Hello Marmam,

My co-authors and I are pleased to share our new publication:

Leander, S., Durban, J., Fearnbach, H., Joyce, T., Sherman, K., Southall, B., & Ballance, L. Seasonal differences in group composition of common dolphins off southern California. Marine Ecology Progress Series.

Abstract: In the eastern North Pacific, common dolphins (Delphinus delphis bairdii and D. d. delphis) often form large, energetic aggregations that make characterization of group composition challenging. Here we demonstrate how photogrammetry from drones can be used to precisely estimate total length distributions and infer group composition and reproductive patterns of 2 abundant dolphin subspecies. We obtained precise length measurements of 3519 dolphins from scaled aerial images of 29 groups of common dolphins off southern California (USA) from 2017 to 2021. Groups were assigned to 1 of 3 strata based on subspecies and month sampled: D. d. bairdii (June), D. d. bairdii (October), and D. d. delphis (October). Similarities in overall length distributions were found between all 3 strata, though the length range of D. d. delphis was shifted 0.3 m smaller than D. d. bairdii. Using a hierarchical Bayesian multinomial model, we estimated significantly more variability in length compositions for D. d. bairdii groups sampled in June than within other strata, implying more variable social composition for this stratum. The model-derived estimates of the typical length distributions for each stratum revealed that D. d. delphis had significantly higher proportions of calves, while both D. d. bairdii strata had significantly higher proportions of larger sub-adults, potentially related to calving peaks in the first half of the year for both subspecies. These results provide a better understanding of their basic biology and ecology, and vulnerability to natural and anthropogenic disturbances.

Best,

Sam Leander (she/her)

Research Associate

SR3, SeaLife Response, Rehabilitation, and Research