Whales in a changing ocean: spatio-temporal patterns of large whale species in offshore development areas in southeastern Australia (Society for Marine Mammalogy SMM Conference 2024)

Summary

Aerial marine mammal surveys combined with validated citizen science contributions from the western and central Bass Strait continental shelf and slope environments between July 2021 and June 2023 provided contemporary data on the temporal and spatial distribution of large whales in the region. Seven large whale species were recorded during aerial surveys: blue, humpback, southern right, sei, fin, Bryde’s and sperm whale. Sightings of blue whales occurred between September and July. These records represent both the earliest the latest seasonal sightings on record. Numbers for this species peaked later in the season than previously reported in the literature. Blue whales occurred throughout the survey area and were often observed feeding. Sightings of humpback whales provided evidence of a migratory pathway through central and western Bass Strait that likely connects with the eastern Australian migratory corridor. The majority of humpback whale observations were associated with feeding behaviour and commonly involved multiple whales (10+) in multi-species assemblages. Temporal overlap in the presence of humpback whales and blue whales was detected offshore from September through to December and in July for blue and southern right whales nearshore. A key outcome of this study indicates that the notion of whale ‘seasons’ must be viewed with caution and a range of ecological and potentially behavioural factors are likely involved. Considering this area is a focus for offshore development and the apparent significance of this region to multiple species of large whales, there is a need to refine expectations around temporal staging of offshore activities and focus on mitigation measures to minimise risk of impact to cetaceans across all seasons.