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Steelhead Oncorhynchus mykiss exhibit complex life-history patterns described by variable freshwater and marine residency periods, maturation patterns, and reproductive characteristics. Over 300 small populations of Steelhead are present in Southeast Alaska, and similar trends in abundance among these populations suggest the influence of population-regulating forces operating on a regional scale. The Situk River, near Yakutat, Alaska, supports the largest known population of Steelhead in Alaska. Stock assessment studies on this river have collected the longest set of biological data and scale samples for Steelhead in the state. For this study, retrospective scale pattern analysis of samples from Situk River Steelhead was synthesized with regional abundance information to investigate patterns in early marine growth among different life-history and demographic groups, as well as to explore linkages between growth, abundance, and marine environmental variables. Positive correlations were identified between freshwater growth, first ocean-year growth, and adult length, while first ocean-year growth was negatively correlated with second ocean-year growth. Early maturing Steelhead were found to have increased first ocean-year growth and reduced adult length relative to later maturing Steelhead, confirming connections between growth and maturation. Correlations in abundance among Southeast Alaska Steelhead populations suggest that marine and climatic drivers may impact these populations in a regionally coherent manner. Correlations among patterns in abundance also varied along a distance gradient: populations located closer to the Situk River were more correlated with the Situk River than more distant populations. Positive relationships between Gulf of Alaska sea surface temperature, North Pacific Gyre Oscillation, and Situk River Steelhead abundance further supported the importance of climate-driven marine conditions to Steelhead productivity. While conservation concerns for Steelhead in Southeast Alaska are currently minimal, proactive investigations into life-history diversity and population linkages may become more relevant with increased marine ecosystem variability related to climate change.
Wild Steelhead Trout, Oncorhynchus mykiss, in the Puget Sound are currently in decline, and very little is known about the early life history of these threatened fish. This study evaluated consequences of early life growth in terms of survival to smolt or adult stages. The objectives of this study were to determine whether significant size-selective mortality (SSM) in Steelhead could be detected between freshwater stages and returning adults; and if so, how the magnitude of size selectivity varied among reaches categorized by three different precipitation zones (snow, mixed rain-snow, or rain). Wild Steelhead in the Skagit River basin were sampled as juveniles, smolts, and adults, and scales were measured to compare back-calculated freshwater growth rates and size distributions of rearing juveniles with individuals that survived from an earlier life stage to the smolt and adult stages. Linear regression of scale radius (SR) and fork length indicated that SR was a reasonable predictor of fork length during freshwater residency. Back-calculated size-at-annulus estimates indicated that fish sampled as adults grew significantly faster to age 1, 2, and 3 annuli compared to fish sampled as juveniles, and faster to the age 2 and 3 annuli compared to fish sampled as smolts. Within precipitation zones, fish sampled as juveniles were consistently smaller at each freshwater annulus compared to those same freshwater annuli on fish sampled as adults. An increased disparity in size-at-annuli 2 and 3 between fish sampled as juveniles, smolts, and adults suggests that fast growth during the period at which Steelhead smoltify is vitally important to survival to adulthood. These findings provide evidence that survival among life stages is an important dynamic in wild Steelhead, and can be attributed, in part, to size attained at earlier life stages. Efforts for recovery of threatened Puget Sound Steelhead could benefit by considering growth- and size-selective mortality in freshwater environments, and identifying factors that limit early life growth at a finer scale of habitat, for example among sub-basins or precipitation zones.
This study used recording fathometer (sonar) and visual observations to count the early portion of the spring steelhead (Oncorhynchus mykiss) immigration to the Situk River near Yakutat in southeast Alaska.
Estuarine environments provide an essential habitat to many aquatic animals and, in some settings, can be susceptible to drastic environmental transformations caused by deviations in connectivity with the ocean. In these intermittently closed estuaries (ICEs), the presence or absence of a barrier beach, naturally controlled by wave action and river flow, determines the mouth state (closed or open). Depending on the frequency and duration of closures and reopenings, ICEs can create a conundrum for inhabitants, especially diadromous fish that must transit between marine and freshwater habitats to reproduce. Changes in connectivity to the ocean not only obstructs migration between the ocean and the river but can also cause deadly conditions, especially for juvenile pacific salmonids (Oncorhynchus spp.) that have a narrow range of physiological tolerances for the abiotic variables susceptible to large fluctuations in ICEs. Despite these hurdles, ICEs constitute essential habitats for threatened populations of steelhead (Oncorhynchus mykiss). This dissertation utilizes a threatened population of juvenile steelhead in the Russian River estuary, northern California, USA as a case study to examine an array of relevant topics about the efficacy of a juvenile anadromous fish occupying an ICE. The intersection of a threatened fish with a plastic and complex life history within an understudied system provides many challenges as well as opportunities. In addition to a brief introduction (Chapter 1) and conclusion (Chapter 6), the main chapters of this dissertation (Chapters 2-5) will address knowledge gaps specific to juvenile steelhead in the Russian River estuary. The second chapter addressed uncertainties regarding what abiotic conditions juvenile steelhead are exposed to and how steelhead may avoid physiologically stressful conditions. Specifically, we answered the following questions: (1) "What are the WQ habitats used by juvenile steelhead during open and closed conditions in an ICE?" and (2) "What behavioural change is evidenced between open and closed conditions that might alter the juvenile steelhead's risk of exposure to stressful WQ?" To answer these questions, we combined thermal sensor encoded acoustic telemetry and coincidental WQ sampling. Chapter two determined that, under open conditions, juvenile steelhead experienced primarily brackish and saline water in the lower and middle reaches and warm freshwater in the upper reach, whereas under closed conditions, they moved greater distances and were found to be aggregating near cool water refugia not used during open mouth conditions. These findings shed light on the abiotic conditions juvenile steelhead are exposed to and emphasize the importance of tributary hydrogeomorphic processes and groundwater linkages in subwatersheds that are sources of cool water refugia in ICEs. The purpose of the third chapter was to evaluate the vertical response of juvenile steelhead to the physiochemical conditions (i.e., temperature, DO, salinity) in the Russian River estuary. This chapter further explored the acoustic telemetry and simultaneously collected WQ data from chapter two to test the following hypotheses: (i) juvenile steelhead will shift their position in the water column based on prevailing physiochemical conditions; (ii) the degree to which juvenile steelhead adjust their position in the water column will vary with fish size; and (iii) smaller juvenile steelhead will risk potentially stressful conditions to take advantage of prey sources. The results indicated the depth of fish varied in response to the present abiotic conditions and typically reflected the occupation of more energetically and physiologically beneficial habitats, with smaller fish being shallower in the water column when proximate salinities are higher. Results indicated management activities that promote open mouth conditions may create challenges for steelhead that are not acclimated to saline conditions but reveal foraging strategies used by juvenile steelhead that are not yet tolerant of higher salinities. Macroinvertebrates are fundamental to the food webs, yet their response to management activities that affect connectivity to the ocean is not well understood. The fourth chapter used systematic sampling of the benthic and epibenthic macroinvertebrates to assess factors that affect the diversity and abundance of key food web taxa. Similar to other ICEs, the macroinvertebrate assemblage of the Russian River estuary was primarily composed of taxa that can deal with the variability, either physiologically or behaviourally. Furthermore, the prominent food web taxa were abundant during both open and closed mouth conditions and were found in large aggregations in habitat only inundated during closed mouth conditions. These increased densities in the closure-inundated habitat may reflect more expansive aggregations of key food web taxa that would lead to more efficient foraging for juvenile steelhead. Although the growth rates of juvenile steelhead in ICEs have been reported near the highest in literature, leading to increased marine survival, the specific factors contributing to this growth have not been specifically evaluated. The fifth chapter incorporated observed growth rates, a diet analysis, and thermal history of juvenile steelhead into a bioenergetics model to explore factors that most influence the growth potential of juvenile steelhead. In this chapter, I confirmed that growth rates of juvenile steelhead in the Russian River estuary rival the highest in literature and are attributed to ample foraging opportunities and the ability of juvenile steelhead to thermo-regulate behaviourally in the heterogeneous abiotic environment. Higher energetic costs due to higher temperatures in the upper reach were possibly buffered by the consumption of more energy dense prey. These results indicated that growth is likely not limiting the recovery of threatened steelhead in the Russian River estuary. With many populations of salmonids imperiled near their southern range, efforts for recovery could benefit from protecting habitats in ICEs and considering the impacts of management activities to the water quality conditions.
This study of numbers of steelhead (Oncorhynchus mykiss) in the Situk River near Yakutat in southeast Alaska uses both visual and recording fathometer (sonar) methods.
The importance of salmon to the Pacific Northwestâ€"economic, recreational, symbolicâ€"is enormous. Generations ago, salmon were abundant from central California through Idaho, Oregon, and Washington to British Columbia and Alaska. Now they have disappeared from about 40 percent of their historical range. The decline in salmon numbers has been lamented for at least 100 years, but the issue has become more widespread and acute recently. The Endangered Species Act has been invoked, federal laws have been passed, and lawsuits have been filed. More than $1 billion has been spent to improve salmon runsâ€"and still the populations decline. In this new volume a committee with diverse expertise explores the complications and conflicts surrounding the salmon problemâ€"starting with available data on the status of salmon populations and an illustrative case study from Washington state's Willapa Bay. The book offers specific recommendations for salmon rehabilitation that take into account the key role played by genetic variability in salmon survival and the urgent need for habitat protection and management of fishing. The committee presents a comprehensive discussion of the salmon problem, with a wealth of informative graphs and charts and the right amount of historical perspective to clarify today's issues, including: Salmon biology and geographyâ€"their life's journey from fresh waters to the sea and back again to spawn, and their interaction with ecosystems along the way. The impacts of human activitiesâ€"grazing, damming, timber, agriculture, and population and economic growth. Included is a case study of Washington state's Elwha River dam removal project. Values, attitudes, and the conflicting desires for short-term economic gain and long-term environmental health. The committee traces the roots of the salmon problem to the extractive philosophy characterizing management of land and water in the West. The impact of hatcheries, which were introduced to build fish stocks but which have actually harmed the genetic variability that wild stocks need to survive. This book offers something for everyone with an interest in the salmon issueâ€"policymakers and regulators in the United States and Canada; environmental scientists; environmental advocates; natural resource managers; commercial, tribal, and recreational fishers; and concerned residents of the Pacific Northwest.