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.
We estimated the effects of a temperature control device (TCD) on a suite of thermodynamic and limnological attributes for a large storage reservoir, Shasta Lake, in northern California. Shasta Dam was constructed in 1945 with a fixed-elevation penstock. The TCD was installed in 1997 to improve downstream temperatures for endangered salmonids by releasing epilimnetic waters in the winter/spring and hypolimnetic waters in the summer/fall. We calibrated a two-dimensional hydrodynamic reservoir water quality model, CE-QUAL-W2, and applied a structured design-of-experiment simulation procedure to predict the principal limnological effects of the TCD under a variety of environmental scenarios. Calibration goodness-of-fit ranged from good to poor depending on the constituent simulated, with an R2 of 0.9 for water temperature but 0.3 for phytoplankton. Although the chemical and thermal characteristics of the discharge changed markedly, the reservoir's characteristics remained relatively unchanged. Simulations showed the TCD causing an earlier onset and shorter duration of summer stratification, but no dramatic affect on Shasta's nutrient composition. Peak inreservoir phytoplankton production may begin earlier and be stronger in the fall with the TCD, while outfall phytoplankton concentrations may be much greater in the spring. Many model predictions differed from our a priori expectations that had been shaped by an intensive, but limited-duration, data collection effort. Hydrologic and meteorological variables, most notably reservoir carryover storage at the beginning of the calendar year, influenced model predictions much more strongly than the TCD. Model results indicate that greater control over reservoir limnology and release quality may be gained by carefully managing reservoir volume through the year than with the TCD alone.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.