Phototaxic Behavior of Subyearling Salmonids in the Nearshore Area of Two Urban Lakes in Western Washington State

Abstract

We conducted field experiments in the nearshore area of two urban lakes (Lake Washington and Lake Sammamish) in western Washington to test the attractive quality of artificial nighttime lighting to subyearling salmonids Oncorhynchus spp. In both lakes, experimental trials were conducted along a uniform 156‐m shoreline section twice a month (one night with lights and one control night without lights) from March to May to correspond with peak nearshore rearing of subyearling salmonids. We examined the effects of three light intensities on nearshore fish abundance: (1) no light, (2) dim light (maximum, 5.0 lx), and (3) bright light (maximum, 50.0 lx). These were compared with abundances from control nights without light treatments. Beach seining was used to determine fish abundance. For each month, the total number of subyearling salmonids (Chinook Salmon O. tshawytscha, Coho Salmon O. kisutch, and Sockeye Salmon O. nerka combined) was greater on the lighted nights (all treatments combined) than it was on the control nights. In both lakes, the most subyearling salmonids were collected in the bright‐light treatments, an intermediate amount in the dim‐light treatments, and few in the no‐light treatments. In some instances, subyearling salmonid abundances in the bright‐light treatments were more than 10 times greater than in the no‐light treatments. The effect of nighttime artificial lighting was generally more pronounced in March than in April or May. The results support our hypothesis that subyearling salmonids exhibit nocturnal phototaxic behavior when exposed to elevated nighttime lighting. A major concern of artificial nighttime lighting for subyearling salmonids is the potential for an increased predation risk, and we believe the prudent management goal would be to minimize artificial nighttime lighting. Received October 23, 2016; accepted March 7, 2017 Published online May 26, 2017

Effects of Artificial Lighting at Night on Predator Density and Salmonid Predation

“…With continuing human development along rivers, estuaries, and coastlines, it will be increasingly important to consider the impacts of ALAN on aquatic organisms and ecosystems (Davies et al 2014;Jechow and Hölker 2019;Zapata et al 2019). Elsewhere, ALAN has attracted young salmonids and their predators, resulting in elevated predation rates (Tabor et al 2004(Tabor et al , 2017. Similarly, introduced ALAN in the Delta increased predator density and relative predation risk of Chinook Salmon smolts; however, these effects were only detected 3 h past sunset and later.…”

“…Additionally, this minimum value may only be relevant to the system and predator community studied here. Previous work has suggested that ALAN intensities should remain as low as possible (<0.1 lx) to mitigate impacts on salmonids during out-migration (Tabor et al 2004(Tabor et al , 2017. To determine a minimum lux management goal, future experimental tests of ALAN intensity with variable treatments among experimental nights are needed.…”

“…Field experiments where free‐swimming acoustically tagged smolts are released under artificially illuminated and dark conditions coupled with a high‐resolution telemetry array could also be used to determine if ALAN affects smolt movement and migration. Artificial illumination may reduce migration speed and survival because salmon out‐migration is predominately nocturnal (Chapman et al 2013; Clark et al 2016; Furey et al 2016) and ALAN attracts and slows juvenile salmonids (Tabor et al 2004, 2017; Celedonia et al 2011; Riley et al 2013). This attraction may bring salmonids closer to shore, exposing them to mammalian (e.g., river otters; Dolloff 1993) and avian piscivores (e.g., herons; Sherker 2020), as well as benthic (e.g., sculpin and catfish) and vegetation‐associated (e.g., Largemouth Bass) piscivorous fishes (Michel et al 2018, 2020a).…”

“…However, in many ecosystems, salmonid out-migration traverses anthropogenically altered habitat and urban centers (Michel et al 2013(Michel et al , 2015Schroeder et al 2015), likely leading to increased ALAN exposure (Jechow and Hölker 2019;Zapata et al 2019). Given that ALAN aggregates and slows out-migrating salmon, attracts predators (including fishes, birds, and mammals), and increases piscivore consumption of salmonids (Yurk and Trites 2000;Tabor et al 2004;Celedonia et al 2011;Tabor et al 2017), increased migratory ALAN exposure likely increases juvenile salmonid predation risk and mortality.…”

Where Predators and Prey Meet: Anthropogenic Contact Points Between Fishes in a Freshwater Estuary

“…Of these six studies, four were focused on juvenile salmonids as prey species. Both (Tabor et al 2017;Tiffan et al 2016) found about a 3-fold decrease in the abundance of juvenile salmon along armored shorelines https://doi.org/10.15447/sfews.2018v17iss4art4 compared with naturalized banks with shallower slopes. No studies have directly quantified the difference in predation rates between these habitat types, yet several authors presume that shoreline armoring increases predation of salmonids, either by excluding them from shallow water habitat (Heerhartz and Toft 2015;Tabor et al 2011) or by increasing abundances of predatory fish such as Smallmouth Bass (Tiffan et al 2016).…”