Sundial Bridge ALAN Experimental Design (sampling metadata and descriptions)
The Sundial Bridge is an iconic illuminated structure in the City of Redding located within the little remaining spawning habitat of endangered winter run Chinook Salmon. To assess the impacts of Sundial Bridge artificial lighting at night (ALAN), we developed a field experiment to test the relationships of predator density and relative predation rate across four different ALAN treatments (0%, 25%, 50%, and 100% illumination intensity). Similar to previous work, we deployed ARIS cameras to quantify the response of relative predator density to ALAN treatments, as well as the temporal relationship of predator density during the transition form day to night. To quantify relative predation risk, we developed micro predation event recorded (mPERS). These were based on the design in Demetras et al. (2016), but we small enough to be casted from fishing poles. This data set is our sampling data for this experiment, including sampling dates, times, and field crews.
ARIS Data (RED ARIS data Sundial ALAN experiment, Yellow ARIS data Sundial ALAN experiment, and ARIS Sundial Continuous Deployment)
During all but the last sampling week, we deployed ARIS (Adaptive Resolution Imaging Sonar, Sound Metrics Corp.) cameras from 1 hour prior to sunset until 4 hours post sunset on each river bank to quantify the relative density of presumably piscivorous Rainbow Trout. On the last week of sampling we deployed an ARIS continually on River Right to quantify the full diel patterns of Rainbow Trout density underneath the Sundial Bridge. To remove background noise, we processed ARIS footage using contiguous samples over threshold (CSOT) in ARIS Fish software and imported this into Echoview software to automatically identify and filter fish. To generate fish tracks, we converted multibeam data to a single-target echogram, removed targets < 200 mm TL, and tracked fish pings to generate individual fish tracks. For each fish track, we exported the number of pings within 10-minute time bins and summed these pings to generate total fish pings per 10 minutes for each ARIS throughout sampling periods. For every 10-minute bin within each ARIS and sampling period, we divided the total number of fish pings by relative beam volume to generate relative fish density. Fish density is a relative measure given that ARIS footage is a 2D representation of a 3D space.
mPER Sundial ALAN
The mPERS are a miniaturization of the original PER design that worked well in the swift flowing Upper Sacramento River. Every second of each deployment, the mPERS recorded the date, time and whether a tethered juvenile salmonid had been predated, and this data was all stored on an internal micro SD card. We could not use endangered winter run fry for this experiment so we tethered rainbow trout fry to our mPERS as a surrogate species. Given that Rainbow Trout are piscivorous and cannibalistic this should not have biased our results. We tethered each fry to the mPER using 2m of 8lb fluorocarbon fishing line and attached each mPER to a fishing pole. During each deployment, we would cast the mPER above the influence of Sundial ALAN, let the PER drift past the bridge under the lights, and then retrieve the mPER once it was downstream of ALAN influence. When a fry was predated, a read switch was trigged and it logged a predation event on the internal micro SD card. We quantified the ALAN intensity of each treatment from a boat and related these lux levels to PER locations and predation events. Unfortunately, we only received 4 events throughout the study so we did not quantitatively analyze this data. However, we did test these mPERS in the Sacramento San-Joaquin Delta and had 60 events out of 520 deployments, ensuring that the sampling method worked well.
