Movements and diving behavior of Risso’s dolphins in the Southern California Bight

Risso’s dolphins ( Grampus griseus ), uncommon prior to the 1970’s, are now regularly observed within Southern California Bight. During long-term cetacean monitoring programs on United States Navy range areas in Bight from 2009–2019, we deployed 16 Argos-linked satellite tags acquire objective, detailed depictions of their movements and behaviors. Individuals were tracked for a median 10.7 days (range = 0.8 – 19.7). Kernel density estimation suggested individuals utilized entire with 50% core use area centered around San Clemente Santa Catalina Islands where most tag deployments occurred. Grand dive depth was 101 m (max 528) duration 5.6 min 11.1). We used generalized mixed models assess seasonal environmental effects distribution diving behavior including month, distance shore, time day, lunar phase, sea surface temperature, chlorophyll- residuals. Animals further shore (including islands) during full versus new moon mainland last first quarter moon. also tended be closer land fall early winter months. Dives deeper yet shorter night, moon, when animals offshore. conducted nearly twice as many dives at night compared though deep (> 500 m) occurred all times day. This study provides insights into behavioral trends while identifying priorities future research.