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Marine heatwaves can impact the distribution and abundance of epipelagic organisms, but their effect on deep pelagic communities is unclear. Using fisheries acoustics data collected in the Central California current from 2013 to 2018, we found that during the warmest years of a large marine heatwave (2015–2016), the estimated center of mass depth of mesopelagic fishes deepened by up to 100 m compared to preheatwave conditions. Using a generalized additive model, we evaluated which biophysical factors may have driven these changes and found that light, dynamic height anomaly, and acoustic backscatter explained 81% of the variability in depth. We attribute the vertical shift by mesopelagic fishes into deeper waters to heatwave-driven compression of upwelling habitat that indirectly increased the amount of light reaching mesopelagic depths. Our results suggest that mesopelagic fishes are interconnected with, and thus sensitive to changes in near-surface oceanographic conditions, which could lead to cascading effects on vertical carbon export and the availability of mesopelagic fishes as prey for top predators under future climate conditions. [ABSTRACT FROM AUTHOR]

Low survival rates of Chinook salmon (Oncorhynchus tshawytscha) smolts in California's Central Valley have been attributed to multiple biological and physical factors, but it is not clear which factors have the largest impact. We used 5 years of acoustic telemetry data for 1709 late-fall Chinook salmon smolts to evaluate the effect of habitat- and predation- related covariates on outmigration survival through the Sacramento River. Using a Cormack-Jolly-Seber mark-recapture model, we estimated survival rates both as a function of covariates (covariate model) and as a function of river location and release year (spatial-temporal model). Our covariate model was overwhelmingly supported as the preferred model based on model selection criteria, suggesting the covariates adequately replicated spatial and temporal patterns in smolt survival. The covariates in the selected model included individual fish covariates, habitat-specific covariates, and temporally variable physical conditions. The most important covariate affecting salmon survival was flow. We describe the importance of these parameters in the context of juvenile salmon predation risk and suggest that additional research on predator distribution and density could improve model estimates. Si les faibles taux de survie des saumoneaux de saumon chinook (Oncorhynchus tshawytscha) dans la vallee centrale de la Californie ont ete attribues a differents facteurs biologiques et physiologiques, l'identite des facteurs exerqant la plus grande influence demeure incertaine. Nous avons utilise 5 annees de donnees de telemetrie acoustique pour 1709 saumoneaux de saumon chinook de la fin de l'automne pour evaluer l'effet de covariables associees a l'habitat et a la predation sur la survie durant la devalaison dans le fleuve Sacramento. En utilisant un modele de marquage-recapture de Cormack-Jolly-Seber, nous avons estime les taux de survie en fonction de covariables (modele des covariables) et en fonction de l'emplacement dans le fleuve et de l'annee du lacher (modele spatiotemporel). Le modele de covariables s'est avere, de loin, le modele a privilegier sur la base de criteres de selection de modeles, ce qui donne a penser que les covariables reproduisent adequatement les motifs spatiaux et temporels de survie des saumoneaux. Les covariables dans le modele selectionne comprennent des covariables associees aux poissons individuels, des covariables propres a l'habitat et des conditions physiques variables dans le temps. La covariable ayant la plus importante influence sur la survie des saumons est le debit. Nous decrivons l'importance de ces parametres dans le contexte du risque de predation de saumons juveniles et suggerons que d'autres travaux sur la repartition et la densite des predateurs pourraient ameliorer les estimations decoulant du modele. [Traduit par la Redaction], Introduction Salmon smoltification and outmigration from freshwater rearing habitats is a time of increased mortality as fish undergo physiological changes and encounter new stressors (Connor et al. 2003; Welch et [...]

Aquatic invertebrates utilize multiple forms of sensory perception including chemical signaling, to evaluate their surrounding environment. The hermit crab Calcinus latens is able to detect external chemical cues within the complex coral rubble habitat. These discrete chemicals whether emanated from a potential predator, competitor or conspecific are received through chemosensory structures and elicit a specific behavioral response. This study examines the effect of four chemical treatments (control-ambient sea water, predator-Octopus bocki, potential competitor-Saron marmoratus and conspecific-Calcinus latens) on the number of times an individual Calcinus latens is observed in active, exploratory behavior verses stationary, defensive behavior. The results demonstrate a significant difference in the amount of time observed in defensive behaviors by the hermit crabs exposed to the treatment containing octopus chemical cues when compared to the other treatments. Across the four chemical treatments, there was a significant difference in the observed use of six specific behaviors, indicating a patterned behavioral response, unique for each treatment. Additionally, an experiment testing the response of Calcinus latens individuals to artificially introduced treatment species, (octopus Octopus bocki, shrimp Saron marmoratus as well as conspecifics) in which tested individuals could utilize all modes of sensory perception, was compared to the chemically stimulated behaviors. Analysis of the response behavior to chemical cues verses multimodal sensory assessment of actual treatment species demonstrated a statistically significant similarity in elicited behavior which underlines the importance of chemical signaling in modulating the behavior of Calcinus latens within the coral rubble microhabitat.

The Sacramento–San Joaquin Delta (hereafter, "the Delta") is one of the estuaries with the most invasive species in the world, and nonnative predators may be a major factor in the observed decline of Central Valley Chinook Salmon Oncorhynchus tshawytscha over recent decades. In order for managers to take actions that might reduce predation‐related mortality for these ecologically, culturally, and economically valuable fish, it is important to understand the factors influencing the distribution and abundance of piscivores in the Delta. In this study, we used a dual‐frequency identification sonar (i.e., DIDSON) to conduct mobile surveys to quantify the abundances of piscivores in the Delta. We then used these data to identify the habitat features that are correlated with the abundance of piscivores. Prior to conducting the surveys, we used DIDSON data from captured fish to develop an algorithm to distinguish piscivores from nonpiscivores with high confidence (98% accuracy). A generalized linear mixed‐effects model fit to these survey data indicated that predator abundances were most associated with areas of increased submerged aquatic vegetation patches, and channels that are straighter, with increased bathymetric complexity. When applied to the entire survey area, this model was successfully able to predict known areas of high predator densities. These results indicate that one approach to reduce predator densities in key locations throughout the Delta, and improve juvenile salmonid outmigration survival, is to reduce the extent of invasive submerged aquatic vegetation. Because experimental predator removals have been largely ineffective in the Delta, efforts to manipulate habitat to discourage nonnative predator recruitment and favor native species recruitment may provide a more effective solution to improve salmonid survival rates. [ABSTRACT FROM AUTHOR]

Predator–prey dynamics can have landscape-level impacts on ecosystems, and yet, spatial patterns and environmental predictors of predator–prey dynamics are often investigated at discrete locations, limiting our understanding of the broader impacts. At these broader scales, landscapes often contain multiple complex and heterogeneous habitats, requiring a spatially representative sampling design. This challenge is especially pronounced in California’s Sacramento–San Joaquin River Delta, where managers require information on the landscape-scale impacts of non-native fish predators on multiple imperiled native prey fish populations. We quantified relative predation risk in the southern half of the Delta (South Delta) in 2017 using floating baited tethers that record the exact time and location of predation events. We selected 20 study sites using a generalized random tessellation stratified survey design, which allowed us to infer relationships between key environmental covariates and predation across a broader spatial scale than previous studies. Covariates included distance-to-nearest predators, water temperature, turbidity, depth, bottom slope, bottom roughness, water velocity, and distance-to-nearest riverbank and nearest aquatic vegetation bed. Model selection determined the covariates that best predicted relative predation risk: water temperature, time of day, mean predator distance, and river bottom roughness. Using this model, we estimated predation risk for the South Delta landscape at a 1-day and 1-km resolution. This effort identified hot spots of predation risk and allowed us to generate predicted survival for migrating fish transiting the South Delta. This methodology can be applied to other systems to evaluate spatio-temporal dynamics in predation risk, and their biotic and abiotic predictors. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "Moving conferences online: lessons learned from an international virtual meeting."