Development of a castable, GPS enabled, Miniaturized Predation Event Recorder (mPER) to quantify predation of juvenile fishes

Over the past decade, predation-event recorders (PERs) have become an effective tool to estimate relative predation rates of juvenile Chinook salmon in California’s Central Valley. However, due to their design, PERs have primarily been limited to studying predation over relatively large spatial scales (up to several hundred meters or more). Due to this limitation, we designed a simple yet effective, castable, GPS enabled miniaturized predation-event recorder (mPER) based on an Arduino platform that can be adapted to meet individual applications. We tested our mPER by evaluating predation around a small-scale water diversion in the Sacramento-San Joaquin Delta. We modeled the relationship between predation risk and time to sunset as well as distance to diversion with a Cox proportional hazards model, a time-to-event model that accounts for censored data. The results of this proof-of-concept analysis indicated that for each elapsed minute, predation risk decreased by a factor of 0.97, as sunset was approached and passed. Similarly, each meter increase in distance from the diversion decreased the predation risk by a factor of 0.86. The mean relative predation rate in our study area was 24%. Our mPERs proved to be an inexpensive, effective, and reliable tool to quantify predation, in a repeatable manner, around targeted locations of interest. We have included the design, material list, Arduino programming code, and Cox proportional hazard analysis code for others to easily design, use, and analyze the resulting data from our mPER design (supplementary information available from the Open Science Framework https://osf.io/ysm2p/). •Predation of fishes is difficult to measure in situ.•Miniaturized predation event recorders (mPERs) are an effective tool for measuring predation.•Integrated GPS and Arduino based processors streamline data collection.•Cox proportional hazards analysis may be used to estimate relative risks to predation.