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...
Invasion by nonnative brook trout (Salvelinus fontinalis) often results in replacement of bull trout (Salvelinus confluentus) in western North America, but the causal mechanisms are not well understood. Removal of brook trout from 1992 to 2000 from Sun Creek in southern Oregon, provided an opportunity to investigate the changes in...
This study examines the spatial and temporal distribution and life history of the "offshore" component of the Northeastern Pacific spiny dogfish (Squalus acanthias) population. Distribution was examined in relation to latitude, depth, the Columbia River plume and large-scale climate changes. Fishery and survey data indicate that the Northeastern Pacific spiny...
Chinook salmon (Oncorhynchus tshawytscha) have been absent from their historic spawning and rearing grounds in the Metolius River Basin in central Oregon since 1968, when fish passage was terminated at the Pelton Round Butte Hydroelectric Project on the Deschutes River. Plans have been developed to reestablish passage of anadromous fish...
Frequent or lengthy predation risk can cause one of two modifications of prey feeding
behavior: 1) postponement of feeding to less risky periods, or 2) resumption of feeding
behavior despite persistent risk. North Pacific flatfishes exhibit both of these responses when confronted with temporal variation in risk, and this experimental...
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...
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...
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....
Northern anchovy (Engraulis mordax) are a dominant forage fish in the California Current large marine ecosystem (CCLME). However, little is known about northern anchovy abundance, distribution, age structure, or population fluctuations relative to ocean conditions in the eastern boundary upwelling system off the U.S. West Coast. This thesis includes three...
Aquatic insects that emerge out of streams to mate represent a potential energy
flux to terrestrial food webs. The relative success of an individual aquatic adult insect
is whether it survives long enough to produce offspring, i.e. mate and return to the
stream to oviposit eggs. Some characteristics of the...