Dolphin cow-calf separation during purse seine fishing operations in the EPO

Despite a > 99% reduction in bycatch-related mortality in the Eastern Tropical Pacific (ETP) purse-seine tuna industry over the past three decades, eastern spinner dolphin (Stenella longirostris orientalis, hereafter referred to as spinner dolphins) and northeastern offshore pantropical spotted dolphin (S. attenuata attenuata, hereafter referred to as pantropical spotted dolphins) populations have not increased as projected and are still considered depleted under the Marine Mammal Protection Act1,2. This suggests that cryptic and unobserved sources of mortality may be occurring, preventing population recovery. For the past two decades, it has been postulated that one such source may be mother-calf separation during fishery interactions, leading to calf mortality2-6. The aim of this project is to use unmanned aerial vehicles (UAVs) to determine: (i) if mother-calf pairs become separated during chase, encirclement, backdown, and/or post-release “run” from the net; and (ii) if/how mother-calf separation may be affecting population growth. These results will help to inform population models and management and conservation actions for dolphins in the ETP.