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

Abstract

Predation of juvenile salmonids within California's Sacramento-San Joaquin Delta (the Delta) has been identified as a contributing factor to low survival during out-migration through the system. Artificial lighting at night (ALAN) may contribute to increased levels of salmonid predation by attracting predators and prey, increasing predator reaction distance, and boosting foraging success. To assess ALAN effects on predator (piscivorous fishes) density and the relative predation risk of Chinook Salmon Oncorhynchus tshawytscha smolts in the Delta, we preformed field-based experiments with introduced ALAN. We used adaptive resolution imaging sonar cameras to generate predator density estimates in light and dark treatments throughout nightly experiments at 30-min intervals. We simultaneously deployed predation event recorders to estimate the impact of ALAN intensity (lux) on relative predation risk of Chinook Salmon smolts. Early in the night (1-3 h past sunset), predator density and relative predation risk of smolts were unrelated to ALAN. However, late in the night (3-5 h past sunset), ALAN presence increased predator density, and the relative predation risk of juvenile salmonids increased with increasing lux. Predation risk was also positively related to predator density, and increased late-night predator density under ALAN, coupled with late-night foraging benefits of ALAN, likely contributed to the lux-risk relationship. The exact mechanism behind this discrepancy between early-and late-night trends is unknown and could be a result of our experimental design or the predator community sampled here. However, if these temporal trends prove robust to future investigations, late-night lighting reduction campaigns during out-migration could maximize the human benefits of ALAN while minimizing the negative impacts on salmonids. Overall, our findings align with others and suggest that ALAN increases juvenile salmonid predation. Although many questions remain unanswered, it appears that reducing artificial illumination is a practical management strategy to reduce predation.

North American diadromous fishes: Drivers of decline and potential for recovery in the Anthropocene

“…In the Pacific Ocean basin, the diversity and effects of non-native fishes are generally greatest in the southern part of the range, as with so many other effects, and diminish northward (although with some exceptions). Not all non-native fishes have significant ecological interactions with native anadromous species, but many are predators, including striped bass and largemouth bass (Micropterus salmoides) in the Sacramento-San Joaquin river system (82), where their effects are exacerbated by artificial light at night (83). The Columbia River has substantial and growing populations of smallmouth bass (Micropterus dolomieu) (84) and walleye (Sander vitreus) as well as native predators (85,86).…”

Effects of artificial light at night on fishes: A synthesis with future research priorities

“…by using covered lights or other shielding), by shortening periods of lighting (e.g. through time limits or motion sensors) (Czarnecka et al, 2019; Gaston et al, 2013; Nelson et al, 2021), using dimmers (McNaughton et al, 2021), or by employing LEDs that tailor spectral quality (Becker et al, 2013). As more research amasses across taxa, the potential for solutions that balance considerations of human safety in built landscapes with the well‐being of wildlife (Longcore et al, 2018) should only increase.…”

Artificial Light Pollution with Different Wavelengths at Night Interferes with Development, Reproduction, and Antipredator Defenses of Daphnia magna

“…For example, brighter nights increase the gathering of small fishes and further attract the large piscivorous fish because of the increased foraging opportunities at night. 11,21 For prey, antipredation strategies must be in place to detect predation risks and take quick evasive actions to avoid being caught. However, ALAN may cause a mismatch between prey response behavior and predation risk.…”

“…22 Thus, ALAN can alter the feeding activity of predators, causing the prey to underestimating the risk of predation, and then leading to the disruption of predator−prey interactions, which may eventually affect the function of the whole aquatic ecosystem. 8,16,21,22 Zooplankton are key organisms in the aquatic food web and the intermediary between primary producers and higher trophic consumers, so they are essential for the functioning of the freshwater community. 23 Daphnia, as an important part of zooplankton that inhabit waterbodies from temporary ponds to large lakes, have become a suitable model organism for studying ecological relevance and predator-induced defense changes.…”

“…As demonstrated in some studies, ALAN is assumed to alter natural light regimes in aquatic ecosystems and can affect light-sensitive processes and behaviors of aquatic organisms. ,− ALAN can also change the predator–prey interactions, , which is the main evolutionary driving force to regulate the behavior of predators and prey. , The distribution of ALAN has complex effects on the predator–prey relationship and richness. For example, brighter nights increase the gathering of small fishes and further attract the large piscivorous fish because of the increased foraging opportunities at night. , For prey, antipredation strategies must be in place to detect predation risks and take quick evasive actions to avoid being caught. However, ALAN may cause a mismatch between prey response behavior and predation risk.…”