Bryde’s whales off the central coast of Ecuador: Distribution, behaviour and ecological insights

Abstract

The Bryde’s whale is a lesser‐known baleen whale. Surveys were conducted to assess the presence and ecology of Bryde’s whales along the central coast of Ecuador during the months of December– May between 2021 and 2024. 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, during which 100 whales were sighted in 62 groups. Whales were found in all surveyed areas, with the majority (58%) detected in waters between 41–60 m depth and only two records 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 included 1.61 whales (SD = 1.13). Mother‐calf pairs were observed in eight groups (12.9%). Feeding behaviour was noted in 13 groups (20.9%) and coincided with a larger group size compared with other behavioural states (P = 0.02). We used generalised 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 vessel collisions, underscoring the need for management strategies to mitigate these interactions.