Humpback whales in Brazil : distribution, abundance and human impacts

Abstract

The humpback whale population breeding in Brazilian waters has greatly increased, after near extinction due to whaling in the twentieth century. Today, these animals are under pressure from human activities in the area. In this thesis, habitat use, distribution, abundance, population status and potential threat from oil spills were investigated to improve knowledge of the population’s ecology and provide useful information for conservation and management. Distribution and habitat use were investigated through spatial models applied to line transect data and to tracking data. Line transect data were also used to estimate abundance. Distribution maps from both data types were used with a simulation of oil dispersion to evaluate risk of impact from oil spills. The new abundance estimates, together with information on population increase from another study, were used to update a Bayesian population dynamics model to re-assess population status. Modelling of line transect data indicated whale density to be higher in slower currents, at shorter distances to both the coastline and shelf edge, and at sea surface temperatures between 24 and 25°C, and to be related to shelter. A higher concentration of animals was predicted in the southern portion of Abrolhos bank, an enlargement of the continental shelf. Modelling of tracking data agreed with those findings, despite differences in the nature of the data and analytical methods. Risk maps of oil spill impact indicated that areas in the south of the breeding range present highest risks to the animals. Abundance estimates (14,264, CV = 0.084, in 2008; 20,389, CV = 0.071, in 2012) provide further evidence that the population is increasing, and contributed to improved precision in the population status assessment. New information provided here will inform conservation of the humpback whale population breeding in Brazilian waters and the need for, and implementation of, any necessary management action.