Using the Vaquita's Acoustic Behavior to Strengthen Priority Conservation Areas

ABSTRACT The vaquita ( Phocoena sinus ) is an endemic porpoise restricted to the upper Gulf of California, Mexico, with a total range of 4048 km 2 . Using expert elicitation, the number of vaquitas detected in and near the Zero Tolerance Area—a 288 km 2 area within the Vaquita Refuge (1263 km 2 )—was estimated at 7 to 10 individuals in 2025 with 67% probability. This estimate reflects the number of distinct individuals observed and should not be interpreted as the total population size. The main threat to its survival is bycatch in gillnets used for shrimp and finfish fisheries, particularly those associated with the illegal totoaba ( Totoaba macdonaldi ) fishery. Vaquitas emit narrow‐band high‐frequency ultrasonic click trains that have been analyzed to study the species population trend. Little is known about spatial and temporal variations in the vaquita's acoustic foraging behavior. We analyze data from a long‐term passive acoustic monitoring program with C‐PODs within the Vaquita Refuge, from June to September between 2011 and 2018. Click trains were classified into three categories based on average inter‐click intervals (ICI): < 2 ms, possible social communication; 2–10 ms foraging buzzes; and > 10 ms, echolocation. Of all click trains, 48,277 (36.3%) were identified as foraging buzzes, 1423 (1.1%) as possible social signals, and 83,251 (62.6%) as echolocation click trains. Foraging activity was greatest in the southwest portion of the refuge, with secondary and temporary activity observed in the northeast portion between 2013 and 2015. The three acoustic behaviors peaked at different times of the day. These findings offer new insights into vaquita acoustic behavior and how they use the Vaquita Refuge.