Sex differentiation in fish is a labile process that allows sex inversion in several species. The inherent capacity of fish germ cells to differentiate into oocytes or spermatocytes constitutes a key factor allowing for functional sex inversion. This thesis set out to determine the mechanism involved in steroid-induced sex differentiation...
Processes of metamorphosis, settlement, and growth were examined in Pacific sanddab
using field studies and otolith microstructure. This flatfish transforms at large sizes, has a
gradual metamorphosis, and settles to a nursery on the middle continental shelf. Eye migration
takes 3 months and "metamorphosis proper" which begins after completion of...
Sex steroids, follicle stimulating hormone (FSH),
luteinizing hormone (LH) and gonadotropin releasing hormone
(GnRH) were measured in monosex and mixed sex populations of
rainbow trout during early development. Steroids declined
following fertilization, increased at hatch, then fell and
remained constant thereafter. Trends toward differences in
steroids between males and females...
A series of experiments with Aeromonas salmonicida and infectious
hematopoietic necrosis virus (IHNV) were carried out to determine dynamics of the
spread of infection in chinook salmon (1.2-1.98g) and rainbow trout (1.2-3.1g). It was
found in experiments with A. salmonicida that fish infected by bath immersion became
infectious at 4...
Co-management is considered an alternative approach to fisheries management,
however, not all co-managed fisheries have been successful. Most studies discussing the
success and failure of co-management have emphasized economic and social attributes of
success and failure, such as fishery rights and institutional arrangements. The effect on
co-management of biological characteristics,...
The composition and distribution of fish assemblages was examined in a
floodplain lake system in the Amazon basin. Quantitative samples were
collected during the 1992-1993 flooding season at Marchantaria Island, Solimoes
River. A total of 25,819 specimens representing 8 orders, 30 families, 101
genera and 139 species of fish were...
From 1998-2000, laboratory studies were conducted to examine factors that impact saltwater-entry behavior and saltwater preference (SWP) of juvenile chinook salmon, Oncorhynchus tshawytscha. These factors included bacterial kidney disease, stress and the presence of trout, O. mykiss. An additional study investigated the orientation of the startle response of chinook salmon...
The work presented in this dissertation examines possible
modes of action for growth inhibition by anthropogenic endocrine
disrupting chemicals (EDCs) as well as endogenous hormones
associated with growth in fish. Using the sheepshead minnow (SHM)
(Cyprinodon variegatus) as a model, I developed methods to examine
perturbations in the endocrine axis...
From 1996 through 1998 I collected mature female black rockfish off Oregon and examined ovaries and otoliths to estimate weekly, age-specific larval production. In all reproductive seasons, older black rockfish extruded larvae earlier in the season, followed by progressively younger fish. Each year, beginning in May, I collected young-of-the-year (YOY)...
The present study investigated the neurocrine and neuroendocrine control of locomotor activity, habitat choice, social behavior, and migratory behavior in juvenile chinook salmon (Oncorhynchus tshawytscha). This was achieved by the manipulation of three neurotransmitter systems; serotonin (5-HT), dopamine (DA), y-amino-n-butyric acid (GABA) and the neuropeptide corticotropin-releasing hormone (CRH). Chemicals were...
Black rockfish (Sebastes melanops) is an important marine recreational species throughout the Pacific Northwest. Recent catch data indicate a trend of age-truncation in the black rockfish population off the Oregon coast, with older females rapidly disappearing from the population. In populations with broad age distributions, older fish may contribute disproportionately...
The purpose of this research was to explore the impact of finfish bycatch on the ocean shrimp Pandalus jordani fishery using two methods. One method looked at the breakage of the shrimp by finfish bycatch in the nets. The other looked at the impact of bycatch on fishing decisions. At-sea...
Questions relating to economic performance, biological conservation and variation in resource abundance and harvest of ocean shrimp have led to increasing pressure for management action. Developing effective management policies for this highly variable resource requires a comprehensive understanding of the fishery and marine processes. Important factors in understanding the fishery...
Current riparian management objectives in the Pacific Northwest promote both retention of existing conifers and conversion of hardwood-dominated areas to conifers. Although understanding of relationships between riparian vegetation and salmonid prey availability is growing, temporal variation in these relationships is poorly understood. Seasonal fluxes in availability of aquatic and terrestrial...
Genetic diversity of two salmonid species, Dolly Varden (Salvelinus malma) and coastal cutthroat trout (Oncorhynchus clarki clarki) in Prince William Sound, Alaska were examined at multiple spatial scales with three molecular markers. Pleistocene glaciers covered what is now Prince William Sound 8,000- 12,000 years ago and both species colonized the...
The purpose of this study was to understand the influence of organic material and nutrients from spawning salmon and supplemented salmon carcasses on stream food webs. My study objectives were to examine 1) assimilation of salmon-derived nutrients (SDN) by producers and consumers in the food web, 2) epilithic biofilm productivity,...
Discrete coldwater patches within warm streams provide potential thermal refuge for coldwater fishes during periods of heat stress. This analysis focused on heterogeneity in stream water temperatures as influenced by local influx of cooler subsurface waters. Using field thermal probes and recording thermistors, we identified and characterized coldwater patches potentially...
Conceptually, the dynamics of wood in streams can be viewed in terms of input and in-channel processes. Input processes are associated with both the riparian (tree fall, bank cutting, windthrow) and upslope forests (mass failures). In-channel processes include log breakage, movement, and decomposition. A mechanistic view of these processes is...
The Middle Fork John Day River is composed of low gradient, alluvial valley
segments separated by constrained, canyon-like reaches, and has a history of multiple
land-uses. These factors can alter the physical and biological structure of streams, and
disrupt the longitudinal river continuum. I examined habitat, fish, macroinvertebrates,
and primary...
Redband trout (Oncorhynchus mykiss gairdneri) are found over a wide range of environmental conditions and are known for their variability in life history traits among watersheds or even within streams. Life history traits and population structure of these trout can be influenced by a variety of anthropogenic changes including habitat...
Sympatric steelhead and resident rainbow trout (Oncorhynchus mykiss) are known
to exist in many rivers throughout the Pacific Rim. Whether sympatric steelhead and
resident rainbow trout are polymorphisms within a single gene pool or two reproductively
isolated populations has significant implications concerning the study and conservation of
this polytypic species....
The Tillamook and Kilchis subbasins of the Tillamook Bay watershed (Oregon Coast Range) have differences in geology and land use history and, therefore, varied environmental conditions that could affect fish assemblages. Fifty-two randomly selected wadeable stream reaches in these two subbasins were surveyed for stream habitat and fish assemblage composition...
The extent of biological invasions, their role on the feeding of
native fishes and their impact on community stability were
investigated in Alsea Bay and Yaquina Bay, two estuaries on the
central Oregon coast, USA. Most nonindigenous species (NIS)
introduced in these intermediately invaded estuaries are
considered byproducts of culturing...
In an effort to identify seasonal distribution patterns and habitat requirements of coastal cutthroat trout Oncorhynchus clarki clarki, movement of tagged and marked individuals (35 radio-tagged, 753 PIT-tagged, and 5,322 fin-clipped) was monitored over a 14-month period in an isolated watershed in southwestern Oregon. Emigration out of the basin was...
I examined hydrological and plant community changes associated with the implementation of a restoration management plan in two riparian meadows located within an agricultural landscape of the central Willamette Valley, Oregon. I established exclosure fencing (a form of passive restoration) in one agricultural field and established fencing and plugged a...
Research on the distribution of juvenile salmonids in streams has been dominated by studies examining small areas over short periods. However, information relevant to freshwater influences on population persistence is likely to derive from longer-term, multi-scale studies. Relationships were examined among juvenile anadromous salmonids, their freshwater habitat, and landscape characteristics...
Organic matter dynamics in riparian ecosystems are largely driven by interactions among hydrology, soil, and vegetation. In two riparian meadows, northeast Oregon, I examined the hypothesis that vegetation and soil characteristics in three plant communities - defined as wet, moist, and dry meadow - were strongly influenced by hydrological and...
This study examined fish movements and assemblage dynamics in the Wenaha, Grande Ronde, Snake river system of northeast Oregon and southeast Washington. I investigated the role of fish movement in the dynamics of stream fish assemblages and evaluated relationships between species movement, assemblage structure, and the heterogeneity of habitat at...
Most fishes exhibit differences in activity patterns from day to night, with a switch from
high to low activity at dusk and reverse at dawn. Marine reef fishes show similar behavior
among sites, despite dissimilar species assemblages, suggesting that common selection pressures
are leading to convergent behavior. Few studies to...
The minnow genus Siphateles is distributed throughout the Great Basin and adjacent drainages of western North America. Three species are currently recognized in the genus: S. alvordensis, Alvord chub, S. boraxobius, Borax Lake chub, and S. bicolor, the tui chub. S. bicolor has long been recognized as a widespread species...
New approaches are needed to quantify and understand spatial patterns of stream fishes and their environment. Concepts in riverine ecology emphasize the importance of thermal zones and gradual longitudinal changes in physical habitat and biota, but little is known about spatial variability within the river continuum. I present a conceptual...
This work sets forth a reformulation of Levins' loop analysis for the qualitative modeling of complex dynamical systems. Relationships between members of ecological communities can be analyzed through a qualitatively specified community matrix, whereby +1, -1, or 0 represent effects of one species upon another. A contribution is made to...