In the latest issue of Estuary Pearls: As organizations and agencies scramble to preserve the Central Valley’s dwindling Chinook salmon runs, a group of scientists believes they may be overlooking a key factor in the decades-long decline of the fish: disease. Current estimates of young salmon lost to the south Delta pumps are based on a smattering of studies from the 1970s and should be updated, according to a new analysis. Fish passage structures can be improved for the benefit of multiple species, if they are designed to account for differences in behavior, physical ability and size, according to a new literature review. Spawning and rearing habitat for important forage-fish species in San Francisco Bay apparently shifts geographically by many miles depending on how much freshwater is flowing into the Estuary. Yet another non-native aquatic species may have made itself at home in the Delta. By looking solely at the results of a single annual fish-counting survey, Californians may be seeing an incomplete reflection of Bay-Delta fish population trends. A unique adaptive behavioral trait that may once have helped winter-run Chinook salmon thrive in the Sacramento River system could now be working against the fish as they face extinction. Better scientific preparation could help Delta water and environmental managers respond to droughts more effectively. Access all Estuary Pearls stories by clicking here.