Ecological correlates of blue whale movement behavior and its predictability in the California Current Ecosystem during the summer-fall feeding season.

• Main Authors: Palacios, Daniel, Bailey, Helen, Becker, Elizabeth, Bograd, Steven, DeAngelis, Monica, Forney, Karin, Hazen, Elliott, Irvine, Ladd, Mate, Bruce
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2019
• Subjects: Balaenoptera musculus; Blue whale; California Current Ecosystem; Decadal variability; Foraging behavior; Movement behavior; Nonparametric multiplicative regression; Satellite telemetry; State-space models
• Online Access: https://escholarship.org/uc/item/8g32p4dv

BACKGROUND: Species distribution models have shown that blue whales (Balaenoptera musculus) occur seasonally in high densities in the most biologically productive regions of the California Current Ecosystem (CCE). Satellite telemetry studies have additionally shown that blue whales in the CCE regularly switch between behavioral states consistent with area-restricted searching (ARS) and transiting, indicative of foraging in and moving among prey patches, respectively. However, the relationship between the environmental correlates that serve as a proxy of prey relative to blue whale movement behavior has not been quantitatively assessed. METHODS: We investigated the association between blue whale behavioral state and environmental predictors in the coastal environments of the CCE using a long-term satellite tracking data set (72 tagged whales; summer-fall months 1998-2008), and predicted the likelihood of ARS behavior at tracked locations using nonparametric multiplicative regression models. The models werebuilt using data from years of cool, productive conditions and validated against years of warm, low-productivity conditions. RESULTS: The best model contained four predictors: chlorophyll-a, sea surface temperature, and seafloor aspect and depth. This model estimated highest ARS likelihood (> 0.8) in areas with high chlorophyll-a levels (> 0.65 mg/m3), intermediatesea surface temperatures (11.6-17.5 °C), and shallow depths (< 850 m). Overall, the model correctly predicted behavioral state throughout the coastal environments of the CCE, while thevalidation indicated an ecosystem-wide reduction in ARS likelihood during warm years, especially in the southern portion.For comparison, a spatial coordinates model (longitude × latitude) performed slightly better than the environmental model during warm years, providing further evidence that blue whales exhibit strong foraging site fidelity, even when conditions are not conducive to successful foraging. CONCLUSIONS: We showed that blue whale behavioral state in ...