Steelhead Smolts Research Articles

The Effect of Hatchery Release Strategy on Marine Migratory Behaviour and Apparent Survival of Seymour River Steelhead Smolts (Oncorhynchus mykiss)

Early marine migratory behaviour and apparent survival of hatchery-reared Seymour River steelhead (Oncorhynchus mykiss) smolts was examined over a four year period (2006–2009) to assess the impact of various management strategies on improving early marine survival. Acoustically tagged smolts were released to measure their survival using estuary and coastal marine receivers forming components of the Pacific Ocean Shelf Tracking (POST) array. Early marine survival was statistically indistinguishable between releases of summer run and winter run steelhead races, night and day releases, and groups released 10 days apart. In 2009, the survival of summer run steelhead released into the river was again trialed against groups released directly into the ocean at a distance from the river mouth. Apparent survival was improved significantly for the ocean released groups. The health and physiological status of the various release groups were monitored in years 2007–2009, and results indicate that the fish were in good health, with no clinical signs of disease at the time of release. The possibility of a disease event contributing to early marine mortality was further examined in 2009 by vaccinating half of the released fish against common fish diseases (vibriosis, furunculosis). The results suggest that marine survival may be enhanced using this approach, although not to the extent observed when the smolts were transported away from the river mouth before release. In summary, direct experimental testing of different release strategies using the POST array to measure ocean survival accelerated the scientific process by allowing rapid collection of data which enabled the rejection of several existing theories and allowed tentative identification of several new alternative approaches that might improve early marine survival of Seymour River steelhead.

Diet estimation in California sea lions, Zalophus californianus

AbstractWe performed a captive feeding experiment using California sea lions to assess biases associated with estimating pinniped diet using scats and spews. Sea lions were fed nine of their natural prey species: anchovy, sardine, Pacific mackerel, jack mackerel, hake, steelhead smolts, shortbelly rockfish, pink salmon, and market squid. Recovery percentages varied among prey species using otoliths and were improved for adult salmon and sardine using the all‐structure method. Numerical and graded length correction factors provided better estimates of number and size of prey consumed. Four models used to determine the proportions of prey species consumed by a sea lion population were tested. The all‐structure method and variable biomass reconstruction model, in conjunction with numerical and graded length correction factors, provided more accurate estimates than without. We provide numerical correction factors for all prey species, including correction factors for specific salmon bones: vertebrae, branchials, radials, teeth, gill rakers, and hypurals.

Estimating Changes in Coho Salmon and Steelhead Abundance from Watershed Restoration: How Much Restoration is Needed to Measurably Increase Smolt Production?

AbstractUsing existing data from evaluations of habitat restoration, we estimated the average change in coho salmon Oncorhynchus kisutch and steelhead O. mykiss parr and smolt densities for common in‐channel (culvert removal, large wood placement, boulder placement, and constructed logjams) and floodplain restoration techniques (constructed side channels and reconnected floodplain habitats). We then used these numbers and a Monte Carlo simulation to predict changes in fish numbers in a model watershed for two restoration scenarios: (1) restoration of all accessible habitat within the watershed and (2) restoration of the average amount historically implemented in Puget Sound watersheds (8% of total restorable areas). Mean increases in coho salmon parr or smolt density after restoration ranged from 0.19 to 2.32 parr/m for in‐channel techniques and from 0.34 to 1.70 parr/m2 for floodplain techniques. Increases in steelhead parr or smolt density ranged from −0.06 to 0.71 fish/m and from 0.03 to 0.06 fish/m2 for in‐channel and floodplain techniques, respectively. Under restoration scenario 1, the predicted mean increase in numbers was 1,459,254 (117%) and 285,302 (140%) for coho salmon parr and smolts and 93,965 (65%) and 28,001 (125%) for steelhead parr and smolts. Under scenario 2, the predicted mean increase in parr and smolts was 59,591 (5%) and 15,022 (7%) for coho salmon and 1,733 (1%) and 1,195 (5%) for steelhead. The percentage of floodplain and in‐channel habitat that would have to be restored in the modeled watershed to detect a 25% increase in coho salmon and steelhead smolt production (the minimum level detectable by most monitoring programs) was 20%. However, given the large variability in fish response (changes in density or abundance) to restoration, 100% of the habitat would need to be restored to be 95% certain of achieving a 25% increase in smolt production for either species. Our study demonstrates that considerable restoration is needed to produce measurable changes in fish abundance at a watershed scale.

Early marine migration patterns of wild coastal cutthroat trout (Oncorhynchus clarki clarki), steelhead trout (Oncorhynchus mykiss), and their hybrids.

BackgroundHybridization between coastal cutthroat trout (Oncorhynchus clarki clarki) and steelhead or rainbow trout (Oncorhynchus mykiss) has been documented in several streams along the North American west coast. The two species occupy similar freshwater habitats but the anadromous forms differ greatly in the duration of marine residence and migration patterns at sea. Intermediate morphological, physiological, and performance traits have been reported for hybrids but little information has been published comparing the behavior of hybrids to the pure species.Methodology/Principal FindingsThis study used acoustic telemetry to record the movements of 52 cutthroat, 42 steelhead x cutthroat hybrids, and 89 steelhead smolts, all wild, that migrated from Big Beef Creek into Hood Canal (Puget Sound, Washington). Various spatial and temporal metrics were used to compare the behavior of the pure species to their hybrids. Median hybrid residence time, estuary time, and tortuosity values were intermediate compared to the pure species. The median total track distance was greater for hybrids than for either cutthroat or steelhead. At the end of each track, most steelhead (80%) were located near or north of the Hood Canal, as expected for this seaward migrating species, whereas most cutthroat (89%) were within 8 kilometers of the estuary. Most hybrids (70%) were detected leaving Hood Canal, though a substantial percentage (20%) remained near the Big Beef Creek estuary. More hybrids (7.5%) than pure cutthroat (4.5%) or steelhead (0.0%) were last detected in the southern reaches of Hood Canal.Conclusions/SignificanceGiven the similarity in freshwater ecology between the species, differences in marine ecology may play an important role in maintaining species integrity in areas of sympatry.

Smolt Transformation in Two California Steelhead Populations: Effects of Temporal Variability in Growth

AbstractWe tested the effect of temporal patterns in food supply on life history decisions in coastal steelhead Oncorhynchus mykiss irideus from a Central California coastal (CCC) population (Scott Creek) and a Northern California Central Valley (NCCV) population (upper Sacramento River basin). We manipulated growth through feeding experiments conducted from May to the following March using warm (2006 cohort) and cool (2007 cohort) temperature regimes. Survival in seawater challenges just before the time of typical juvenile emigration provided an index of steelhead smolt versus nonsmolt life history pathways. Survival varied significantly with fish size (with larger fish being more likely to survive than smaller fish) and by source population (with CCC steelhead being more likely to survive than NCCV steelhead of the same size). The timing of increased food supply (treatment group) did not significantly affect seawater survival rates in either NCCV or CCC steelhead. For both strains, the eventual survivors of seawater challenges (putative smolts) diverged from the eventual mortalities (putative nonsmolts) in both size and growth rate by June in both years, suggesting that the initial growth advantages were maintained throughout the experiments. A significant divergence in condition factor between smolts and nonsmolts by December matched the expected morphological transition of smolts, which showed faster growth in length than weight compared with nonsmolts. The apparent timing of the decision window, several months before the typical period of smolt emigration, matches the patterns observed for other salmonids. In coastal California, this decision must occur before fish have had the opportunity to take advantage of improved winter–early spring feeding conditions. These results support the role of early growth opportunity in life history decisions and provide insight into the applicability of life history models for managing California steelhead.

A Comparison of the Survival and Migratory Behavior of Hatchery‐Reared and Naturally Reared Steelhead Smolts in the Alsea River and Estuary, Oregon, using Acoustic Telemetry

AbstractWe tracked three groups of steelhead Oncorhynchus mykiss smolts implanted with acoustic transmitters to determine whether the degree of hatchery domestication or the juvenile rearing environment (hatchery raceway versus natural stream) influenced migration timing and survival in the Alsea River and estuary, Oregon. Two groups consisted of age‐1 smolts reared in concrete raceways. One hatchery‐reared group (traditional brood group) was derived from the traditional Alsea River broodstock initially developed in the 1950s. The second hatchery‐reared group (new brood group) was derived from naturally reared Alsea River adult steelhead that were captured and spawned at the hatchery beginning in the winter of 2000–2001. The third group (naturally reared group) consisted of age‐2 naturally reared smolts captured in a downstream migrant trap located in a tributary stream near the hatchery. We placed transmitters in 74 traditional brood smolts, 76 new brood smolts, and 72 naturally reared smolts. Thirty‐one acoustic receivers were located throughout the Alsea River and estuary and in the ocean offshore of the river mouth to monitor smolt movement. We found no significant difference between groups in their survival to the head of tide or to the mouth of the estuary. Most smolts from all three groups were detected at the head of tide (87% of fish from the traditional brood group, 78% from the new brood group, and 84% from the naturally reared group). However, survival was poor in the lower estuary for all three groups; we estimated that only 37% of the traditional brood group, 45% of the new brood group, and 47% of the naturally reared group survived to the ocean. The timing of migration through the river was highly variable in all three groups, and we found no significant differences in the rate of downstream movement from the release site to the head of tide. Mean residence time within the estuary was similar for all groups, although smolts from the naturally reared group showed less variability in estuary residence time than hatchery‐reared smolts.

Early Marine Survival and Behavior of Steelhead Smolts through Hood Canal and the Strait of Juan de Fuca

AbstractThe depressed status of Puget Sound populations of steelhead Oncorhynchus mykiss contrasts with the healthier condition of those along the coast of Washington and suggests that there is substantial smolt mortality during the migration through Puget Sound to the Pacific Ocean. Acoustic telemetry transmitters and stationary receivers were used to investigate the survival, migration timing, and migratory behavior of 159 steelhead smolts in 2006 and 187 smolts in 2007 from four Hood Canal (part of Puget Sound) streams and one stream flowing into the Strait of Juan de Fuca. The estimated population‐specific survival rates for wild and hatchery smolts from the river mouths to the northern end of Hood Canal (28.1–75.4 km) ranged from 55% to 86% in 2006 and from 62% to 84% in 2007. Survival was much lower from the northern end of Hood Canal to the Strait of Juan de Fuca (135 km) in 2006 (23–49%) and could not be reliably measured in 2007. Travel rates through Hood Canal (8–10 km/d) were significantly lower than those estimated as the fish migrated through northern Puget Sound and the Strait of Juan de Fuca (26–28 km/d), while the mortality rates per unit of distance traveled were very similar in the two segments. The high daily mortality rates estimated during the early marine phase of the steelhead life cycle (2.7%/d) suggest that mortality rates decrease substantially after steelhead enter the Pacific Ocean.

Returns of Hatchery Steelhead with Different Fin Clips and Coded Wire Tag Lengths

AbstractLeft ventral (LV) fin clips have routinely been used in the Columbia River basin to visually identify the presence of a coded wire tag (CWT) in steelhead Oncorhynchus mykiss. Managers and researchers alike have expressed concern that the ventral fin clip may negatively affect survival. Adult returns from summer steelhead smolts released from Lyons Ferry Hatchery (LFH), Washington State, between 1996 and 1999 having combinations of adipose (AD) and LV fin clips and 1.1‐ or 1.6‐mm‐long CWTs were compared. The CWT loss rate calculated from release to adult recovery was 1.9% and the LV fin clip regeneration rate was 2.4%; neither of these rates influenced our recovery results. We found slight, nonsignificant differences in return rates between fish with AD fin clips and those with both AD and LV fin clips (ADLV) and between fish with 1.1‐mm CWTs and those with 1.6‐mm CWTs. Overall, fish with ADLV fin clips had LFH return rates that were 5% greater than those of fish with AD‐only clips, and fish with 1.6‐mm CWTs had LFH return rates that were 6% higher than those of fish with 1.1‐mm CWTs. Increased straying because of the 1.6‐mm CWT length was not evident, although there was likely sampling bias at other hatcheries or traps that did not conduct electronic CWT scans of fish that lacked LV clips. Two variables that may have influenced our results were examined, but neither was determined to be a factor in our results. Our study results suggest that a ventral fin clip or longer CWT does not impair adult returns (survival) of hatchery summer steelhead. Unfortunately, study limitations reduced our statistical power to definitively conclude that there was no significant difference in survival, and additional study may be necessary. However, our study provides sufficient information for fishery managers to consider use of the LV clip on hatchery steelhead as a visual cue for CWT recovery when electronic scanning of fish will be inconsistently used or is unavailable. Also, we suggest the use of 1.6‐mm CWTs if electronic detection is to be the primary recovery method as it does not appear to affect survival in hatchery steelhead. We strongly caution managers to ensure that 100% electronic scanning of fish occurs throughout the region before foregoing standard LV fin clip marks on steelhead that contain CWTs.

Rethinking Dams: Pacific Salmon Recovery May Rest on Other Factors

Rethinking Dams: Pacific Salmon Recovery May Rest on Other Factors

Adult Returns of Volitionally Migrating and Pond‐Sedentary Hatchery‐Reared Steelhead Smolts

AbstractAdult return rates of steelhead Oncorhynchus mykiss that volitionally emigrated as smolts were compared with those of pond‐sedentary juveniles forced from a raceway after being allowed 6 weeks of volitional migration opportunity. In 5 years of releases, an average of 7.2% of the smolts remained in the raceway after the volitional migration opportunity. Adult returns of volitional and pond‐sedentary fish were statistically similar in all but 1 year of release; in that year, pond‐sedentary returns were significantly greater than those from the volitional release. The results suggest that pond‐sedentary juvenile steelhead should not be destroyed or placed in nonanadromous waters out of concern for poor adult survival.

The Effect of an Introduced Summer Steelhead Hatchery Stock on the Productivity of a Wild Winter Steelhead Population

AbstractWe investigated the effect of a hatchery program for summer steelhead Oncorhynchus mykiss on the productivity of a wild winter steelhead population in the Clackamas River, Oregon. We used a suite of Ricker and Beverton–Holt stock–recruitment models that incorporated species interaction variables to demonstrate that when high numbers of hatchery summer steelhead adults were present the production of wild winter steelhead smolts and adults was significantly decreased. We found that large releases of hatchery smolts also contributed to the decrease in wild adult productivity. Averaged over the results of our models, a 50% decline in the productivity parameter (the number of recruits per spawner at low densities) and a 22% decline in the maximum number of recruits produced in the basin were observed when high numbers of hatchery fish were present. We concluded that over the duration of the hatchery program, the number of hatchery steelhead in the upper Clackamas River basin regularly caused the total number of steelhead to exceed carrying capacity, triggering density‐dependent mechanisms that impacted the wild population. The number of smolts and adults in the wild winter steelhead population declined until critically low levels were reached in the 1990s. Hatchery fish were removed from the system in 2000, and early results indicate that the declining trends have reversed.

Caspian Tern Predation on Juvenile Salmonids in the Mid‐Columbia River

AbstractWe used a bioenergetics approach to determine the magnitude of predation by Caspian terns Sterna caspia on juvenile salmonids Oncorhynchus spp. in the mid‐Columbia River during 2000 and 2001. Caspian terns nesting on Crescent Island, Washington, located below the confluence of the Snake and Columbia rivers, consumed several hundred thousand juvenile salmonids each year of the study. Tern consumption of smolts was higher in 2001 (679,000 smolts; 95% confidence interval (CI): 533,000–825,000 smolts) than in 2000 (465,000 smolts; 95% CI: 382,000–547,000 smolts) as a result of an increase in tern breeding pairs, fledging success, and percentage of salmonids in the diet. On‐colony detection rates of passive integrated transponder tags from in‐river migrating smolts were also higher in 2001 (0.90–12.40%) than in 2000 (0.03–1.60%); the higher predation rates in 2001 were probably caused by extreme drought conditions that resulted in reduced spill from hydroelectric dams, lower river flows, and increased travel times for in‐river migrating smolts. Tern predation rates on juvenile steelhead O. mykiss were higher than those on yearling Chinook salmon O. tshawytscha in both years. The impacts of tern predation on steelhead smolts and yearling Chinook salmon from the Snake River were slight after accounting for the high proportion of smolts collected for transportation above Crescent Island. Survival of steelhead smolts from the upper Columbia River that are not transported above Crescent Island may be significantly affected by tern predation, particularly in low‐flow years. Appreciably higher predation rates on salmonids by Crescent Island terns than those observed in 2001 are unlikely considering the constraints on tern colony expansion, limited capacity for increased per capita smolt consumption by terns, and current high transportation rates for Snake River smolts.

Fine‐Scale Behavioral Responses of Pacific Salmonid Smolts as They Encounter Divergence and Acceleration of Flow

AbstractWe assessed fine‐scale behavioral responses of the smolts of four Pacific salmonid species to open and constricted channels in a flume. Natural migrants encountered two geometrically similar parallel channels with different hydraulic conditions representing constricted and open treatments. Observation of route selection under alternate discharge scenarios provided evidence of behavioral choice by smolts. As expected, the majority of smolts passed through the open channel in a ratio consistent with flow. After controlling for the influence of flow, both initial channel selection and subsequent channel rejection was higher for the constricted channel; rejection was probably due to fish detecting an area of rapidly accelerating flow. The majority of smolts traveled downstream headfirst and faster than the mean midcolumn water velocity. Those that faced the flow passed at a slower rate and tended to select the open treatment. The few yearling Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch smolts that did not pass through the treatment channels, but held position within the flume, were larger than their conspecifics that passed downstream. Large steelhead (anadromous rainbow trout O. mykiss) smolts and subyearling Chinook salmon were more likely to pass the constricted channel than smaller fish. These results suggest that efforts to effectively guide fish with diversion structures will require understanding how the structures alter the local hydraulic environment and, thus, influence fish behavior.

Effects of an increase in large wood on abundance and survival of juvenile salmonids (Oncorhynchus spp.) in an Oregon coastal stream

We examined the effect of an increase in large wood on the summer population size, smolt abundance, and freshwater survival of steelhead (Oncorhynchus mykiss), coastal cutthroat trout (Oncorhynchus clarki clarki), and coho salmon (Oncorhynchus kisutch). We examined these parameters for five brood years prior to the addition of wood and five brood years after in Tenmile Creek, a direct ocean tributary on the Oregon coast. Over the same time frame, a nearby reference stream, Cummins Creek, was also sampled for the same parameters. The input of large wood into Tenmile Creek resulted from a planned habitat restoration project in 1996 and an unplanned addition of wood from a winter storm the same year. Steelhead smolt abundance, steelhead freshwater survival, and coho salmon freshwater survival increased in Tenmile Creek after the input of large wood. Steelhead age-0+ summer populations and steelhead smolt populations increased in the reference stream, although steelhead freshwater survival did not. Coho salmon populations remained unchanged in the reference stream. Our results illustrate the potential shortcomings of the before-after-control-impact study design under field conditions and the potential for misinterpreting results had we employed a more modest sampling plan.

Early ocean survival and marine movements of hatchery and wild steelhead trout (Oncorhynchus mykiss) determined by an acoustic array: Queen Charlotte Strait, British Columbia

Early ocean movements, residency, and survival of steelhead (Oncorhynchus mykiss) were examinedin Queen Charlotte Strait, a large (20 � 100 km 2 ) marine area separating Vancouver Islandfrom the mainland . The results provide the first detailed data on the ocean biology of hatchery and wild steelhead smolts. Initial ocean movements were not strongly directed, with most smolts swimming in the range of 0.2–0.5 body length (BL) s � 1 . The majority (78%) vacatedQueen Charlotte Strait within 1 week of release in freshwater. Relative marine survival of hatchery smolts surgically implanted1 month prior to release was id entical to that of wildsmolts implantedon the d ay of release; survival of hatchery smolts transported to the study site, implanted, and released all on the same day was significantly lower. The results suggest that the early marine survival of hatchery andwildsmolts may be fundamentally similar, but that the cumulative stress of transportation andsurgery may red uce post-surgery survival. Hatchery smolts movedat higher average swimming speeds than wild smolts, but the difference was not statistically significant. Early marine survival within the study region appears to be relatively high (X55%), contradicting assumptions that the early marine phase is the critical periodfor d etermining salmon recruitment. r 2004 Elsevier Ltd. All rights reserved.

Naturally Spawning Hatchery Steelhead Contribute to Smolt Production but Experience Low Reproductive Success

We used genetic mixture analyses to show that hatchery summer-run steelhead Oncorhynchus mykiss, an introduced life history in the Clackamas basin of Oregon, where only winter-run steelhead are native, contributed to the naturally produced smolts out-migrating from the basin. Hatchery-produced summer steelhead smolts were released starting in 1971, and returning adults were passed above a dam into the upper Clackamas River until 1999. In the 2 years of our study, summer steelhead adults, mostly hatchery fish, made up 60% to 82% of the natural spawners in the river. Genetic results provided evidence that interbreeding between hatchery summer and wild winter steelhead was likely minor. Hatchery summer steelhead reproductive success was relatively poor. We estimated that they produced only about one-third the number of smolts per parent that wild winter steelhead produced. However, the proportions of summer natural smolts were large (36–53% of the total naturally produced smolts in the basin) because hatchery adults predominated on the spawning grounds during our study. Very few natural-origin summer adults were observed, suggesting high mortality of the naturally produced smolts following emigration. Counts at the dam demonstrated that hatchery summer steelhead predominated on natural spawning grounds throughout the 24-year hatchery program. Our data support a conclusion that hatchery summer steelhead adults and their offspring contribute to wild winter steelhead population declines through competition for spawning and rearing habitats.

Sex-biased dispersal in a salmonid fish.

We tested the hypothesis that dispersal is sex biased in an unexploited population of brook trout, Salvelinus fontinalis, on Cape Race, Newfoundland, Canada. Based on the assumptions that trout are promiscuous and that reproductive success is limited primarily by either number of mates (males) or fecundity (females), we predicted that males would disperse greater distances than females. We also tested the hypothesis that trout populations comprise stationary and mobile individuals, predicting that males have greater mobility than females. Based on a mark-recapture study of 943 individually tagged fishes, 191 of which were recaptured over 5 years, we find strong support for our hypothesis of male-biased dispersal in brook trout. Averaged among all 11 resampling periods, males dispersed 2.5 times as far as females; during the spawning period only, male dispersal exceeded that by females almost fourfold. Both sexes were heterogeneous with respect to movement, with a lower incidence of mobility among females (29.6%) than males (41.1%); mobile males dispersed six times further than mobile females. We conclude that this sex bias reduces mate competition among male kin and decreases the probability that males will reproduce with related females.

Diet of Caspian Terns in Commencement Bay, Washington

The coastal states of western North America and Mexico are home to a population of Caspian Terns (Sterna caspia) that are geographically disjunct and probably genetically isolated from other Caspian Terns in North America. About 74% of these birds nest at a single colony, East Sand Island, near the mouth of the Columbia River between Washington and Oregon. It is estimated by others that when the terns nested in 1998 on Rice Island, 26 km further east in the Columbia River estuary, they consumed Steelhead smolts (Oncorhynchus mykiss), Coho smolts (O. kisutch), and spring/summer Chinook smolts (O. tshawytscha) that reached the Columbia River estuary, thus involving species listed under the United States Endangered Species Act. In addition, because such a large percentage of the west coast population breeds at a single colony, there is concern that a natural or anthropogenic event at this colony may adversely impact the entire population. As a result, many federal, state, tribal and private natural resource managers are trying to develop a management plan to disperse a fraction of these terns from East Sand Island to other historic and/or newly created nesting sites throughout western North America. Among factors to be considered, managers must assess the potential impact that terns would have on fisheries, especially salmonids, at potential relocation sites before attempts are made to relocate the birds. This study documents the diet of terns in one prospective relocation area, Commencement Bay, Washington. Relative abundance of prey species, including salmonids, delivered to the colony by adults differed significantly from month to month during the breeding season, but overall terns brought an average of 52% juvenile salmonids back to the colony, a higher percentage of salmonids than are consumed by terns on East Sand Island. Therefore, we conclude that Commencement Bay may not be an appropriate relocation site for Caspian Terns.

Population Biology of Steelhead Spawning Runs in Three Pennsylvania Tributaries to Lake Erie

Little is currently known about the population biology of steelhead ( Oncorhynchus mykiss) that spawn in Pennsylvania's Lake Erie tributaries or the role of natural reproduction in supporting this fishery despite its popularity and importance. The goal of this study was to describe the population characteristics of steelhead spawning runs in Crooked Creek, Godfrey Run, and Trout Run, three Pennsylvania Lake Erie tributaries that are annually stocked with 80,000 to 200,000 yearling steelhead. From fall 1997 to spring 1999, returning adult steelhead were sampled during both fall and spring spawning runs using seines and backpack electrofishing gear. Sex was determined using external characteristics, total length was measured, and a scale sample was collected from each fish. Scales were analyzed to determine age, life history patterns, and relative contributions of wild and hatchery-reared fish to seasonal spawning runs. Male steelhead dominated sex ratios in both Godfrey Run and Trout Run during both seasons, while female steelhead were more prevalent in Crooked Creek. Stream-age 1 steelhead were predominant in both fall and spring runs in all three streams. During both seasons in all streams, the majority of males returned after spending only one summer in Lake Erie while most female steelhead returned at lake-age-2. The relative contribution of wild steelhead to Pennsylvania spawning runs was minimal in all three streams for both seasons. As a result, future success of Pennsylvania's steelhead fishery will likely require the continuation of annual tributary stocking of steelhead smolts.

Estimating in-river survival of migrating salmonid smolts using radiotelemetry

A field study to estimate the survival of outmigrating steelhead (Oncorhynchus mykiss) smolts using radiotelemetry methods is illustrated. A paired release–recapture design was used to estimate pool (i.e., reservoir), dam, and project (i.e., reservoir plus dam) survival at two mid-Columbia River hydroprojects based on maximum likelihood estimation. The release and detection scheme was designed to minimize the possibility of detecting false-positive radio signals from smolts that might have died upstream during the hydroproject passage. Model assumptions and possible violations are discussed. Releases of radio-tagged and passive integrated transponder (PIT) tagged steelhead smolts were also compared to assess the possible effects of tag type on migration behavior. Survival through the Rocky Reach project (P = 0.86) and Rock Island project (P = 0.41) and bypass diversion probabilities at Rocky Reach Dam (P = 0.39) were found to be similar between tag types. Small but significant differences in arrival patterns (P = 0.02) and travel times (P = 0.01) were observed between radio-tagged and PIT-tagged smolts.