Oceanographic and Climate Effects on Migratory Propensity of a Hawaiian Freshwater Fish

Climate change can affect species ranges and migration yet it is unclear how large scale environmental forces influence fishes that show migration polymorphisms such as partial migration (PM). Awaous stamineus, a Hawaiian freshwater fish, is known to exhibit PM with spatiotemporal variability in migratory history. Larvae can migrate to sea with juveniles returning to freshwater to spawn; however, some fish maintain lifetime freshwater residency. We tested whether migration propensity is correlated with the El Niño Southern Oscillation (Oceanic Niño Index ONI) a large-scale climatic pattern. A. stamineus otoliths were collected from fish throughout the Hawaiian archipelago during 2009 and 2011 (n=251, 35 streams). Hatch date and migration window (hatch month) were estimated using otochronology (otolith aging). Oceanic migrations were determined using otolith trace-element chemistry; otolith cores with high Sr:Ca were considered migrants and those with low Sr:Ca were deemed freshwater residents. Logistic regression analysis determined that significantly fewer migrants recruited to streams during El Niño phases while more migrants recruited during La Niña phases. Driving mechanisms are explored through spatial correlation mapping between oceanographic and biological variables for a large spatial extent of the Pacific Ocean (10˚S-60˚N,-90˚E-150˚W) to better understand the effects of basin-scale climatic processes on this species migration.