alaska) from August to October to record the vocalizations of marine mammals including Pacific walruses and bowhead whales. Three of these receivers were placed in a triangular arrangement approximately 400 m apart near the Hanna Shoal (northwest of Wainwright, Alaska). A sequence of walrus knock vocalizations from this data set was processed using the localization algorithm developed in this thesis, yielding a track whose estimated swim speed is consistent with current knowledge of normal walrus swim speed. An examination of absolute and relative walrus location uncertainties demonstrated the usefulness of considering relative uncertainties for applications where the precise location of the mammal is not important (e.g., estimating swim speed). / Graduate

No description available.

This thesis examines the use of various osseous raw materials in craft activities in the Mälaren region during the Middle Ages. Places studied are: Birka, Sigtuna, Nyköping, Strängnäs and Uppsala. The aim is to capture both chronological and spatial changes in the use of osseous raw materials. Species and materials used reflect regional as well as international networks and how they change during time. The spatial distribution of waste from craft activities, its materiality and temporality mirror activities in different social contexts.  Quantitative and qualitative changes in the handling and exploitation of raw materials reflect varying and changing views of its value and how craft and exchange is affected by both a social and economic agency. In Birka, osseous waste material associated with craft was collected by Hjalmar Stolpe in the 1870s. An examination of the assemblage shows that imported material comprises a significant part of the collection. About a third of the waste consists of imported antler of red deer and reindeer. Red deer is particularly abundant (21%), signifying the importance of southern trading networks. The presence of whalebone can also be linked to south-western trading routes. The waste material collected during excavations in Sigtuna and representing the period c. 980-1300 has a different composition, reflecting different networks and perhaps different means of trade and production. As in Birka, elk antler constitutes the main bulk of the raw material used. Red deer antler is extremely limited, forming less than 1% of the material, appearing continuously though in small amounts from c. 1020-1300.  Reindeer antler is distinctly present in the oldest phase, c. 980-1000. This occurrence might represent a relic of the northern network manifested at Birka. An isotopic study indicates an origin in a forested biotope. After this initial phase the use of reindeer antler becomes as rare as that of red deer until the second half of the 12th century, indicating that the antler craft operated on a minor scale without any demand for long-distance trade in raw materials. A change occurs in the last quarter of the 12th century when large quantities of reindeer antler appear once more. Isotope signatures indicate an origin in more mountainous regions. This coincides with the introduction of another traded raw material of an arctic origin: walrus tusk. The craft had become more marked oriented. This is manifested in larger deposits of debris, a wider range of materials used, including bones from various domestic animals, but also the handling and exploitation of the material changes indicating a different view of production, trade and the value of raw materials than previous. This shift coincides with the introduction of minted silver. Western influences are evident both in the material culture and in the faunal assemblage. It is likely that a majority of the reindeer antler as well as the walrus tusk present in these later phases have a Norwegian origin. In the late 1100s and early 1200s craft in osseous material occur in other towns that emerge in the region but it seems to appear in new social contexts. Small assemblages of antler debris have been found in Uppsala, but the activities they represent lack the spatial continuity that exist in contemporary environments in Sigtuna and Strängnäs, indicating short lived occasional activities in a loosely regulated urban environment. Craft activities dependent purely on bone from domestic animals appear in the 1200s in Nyköping, Uppsala and Strängnäs. They represent craft activities in a new social context outside the private sphere of the local elite and instead subordinated other craft activities where domestic animals have been exploited on a large scale beyond the domestic household. Antler craft represents a social practise in the realms of the local elite with a continuity stretching back to the Iron Age. Monetization and an increasingly feudal society redefine social relations and practise. This can be seen in the occurrence of craft in new contexts in the late 1100s and 1200s, reflecting heterogeneity in social and economic functions in and between the towns in the region.