Stray Rates of Natural‐Origin Chinook Salmon and Steelhead in the Upper Columbia River Watershed

Abstract

Despite the importance of straying in understanding the ecology of Pacific salmon Oncorhynchus spp. and steelhead O. mykiss, most of what is known about salmon and steelhead straying comes from tagged hatchery fish. We provide estimates of donor straying by natural‐origin spring, summer, and fall Chinook Salmon O. tshawytscha and summer steelhead at three spatial scales in the upper Columbia River watershed by using PIT tags. In total, 823,770 natural‐origin Chinook Salmon and steelhead were PIT‐tagged as juveniles in the Wenatchee, Entiat, Methow, and Okanogan River subbasins and tributaries and the upper Columbia River between 2002 and 2017. Anadromous adults with PIT tags (n = 2,611) were detected at a variety of antenna arrays in the Columbia River basin between 2004 and 2018. Mean donor stray rates of each population were less than 1% at the basin scale (range = 0.0–0.7%), less than 10% at the subbasin scale (range = 0.0–9.8%), and less than 15% at the tributary scale (range = 0.0–14.3%). Many of the populations (11 of 28) that were evaluated across all spatial scales did not have any strays detected, and the mean of means for both species’ stray rates at all spatial scales was generally less than 5% (range = 0.2–4.0%). Chinook Salmon and steelhead strayed at similar rates when originating from the same subbasins and tributaries. Most straying occurred in an upstream direction at the subbasin (84%) and tributary (94%) scales. Variation in stray rates was most consistently associated with spatial scale and location and was less than 15% for both species at all spatial scales.

Retracted: Monitoring Hatchery Broodstock Composition and Genetic Variation of Spring/Summer Chinook Salmon in the Columbia River Basin with Multigeneration Pedigrees

“…There are also potential benefits of straying in natural populations of salmonids, as it can lead to critical evolutionary advantages through recolonization of newly accessible habitat, such as after de‐glaciation or dam removal (Keefer and Caudill 2014; Pess et al 2014; Pitman et al 2010). In the upper Columbia River, the overall stray rate of natural‐origin Chinook Salmon and steelhead has been estimated at between 1.3% and 5.0% (Ford et al 2015; Pearsons and O’Connor 2020), and rates tended to increase (up to 3 out of 18 fish) as the spatial scale decreased (Pearsons and O’Connor 2020). Stray rates have been shown to increase when fish are of hatchery origin or had at least one hatchery‐origin parent (Ford et al 2015).…”

Straying and Life History of Adult Steelhead in a Small California Coastal Stream Revealed by Otolith Natural Tags and Genetic Stock Identification

“…Population genetic analyses of steelhead populations in coastal California indicate that there is some level of exchange among populations that generally declines with distance (Garza et al 2014), but there is very little direct evidence of straying in natural populations due to the difficulty of sampling adult steelhead, distinguishing natural‐origin strays from returning fish, or identifying the natal source of strays. In a review of the straying literature using Google Scholar and citations within studies to identify all available data for steelhead on the West Coast of North America, we found 25 papers with data on straying, but most were from hatchery populations and there were only five papers that examined natural populations: four for interior summer‐run steelhead in the Columbia River basin (Keefer et al 2005, 2008; Marsh et al 2012; Pearsons and O’Connor 2020) and only a single study for coastal winter‐run steelhead (Shapovalov and Taft 1954), which found a low level of straying between two nearby streams (8 km apart) in central California. Studies of hatchery‐origin steelhead suggest that donor straying rates are generally low and most straying appears to be among populations from neighboring streams (Westley et al 2013; Keefer and Caudill 2014), although long‐distance straying (100 to 450 km) may occur less frequently (Schroeder et al 2001).…”

Overwintering Distribution and Postspawn Survival of Steelhead in the Upper Columbia River Basin

“…We were unable to estimate straying because the natal origin of sampled adults was unknown. A recent analysis (Pearsons and O’Connor 2020) that focused on natural‐origin steelhead PIT‐tagged as juveniles in the same system revealed more frequent straying within the upper Columbia River basin to sites upstream of natal sites, though there was some uncertainty in distinguishing overshoot/temporary strays from permanent strays due to the challenge of detecting downstream movements with PIT tags. Ideally, future studies would be able to distinguish overshoot fallback, temporary straying, and permanent straying from successful homing and spawning by establishing the natal origin of adults at the time of tagging using PIT tags implanted in juveniles at natal sites or via genetic approaches (e.g., parentage‐based tagging; Keefer et al 2018).…”

“…Future analyses of the influence of winter thermal conditions may be useful for elucidating habitat selection by steelhead in the upper Columbia River and in other systems. Such population‐, season‐, and location‐specific information may be especially important because recent analyses by Pearsons and O’Connor (2020) indicate that straying among tributaries of the upper Columbia River basin is relatively rare and, thus, populations likely are largely demographically independent (e.g., some populations, such as the Entiat River population, may not be greatly subsidized by strays). Similar consideration of winter distribution among populations may be important because we found uneven spatial distribution of steelhead during winter, although we note that annual overwintering rates varied from 0.11 to 0.43 among the three other major tributaries in the upper Columbia River basin; therefore, planning would need to integrate such interannual variation in overwinter distribution.…”

“…Freshwater overwintering behavior in stream‐maturing steelhead has been hypothesized as one of a suite of traits allowing migration to spawning habitats that would otherwise be inaccessible because of flow and/or temperature conditions (Robards and Quinn 2002; Trudel et al 2004). Notably, monitoring of radio tags and PIT tags has revealed complex behaviors in migrating adult steelhead, including tributary overshoot and fallback, use of main‐stem habitats rather than tributary habitats during winter (e.g., Keefer et al 2008a; Richins and Skalski 2018), and complex movements near natal reaches, including temporary and permanent straying (Keefer and Caudill 2014; Pearsons and O’Connor 2020). Overwintering mortality (including prespawn mortality) has been attributed to a variety of mechanisms (Keefer et al 2008a; Bowerman et al 2016) and potentially includes indirect fishing mortality of natural‐origin steelhead (which are not available for harvest) when winter distributions of nonharvestable and harvestable steelhead overlap (Feeken et al 2019).…”