The lingcod (Ophiodon elongatus) is an important groundfish species in both recreational and commercial fisheries of the Northeastern Pacific. It is a large, fast-growing, generalist predator of invertebrates and fishes. In response to concerns that lingcod may limit populations of rockfishes (Sebastes spp.), I compared the diets of 375 adult...
Nest counts from the largest subpopulation of the loggerhead sea turtle (Caretta caretta) in the Atlantic, peninsular Florida, have been declining since 1998. Analyzing trends of nests and adult females is insufficient to determine the overall status of a sea turtle population, due to variation in nesting frequency and a...
Tidal wetland channels provide rearing habitat for juvenile Chinook salmon as they emigrate from freshwater habitat and prepare to enter the ocean. Widespread diking and drainage of estuarine marshes for agricultural and urban development may have contributed to a decline in salmon abundance in the Pacific Northwest, prompting efforts to...
The myxozoan parasite, Ceratomyxa shasta, is the most significant pathogen of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Klamath River, CA, USA. This parasite requires two hosts - a freshwater polychaete (Manayunkia speciosa) and a salmonid - to complete its life cycle. The complex life cycle and large geographic area...
Biological invasions are the second largest threat to biodiversity following habitat loss, and studying invasions has been a focus of ecological the past two decades. Despite the intense research, many basic questions remain empirically unanswered, particularly in the realm of behavior. The purpose of this research was to explore the...
Salmonids in arid high-elevation streams find themselves at the fringe of their tolerance range. Under the conditions they endure in such environments, long-distance migratory movements among widely dispersed habitats may be an important mechanism for some fish to persist, and even thrive. The Donner und Blitzen (Blitzen) River redband trout...
To best manage Eagle Creek National Fish Hatchery and minimize any negative impacts that the current hatchery program may be having on Endangered Species Act-listed salmonids in the Eagle Creek Basin, I determined if wild fish are being displaced from preferred habitats by hatchery salmonids Oncorhynchus spp. This thesis had...
South Pacific humpback whales were devastated by commercial whaling in their Antarctic feeding areas during the 20th century. Understanding migratory connections and current abundance of these isolated breeding stocks is crucial for the allocation of historical Antarctic catches in population dynamic models used to assess current recovery. However, only a...
Alternative male phenotypes in salmonine fishes arise from individuals that mature as either larger and older anadromous marine-migrants or as smaller and younger freshwater residents. Variability in age and size of males at maturity is hypothesized to be preceded by early differences in growth in size and lipid storage. Water...
For Pacific salmon, the evolution of local adaptations depends upon the species' propensity to return, or "home", to natal streams at time of reproduction. Pacific salmon use olfactory cues to guide homing behavior, yet little is known about the genetics of olfaction in salmon. In this study, I use putatively...
Hatcheries whose purpose is to provide for a recreational fishery must minimize impacts on wild fishes. Management to reduce hatchery and wild interactions is especially important on river systems that contain Endangered Species Act (ESA) listed species. I examined adult hatchery summer steelhead, Oncorhynchus mykiss, behavior, current management and a...
Partial migration is a common migratory behavior where some individuals in a population migrate and others do not. Patterns of partial migration can vary dramatically, especially for species that inhabit a wide range of environments. I described and predicted spatial variation in marine migration (anadromy) of female Oncorhynchus mykiss (steelhead...
The Pacific Northwest has a relatively low diversity of primary freshwater fishes with most of the endemism and diversity in the Columbia River and Klamath River. However, the Oregon Coastal Subprovince defined as the coastal rivers from Miami River in the north to Sixes River in the south, has a...
Zebrafish, Danio rerio, are widely used as vertebrate research organisms yet little is know about their responses to husbandry stressors. This dissertation examined the whole-body cortisol responses of zebrafish to husbandry stress. Additionally, the effects of stress on the susceptibility to mycobacteriosis and microsporidiosis (Pseudoloma neurophilia) were determined including effects...
Determining age in crustaceans is inherently imprecise because they molt
periodically and do not retain hard structures throughout their lifespan. Morphological
measurements, such as carapace length, are often used to estimate age because
methods for direct ageing do not exist. However, variability in individual growth rate
and molt frequency can...
We assessed use and selection of cover by coastal cutthroat trout (Oncorhynchus clarkii
clarkii) in six headwater streams in three watersheds in western Oregon, USA during the summer low flow period from 1 August and September 30, 2007. We tagged 1037 coastal cutthroat trout (>100 mm) with passive integrated transponder...
This study evaluates the functional organization of stream fish assemblages in response to streamflow factors and biotic interactions across a range of spatial scale. The study area for this project includes 109 stream reaches located on tributaries to the upper Missouri River in the northern Great Plains. Fish distribution data...
The decline of many Pacific salmon stocks has stimulated interest in the early life history and habitat requirements of juvenile salmon. Although estuarine habitat associations of juvenile salmon have been investigated in many coastal areas of the eastern Pacific Ocean, until recently, little was known about juvenile salmonid ecology within...
I examined the relative roles of biotic and abiotic factors in structuring redband trout
Oncorhynchus mykiss distributions in the South Fork John Day. I first examined the
relationship between the biological traits of the fish assemblage and riparian-geomorphic features in context of prevailing theories of stream ecology stemming from the...
Small low-head diversion dams are capable of removing much of the flow of a river, often resulting in increased water temperatures and habitat loss. Warmer temperatures have been shown to accelerate aquatic invertebrate growth and development, and discharge reductions can reduce instream habitat, suggesting that water withdrawals may alter both...