Avian Predation on Juvenile Salmonids: Spatial and Temporal Analysis Based on Acoustic and Passive Integrated Transponder Tags

Evans, Allen F.; Payton, Quinn; Turecek, Aaron; Cramer, Bradley M.; Collis, Ken; Roby, Daniel D.; Loschl, Peter J.; Sullivan, Leah; Skalski, John R.; Weiland, Mark A.; Dotson, Curtis

doi:10.1080/00028487.2016.1150881

Cited by 30 publications

(70 citation statements)

References 32 publications

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“…Birds nesting at some of the colonies included in this study were capable of foraging in multiple river reaches (i.e., upstream and downstream of an array used to delineate a river reach; Evans et al. ; Hostetter et al. ), which required predation rates to be partitioned by river reach (Figure ).…”

Section: Methodsmentioning

confidence: 99%

“…Previous research indicated that predation rates by birds from particular colonies were spatially proportionate amongst river reaches across years (Evans et al. ; Hostetter et al. ).…”

Section: Methodsmentioning

confidence: 99%

“…; Evans et al. ). Multiple species of piscivorous colonial waterbirds nest in the region, and previous research indicates that Caspian terns Hydroprogne caspia , double‐crested cormorants Phalacrocorax auritus , California gulls Larus californicus , and ring‐billed gulls L. delawarensis are the principal avian predators of juvenile salmonids in the Columbia River basin (Collis et al.…”

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confidence: 98%

“…; Evans et al. ). These studies relied on marking (tagging) fish and then using subsequent recapture (or detection) and recovery events to estimate survival and cause‐specific mortality (e.g., predation, harvest, and dam passage).…”

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confidence: 98%

“…Determining the extent to which avian predation limits smolt survival relative to these other sources of mortality may be critical for prioritizing recovery actions for ESA‐listed salmonid populations (Evans et al. ).…”

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confidence: 99%

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Cumulative Effects of Avian Predation on Upper Columbia River Steelhead

et al. 2019

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To investigate the cumulative effects of colonial waterbird predation on fish mortality and to determine what proportion of all sources of fish mortality (1 − survival) was due to bird predation, we conducted a mark–recapture–recovery study with upper Columbia River steelhead Oncorhynchus mykiss that were PIT‐tagged and released (N = 78,409) at Rock Island Dam on the Columbia River, USA. We used a state–space Bayesian model that incorporated live detections and dead recoveries of tagged fish to jointly estimate predation and survival probabilities during smolt out‐migration to the Pacific Ocean over an 11‐year study period. Estimated cumulative (all colonies combined) avian predation probabilities ranged from 0.31 (95% credible interval [CRI] = 0.27–0.38) to 0.53 (95% CRI = 0.42–0.64) annually, indicating that avian predation was a substantial source of mortality. Of the predator species evaluated, predation by Caspian terns Hydroprogne caspia was often the highest, with predation probabilities ranging from 0.11 (95% CRI = 0.09–0.14) to 0.38 (95% CRI = 0.29–0.47). Probabilities of predation by double‐crested cormorants Phalacrocorax auritus and mixed colonies of California gulls Larus californicus and ring‐billed gulls L. delawarensis were generally lower than the probabilities for terns but were also substantial, with upwards of 0.04 (95% CRI = 0.03–0.07; cormorants) and 0.31 (95% CRI = 0.25–0.39; gulls) of steelhead consumed. Comparisons of total smolt mortality with mortality due to avian predation indicated that avian predation accounted for 42% (95% CRI = 30–56%) to 70% (95% CRI = 53–87%) of total mortality, suggesting that more steelhead were consumed by avian predators than died from all other mortality sources combined. Results indicate that avian predation, although not the original cause of steelhead declines in the basin, is now a factor limiting the survival of upper Columbia River steelhead. Using the analytical framework developed in this study, future studies can consider the cumulative impact of multiple mortality sources across large spatial and temporal scales to more fully understand the extent to which they limit fish survival.

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Section: Methodsmentioning

confidence: 99%

“…Previous research indicated that predation rates by birds from particular colonies were spatially proportionate amongst river reaches across years (Evans et al. ; Hostetter et al. ).…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 98%

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confidence: 98%

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confidence: 99%

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Cumulative Effects of Avian Predation on Upper Columbia River Steelhead

et al. 2019

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Measuring the additive effects of predation on prey survival across spatial scales

Payton

Evans

Hostetter

et al. 2020

Ecological Applications

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The degree to which predation is an additive vs. compensatory source of mortality is fundamental to understanding the effects of predation on prey populations and evaluating the efficacy of predator management actions. In the Columbia River basin, USA, predation by Caspian Terns (Hydroprogne caspia) on U.S. Endangered Species Act (ESA)listed juvenile salmonids (smolts; Oncorhynchus spp.) has led to predator management actions to reduce predation; however, the assumption that reduced predation translates into greater salmonid survival, either within the life stage where predation occurs or across their lifetime, has remained untested. To address this critical uncertainty, we analyzed a long-term (2008-2018) mark-recapture-recovery data set of ESA-listed steelhead trout (O. mykiss) that were tagged (n = 78,409) and subsequently exposed to predation during smolt out-migration through multiple river reaches (spatial scales), jointly estimating weekly probabilities of steelhead survival, mortality due to bird predation, and mortality due to other causes. This concurrent estimation across time-stratified cohorts allowed for the direct measurement of the strength, magnitude, and direction of relationships between survival and Caspian Tern predation. Estimates of Tern predation on steelhead were substantial in most years, with cumulative annual estimates ranging from 0.075 (95% creditable interval = 0.058-0.099) to 0.375 (0.290-0.461). Increases in Tern predation probabilities were associated with statistically significant decreases in steelhead survival probabilities in all evaluated years and salmonid life stages (smolt out-migration and smolt-to-adult returns). Results provide novel evidence that predation by Caspian Terns may have been a super-additive source of mortality during the smolt life stage and a partially additive source of mortality to the adult life stage. Annual estimates of the difference between observed survival and baseline survival (i.e., in the absence of Tern predation) ranged from 0.052 (0.017-0.103) to 0.314 (0.172-0.459) during the steelhead smolt life stage and from 0.011 (0.001-0.029) to 0.049 (0.025-0.078) to the adult life stage. The estimated levels of compensation have important implications for predator management actions aimed at increasing the survival of endangered salmonids, and the modeling approach developed herein provides a framework to directly quantify the impacts of source-specific mortality factors on prey populations.

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Predation probabilities and functional responses: How piscivorous waterbirds respond to pulses in fish abundance

et al. 2022

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How predators respond to changes in prey abundance (i.e., functional responses) is foundational to consumer-resource interactions, predator-prey dynamics, and the stability of predator-prey systems. Predation by piscivorous waterbirds on out-migrating juvenile steelhead trout (Oncorhynchus mykiss) is considered a factor affecting the recovery of multiple Endangered Species Act-listed steelhead populations in the Columbia River basin. Waterbird functional responses, however, may vary by predator species and location, with important implications to predator management strategies. We used a 13-year dataset on waterbird abundance across seven breeding colonies (three Caspian tern [Hydroprogne caspia], two double-crested cormorant [Nannopterum auritum], and two California and ring-billed gull [Larus californicus and Larus delawarensis] colonies) and steelhead tag-recovery data (>645,000 tagged and >32,000 recovered steelhead) to quantify weekly predation probabilities and functional responses across waterbird species, colonies, and years. Weekly predation probabilities were highly variable, ranging from 0.01 to 0.30 at tern colonies, 0.01 to 0.20 at cormorant colonies, and 0.03 to 0.13 at gull colonies.Per capita predation probabilities were an order of magnitude higher at inland tern and cormorant colonies relative to estuary colonies of the same species.Terns displayed Type II functional responses across colonies and years, where predation probabilities peaked at low steelhead abundances and declined as steelhead abundance increased (i.e., predator swamping). Cormorants nesting at the large estuary colony (several thousand birds) displayed a Type III functional response, but cormorants nesting at the smaller inland colony (several hundred birds) displayed a Type II response. Consumption probabilities of steelhead by gulls remained consistent across a large range of steelhead availability, suggesting a Type I or a Type III functional response, but a lack of colony abundance data prevented quantifying functional responses. The level of tern predation combined with Type II functional responses indicate possible

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Avian Predation on Juvenile Salmonids: Spatial and Temporal Analysis Based on Acoustic and Passive Integrated Transponder Tags

Cited by 30 publications

References 32 publications

Cumulative Effects of Avian Predation on Upper Columbia River Steelhead

Cumulative Effects of Avian Predation on Upper Columbia River Steelhead

Measuring the additive effects of predation on prey survival across spatial scales

Predation probabilities and functional responses: How piscivorous waterbirds respond to pulses in fish abundance

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