Kamchatka Steelhead Project Science Report for the Utkholok River. Mara S. Zimmerman, Washington Department of Fish and Wildlife

Transcription

1 2016 Science Report for the Utkholok River Mara S. Zimmerman, Washington Department of Fish and Wildlife This science report provides preliminary results from work completed on the Utkholok River in 2016 as part of the under the terms of the WDFW-The Conservation Angler MOU. Background Oncorhynchus mykiss exhibit notable life history diversity in the rivers of western Kamchatka. At least six different life histories are defined by scale growth patterns (Kuzishchin et al. 1999). The life histories all begin with 2-5 years of freshwater growth and followed by an additional 1-4 years of growth either in the high seas, estuary, or river or some combination of these environments. Among rivers, different combinations of life histories are consistently observed and have been attributed to the physical complexity of the riverine environment (Pavlov et al. 2008; Kendall et al. 2015). Within rivers, the relative numbers of each life history also fluctuate over time (Savvaitova et al. 2002; Savvaitova et al. 2003). Genetic differentiation is observed among rivers but not among life histories (McPhee et al. 2007). The coexistence of different O. mykiss life histories in rivers of western Kamchatka provides an opportunity to study steelhead diversity and ecology in an environment with minimal anthropogenic influence. The connection between energetic requirements and life history diversity is relevant to O. mykiss populations in Kamchatka as well as more broadly across the species range. Throughout their life cycle O. mykiss stores energy as lipids in white muscle tissue (Penney and Moffitt 2014), and the rate of storage is influenced by genetics, food availability, and the stream environment (i.e., temperature, gradient). Lipid storage in juvenile O. mykiss is one factor linked to whether the O. mykiss adopts a riverine (resident) or anadromous life history (McMillan et al. 2012; Sloat et al. 2014; Kendall et al. 2015). If food resources are too scarce or metabolic demands too high, this triggers a conditional response to move to a new environment for the next stage of their life history (Sloat et al. 2014). In some rivers, productivity of the freshwater environment is adequate for some or all of the population to forgo an ocean migration and the majority of the population adopts a riverine life history. In other rivers, O. mykiss must migrate to the highly productive but dangerous (high mortality risk) marine environment to locate adequate growth conditions. The link between energy storage and life history diversity of O. mykiss is better described for fish that are going to sea than those returning from sea. Anadromous O. mykiss returning from sea cease feeding in freshwater. In order to undergo upstream spawning migrations and long periods of fasting in freshwater, they use energy that was stored as lipids during their ocean feeding phase. Lipid depletion during migration and spawning of anadromous O. mykiss can be substantial. For example, the lipid content in white muscle tissue of anadromous O. mykiss returning to the Snake River (U.S.) declined by WDFW Science Report

2 ~94% during upstream migration and spawning (Penney and Moffitt 2014). In comparison, riverine O. mykiss are believed to feed continuously in freshwater providing continuous energy inputs during their own migration and spawning activities. As a result of different feeding and metabolic requirements, one might expect that the different patterns of energy storage to be observed among the O. mykiss life histories. The study planned for the Utkholok River will address the connection between energy storage and the life history diversity of O. mykiss. At the adult life stage, anadromous life histories are expected to store more lipids than the riverine life history in order to meet the energetic requirements of returning to overwinter and mature in freshwater. This assumes that the anadromous life histories cease feeding in freshwater but that the riverine life history continues to feed during the overwinter period. Females are expected to store more lipids than males in order to meet the energetic requirements of reproductive maturation (Hendry and Berg 1999). This assumes that females returning to Kamchatka rivers in the fall months adopt a stream-maturation strategy similar to that observed in summer-run steelhead in North America. This study will also use stable isotope techniques to validate the feeding environment interpreted from the scale growth patterns. This technique can distinguish feeding in different food webs based on the carbon and nitrogen source for that food web. Carbon-13 isotope ratios are used to differentiate feeding in coastal versus offshore food webs (Johnson and Schindler 2009) and nitrogen-15 isotope ratios are used to differentiate freshwater versus marine food webs (Kline et al. 1990) as well as trophic level within a food web (Vander Zanden and Rasmussen 2001; Post 2002). The δ 13 C and δ 15 N values in the fish tissue are expected to reflect the environment in which they undergo the most growth, i.e., after the smolt period. Previous studies have used this technique to compare ocean feeding of among species of Pacific salmon (Johnson and Schindler 2009) as well as differences among steelhead stocks from the same river (Quinn et al. 2012). At the adult life stage of O. mykiss in Kamchatka rivers, the anadromous life history is expected to have a lower δ 13 C than the estuarine life history, reflecting a more offshore basis for the anadromous feeding ecology and the riverine life history is expected to have a lower δ 15 N than the estuarine or anadromous life histories, reflecting a more terrestrial and freshwater basis for the riverine feeding ecology. Study Objectives Identify life histories of O. mykiss present in western Kamchatka rivers, Compare the adult body condition (somatic lipid content) and post-smolt feeding (stable isotopes) among life history types, and Compare these results to O. mykiss populations in the Pacific northwest. Study Site The Utkholok River flows 130 km from its headwaters to the Sea of Okhotsk. The river is low gradient (5 m/km) with base flows between 60 and 70 meter 3 /second (Pavlov et al. 2005). The Utkholok is a tundra-type river with a simple channel structure, tannic colored water, and river banks lined with willow trees. The river is primarily a meandering, single channel with combinations of riffles, pools, and WDFW Science Report

3 long runs. The presence of off-channel sloughs, backwater areas, and tributaries increases in an upstream direction. Several of the tributaries are known to provide spawning and rearing opportunities O. mykiss (M. Gruzdeva, Moscow State University, personal communication). Scientific study of O. mykiss in the Utkholok River occurred in the 1970s and again in the mid-1990s to early 2000s. Anadromous, estuarine, and riverine life histories were identified, although the majority of O. mykiss in this river are anadromous (Savvaitova et al. 2003; Pavlov et al. 2008). In the early 1990s, the anadromous portion of the O. mykiss population was reduced following an increase in illegal fishing (Savvaitova et al. 1997; Savvaitova et al. 2002). O. mykiss have not been sampled in this river for a nearly 15 years and the current composition of life histories is unknown. Methods In 2016, field work was planned for 21 days between September 17 and October 7. The sampling team included four sponsors, one scientist, and two guides. Biological sampling included identifying gender, measuring length, girth, and fat content, and collecting scales and a fin clip. Gender was identified from external features including the jaw length (tip of jaw extends past the eye = male, tip of jaw not past the eye = female) and the presence of worn ventral edge of the caudal fin (prior redd digging = female). Length was the fork length measured from the tip of the snout to the fork in the caudal fin. Girth was the largest circumference of the body anterior to the dorsal fin. Weight (W, in pounds) of each fish was calculated based on the equation: (1) W = L G2 680 Prior to calculation, length (L) and girth (G) measures were converted to inches. Twenty scales (10 each side) were collected from the area above the lateral line and posterior to the dorsal fin. Scales will be used to assign age and life history and for stable isotope analysis. Fat content of the dorsal muscle tissue was measured using a handheld microwave energy meter (Distell Fish Fatmeter, Model Number FM 692, Distell Inc., West Lothian, Scotland). This meter estimated water content and converted this value to percent lipids using the strong inverse relationship between the two substances in fish tissue. The Trout-1 setting of the energy meter used in this study was calibrated to O. mykiss by the manufacturer. Following the manufacturer s instructions, meter calibration was verified at the beginning of each sampling day. Eight readings were collected (four on each side) from the dorsal muscle tissue above the lateral line, consistent with the manufacturer s instructions and with the methods used in similar research (Crossin and Hinch 2005; Lamperth et al. 2016). Observations on fish condition (sea lice, lamprey wounds, seal or other predator scars) were recorded. Prior to release, each fish was tagged with a single numbered floy tag and photographed. Data was recorded on scale envelops in the field and transcribed to a field notebook each evening. WDFW Science Report

4 FIGURE 1. Biological sampling of O. mykiss captured in the Utkholok River, fall Sampling Effort Results Weather conditions limited helicopter transport to and from the field camp in As a result, fishing activities started on September 21, 2016 and concluded on October 3, 2016 (thirteen days of effort). Seven of these thirteen fishing days had water levels and clarity suitable for effectively use of fly fishing gear. Daily fishing effort was eight or nine hours with four to six rods fished each day. Fishing effort covered 9.8 miles (15.8 kilometers) of the Utkholok River (Figure 2). Catch per unit effort was 0.8 to 2.5 O. mykiss per rod per day. A total of 54 O. mykiss were hooked and 32 were successfully landed (Figure 3). Thirty (94%) of the landed O. mykiss were sampled for biological data. The additional two landed fish escaped prior to biological sampling. Biological Characteristics Fork length and estimated weight of all O. mykiss sampled averaged 74.3 cm (range 33 to 89 cm) and 11.7 lbs (range 1.1 to 18.4 lbs, Figure 4). The distribution of lengths and weights were bimodal with one mode around 50 cm and 5 lbs and a second mode around 80 cm and 13 lbs (Figure 4). A single 33 cm fish (1.1 lbs) appeared at the lowest extreme of the size distribution. WDFW Science Report

5 Life Histories Field Observations The visual appearance of O. mykiss could be recognized in the field as belonging to at least two different phenotypes that differed in size and coloration (Figure 5). These phenotypes may represent different life histories (i.e., freshwater and ocean growth patterns), although the final assignment of life histories will be made based on scale analysis. The smallest fish captured (33 cm FL, 1.1 lbs) fit neither of these visual groupings and is described separately. Phenotype 1 Fork length ranged from 70 to 89 cm. Fish had an elongate body shape with black and chrome coloration. Some fish with this phenotype were developing a freshwater coloration with black spots along the dorsal body surface and pink coloration on the cheek and along the lateral line. All fish lacked the chrome-olive hue observed in the smaller sized phenotype. Sea lice were occasionally observed. None of the females were observed to have worn ventral edges to their caudal fins. For the purpose of this report, this phenotype will be referred to as the anadromous life history although this assignment needs to be confirmed by scale analysis. Phenotype 2 Fork length ranged from 52 to 66 cm. Fish had a football body shape. All fish had a freshwater coloration with black spots along the dorsal body surface, pink coloration on the cheek and along the lateral line. All fish had a distinctive chrome-olive hue to the body coloration above the lateral line. No sea lice were observed. Several females had worn ventral edges to their caudal fin indicating prior spawn events. For the purpose of this report, this phenotype will be referred to as the riverine life history although this assignment needs to be confirmed by scale analysis. Phenotype 3 A single 33-cm FL O. mykiss had an oblong body shape with black spots across the body and fin surface. Coloration was chrome with lateral pink stripe. The small size of this fish made it distinctive from the others captured. For the purpose of this report, this phenotype will be referred to as the half pounder life history although this assignment needs to be confirmed by scale analysis. Fat Content Fat content was measured in 24 of the 30 fish that were biologically sampled (Figure 6). Measures were missed due to training on the first day of sampling and to the availability of one (rather than two) devices for the latter part of the season. Fat content of the dorsal muscle averaged 2.9% (range 1.5% to 4.8%). Average fat content of female O. mykiss (average = 3.7%, range = 2.8 to 4.8%) was 1.5 times that of males (average = 2.4%, range = 1.5 to 3.5%). When males were broken out by field-assigned phenotypes, the average fat content of phenotype 1 (anadromous) was 32% higher (difference of 0.7%) than the average fat content of phenotype 2 (riverine, Figure 7). Although this difference was consistent with our hypothesis about energy storage, a power analysis (α = 0.05, β = 0.8) indicated that a sample size of 40 males (20 each phenotype) would be needed to detect a statistical difference of this magnitude. Our sampling of males in 2016 provided 35% (n = 14) of the sample size needed for this comparison. WDFW Science Report

6 When females were broken out by field-assigned phenotypes, the average fat content of phenotype 1 (anadromous) was 10% lower than the average fat content of phenotype 2 (riverine, Figure 7). This difference was not consistent with our hypothesis but also reflected very low sample sizes (phenotype 1: n = 7, phenotype 2: n = 2). If females have similar magnitude of difference as males between life histories, our sampling of females in 2016 provided 22% of the needed sample size for this comparison. FIGURE 2. Satellite photo showing location of the Utkholok River field camp on Kamchatka peninsula (upper panel) and the 2016 study area within the Utkholok River (lower panel). In the lower panel, the river main stem is shown in dark blue and the area fished is shown in light blue. WDFW Science Report

7 Number of O. mykiss Number of O. mykiss Number of O. mykiss Not Landed Landed Sep 23-Sep 25-Sep 27-Sep 29-Sep 1-Oct 3-Oct FIGURE 3. Number of O. mykiss caught in fishing effort on the Utkholok River, Fork Length (cm) Weight (lbs) FIGURE 4. Distribution of length (left panel) and weight (right panel) of O. mykiss captured in the Utkholok River, Weight was estimated from length and girth measures. WDFW Science Report

8 FIGURE 5. Variation in O. mykiss observed during field sampling in the Utkholok River, Top panel is an 81 cm female (phenotype 1), and bottom panel is a 54 cm male (phenotype 2). A field photo of the putative third phenotype is not available. WDFW Science Report

9 Fat Content (%) Fat Content (%) Female Male Fork Length (cm) FIGURE 6. Fat content (%) of the dorsal muscle of O. mykiss from the Utkholok River, Fat content versus fork length are shown for males and females separately Female n = 7 n = 2 Male n = 10 n = 4 1 (Anadromous) 2 (Riverine) Phenotype (Field Call) FIGURE 7. Fat content (%) of the dorsal muscle of O. mykiss from the Utkholok River, Fat content is summarized by field-assigned phenotypes 1: anadromous, 2: riverine. Average and standard deviation for males and females are shown separately. WDFW Science Report

10 Discussion and Recommendations Results from the 2016 field season were promising but incomplete. Our work demonstrated the continued presence of multiple O. mykiss life histories in the Utkholok River, suggesting that this river continues to be a good location for studying the ecological requirements of different life histories. Anadromous and riverine phenotypes were observed in all areas of the river that we fished, and, based on visual assignments and a limited sample size, the riverine phenotype represented 20% of the landed catch. The addition of the fatmeter to the sampling protocol added minimal time (maximum of one minute) to the sampling process for each fish. During the first half of the study, we used of two fatmeter units and measures were taken by each of the two fishing teams. However, data on fat content was limited by the availability of one meter (versus two) in the latter portion of the study. Fat content of the O. mykiss caught in the Utkholok River was relatively low compared to known values from North American populations (Penney and Moffitt 2014; Lamperth et al. 2016). Differences in energy storage among stream-maturing steelhead populations may reflect fine tuning to the metabolic requirements of their respective freshwater environments. In the Utkholok River (Kamchatka) the earliest returning steelhead are observed in the months of September and October, eight or nine months prior to spawning. They migrate relatively short distances (tens of kilometers) through a low gradient river and overwinter under relatively cold stream temperatures. In the Columbia River (U.S.), the earliest returning summer steelhead are observed in May or June, approximately nine months prior to spawning. They migrate relatively long distances (hundreds of kilometers) through high gradient stretches of river and over-summer and over-winter under relatively warm stream temperatures. All of these factors distance of migration, strenuous conditions during migration, and stream temperature are likely to result in higher metabolic requirements for steelhead returning to the Columbia River populations than the Utkholok River. Consistent with these potential metabolic requirements, summer steelhead entering the Columbia River had an average of 5-6% fat content (Penney and Moffitt 2014; Lamperth et al. 2016) which is almost two times more than the average of 3% lipid content observed for anadromous O. mykiss returning to the Utkholok River. The higher fat content observed in female than male O. mykiss was consistent with energetic requirements for reproductive maturation and spawning (Hendry and Berg 1999). Energy reserves are used by females to complete egg development and construct redds for spawning and by males to complete reproductive maturation and mate competition. Although based on a limited sample size, the female-male difference was observed in both the anadromous and riverine phenotypes suggesting that the energetic requirements of reproductive maturation may be at least partially robust to different feeding behaviors of the two life histories in the freshwater environment. We were not able to fully test the hypothesis that energy storage would differ between anadromous and riverine life histories. The differences, if they exist, are small in magnitude and statistical detection of any differences was not possible with the limited number of samples obtained in With four to six rods fishing each day, we landed and sampled an average of four O. mykiss each day. Under the WDFW Science Report

11 planned twenty one days of fishing effort, this sampling rate would have provided an adequate sample size for statistical comparison of fat content of the different phenotypes (sample size ~ 80). Given these calculations, a statistically robust number of samples should be attainable given an additional field season to complete this study on the Utkholok River. Next Steps to Complete the Planned Research Research initiated on the Utkholok River in the 2016 demonstrated good potential to further scientific understanding of O. mykiss diversity. Multiple life histories were clearly apparent in the catch and variation in fat content was observed among individuals. A comparison of Kamchatka and North American populations provides important insight into the energetic requirements of anadromous steelhead in different ecosystems. However, the work on the Kamchatka study is incomplete due to low catch numbers that resulted from the unusually heavy rains that caused the river to be high, muddy and unfishable for significant portion of the field season and severely limited our ability to collect samples. The sample size was about 30% of that needed to achieve the study objectives and additional data collection will be needed to complete the work as planned. Recommendations to complete the study objectives are: Increase sample size for fat content measures with a goal of individuals Complete life history assignments from collected samples Complete stable isotope analysis on a subset of available samples (anadromous, riverine, etc.) to determine the sample size needed for final analysis Explore and implement ultrasound technology to validate male/female assignment in the field in future years (e.g., Evans et al. 2004; Macbeth et al. 2011) Programmatic Recommendations for Future Years Plan backup collection methods. The exemplifies a successful collaboration between scientists and avid fly fishers. In typical years, participation in the project has met the expectations of both sets of collaborators. However, the KSP was developed and is permitted as a scientific expedition. As such, back-up methods for sampling the fish should be considered in atypical years when river conditions are not suitable for collecting samples by angling. In 2016, a portion of the fishing time was limited by transport windows into and out of camp and this limitation can not be addressed by alternate collection techniques. However, there were a number of days when staff and sponsors were in camp and the river ran high and turbid. During these days, collection techniques other than fly fishing (e.g., tangle nets) would have been more suitable for catch and release of fish for scientific study. Given the large investment of time and funds to support the scientific study, I would recommend a discussion about backup fish collection techniques with scientists from Moscow State University in order to ensure success of the annual study efforts. These discussions would need to occur prior to the annual permit application process. Help sponsors connect fish they catch to scientific discovery. To some extent, each of the sponsors has selected this trip because their interest goes beyond catching fish to the fish themselves. The time spent in camp is a unique opportunity to have conversations about fish, science, and conservation. The WDFW Science Report

12 sponsors, guides and scientists bring their own experiences and this generates conversation that draws attention to the science as well as the fun of catching large robust steelhead. The science presentation provided by Moscow State University is a very informative overview of the history of the Kamchatka Steelhead Project. However, given the large amount of expertise and information available, we can do more to engage sponsors in the science aspects of the project and provide new information to sponsors that return each year. In 2016, I left a folder of Kamchatka publications in the dining cabin after a few people asked about them. Many of the sponsors ended up reading the material which was helpful for starting discussions about steelhead science and the rivers of Kamchatka. However, scientific publications provide too much detail for a non-technical audience. Ideas for future years include: (1) Handouts for the dining table Summarize information on fish lengths, ages, and repeat spawn rates into a few graphs, assemble into laminated handouts, and leave for viewing in the dining cabin. (2) Posters for the walls Assemble pictures of the different O. mykiss life histories, scale growth patterns, proportions of life history by river into a laminated poster and nail to the wall of the dining cabin. Moscow State University scientists may already have such posters and they could be replicated to be shared in field camp. (3) Additional evening presentations Russian and U.S. scientists could diversify the evening discussions by providing additional presentations that highlight their current research with O. mykiss in Kamchatka (or U.S.) rivers. Bring a light microscope to view scale samples in camp. Several of the sponsors expressed interested in seeing for themselves how fish are aged and what scale growth patterns look like. It would not be too difficult to bring a dissecting microscope to camp for this purpose. Providing an opportunity for people to see for themselves what the scales look like under the microscope would be a next step into the science that would connect the angling and science experience for interested participants. Acknowledgements Justin Miller and Eduard Golzhe guided the fishing effort. Angling effort in Session 1 was provided by Michael Comb, Dave Comb, Matt Comb, Tristan Comb, Justin Miller, and Mara Zimmerman. Angling effort in Session 2 was provided by Dan Bolin, Asa Carpenter, Otis Fugelso, Nathan Janos, Justin Miller, and Mara Zimmerman. Marina Gruzdeva provided scientific oversight and consultation. This work is collaboration with Moscow State University, The Conservation Angler, and the Wild Salmon Center. Tom Quinn (University of Washington) and Matt Sloat (Wild Salmon Center) loaned fat meters for the study. Tom Quinn (University of Washington) will collaborate on the stable isotope analysis. Participation of WDFW scientists in the was possible due to financial support from The Conservation Angler. WDFW Science Report

13 References Crossin, G. T., and S. G. Hinch A nonlethal, rapid method for assessing the somatic energy content of migrating adult Pacific salmon. Transactions of the American Fisheries Society 134: Evans, A. F., M. S. Fitzpatrick, and L. K. Siddens Use of ultrasound imaging and steroid concentrations to identify maturational status in adult steelhead. North American Journal of Fisheries Management 24(3): Hendry, A. P., and O. K. Berg Secondary sexual characters, energy use, senescence, and the cost of reproduction in sockeye salmon. Canadian Journal of Zoology 77: Johnson, S. P., and D. E. Schindler Trophic ecology of Pacific salmon (Oncorhynchus spp.) in the ocean: a synthesis of stable isotope research. Ecological Research 24(4): Kendall, N. W., J. R. McMillan, M. R. Sloat, T. W. Buehrens, T. P. Quinn, G. R. Pess, K. V. Kuzishchin, M. M. McClure, and R. W. Zabel Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns. Canadian Journal of Fisheries and Aquatic Sciences 72: Kline, T. C. J., J. J. Goering, O. A. Mathisen, P. H. Poe, and P. L. Parker Recycling of elements transported upstream by runs of Pacific Salmon: 1. d15n and d13c evidence in Sashin Creek, southeastern Alaska. Canadian Journal of Fisheries and Aquatic Sciences 47: Kuzishchin, K. V., K. A. Savvaitova, and M. A. Gruzdeva Scale structure as criteria for the determination of local stocks of mikizha Parasalmo mykiss from western Kamchatkan and North American rivers. Journal of Ichthyology 39(6): Lamperth, J. S., T. P. Quinn, and M. S. Zimmerman Levels of stored energy but not marine foraging patterns differentiate seasonal ecotypes of wild and hatchery steelhead trout, Oncorhynchus mykiss, returning to the Kalama River, Washington. Canadian Journal of Fisheries and Aquatic Sciences Macbeth, B. J., H. D. Frimer, J. R. Muscatello, and D. M. Janz Use of portable ultrasonography to determine ovary size and fecundity non-lethally in northern pike (Esox lucius) and white sucker (Catostomus commersoni). Water Quality Research Journal of Canada 46(1): McMillan, J. R., J. B. Dunham, G. H. Reeves, J. S. Mills, and C. E. Jordan Individual condition and stream temperature influence early maturation or rainbow and steelhead trout, Oncorhynchus mykiss. Environmental Biology of Fishes 93: McPhee, M., F. Utter, J. Stanford, K. Kuzishchin, K. Savvaitova, D. Pavlov, and F. Allendorf Population structure and partial anadromy in Oncorhynchus mykiss from Kamchatka: relevance for conservation strategies around the Pacific Rim. Ecology of Freshwater Fish 16(4): Pavlov, D., K. Kuzishchin, P. Kirillov, M. Gruzdeva, E. Maslova, A. Y. Mal tsev, D. Stanford, K. Savvaitova, and B. Ellis Downstream migration of juveniles of Kamchatka mykiss Parasalmo mykiss from tributaries of the Utkholok and Kol rivers (Western Kamchatka). Journal of Ichthyology 45(suppl 2): Pavlov, D., K. Savvaitova, K. Kuzishchin, M. Gruzdeva, A. Y. Mal Tsev, and J. Stanford Diversity of life strategies and population structure of Kamchatka mykiss Parasalmo mykiss in the ecosystems of small salmon rivers of various types. Journal of Ichthyology 48(1): Penney, Z. L., and C. M. Moffitt Proximate composition and energy density of stream-maturing adult steelhead during upstream migration, sexual maturity, and kelt emigration. Transactions of the American Fisheries Society 143: Post, D. M Using stable isotopes to estimate trophic position: Models, methods, and assumptions. Ecology 83(3): WDFW Science Report

14 Quinn, T. P., T. R. Seamons, and S. P. Johnson Stable isotopes of carbon and nitrogen indicate differences in marine ecology between wild and hatchery-produced steelhead. Transactions of the American Fisheries Society 141: Savvaitova, K., K. Kuzishchin, M. Gruzdeva, D. Pavlov, D. Stanford, and B. Ellis Long-term and short-term variation in the population structure of Kamchatka steelhead Parasalmo mykiss from rivers of western Kamchatka. Journal of Ichthyology 43(9): Savvaitova, K. A., K. V. Kuzishchin, S. V. Maksimov, and D. S. Pavlov Population structure of mikizha Parasalmo mykiss from rivers of northwestern Kamchatka and North America. Journal of Ichthyology 39: Savvaitova, K. A., M. A. Tutukov, K. V. Kuzishchin, and D. S. Pavlov Changes in the population structure of mikizha Parasalmo mykiss from the Utkholok River, Kamchatka, during the fluctuation in its abundance. Journal of Ichthyology 42: Sloat, M. R., D. J. Fraser, J. B. Dunham, J. A. Falke, C. E. Jordan, J. R. McMillan, and H. A. Ohms Ecological and evolutionary patterns of freshwater maturation in Pacific and Atlantic salmonines. Reviews in Fish Biology and Fisheries 24(3): Vander Zanden, M. J., and J. B. Rasmussen Variation in delta N-15 and delta C-13 trophic fractionation: Implications for aquatic food web studies. Limnology and Oceanography 46(8): WDFW Science Report