Two similar salmonids, coho and steelhead, cohabit many coastal rivers of British Columbia. Field collections reveal that the distributions of underyearling coho and steelhead are similar along the length of these streams. However, the microhabitat distribution of the two species is different. In spring and summer, when population densities are high, coho occupy pools, trout occupy riffles. In autumn and winter, when numbers are lower, both species inhabit the pools. Nilsson (1956) stated that segregation (such as that shown by coho and trout in spring and summer) may be indicative of competition resulting from similar ecological demands. To test this hypothesis the distribution and behavior of coho and steelhead were compared in a stream aquarium at different seasons with gradients of light, cover, depth or depth/velocity and in experimental riffles and pools. Distributions, and preferences of the two species in the experimental environments were most similar in spring and summer, the seasons when segregation occurred in nature, and least similar in autumn and winter, the seasons when the two species occurred together in nature. Spring and summer segregation in the streams is probably the result of interaction which is produced by ecological similarities of the species and accentuated by dense populations and inherently high levels of aggressiveness. The species do not segregate in streams in winter because certain ecological demands are different, numbers are lower and inherent levels of aggressiveness are low. When the two species were together in the experimental riffle and pool environment, trout were aggressive and defended areas in riffles .but not in pools; coho were aggressive in pools but less inclined to defend space in the riffles. These differences in behavior probably account for the distribution of trout and coho in natural riffles and pools. The data support the basic contention of Nilsson (1956) and illustrate the role of behavior in segregation produced by competition for space. / Science, Faculty of / Zoology, Department of / Graduate

Rainbow trout {Oncorhynchus mykiss) and coho salmon (0. kisutch) produce males which mature at an abnormally early age. The objectives of this study were to critically describe the role of growth rate in early sexual maturation of male salmonids by monitoring growth rate and precocious sexual development in individually identified fish. Underyearling rainbow trout were individually identified using coded tags. These fish were reared at 9°C and 15°C and growth was monitored twice a month in both groups over a 9 month period starting January 24, 1989. The number of precocious males in the 9°C and 15°C groups were 11% and 18% respectively. Yearling coho salmon were similarly tagged, reared at ambient temperature, and monitored for growth over an 8 month period starting March 22nd, 1989. Ten percent of the coho salmon matured precociously. In both experiments there was a similar relationship between fast growth in early spring and precocious maturation. The growth rate of fish that matured declined in autumn relative to non-maturing individuals. Condition factor (length to weight relationship) was greater among those fish that matured precociously. Plasma growth hormone was monitored in the coho salmon. Most samples fell below the detection limits of the assay (1.5. to 3.0 ng/ml). A strategy to reduce the number of precocious males in cultured salmonids is suggested. / Land and Food Systems, Faculty of / Graduate

In the first experiment, sexually immature male and female coho salmon were exposed for 21 days to dietary DDT at a level of 10 or 100 parts per million (ppm), or to methoxychlor at a level of 100 ppm. Exposure to 100 ppm DDT was found to increase the level of liver microsomal Cytochrome P-450 from a control level of 1.32 ± .04 nmoles/1000 mg liver to a level of 1.98 ± .04 nmoles/1000 mg liver, a statistically significant difference (P<.001). None of the treatments were found to affect the hepato-somatic index. In the second experiment, liver slices from sexually maturing male and female coho salmon fed 100 ppm DDT for 21 days or a control diet were incubated with 4-C¹⁴-estradiol-17β in vitro. Metabolites produced were extracted with dichloromethane, separated by thin-layer chromatography and assayed using scintillation counting techniques. Produced in the incubation were estrone, estriol and one other unidentified polar metabolite. DDT treatment was found to significantly increase the amount of estriol and unidentified metabolite produced (P< .001). In the third experiment, sexually maturing male and female coho salmon fed 100 ppm DDT for 21 days or for 7 days or a control diet were injected with 625,500 dpm 4-C¹⁴-estradiol-17β and permitted to metabolize the hormone in vivo. Serial blood samples were extracted, chromatographed and subjected to scintillation counting techniques to obtain values for Metabolic Clearance Rate, Half-life Time and Volumes of Distribution of the injected steroid. It was found that ingestion of DDT had no significant effect upon any of these parameters (P<.001). The pattern of metabolites produced in vivo closely resembled that produced in vitro. The evidence presented in this study suggests that enhancement of the activity of the Mixed Function Oxidase system in coho salmon may occur upon ingestion of an organochlorine insecticide, but that the phenomenon may have little significance in vivo. / Science, Faculty of / Zoology, Department of / Graduate

The fry of the very similar salmonids, coho salmon (Oncorhynchus kisutch) and steelhead trout (Salmo gairdnerii), live in very close association with each other during their first year of life in fresh water. The present study was designed to measure the effects of competition between these species. Populations of different densities of coho and steelhead fry in four identical artificial stream-channels were studied. Observations were made on survival, growth rates, and some aspects of behavior. Among the various groups of fry, survival was apparently dependent upon interspecific factors; the presence of another similar species had no observable effect. Low-density populations survived well, even when another species was present at a high-density. Survival of the fish at high-densities was always depressed, even when the companion species was present at low density. Steelhead fry demonstrated a faster initial growth rate than the coho, enabling them to exceed the coho in growth despite the latter’s earlier hatching and consequent initial size advantage. Growth rates were inversely related to density, both inter- and intraspecific effects being noticeable. The two species tend to be spatially segregated, coho occupying positions in the middle and upper layers of the streams, and steelhead remaining close to the bottom. This stratification was reflected in their feeding behavior and diet. Emigration activity occurred to a greater degree among the coho than the steelhead. Emigrants of both species were observed, to undergo substantial weight loss subsequent to their disappearance from the stream-channels. It was concluded that coho and steelhead fry live in close association with one another without experiencing extensive interspecific competition. This is because of segregation of the species by having differing habitats, feeding habits, growth and survival rates, and consequent population dynamics. / Science, Faculty of / Zoology, Department of / Graduate

Scotts Creek, located in northern Santa Cruz County, maintains the southernmost persistent population of Central California Coast (CCC) Coho Salmon (endangered) in addition to CCC steelhead (threatened). Fisheries biologists believe overwinter mortality due to lack of refuge habitat is the primary factor limiting salmonid production. Instream rearing habitat may also be limiting, especially during drought years. The legacy effects of historic land use practices, including dredging, wood removal, and the construction of levees, continued to limit refuge and rearing opportunities. A restoration project was implemented to improve refuge and rearing opportunities for salmonids along lower Scotts Creek by removing portions of the deteriorating levee, grading new connections with existing off-channel features, enhancing tributary confluences, constructing alcove habitat features at the margins of the stream channel, and constructing large wood complexes (LWCs) instream. Novel restoration techniques were employed on an experimental basis. Whole in-situ alder trees were pushed into the stream channel with their root systems left partially intact to establish living key pieces. Individual log, boulder, and rootwad LWC components were attached together with couplers that permitted some freedom of independent movement among the individual components. LWCs were braced against live, standing trees and stabilized with boulder ballasts placed on the streambed, which eliminated excavation of the streambed/banks and the need to dewater or divert the stream during construction. Project performance, changes to physical habitat characteristics, and changes to stream morphology associated with implementation were monitored using habitat assessment methods derived from the California Department of Fish and Wildlife’s (CDFW) salmonid habitat survey protocol (Flosi et al. 2010), and topographic survey techniques and data analysis adapted from Columbia Habitat Monitoring Protocol (Bouwes et al. 2011). Preliminary results indicated that LWCs remained stable and functional. In addition, implementation of the restoration project increased pool frequency, low-flow pool volume, instream cover, frequency of instream, alcove, and off-channel refuge habitat features, and frequency of points of connectivity with the floodplain. Long-term monitoring will be required to determine the survivorship, decay rates, and overall persistence of alder recruits.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 92-102). Also available on the World Wide Web.

Coho salmon (Oncorhynchus kisutch) from six hatcheries operated by the Canadian Department of Fisheries and Oceans Salmonid Enhancement Project, were reared in a common facility and then subjected to a series of standardized challenge tests. Results suggest that there are genetically based differences in the response to stressful challenges among stocks of coho salmon from southern British Columbia. The challenge tests were: saltwater (30ppt); saltwater and an increase in temperature (30ppt and 4°C); high pH (9.4 and 10.0); low pH (3.55, 3.65, 3.75 and 4.1); thermal tolerance (1°C/h); and handling (30s netting). The measured parameters were plasma sodium and chloride ion concentrations for the saline and pH challenges, time to dysfunction in the thermal tolerance challenge and plasma glucose concentration in the handling challenge. No differences among stocks were found in responses to the high pH and thermal tolerance challenges. The Chehalis River stock had the smallest plasma ion increase in salt water but showed the largest plasma ion decrease in acidic waters. In some of the low pH challenges the Tenderfoot Creek stock showed less plasma ion loss than other stocks. The stock from Eagle River had the lowest plasma glucose concentration increase during handling challenges. The combined saltwater and temperature increase challenge demonstrated the cumulative effect that stressors can have. Sampling associated with the handling challenges revealed a diurnal fluctuation in resting plasma glucose concentrations. The low pH and handling challenges showed that stock performance and the magnitude of the response observed varied with rearing conditions. Although there was some variation in the magnitude of the stock response to challenges between the two rearing conditions used, differences among stocks were consistent. When the response to all challenges were assembled into a relative challenge response profile (or performance profile), each stock was unique. / Land and Food Systems, Faculty of / Graduate

Policy decisions in fishery management are becoming increasingly complex and difficult. This is especially true for the salmon fisheries where policy outcomes affect the productivity of the salmon resource and the subsequent well-being of commercial fishermen, charter boat operators, Indian fishermen, and sport anglers. The objective of this study was to advance methodology from statistical decision analysis which would assist fishery managers in Oregon who must make particularly difficult choices with respect to allocation and production of coho salmon while recognizing uncertainties in the environment, incomplete state of knowledge, and the conflicting needs and desires of different interest groups. The method chosen given multiple objectives and uncertainty is multiattribute utility analysis. The approach consists, of two main components: (1) a computer model which simulates the life cycle of hatchery and stream spawning coho salmon given environmental variation, different hatchery juvenile release levels and harvest rates; and (2) an objective function which relates the different outcomes from alternative release levels and harvest rates to an assessment of the degree to which individual objectives are met. The approach was used to evaluate and rank the expected outcomes from twelve proposed policies under different hypothesized ocean environments. Analysis of the results suggest that (1) the most effective policy is achieved with a relatively low harvest rate and high smolt release level; (2) selection of a particular harvest rate is the most important decision variable; and (3) a large smolt release level can be maintained unless such releases adversely decreases the ocean survival of stream spawning coho. Because the coho fishery is a mixed stock fishery consisting of hatchery and wild stocks, the results suggest that too high a harvest rate will lead to depletion of wild stocks, considered important because of their potential contribution to production and diverse genetic traits and characteristics. Conversely, too low a harvest rate will lead to excessive escapement of coho and thus reduce the total catch. As is illustrated, formulating the coho decision problem in a multiattribute utility analysis framework is useful in two ways. First, by quantifying the objectives of the decision maker, consistent results from following alternative policies can be determined. These results provide a basis for comparison and serve as a guide for decision making involving uncertainty. Second, the approach is useful in isolating major objectives and conflicts, value judgments, trade-offs, and needed empirical evidence. / Graduation date: 1982

This study was designed to provide information about the juvenile life history of coho salmon, Oncorhynchus kisutch, in the Tenmile Lakes in Oregon by 1) classifying scales of spawning fish and outgoing smolts (1+), 2) assessing the contribution of juvenile life history types to the returns of adults (3₂) and jacks (2₂), and 3) comparing growth rates and survival of different types. Scales of outmigrating smolts from one brood year, jacks from two brood years, and scales of adults from four brood years were classified into juvenile life histories and examined for several scale characters. A linear discriminant function analysis was used to show the separation of the types and to determine the most distinguishing scale characters. Length of smolts at ocean entry back-calculated from scales of jacks and adults was compared with the length of the observed group of emigrating smolts. Based on variation in numbers and spacing of circuli and the size of the freshwater scale zone, believed to represent different residence time in the tributaries and the lakes, four types of juvenile life histories were defined. Fish classified as type 1, stream-reared, are believed to have reared in the tributaries until migrating as smolts in the following year. Type 2, stream-lake-reared, fish are thought to have reared in the tributaries for almost a year but then moved down to the lakes, where rearing continued until smolt migration in spring. Type 3, stream-lake- reared, are believed to have reared for a short time in the tributaries, then moved down to the lakes sometime in their first year of life. Rearing continued in the lakes until spring of the following year. Type 4, lake-reared, are thought to have moved down to the lakes shortly after emergence from the gravel, where they reared until migrating as smolts in the following spring. Scales of smolts, jacks, and adults were sorted into these four types. Presently, coho salmon fry and yearlings appear to be moving out of tributaries in late spring and from March to beginning of May, respectively. Migration of smolts out of the lake system to the ocean occurs mostly within the month of May. Recent habitat surveys show that dramatic seasonal changes occur in use of rearing habitat by juvenile coho salmon in the Tenmile Lakes tributaries from summer to winter. In winter juveniles appear to be using more low gradient, low velocity, off-channel areas than in summer. Fish of type 4 represented 90%, 43%, and 74% of the returns of adults in 1957- 58, 1963-64, and 1971-72, respectively, and 90% of the returns of jacks in 1962-63 and 1970-71. However, no type 4 fish was represented in the returns of adults in 1985-86, whereas type 1 fish represented 89% of the returns. Type 4 appeared to have grown better in fresh water, reached a larger size at outmigration, and have a greater relative survival than fish of type 2, when compared among the observed group of smolts, returning jacks, and adults. The large proportion of the escapement returning as jacks for some of the years may indicate good growing condition for juvenile coho salmon in fresh water. According to the classification of jack scales a large proportion of fish returning as jacks were lake-reared and were found to be larger at migration to ocean than fish returning as adults. This may suggest that fish that reared well in the lakes and reached a large size at outmigration had the tendency to mature early and return as jacks. Based on the analysis of scales, lake-reared juvenile coho salmon formerly contributed well to adult returns. The former high returns of jacks and adults reflect the importance of the lake habitat for the coho salmon populations of this system. In order to enhance this stock to a higher level, management strategies should be focused on making the lake habitat available to juvenile coho salmon for at least some part of their freshwater life. / Graduation date: 1992

Experiments were carried out in fall and winter, 1990 and spring and summer, 1991 , to determine growth and mortality of juvenile Pacific oysters {Crassostrea gigas) in effluent from cultured coho salmon {Oncorhynchus kisutch) , and effluent from salmon in which the red macroalga Palmaria mollis was cultured. Ambient sea water from Yaquina Bay was used as a control. Juvenile Manila clams {Tapes japonica) were also tested in summer, to compare the growth response of clams with that of Pacific oysters. Measured growth parameters included: increase in mean individual live weight, specific growth rate (% increase of mean live weight per day) and mean individual organic (ash-free) weight. Temperature, chlorophyll a, phaeopigment, carbon and nitrogen concentrations and C/N ratio for all treatments were also recorded during spring and summer, 1991. The oysters grew significantly faster in effluent from salmon and salmon conditioned by macroalgae than in the control during the Fall Experiment (September 7- 0ctober 31, 1990). Mean water temperature was 13-16°C. Growth rates were significantly greater in oysters cultured in salmon effluent than in the control during the Winter Experiment (December 7, 1990-February 15, 1991). However, growth was very poor due to low water temperatures (7-10°C). Growth of oysters was significantly greater in the control than in effluent from salmon and salmon conditioned by macrolagae in the Spring Experiment (March 7-May 24, 1991). Mean water temperature was 12°C. In the Summer Experiments, (June 3-July 4 and July 19-August 17, 1991) growth of oysters was more rapid in treatments with macroalgae as compared to treatments without macroalgae Comparative experiments with juvenile Manila clams gave similar results. Percentage mortality for both oysters and clams ranged from 0 to 5% and was highest during winter and lowest during summer. Mean chlorophyll values ranged from 1 μg/1 in spring, 1991 to 11 μg/1 summer, 1991. / Graduation date: 1992