Timing is Everything: Drivers of Interannual Variability in Blue Whale Migration

The growth and survival of large-bodied marine predators depend on temporal synchrony with resource availability. Baleen whales migrating long distances must therefore respond to interannual variability to avoid a predator-prey mismatch. Highly migratory and acoustically active, blue whales are a model species for investigating the drivers and timing of migration. Using long-term passive acoustic monitoring, we examined the relationship among migration timing (inferred from the timing of blue whale D and B calls), environmental indices, and euphausiid (prey) biomass spanning 11 years. The leading driver, sea surface temperature (SST) at the Costa Rica Dome breeding grounds, predicted arrival time at the Southern California feeding grounds. Interannual variations revealed that colder SSTs correlated with earlier arrival and greater krill biomass in Southern California. In years with greater krill biomass, whales switched earlier from D calls to reproductive-related B calls while at the feeding grounds. Our results show a plastic response to interannual environmental variability and allowed us to examine the consequences of long-term climate change on plasticity. A notable trend of increasing temperatures over the 11-year study period resulted in an additional two months on the feeding grounds. Changes in migration phenology may increase anthropogenic impacts for this endangered species, such as ship strikes and entanglements in fishing gear.