Search

Abstract Artificial light at night (ALAN) has emerged as a prevalent anthropogenic stressor in many aquatic ecosystems impacting a wide range of taxa and ecological processes. In fishes, ALAN attracts both predators and prey, potentially resulting in increased predation mortality and sublethal impacts. Increased predation mortality is especially problematic in anadromous fishes, given that many populations are diminished and out‐migrating juveniles must transit illuminated waterways. Additionally, ALAN management is complex, because lighting benefits human safety, economies, and recreational pursuits. The Sundial Bridge (Redding, CA) is an iconic illuminated structure that spans a section of the little remaining spawning habitat of the endangered winter‐run Chinook Salmon. It was hypothesized that bridge ALAN increased Rainbow Trout predation of winter‐run fry, and a lighting management plan was implemented. However, ALAN impacts on this predator–prey interaction and species‐specific responses were unknown. Therefore, we used tethered salmonid fry and ARIS sonar cameras to determine whether variable ALAN treatments (0%, 25%, 50%, and 100% intensity) altered Rainbow Trout density (RTD) and fry predation risk, while investigating the temporal relationships of RTD with ALAN. ALAN significantly increased RTD on river right when any amount of ALAN was present, potentially leading to competition and fitness consequences; RTD did not change significantly in response to ALAN on river left. Although RTD generally increased in response to ALAN, salmonid fry predation was almost nonexistent. Therefore, while ALAN may decrease out‐migrant survival in other waterways, there was no evidence at our study site. Furthermore, the discrepancies between riverbanks demonstrate the complexity of ALAN and how it interacts with other environmental parameters potentially providing optimal foraging habitat. The Rainbow Trout attraction to ALAN, which occurred immediately with diminishing ambient light, indicates that complete ALAN removal may be necessary to mitigate ecological consequences of ALAN. When removal is unrealistic, ALAN should be diminished as early in the night as possible to minimize aquatic ecosystem impacts, while maintaining benefits for human populations.

Passive acoustic monitoring (PAM) in a variety of marine habitats has revealed distinct spatial and temporal variation of fish sounds that are predicted to vary in association with species composition and abundance, as well as diel and seasonal influences. Reefs in the Alabama Artificial Reef Zone (AARZ) in the northern Gulf of Mexico (nGOM) have an associated fish fauna composed of warm-temperate and tropical reef associated species. AARZ reefs are made of different structures (e.g. bridge rubble, concrete pyramids, etc.) and as a result, their fish species composition is predicted to vary. We used PAM to describe fish sounds on 18 shallow slope (20-33 m) AARZ reefs in 2017 and 2018. We detected calls from unknown sources, as well as sounds from leopard toadfish Opsanus pardus, cocoa damselfish Stegastes variabilis, and cusk-eels (Ophidiidae). We developed semi-automated screening methods to detect specific sound types and described diel and spatial patterns. Sound detection rates varied widely among reefs, but not by reef type. Number of sound types increased with species richness, but detection rates of specific sounds differed on reefs with similar species composition. Our results indicate that many frequently occurring sounds may not be associated with visually conspicuous fishes. Further research is needed to determine source species and associated behavior for common sounds in these habitats. Soundscape variability among nGOM artificial reefs may be a consideration for management, as biological sound can provide an acoustic cue for reef location by some larval and adult fish species.