Tag Recoveries Research Articles

Translocation of Humpback Chub into Tributary Streams of the Colorado River: Implications for Conservation of Large‐River Fishes

AbstractThe Humpback Chub Gila cypha, a large‐bodied, endangered cyprinid endemic to the Colorado River basin, is in decline throughout most of its range due largely to anthropogenic factors. Translocation of Humpback Chub into tributaries of the Colorado River is one conservation activity that may contribute to the expansion of the species’ current range and eventually provide population redundancy. We evaluated growth, survival, and dispersal following translocation of approximately 900 Humpback Chub over a period of 3 years (2009, 2010, and 2011) into Shinumo Creek, a tributary stream of the Colorado River within Grand Canyon National Park. Growth and condition of Humpback Chub in Shinumo Creek were consistent among year‐classes and equaled or surpassed growth estimates from both the main‐stem Colorado River and the Little Colorado River, where the largest (and most stable) Humpback Chub aggregation remains. Based on passive integrated tag recoveries, 53% (= 483/902) of translocated Humpback Chub dispersed from Shinumo Creek into the main‐stem Colorado River as of January 2013, 35% leaving within 25 d following translocation. Annual apparent survival estimates within Shinumo Creek ranged from 0.22 to 0.41, but were strongly influenced by emigration. Results indicate that Shinumo Creek provides favorable conditions for growth and survival of translocated Humpback Chub and could support a new population if reproduction and recruitment occur in the future. Adaptation of translocation strategies of Humpback Chub into tributary streams ultimately may refine the role translocation plays in recovery of the species.

Flexible, fast and accurate sequence alignment profiling on GPGPU with PaSWAS.

MotivationTo obtain large-scale sequence alignments in a fast and flexible way is an important step in the analyses of next generation sequencing data. Applications based on the Smith-Waterman (SW) algorithm are often either not fast enough, limited to dedicated tasks or not sufficiently accurate due to statistical issues. Current SW implementations that run on graphics hardware do not report the alignment details necessary for further analysis.ResultsWith the Parallel SW Alignment Software (PaSWAS) it is possible (a) to have easy access to the computational power of NVIDIA-based general purpose graphics processing units (GPGPUs) to perform high-speed sequence alignments, and (b) retrieve relevant information such as score, number of gaps and mismatches. The software reports multiple hits per alignment. The added value of the new SW implementation is demonstrated with two test cases: (1) tag recovery in next generation sequence data and (2) isotype assignment within an immunoglobulin 454 sequence data set. Both cases show the usability and versatility of the new parallel Smith-Waterman implementation.

Quantifying Avian Predation on Fish Populations: Integrating Predator‐Specific Deposition Probabilities in Tag Recovery Studies

AbstractAccurate assessment of specific mortality factors is vital to prioritize recovery actions for threatened and endangered species. For decades, tag recovery methods have been used to estimate fish mortality due to avian predation. Predation probabilities derived from fish tag recoveries on piscivorous waterbird colonies typically reflect minimum estimates of predation due to an unknown and unaccounted‐for fraction of tags that are consumed but not deposited on‐colony (i.e., deposition probability). We applied an integrated tag recovery modeling approach in a Bayesian context to estimate predation probabilities that accounted for predator‐specific tag detection and deposition probabilities in a multiple‐predator system. Studies of PIT tag deposition were conducted across three bird species nesting at seven different colonies in the Columbia River basin, USA. Tag deposition probabilities differed significantly among predator species (Caspian terns Hydroprogne caspia: deposition probability = 0.71, 95% credible interval [CRI] = 0.51–0.89; double‐crested cormorants Phalacrocorax auritus: 0.51, 95% CRI = 0.34–0.70; California gulls Larus californicus: 0.15, 95% CRI = 0.11–0.21) but showed little variation across trials within a species or across years. Data from a 6‐year study (2008–2013) of PIT‐tagged juvenile Snake River steelhead Oncorhynchus mykiss (listed as threatened under the Endangered Species Act) indicated that colony‐specific predation probabilities ranged from less than 0.01 to 0.17 and varied by predator species, colony location, and year. Integrating the predator‐specific deposition probabilities increased the predation probabilities by a factor of approximately 1.4 for Caspian terns, 2.0 for double‐crested cormorants, and 6.7 for California gulls compared with traditional minimum predation rate methods, which do not account for deposition probabilities. Results supported previous findings on the high predation impacts from strictly piscivorous waterbirds nesting in the Columbia River estuary (i.e., terns and cormorants), but our findings also revealed greater impacts of a generalist predator species (i.e., California gulls) than were previously documented. Approaches used in this study allow for direct comparisons among multiple fish mortality factors and considerably improve the reliability of tag recovery models for estimating predation probabilities in multiple‐predator systems.Received August 1, 2014; accepted November 11, 2014

Evaluating Effects of Exploitation on Annual Apparent Mortality Rates of Paddlefish Using Mark–Recapture Data

AbstractKnowledge of the effects of exploitation on population dynamics is critical to effective conservation and management of fish populations. To improve our understanding of the effects of sport fishery exploitation on populations of Paddlefish Polyodon spathula, we tested eight additive and compensatory harvest mortality hypotheses for the Paddlefish population in Lake Francis Case (LFC), South Dakota, with 33 years of tag recovery data using dead recovery models in Program MARK. We evaluated additive and compensatory harvest mortality hypotheses by modeling the effects of sport fishery closures on annual apparent survival and tag recovery rates. Our most‐supported hypotheses indicated that exploitation prior to the functional closure of the sport fishery (i.e., when exploitation became negligible) was an additive source of mortality. Annual apparent mortality estimates (i.e., 1 − annual apparent survival) of our most‐supported model decreased from 0.237 (SE = 0.036) to 0.110 (SE = 0.063) following the functional closure of the sport fishery and coincided with a decrease in recovery rate from 0.095 (SE = 0.015) to 0.010 (SE = 0.004). These results suggest that relatively unregulated sport fishery exploitation can substantially increase mortality rates of Paddlefish populations. The effects of exploitation on mortality likely differ between populations and temporally within populations due to differences in density‐dependent mortality rates.Received January 7, 2014; accepted November 19, 2014

Using parentage analysis to estimate rates of straying and homing in Chinook salmon (Oncorhynchus tshawytscha).

We used parentage analysis based on microsatellite genotypes to measure rates of homing and straying of Chinook salmon (Oncorhynchus tshawytscha) among five major spawning tributaries within the Wenatchee River, Washington. On the basis of analysis of 2248 natural-origin and 11594 hatchery-origin fish, we estimated that the rate of homing to natal tributaries by natural-origin fish ranged from 0% to 99% depending on the tributary. Hatchery-origin fish released in one of the five tributaries homed to that tributary at a far lower rate than the natural-origin fish (71% compared to 96%). For hatchery-released fish, stray rates based on parentage analysis were consistent with rates estimated using physical tag recoveries. Stray rates among major spawning tributaries were generally higher than stray rates of tagged fish to areas outside of the Wenatchee River watershed. Within the Wenatchee watershed, rates of straying by natural-origin fish were significantly affected by spawning tributary and by parental origin: progeny of naturally spawning hatchery-produced fish strayed at significantly higher rates than progeny whose parents were themselves of natural origin. Notably, none of the 170 offspring that were products of mating by two natural-origin fish strayed from their natal tributary. Indirect estimates of gene flow based on FST statistics were correlated with but higher than the estimates from the parentage data. Tributary-specific estimates of effective population size were also correlated with the number of spawners in each tributary.

Move it or lose it: movement and mortality of sablefish tagged in Alaska

A basic step in understanding the dynamics of a fish population is to quantify movement and mortality rates. Conventional mark–recapture experiments have provided the foundation for studies on animal movement, particularly for fish. Previous studies have shown rapid mixing of sablefish (Anoplopoma fimbria) among fishery regulatory areas, with the pattern of movement related to fish size. Over 300 000 tag releases in Alaska and over 27 000 tag recoveries from 1979 to 2009 were analyzed. We used a Markov model to quantify annual movement probabilities among areas for three size groups of sablefish. The negative-binomial likelihood was used to model the tag-recovery data because of significant overdispersion. Annual movement probabilities were high, ranging from 10% to 88% depending on area of occupancy at each time step and size group. Overall, movement probabilities were very different between areas of occupancy and moderately different between size groups. Estimated annual movement of small sablefish from the central Gulf of Alaska had the reverse pattern of a previous study, with 29% moving westward and 39% moving eastward. Movement probabilities also varied annually, with decreasing movement until the late 1990s and increasing movement until 2009. Year-specific magnitude in movement probability of large fish was highly negatively correlated with female spawning biomass estimates from the federal stock assessment. Mean mortality estimates from time at liberty were similar to the federal stock assessment. Incorporating these tag-recovery and movement data into a fully age-structured spatial stock assessment model will inform harvest apportionment strategies to conserve spawning biomass and maximize future yields.

Match-mismatch dynamics and the relationship between ocean-entry timing and relative ocean recoveries of Central Valley fall run Chinook salmon

The match-mismatch hypothesis suggests there is an optimal window for organisms to undergo key life cycle events. Here, we test the importance of match-mismatch dynamics in the timing of salmon arrival to the ocean, relative to ecosystem phenology, for the ocean survival rates of hatchery-origin fall run Chinook salmon originating from California's Central Valley. Specifi- cally, we considered tag recovery data for releases of coded-wire tagged fish released into the San Francisco Estuary during the years 1978 to 2010. We determined a time lag for each release relative to the local spring transition date (initiation of net upwelling). Additionally, we obtained information on fish condition and size at release, the number of fish released corresponding to distinct tag codes, and yearly stock-specific harvest rate estimates. We used generalized linear models, generalized additive models, and cross-validation to identify the best-supported models for the effects of release timing and other covariates on age-3 ocean fishery recovery rates, a proxy of ocean survival rates. Release time is a useful predictor of within-year variation in survival rates, above and beyond the effects of size at release, presence of disease, and the use of net pens, and the lag relative to spring transition was a slightly better predictor than year-day. The optimal release timing appeared to occur around the end of May, and the optimal time lag appeared to be approximately 70 to 115 d after the spring transition date. However, timing is only one of many factors that affected within- and among-year variation in survival.

Frailty models for the estimation of tag shedding rates with tagger effects

Double tagging studies are used to estimate the proportion of originally tagged fish that shed their tags prior to recapture, but models typically fitted to double tag recoveries have been subject to restrictive assumptions. For example, a common assumption is that the shedding rates of all tags are identical. Hearn et al. (Hearn, W.S., Leigh, G.M., Beverton, R.J.H., 1991. ICES J. Mar. Sci. 48, 41–51) found differences in shedding rates between taggers, and demonstrated algebraically that such differences lead to biases in estimators of shedding rates. However, widely applicable models that account for differences in shedding rates between taggers have not been developed. We adapt the proportional hazards model to the problem of estimating tag shedding rates from double-tag recovery data. Differences in shedding rates between taggers are modelled using multiplicative random effects or frailties. The frailty models are fitted to recoveries from a 1990s tagging study of southern bluefin tuna (Thunnus maccoyii) at exact times-at-liberty and the results compared with models previously applied for this species.

Southern bluefin tuna (Thunnus maccoyii) shed tags at a higher rate in tuna farms than in the open ocean — two-stage tag retention models

Tag shedding rates are estimated for southern bluefin tuna (SBT, Thunnus maccoyii) from double-tagging data arising from two tagging studies run in the 1990s and 2000s. Since the early 1990s, a high proportion of SBT tag recoveries has been sourced from juveniles captured by purse seine vessels in the Great Australian Bight and transferred to tuna farms off Port Lincoln in the state of South Australia. When tags have been shed by wild-caught SBT fattened in tuna farms, it is generally not known if the tags were shed in the open ocean before purse seine capture or after purse seine capture while the fish were on farm. Using a Bayesian approach, we fit separate tag retention curves for time in the ocean and time on farms as Weibull distribution reliability functions. The study suggests SBT shed tags at a much higher rate in on-farm enclosures than in the open ocean. Biofouling on tags in tuna farms may contribute to higher tag shedding rates.

Migrations of green turtles (Chelonia mydas) between nesting and foraging grounds across the Coral Sea.

Marine megafauna tend to migrate vast distances, often crossing national borders and pose a significant challenge to managers. This challenge is particularly acute in the Pacific, which contains numerous small island nations and thousands of kilometers of continental margins. The green sea turtle, Chelonia mydas, is one such megafauna that is endangered in Pacific waters due to the overexploitation of eggs and adults for human consumption. Data from long-term tagging programs in Queensland (Australia) and New Caledonia were analysed to investigate the migrations by C. mydas across the Coral Sea between their nesting site and their feeding grounds. A review of data collected over the last 50 years by different projects identified multiple migrations of C. mydas to and from New Caledonia (n = 97) and indicate that turtles foraging in New Caledonia nest in the Great Barrier Reef (Australia) and vice versa. Several explanations exist for turtles exhibiting this energetically costly movement pattern from breeding to distant foraging grounds (1200–2680 km away) despite viable foraging habitat being available in the local vicinity. These include hatchling drift, oceanic movements and food abundance predictability. Most of the tag recoveries in New Caledonia belonged to females from the south Great Barrier Reef genetic stock. Some females (n = 2) even showed fidelity to foraging sites located 1200 km away from the nesting site located in New Caledonia. This study also reveals previously unknown migrations pathways of turtles within the Coral Sea.

Evaluation of tag mixing assumptions in western Pacific Ocean skipjack tuna stock assessment models

Fish population estimators (for abundance, mortality and movement) from conventional tagging (mark-recapture) programmes require the assumption that tagged individuals are equally vulnerable to recapture as the (relevant portion of the) untagged population. Most commercial tuna species are distributed over millions of square km, with poorly understood stock structure and movement dynamics, while tags tend to be released in much smaller areas that are selected for logistical reasons. If the tags do not mix sufficiently with the general population this could substantially bias tuna stock assessments. We outline two simple quantitative methods for evaluating tag mixing, and apply them to western Pacific Ocean skipjack tuna (Katsuwonis pelamis). The first approach compares, in a discrete time window, the spatial distributions of tag recoveries from pairs of release events that were separated in space and/or time. Significant differences between the recovery distributions indicate that tags from the two release events are not fully mixed with each other, such that one or both release events cannot be fully mixed with the general population either. The second approach tests whether tag density (number of recovered tags per unit of catch) is spatially homogeneous for an individual release event. Both tests focus on detecting incomplete mixing and neither can prove that full mixing has been achieved. The analyses provide strong evidence that tag mixing assumptions are not being met in recent western Pacific skipjack tuna stock assessments. Simple diffusion models were fit to the tag density observations and used to simulate the potential magnitude of mixing biases using simple estimators for abundance and natural and fishing mortality. Options for reformulating the skipjack assessment are discussed.

Fifty years of dart tag recoveries for tropical tuna: A global comparison of results for the western Pacific, eastern Pacific, Atlantic, and Indian Oceans

Over the last 50 years, numerous dart tagging programs have been conducted on tropical tunas worldwide. Through these programs more than 1.4million tunas have been tagged across the Pacific, Atlantic, and, most recently, Indian Oceans with the majority of individuals tagged being skipjack (Katsuwonus pelamis, 858,000 individuals) and yellowfin tuna (Thunnus albacares, 360,000 individuals). The subsequent recovery of 173,574 tagged tunas (skipjack: 94,835, yellowfin: 49,079, and bigeye, Thunnus obesus: 29,660) presents a significant opportunity to obtain a wide range of scientific results. In this paper, we used recovery data from a variety of programs to compare the growth rates from the period between tagging and recovery of three tropical tuna species from four oceanic regions. We also analyzed the maximum time durations between tagging and recovery events as an indication of each species’ longevity, as well as apparent movement patterns and distances traveled by the tuna. Collectively, these comparisons revealed major similarities between tropical tuna species of the basic biological parameters studied. In some instances, our analysis also revealed that the same species show major differences between areas. In addition, this paper also examines the current interest in conducting large-scale, simultaneous tagging of the three tropical tuna species and highlights the importance of improving the quality of recovery data. In particular, there need is paramount to increase the percentage of recoveries that have been fully validated in terms of the fishing zone, recovery date, length and sex of the tagged tunas. Our assessment suggests that large-scale, multi-species tagging programs should become a routine scientific obligation for all tuna regional fisheries organizations, as they are necessary in providing the basic parameters of all stock assessment models.

The role of conservation partnerships between scientists and nonprofit agencies in freshwater science and management

The role of conservation partnerships between scientists and nonprofit agencies in freshwater science and management

Factors Affecting Partial Migration in Puget Sound Coho Salmon

AbstractPartial migration, the behavior pattern in which a portion of a population migrates while others do not, is a widespread phenomenon with ecological and evolutionary consequences. Most Coho Salmon Oncorhynchus kisutch from Puget Sound, Washington, migrate to feed over the continental shelf or offshore in the North Pacific Ocean, but some remain in the semiestuarine waters of Puget Sound and are termed residents. The objective of this study was to determine which of several factors influenced residency in Puget Sound Coho Salmon. Coded wire tag recovery data showed that resident Coho Salmon were smaller than their migratory counterparts, and we used this size difference and the relative catch patterns along the coast and in Puget Sound to classify Coho Salmon caught in Puget Sound between November and August as residents. We then analyzed the effects of location of origin, day of release, weight at release, hatchery or wild rearing, and year on the proportion of fish caught as residents. Based on 268 release groups between 1975 and 1992, we classified 3.4% of fish recovered as residents, 61.3% as migrants, and 35.3% as ambiguous because they were recovered in Puget Sound in September and October, when residents and migrants were mixed. The proportion of residents varied as a function of year, basin, and day of the year. Releases into south Puget Sound produced the highest proportion of residents, and resident fish tended to be recovered in the basin where they entered Puget Sound. While other factors may influence residency in Coho Salmon, the effects of day of release and location of origin may be useful for management of these populations, as the tendency to remain in Puget Sound or migrate to the coast affects the fisheries in which the fish are taken and their growth rate, their uptake of contaminants, and their role in food webs.Received August 15, 2013; accepted February 3, 2014

American White Pelican Predation on Cui‐ui in Pyramid Lake, Nevada

AbstractAnthropogenic changes to the Pyramid Lake–Truckee River ecosystem in Nevada are suspected to have altered the predator–prey balance between American white pelican Pelecanus erythrorhynchos and Cui‐ui Chasmistes cujus. We estimated the loss of the adult Cui‐ui population to pelican predation over a 13‐year period by netting and tagging Cui‐uis as they aggregated at the mouth of the Truckee River prior to their spawning migration into the Truckee River. Cui‐ui access to the Truckee River typically required traversing a shallow delta (a foraging advantage for these American white pelicans). Dams and greater frequency of low stream flows also contributed to American white pelican foraging success. We used tag recoveries from Pyramid Lake's nesting colony of American white pelicans along with an experiment to estimate the chance of tag recovery within the colony to calculate the number of tagged fish taken by American white pelicans. We also used numbered tags to test whether there was a size preference for Cui‐uis taken. Our results showed that the primary source of adult Cui‐ui mortality was from American white pelican predation in the Truckee River. Within a 13‐year period American white pelicans had taken 90% of the tags deployed during the first 7 years of the interval. There was no preference for the size of Cui‐uis taken. A better understanding of the effects of heavy cropping by American white pelicans on Cui‐ui population dynamics is still needed.Received March 26, 2013; accepted October 8, 2013Published online January 24, 2014

Hatchery Steelhead Smolt Release Size Effects on Adult Production and Straying

Studies have demonstrated higher postrelease survival for larger hatchery steelhead Oncorhynchus mykiss smolts than for smaller ones. However, the ideal release size should also maximize adult returns and minimize interactions of hatchery fish with wild fish. We conducted a study over five release years with paired groups of anadromous hatchery steelhead smolts reared to target sizes of either 90 g (small size) or 113 g (large size). After stream release, we monitored out-migration travel times and survival to a downstream dam using freeze-brand marks in a subsample of each release group. Steelhead smolts that out-migrate quickly may interact less with wild fish. Across all release groups, travel time was about 3 d slower for small-sized smolts than for large ones, but this difference was not statistically significant, and there was no significant difference in the percentage of brands detected at the dam between the two smolt sizes. Coded wire tag recovery was used to compare smolt-to-adult survival (SAS), the number of adults produced per 100 kg of smolts released, and the percentage of adults that strayed. Across all years, large-sized smolts had an average SAS of 1.31% compared with 0.92% for small-sized smolts, a statistically significant difference of 42.0%. The average number of adult steelhead produced per 100 kg of smolts released also was higher for the large-sized group (11.4 adults/100 kg of smolts) over the small-sized group (10.1 adults/100 kg of smolts), though the 12.8% difference was not statistically significant. Adults originating from large-sized smolt releases strayed at a rate of 13.1% compared with a 7.9% rate for the small-sized smolt groups, a difference that was statistically significant. In this study, larger hatchery steelhead smolts had a higher survival after release; however, we found tradeoffs between management objectives associated with maximizing adult production and those aimed at minimizing ecological risks.

Observations of Seasonal Movement from a Single Tag Release Group of Pacific Cod in the Eastern Bering Sea

AbstractThe Pacific Cod Gadus macrocephalus in the eastern Bering Sea is the target of one of the most lucrative fisheries in Alaska; however, relatively little is known about the movement of Pacific Cod and how this interacts with intense fishing on local spawning aggregations of cod every spring (January–April). This study aimed to draw inferences on Pacific Cod movement using a single tag release group of fish and the fishery as a representative for movement by qualitatively examining both temporal and spatial patterns of tag recoveries. Based on the tag recoveries in this study and past genetic studies, there is evidence that Pacific Cod show both homing tendencies and site fidelity during the spring when large aggregations of cod form to spawn. This study also supports results from an earlier study on Pacific Cod movement in this region and presents new insights into cod movement patterns. The cod in this tag release group were widely distributed across the Bering Sea during the summer and fall months and returned to the vicinity of the release site in the spring, presumably to spawn. Understanding the movement of cod and their interactions with the fishery is essential to the successful management of the Pacific Cod stock.Received May 12, 2014; accepted October 7, 2014

Spatially Varying Population Demographics and Fishery Characteristics of Lake Erie Walleyes Inferred from a Long‐Term Tag Recovery Study

AbstractAlthough the Lake Erie population of Walleyes Sander vitreus exhibits complex spatial structuring, the extent to which population demographics also vary spatially is unknown. Using a spatial tag recovery model, we estimated region‐ and age‐specific mortalities and regional movement probabilities by using recoveries from a jaw tagging study initiated in 1990. The best‐performing model based on a comparison of quasi‐likelihood Akaike's information criterion values had age‐group‐specific movement probabilities, age‐ and region‐specific natural mortalities, and age‐group‐ and region‐specific annual fishing mortalities. Commercial fishing mortality varied considerably during the study, while recreational fishing mortality was more static. Natural mortality of age‐5 and older Walleyes was lower than that of younger fish in all regions, with values ranging from 0.30 to 0.40 for age‐4 and younger fish and from 0.13 to 0.27 for age‐5 and older fish. In Lake Erie's western basin, natural mortality of age‐4 fish was lower than that of age‐3 fish. Sensitivity analyses indicated that some natural mortality estimates were sensitive to (1) prior probability distributions assigned to mortality components and (2) assumed movement probabilities in regions where no tagging was conducted. The decline in natural mortality with age in Lake Erie's western basin matches what has been found for other populations, suggesting that such patterns are perhaps common in exploited Walleye populations. Movement probabilities in the western basin were greater than those in the combined central and eastern basins. The mortality rates and movement probabilities estimated in this study should assist in the parameterization and scaling of a spatially explicit Lake Erie Walleye assessment model, the development of which has been recommended for the lake's quota management system. Our study is one of the first to apply a spatial tag recovery model to a freshwater fish population for estimating mortality components. We encourage wider use of this method to improve the understanding of how mortality components and movements vary regionally within freshwater systems.

Precision and Accuracy of Age and Growth Estimates Based on Fin Rays, Scales, and Mark-Recapture Information for Migratory Bull Trout

Abstract Accurate quantitative descriptions of bull trout (Salvelinus confluentus) growth are important for understanding life history and developing reliable stock assessments. In the absence of age validation, important steps are to review the precision of age estimation methods and evaluate whether age estimates yield growth rates consistent with known fish growth based on tag recoveries. We assessed the precision of age estimates using pelvic fin rays and scales for migratory bull trout (297–605 mm total length) from the North Fork Clearwater River, and then compared growth estimates derived from both structures with growth based on tag recoveries. Fin rays produced a lower coefficient of variation (CV = 5.84) than scales (CV = 12.56). Ages estimated from scales were higher for fish aged < 5 with fin rays and lower for fish aged ≥ 5. Comparisons of growth estimates derived from 70 tagged bull trout at large from 0.35 to 3.02 years with age-length equations based on fin ray and scale annuli indicated t...

Rates of straying by hatchery-produced Pacific salmon (Oncorhynchusspp.) and steelhead (Oncorhynchus mykiss) differ among species, life history types, and populations

Here we ask whether straying differs among species, life history types, and populations of adult hatchery-produced Pacific salmon (Oncorhynchus spp.) and steelhead (Oncorhynchus mykiss) in the Columbia River basin. Previous estimates of straying have been confounded by various factors influencing the probability of individuals returning to non-natal sites (e.g., off-station releases), whereas analyses undertaken here of nearly a quarter million coded-wire tag recoveries control for these factors. Our results revealed large and generally consistent differences in the propensity to stray among species, life history types within species, and populations. Paired releases indicated that (i) Chinook salmon (Oncorhynchus tshawytscha) strayed more (mean population range 0.11%–34.6%) than coho salmon (Oncorhynchus kisutch) (0.08%–0.94%); (ii) ocean-type Chinook (5.2%–18.6%) strayed more than stream-type Chinook (0.11%–10%); and Chinook salmon (0.90%–54.9%) strayed more than steelhead (0.30%–2.3%). We conclude these patterns are largely the result of species-specific behavioral and endocrine factors during the juvenile life stages, but analyses also suggest that environmental factors can influence straying during the adult upstream migration.