Search

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.

We consider the opportunities and challenges associated with organizing a conference online, using a case study of a medium-sized (approx. 400 participants) international conference held virtually in August 2020. In addition, we present quantifiable evidence of the participants' experience using the results from an online post-conference questionnaire. Although the virtual meeting was not able to replicate the in-person experience in some aspects (e.g. less engagement between participants) the overwhelming majority of respondents found the meeting an enjoyable experience and would join similar events again. Notably, there was a strong desire for future in-person meetings to have at least some online component. Online attendance by lower-income researchers was higher compared with a past, similar-themed in-person meeting held in a high-income nation, but comparable to one held in an upper-middle-income nation. This indicates that online conferences are not a panacea for diversity and inclusivity, and that holding in-person meetings in developing economies can be at least as effective. Given that it is now relatively easy to stream contents of meetings online using low-cost methods, there are clear benefits in making all presented content accessible online, as well as organizing online networking events for those unable to attend in person.