Salinity and diel timing affect group structure in Delta Smelt

Delta Smelt are thought to be on the precipice of extinction. Studies that examine how this endangered species responds to environmental change are important to informing conservation efforts. In the wild, Delta Smelt are likely to encounter wide variation in the salinity of their environment that is influenced by both natural and anthropogenic factors. We examined how salinity affects the group structure of Delta Smelt across multiple diel cycles. We found that the interaction between salinity (0, 5, 10 and 15 ppt) and time period (Day 1, Night 1, Day 2 and Night 2) influenced their spatial distribution within a group. Specifically, Delta Smelt were less dispersed, more cohesive and more homogenously distributed in saline water than in freshwater, but only on the first day, and this difference was not statistically significant. We also found that Delta Smelt were significantly less dispersed, more cohesive and more homogenous during the day than at night. Thus, Delta Smelt appear to behaviourally adapt to the initial stress of acute salinity exposure, which may mirror their physiological ability to acclimate to such conditions. Additionally, Delta Smelt group structure appears to shift depending on the time of day, suggesting that diel timing may influence conspecific interactions and should be considered in the experimental design of future studies. These findings further our understanding of how Delta Smelt behaviourally respond to environmental and diel variation. We examined how salinity affects the group structure of Delta Smelt across two diel cycles. We found that Delta Smelt grouped more closely (1) in saline water compared to freshwater, but only on the first day, and (2) during the day than at night. Thus, Delta Smelt appear to behaviourally adapt to the initial stress of acute salinity exposure, and diel timing may influence conspecific interactions. image

Automated summary

This study examines how salinity and time of day affect the group structure of Delta Smelt, an endangered species on the brink of extinction. The results show that Delta Smelt exhibit behavioral adaptations based on salinity exposure and diel timing. They are more closely grouped in saline water, especially on the first day, and during the day compared to at night. These findings deepen our understanding of how Delta Smelt behaviorally respond to environmental and diel variation.