The waters surrounding Abrolhos Archipelago, Brazil, serve as one of several winter grounds for southern-hemisphere humpback whales (Megaptera novaeangliae). Development of tourism in this region has caused concern over disturbance effects to breeding and nursing whales. To document the chronology of humpback abundance around Abrolhos, three years of visualscan data obtained during July through November 1998-2000 were analyzed. During 1-hour scans, observers visually tracked all groups within 9.3km and nearly 360° around a land-based theodolite station to determine group size, composition and behavior. Including only groups of known size, hourly counts (n=462) of adult and calf humpback whales ranged from 0-31 and 0-9, respectively. Group size could not be determined for 255 of 2146 groups observed. Humpback whale abundance was seasonal: there were few in early July when surveys began, peaked in early September, and then gradually declined to zero by late November. Based on Poisson regression, the annual chronology of whale occupancy was relatively invariant. Peak counts averaged about 15 adult whales per hour. Although no evidence was found that the timing of peak counts varied, peak abundance varied among years, and more whales were seen during morning than afternoon. The mean number of adults per group did not vary over time (year, day of year, or time of day), but the likelihood of group size being indeterminate varied predictably. Thus, indices of abundance could be adjusted by assuming that the size of indeterminate groups equals mean group size. Calf abundance varied with adult abundance, and the proportion of groups with calves increased from July through November. The high frequency of groups containing a calf (49.8%) within 9.3km of the Abrolhos Archipelago demonstrated the importance of this area for calves, and proper management is recommended.Resumo As águas ao redor do Arquipélago dos Abrolhos, Brasil, são uma das muitas áreas de inverno para as baleias jubarte (Megaptera novaeangliae) no hemisfério sul. O desenvolvimento do turismo nessa região e seus efeitos nas atividades de reprodução e cria das baleias, causam preocupação. Para documentar a abundância cronológica de baleias jubarte ao redor de Abrolhos, foram analisados três anos de dados obtidos a partir de varredura visual entre julho e novembro de 1998 a 2000. Durante varreduras de uma hora, observadores acompanharam visualmente todos os grupos de baleias presentes em 9,3km e aproximadamente 360° em torno de um ponto fixo equipado com teodolito, para determinar tamanho, composição e comportamento dos grupos. Incluindo somente grupos com tamanho conhecido, as contagens de adultos e filhotes nas varreduras (n=462) variaram entre 0-31 e 0-9 respectivamente. O tamanho de grupo não pôde ser determinado em 255 dos 2146 grupos observados. A abundância foi sazonal: havia poucas baleias no início de julho quando as observações iniciaram, atingindo o pico no início de setembro e decaindo gradativamente até zero no final de novembro. Baseado ...

To characterize temporal patterns of humpback group structure around Abrolhos Archipelago, Brazil, seven years (1998–2004) of data obtained from July through November were analysed. During one-hour scans, observers determined group composition within 9.3 km around a land-based station. A total of 930 scans, comprising 4288 groups were analysed. Seven group categories were identified and their frequencies were 14.6% of 1AD (lone whale), 25.2% of DYAD (two adult whales), 7.3% of TRIO (three adult whales), 5.2 of TRIO+ (more than three adults), 24.9% of MOC (mother and calf), 19.6% of MOCE (mother, calf and one escort), and 3.1% of MOCE+ (mother, calf and more than one escort). Proportions of whale-group categories did not change between morning and afternoon, nor among years. However, as the season progressed, groups with calves increased while groups without calves decreased. This progression may be explained by the segregated migration patterns of humpback whales and also by changes in the social status of individuals. The Abrolhos Reef provides protection from the prevailing winds, which may explain the higher proportion of groups with calves in the area.

The humpback whale (Megaptera novaeangliae) population that uses Abrolhos Bank, off the east coast of Brazil as a breeding ground is increasing. To describe temporal changes in the relative abundance of humpback whales around Abrolhos, seven years (1998–2004) of whale count data were collected during July through to November. During one-hour-scans, observers determined group size within 9.3 km (5 n.m.) of a land-based observing station. A total of 930 scans, comprising 7996 sightings of adults and 2044 calves were analysed using generalized linear models that included variables for time of day, day of the season, years and two-way interactions as possible predictors. The pattern observed was the gradual build-up and decline in whale counts within seasons. Patterns and peaks of adult and calf counts varied among years. Although fluctuation was observed, there was generally an increasing trend in adult counts among years. Calf counts increased only in 2004. These fluctuations may have been caused by some environmental conditions in humpback whales' summering grounds and also by changes in spatial–temporal concentrations in Abrolhos Bank. The general pattern observed within the study area mirrored what was observed in the whole Abrolhos Bank. Knowledge of the consistency with which humpback whales use this important nursing area should prove beneficial for designing future monitoring programmes especially related to whale watching activities around Abrolhos Archipelago.