Temporal characterization of humpback whales (Megaptera novaeangliae) group structure and behavior in Abrolhos Archipelago breeding area (Bahia, Brazil).

Baleias jubarte usam a costa leste do Brasil como área de reprodução e cria. As águas ao redor do Arquipélago dos Abrolhos são importantes devido a grande concentração de grupos com filhotes. Um estudo de 7 anos (entre 1998 e 2004) foi realizado, a partir de um ponto fixo de observação em terra, a fim de se investigar padrões temporais na estruturação de grupos e no comportamento de baleias jubarte. Dependendo das condições climáticas e de visibilidades eram realizadas varreduras com duração de 1 hora e na seqüência, observações de grupo ou indivíduo focal. Concomitante com o aumento da população brasileira de baleia jubarte, o número de avistagens de baleias adultas ao redor do Arquipélago aumentou, especialmente de 2002 a 2004, porém avistagens de filhotes somente aumentaram durante a temporada 2004. De uma forma gradual baleias chegam, se concentram e partem de Abrolhos, refletindo a migração segregada e as alterações de status sociais dos indivíduos. A medida que a temporada progride, ocorre uma mudança na freqüência das diferentes categorias de grupo de baleia jubarte, de grupos sem filhotes para grupos com filhotes, assim como os comportamentos, os quais, dentro de cada categoria de grupo, parecem estar adequado ao estágio de desenvolvimento do filhote (para aqueles grupos com filhote) e refletem o que parece estar relacionado a busca por oportunidades de acasalamentos e interações sociais. Ao longo das 7 temporadas estudadas, não houve mudanças na estruturação de grupos de baleias jubarte, nem houve alterações comportamentais marcantes. Porém, verificou-se que na presença de barcos num raio de 100-300 metros, fêmeas (mães) permanecem menos tempo em repouso e filhotes ficam menos tempo em comportamento de provável amamentação. Existe a preocupação de que repetidas mudanças comportamentais decorrentes de fatores antrópicos possam levar a população a risco, já que em espécies como baleias, as alterações a nível populacional podem levar muitos anos para ser detectadas. Logo é sugerido que estudos seguindo a mesma metodologia sejam continuados para que comparações sejam possíveis. Um estudo de longo-prazo permitiria uma investigação continua dos padrões (ou alterações deles) com que as baleias jubarte utilizam a área e como vêm respondendo as pressões antrópicas.Humpback whales use the east coast of Brazil as a breeding and calving area. The waters surrounding Abrolhos Archipelago are important because of the high concentration of humpback whale groups with calves. A seven-year study (1998 - 2004) was conducted, from a land base station, to investigate temporal patterns of group structure and behavior of humpback whales. Depending on weather and sightability conditions, one-hour-scans were done followed by observations of animal or group focal follows. Concomitant with the observation of an increasing Brazilian humpback whale population, the number of adult whales sighted around the Archipelago increased, especially from 2002 to 2004. However, sightings of calves only increased during 2004 season. The humpback whales gradually arrive, concentrate and leave the region, reflecting segregated migration and individual social changes. As the season progresses, the frequency of different groups categories changes, from groups without calf to groups with calf, as well as the behaviors, which, within each group category, seems to be appropriate to calf development stages (for groups with calf) and reflect what seems to be related to the search for mating opportunities and other social interactions. During those 7 seasons, there were no changes in humpback whale group structure, nor were there strong behavioral changes. However, it was observed that, in the presence of vessels around 100 to 300 meters, mothers spent less time resting and calves spent less time in activities probably related to suckling. There is a concern that behavioral changes caused by anthropogenic factors may put the population at risk and changes at population level may take several years to be detected. So, it is suggested that studies following the same methodology continues, allowing further future comparisons. A long-term study would permit continued investigation of humpback whale use patterns (or theirs alterations) showing their responses to anthropogenic pressures

Aspects of habitat use patterns of humpback whales in the Abrolhos bank, Brazil, breeding ground

The Abrolhos Bank (off the State of Bahia, northeastern Brazil) is the most important breeding and calving ground for humpback whales, Megaptera novaeangliae, in the western South Atlantic. The area is shallow with a mean depth of 30m and a group of five islands (the Abrolhos Archipelago) is located in the northern portion of the Bank. Data collected from 1992 to 1998 were analysed to identify possible different habitat use patterns by different humpback whale group types. An analysis of variance found differences in the mean water depths where different group types were recorded: single whales, 18.9m (se = 0.505); pairs, 18.6m (se = 0.386); competitive groups, 19.1m (se = 0.573); mother-calf pairs, 15.8m (se = 0.373); mother-calf-principal escort, 14.9m (se = 0.489); and competitive group with mother-calf pair, 16.4m (se = 0.889). With the exception of competitive groups, those containing calves (mother-calf alone or mother-calf-principal escort) occurred in significantly shallower water than non-calf groups (Tukey test, p<0.05). In addition, groups containing calves were found significantly more often nearer the Archipelago (within 4 nautical miles) than other groups (two-sample Kolmogorov-Smirnov test, D = 0.139; 2 = 18.516, p<0.05). Accordingly, a spatially stratified management scheme is recommended in order to protect mother-calf pairs from possible harassment by whale watching operations in the area