Humpback whales (Megaptera novaeangliae) migrate annually along the coast of Western Australia (WA) from their summer Antarctic feeding grounds to warm tropical waters in the Kimberley for breeding.

Given the remote nature of the Kimberley marine environment and the very large range of humpback whales across known breeding and resting areas, it can be difficult to gather sufficient data to assess their distribution and to monitor population health. A four year project underway at Two Moons Whale and Marine Research Base at Pender Bay, WA (McKay and Thiele 2008, Blake and Dapson 2011) offered an opportunity to assess the value of using a land based site manned by volunteers as a cost effective means of gathering suitable data. The purpose of this project was to evaluate the data collection methods used at this research station, extend data collection for an additional year and evaluate the 5 year dataset to understand humpback whale use of Pender Bay.

Data collection included counts of all humpback whale groups (noting size and presence of calves) observed at 20 minute intervals from a cliff top viewing platform. Additional information was recorded on environmental variables (tide, sea state, weather) and the presence of vessels. These data were evaluated to assess the timing of the migration season, including peak in the number of individuals and the number of calves across the season and the distribution of whales within the Bay and adjacent waters.

Overall a total of 3,695 groups of whales (5,521 individuals) were sighted over the 88 days when observations took place throughout the season. Calves were observed in 187 of these groups. While the peak in number of groups with calves occurred in mid August to September, there was a higher proportion of groups with calves early in the season.