Joshua Smith

Humpback whale migration between tropical breeding grounds and polar feeding grounds is an energy-intensive activity undertaken on finite energy stores. The use of stopover sites to rest reduces energetic expenditure and provides enhanced opportunity for calves to nurse during migration. Moreton Bay is a newly identified migratory stopover for Australia’s east coast humpback whale population. Understanding the functional roles of stopovers is essential for a holistic understanding of population dynamics and connectivity. Therefore, contextualising the significance of Moreton Bay relative to a well-established stopover like Hervey Bay can provide valuable insights into their functional roles within the broader migratory network, helping to inform targeted conservation efforts. To investigate this, we conducted a total of 865km of systematic, boat-based line transects across the two distinct geographical regions during temporally staggered periods (August and September – October) of the 2021 humpback whale migration. We examined population structure, behaviour, and habitat segregation, and developed spatial density surface models to predict density distribution patterns at each respective site. Our results show that Hervey Bay supports a more heterogeneous mix of demographic groups, while Moreton Bay had a significantly greater number of calf-groups (z = 4.53, p = 0.017). Both bays exhibited similar resting behaviours, but social interactions among juveniles were unique to Hervey Bay. These findings suggest Moreton Bay serves a more utilitarian role as a stopover, functioning primarily as a resting site for mother-calf pairs, rather than the multifaceted use described in Hervey Bay. As lactating females and their calves are particularly vulnerable to anthropogenic threats like vessel strike, it is imperative to understand how different habitats contribute to the success of migration and ensure adequate protection is maintained.

Aerial surveys of southern right whales (Eubalaena australis) were undertaken off the southern Australian coast to monitor the recovery of this endangered species following extreme 19th and 20th Century commercial whaling. The aerial survey was undertaken in the coastal waters from Perth (Western Australia) to Ceduna (South Australia) between the 12th and 19th August 2022, to maintain the annual series of surveys and inform the long-term population trend. The survey resulted in a total 526 whales sighted, consisting of 247 cow-calf pairs, 31 unaccompanied adults and 1 yearling. The ‘western’ population of southern right whales in Australian waters is increasing in size (~5.3% per year based on female/calf pairs and a population estimate of 2675 whales) based on the long-term population trend data from the annual aerial surveys. This represents the majority of the Australian population given the very low numbers in the ‘eastern’ population. The 2022 surveys recorded the lowest number of unaccompanied animals (i.e. males and females without a calf) ever throughout the time-series of the annual aerial surveys since 1993 when survey coverage between Cape Leeuwin and Ceduna first began. Across this time series, there is a particularly notable decline in sightings of unaccompanied animals over the past five years. It is currently unclear what factors account for the decline in these sightings or may influence the variation in numbers of unaccompanied animals on the southern Australian coast. Lower than expected counts in the long-term data may provide evidence of a slowing population growth rate, which can only be assessed by continued annual population surveys to assess population trend data.