THE BRYDE’S WHALE ON THE CENTRAL COAST OF ECUADOR, DISTRIBUTION, BEHAVIOR AND ECOLOGICAL INSIGHTS

The Bryde’s whale is a lesser-known baleen whale. From December through May 2021-2024, surveys were conducted along the central coast of Ecuador to assess its presence and associated ecological aspects. The study area covered 6,700 km² of coastal and open waters, with depths reaching up to 1,000 m. The effort included 46 trips, covering 5,018 km of survey, during which 100 whales in 62 groups were recorded. Whales were found in all surveyed areas, with the majority detected in waters between 41-60 m depth (58%). Only two records were made in waters shallower than 30 m. The average relative abundance was estimated at 0.016 whales/km of survey (SD = 0.057). The average group size was 1.61 whales (SD = 1.13). Mother-calf pairs were observed in eight groups (12.9%). Feeding behavior was noted in 13 groups (20.9%) and groups were significantly larger than those in other behavioral states (P = 0.02). We used generalized linear modeling (GLM) with a negative binomial distribution to explain the variability of whale relative abundance. Six explanatory variables (month, depth, SST, chlorophyll a, ONI, and ICEN), and effort as an offset variable were used to fit models. The model that best fit the data revealed a significant positive correlation with month and a negative correlation with chlorophyll a. Thus, whales increased abundance toward the end of the research season. The negative correlation with chlorophyll a suggests that other ecological factors, including the lagged response of prey to productivity and shifts in prey distribution, may play a more critical role and warrant further investigation. The coastal distribution of Bryde’s whales exposes them to fishing gear and ship collisions, underscoring the need for management strategies to mitigate these interactions.