Assessing collision risk between humpback whales and multiple vessel fleets in Brazil

Abstract

Abstract Increasing anthropogenic threats in the marine environment requires continued assessments of their potential effects on the marine megafauna. In recent years, ship strikes have become an important source of mortality to large whales. Here we integrated telemetry and traffic data to assess vessel collision risk on humpback whales (Megaptera novaeangliae) off the central coast of Brazil between 2016 and 2019. A state-space model was used to account for observation error and to regularize telemetry data. Residence time and proportion of time spent at the surface (i.e., the upper 10m layer of the water column) by whales combined with fleet-specific vessel density were used as proxies to estimate the relative probability of vessels encountering whales available to a collision. We also identified areas where potential encounters were likely to inflict lethal injuries on whales based on vessel length and speed. The cargo fleet was the most densely distributed, and along with the tanker fleet, represent a great concern to humpback whales in Brazil. A higher risk of collision was recorded on the Abrolhos Bank, the main breeding ground for this population. By incorporating comprehensive whale- and vessel-related information, this study highlights the importance of spatially explicit risk assessments for the conservation of humpback whales in Brazil.