1. Prey evaluate risk and make decisions based on the balance between the costs of predation and those of engaging in antipredator behavior. Economic escape theory has been valuable in understanding responses of stationary prey under predation risk; however, current models are not applicable for directionally moving prey.

2. Here we present an extension of existing escape theory that predicts how much predation risk is perceived by directionally moving prey. Perceived risk is measured by the extent antipredator behavior causes a change in travel speed (the distance to a destination divided by the total time to reach that destination). Cryptic or cautious antipredator behavior slows travel speed, while prey may also speed up to reduce predator-prey overlap. Next, we applied the sensitization hypothesis to our model, which predicts that prey with more predator experience should engage in more antipredator behavior, which leads to a larger change in travel speed under predation risk. We then compared the qualitative predictions of our model to the results of a behavioral assay with juvenile Chinook salmon (Oncorhynchus tshawytscha) that varied in their past predator experience.

3. We timed salmon swimming downstream through a mesh enclosure in the river with and without predator cues present to measure their reaction to a predator. Hatchery salmon had the least predator experience, followed by wild salmon captured upstream (wild-upstream) and wild-salmon captured downstream (wild-downstream).
4. Both wild salmon groups slowed down in response to predator cues, while hatchery salmon did not change travel speed. The magnitude of reaction to predator cues by salmon group followed the gradient of previous predator experience, supporting the sensitization hypothesis.
5. Moving animals are conspicuous and vulnerable to predators. Here we provide a novel conceptual framework for understanding how directionally moving prey perceive risk and make antipredator decisions. Our study extends the scope of economic escape theory and improves general understanding of non-lethal effects of predators on moving prey.

This dataset comes from field collections of juvenile salmon, which were used in a behavioral assay. We timed salmon swimming downstream through a mesh enclosure with and without predator cues to observe their change in travel speed via antipredator behavior. Travel speed was recorded when juvenile salmon, embedded with a Passive Integrated Transponder (PIT) tags, passed through PIT antennae. The PIT detections were processed in R to summarize the values for time and speed through enclosure segments (antenna 1 to antenna 2, and antenna 2 to antenna 3).

The processed datafile for the behavioral assay are uploaded here. Also, the R files for the analyses for the manuscript.

 

Authors

Megan C. Sabal

University of California Santa Cruz, Department of Ecology and Evolutionary Biology

130 McAllister Way, Santa Cruz, CA 95060

msabal@ucsc.edu

 

Joseph E. Merz

University of California Santa Cruz, Department of Ecology and Evolutionary Biology

130 McAllister Way, Santa Cruz, CA 95060

Cramer Fish Sciences

3300 Industrial Blvd #100, West Sacramento, California 95691

jmerz@fishsciences.net

 

Suzanne H. Alonzo

University of California Santa Cruz, Department of Ecology and Evolutionary Biology

130 McAllister Way, Santa Cruz, CA 95060

shalonzo@ucsc.edu

 

Eric P. Palkovacs

University of California Santa Cruz, Department of Ecology and Evolutionary Biology

130 McAllister Way, Santa Cruz, CA 95060

epalkova@ucsc.edu

 

File list

sabal_et_al_2020_behavioral_assay_analyses_dryad.R

sabal_et_al_2020_supplemental_analyses_dryad.R

sabal_et_al_2020_behavioral_assay_data.txt

sabal_et_al_2020_environmental_data.txt

 

File descriptions

sabal_et_al_2020_behavioral_assay_analyses.R – the only R file needed to run the analyses from the main text. Must set working directory to location of sabal_et_al_2020_behavioral_assay_data.txt file.

 

sabal_et_al_2020_supplemental_analyses.R – this R file describes analyses for the supplemental material, including Appendices A and B. Must set working directory to location of sabal_et_al_2020_behavioral_assay_data.txt and sabal_et_al_2020_environmental_data.txt files.

 

sabal_et_al_2020_behavioral_assay_data.txt – the only data file you need to run the main analyses. Each line is a unique trial. Salmon data, trial data, and PIT detection data have already been combined.

date: year-month-day format

fish_no: unique fish number

salmon_group: hatchery, wild-downstream, wild-upstream

split: the split in the flume over which speed was measured. “A1_A2” is the stretch

between antennas A1 and A2. “A2_A3” is the stretch between antennas A2 and A3.

pred_treat: predator treatment. “no_pred”: predator absent, “pred”: predator present

order: order of predator treatment for individual salmon. 1: predator treatment was run first, 2: predator treatment was run second (no predator treatment was run first).

time_start: the general time of day the trail started as recorded by researchers, not the first detection at antenna A1.

time: The total time from the first detection at antenna A1 until the first detection at A2 (for split A1_A2), or from the last detection at A2 until the first detection at A3 (for split A2_A3).

time.secs: same as column “time”, but as an integer, units: seconds

time.cox: same as column “time.secs”, but salmon that failed to reach an antenna (NAs in “time.secs” column), are recorded as the cut off time (600 seconds). This is necessary for the cox models.

censor: 1: salmon reached the antenna in the allotted time limit. 0: salmon failed to reach the antenna in the allotted time limit (NAs in column “time.secs” and value of 600 in column “time.cox”).

speed.ms: distance traveled (0.9144 meters per split) divided by “time.secs”

FL: fork length, units: mm

WT: weight, units: grams

Kbcond: Fulton’s condition factor K, units: index

ATPresid: ATPase activity, units: index

 

sabal_et_al_2020_environmental_data.txt – this data file contains environmental measurements for each day behavior trials were run.

date: year-month-day format

airtempC: air temperature, units: degrees Celcius

watertempC: water temperature, units: degrees Celcius

turbidity: turbidity, units: NTUs

watervelocity: surface water velocity, units: m/s

cloudcover: approximated cloud cover, units: between 0 and 100 percent