UC San Diego

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 passive acoustic recordings collected from 2007 to 2017, we examined the relationship among migration timing (inferred from blue whale “D” and “B” calls), environmental indices, and measured krill abundance. Arrival to Southern California feeding grounds was correlated with sea surface temperatures (SST) on Costa Rica breeding grounds (r = 0.81, <0.01). Colder SSTs in both regions resulted in early arrival and correlated with greater krill abundance in Southern California (r2 = 0.47, p = 0.03). The correlation between krill abundance and the transition from D to B calls (r2 = 0.55, <0.01) suggested that in high-krill-abundance years, whales switched earlier from social to reproductive-related behavior on their feeding grounds. This phenotypic plasticity may allow blue whales to accommodate environmental variability while balancing important biological needs. However, D call onset dates increased significantly over the 11-year study (r = 0.68, p = 0.03), shifting arrival two months earlier. Longer time on the feeding grounds may increase ship-strike and entanglement risk for this endangered species.