Seasonal changes in pod characteristics of eastern Australian humpback whales (Megaptera novaeangliae), Hervey Bay 1992–2005

We investigated the characteristics and composition of 4,506 humpback whale pods observed in Hervey Bay between 1992 and 2005. We use these data to analyze and model the variability of pod size and composition, and to assess the importance of Hervey Bay for particular classes of humpback whales. Pods ranged in size from one to nine individuals. Pairs were the most frequent pod type (1,344, 29.8%), followed by mother-calf alone (1,249, 27.7%), trios (759, 16.8%), singletons (717, 15.9%), and 4+ whales (437, 9.7%). Of the 4,506 pods, calves were present in 40%, and 10.8% of all pods had one or more escorts present. Of the 1,804 pods observed with calves present, 1,251 (69.4%) were mothers alone with their calves. The size and composition of pods in the study area varied significantly as the season progressed. Pods with calves present were rarely recorded early in the season but dominated later in the season. A significant increase over years in larger groups may be related to social and behavioral changes as the population expands. The data indicate that Hervey Bay is important to immature males and females early in the season, to mature males and females in mid-season, and to mother-calf pairs (either alone or with escorts) in mid-to-late season.