The Cooperative Institute for Climate, Ocean, and Ecosystem Studies

This summer, the CICOES REU program connected me with the USGS Western Fisheries Research Center to research the impact of artificial light at night on juvenile freshwater salmonid predation under Tessa Code and Dave Beauchamp.

Understanding and maximizing survivorship through the Lake Washington ship canal is a key part of conservation efforts of juvenile anadromous salmon, as the canal is the primary outmigration route for anadromous species. Key piscivorous predators such as Coastal Cutthroat Trout are visual foragers, and remain highly effective predators through twilight.

Artificial Light at Night (ALAN) perpetually extends twilight light levels and thus significantly expands predation opportunities.

We chose to center the focus of my project on the Fremont Bridge. The bridge has a unique combination of light sources, making it an ideal case study: art lighting underneath the bridge shines onto the structure of the bridge, bright street lights shine down directly on the water, and the bridge is situated near bright urban infrastructure, such as from Google’s Fremont campus.

The USGS was commissioned by the Seattle Department of Transportation to assess the ecological impact of the lighting in 2019 after the art lights were installed. However, the team has since outlined several weaknesses of the technology they had available for that study, so we decided to reassess the Fremont Bridge with the capabilities of a new piece of equipment we got from Biospherical Instruments, the C-OPS.

The C-OPS, or Compact Optical Profiling System, has sets of microradiometer arrays that measure irradiance across the visible spectrum in key ways–  for our purposes, downwelling surface irradiance and downwelling in-water irradiance. This allowed us to measure the intensity of light of each color along the spectrum at night, to quantify the impact of the art lighting, as well as spectral attenuation through the water during the day. We then modeled spectral attenuation with the nighttime surface readings to determine whether the impact of the art lighting was significant.

We determined that while the art lighting had a prominent spectral “footprint” near the bridge, the number and position of bright street lighting rendered that footprint statistically insignificant on overall light levels on either side of the bridge.

Thus, we decided to model predator search volumes at a variety of depths along a transect perpendicular to the bridge. We utilized a visual foraging model parameterized for cutthroat trout, which is sensitive enough in low-light conditions to show marked differences in search volume based on the differing light levels near the bridge. Our overall conclusion was that predator search volume, and therefore predation risk, is significantly elevated near the bridge due to urban lighting infrastructure, but that the art lights are not a significantly significant culprit.

This project was an amazing introduction to formal research, and I also got plenty of opportunity to assist with other research, from processing stream macroinvertebrate drift samples, to deploying cameras in Skagit Bay, to functional response trials, to midwater trawling, and more.

Thank you to everyone at USGS Western Fisheries for making this possible, especially Dave Beauchamp, Tessa Code, Shelley Johnson, Marshal Hoy, Steve Rubin, and Ben Jensen, as well as our C-OPS collaborator, Jen Schulien.

Project Introduction

Research Poster