Sometimes whale mums need a rest and Queensland’s ideal

Migrating humpback whales have long used Queensland’s Hervey Bay as a playground during their annual 10,000km round-trip migration between Australia’s Great Barrier Reef and Antarctica. Now it appears that Moreton Bay, about 240 km south, also offers respite, particularly for females and their calves, say Australian marine biologists.

The majority of registered recreational vessels in Queensland are within the Moreton Bay area near the state capital, Brisbane, so studying behaviour is important for protection and conservation in that area.

“Humpback whales are seen in Australian waters from April to November,” says cetacean researcher, Dr Raphael Mayaud of Griffith University in Brisbane. Calves are born in the warm waters of the Great Barrier Reef around August, reaching Hervey Bay at the end of that month, with peak in numbers around September, and then they reach Moreton Bay from the end of September into October.”

The cetaceans also don’t feed during their migration, he adds.

“The same whales come to Hervey Bay year after year”.  Some are so regular and recognisable that they have been given names — ‘Nala’ has been bringing calves into Hervey Bay for years, he says.  

Nala is identifiable by the distinctive patterns on her tail fluke. These patterns, including colour, are like fingerprints, and are visible as the whales raise their flukes before a dive, says Mayaud. “Some whale tails are much darker than others. Some are completely white. So, it does vary.”

Hervey Bay is a crucial social habitat for humpback whales and has previously been described as a “Cavanbah” a word defined by the Bundjalung People to describe a safe annual social meeting place. With a more equal proportion of group types and evident interactions between juvenile whales, this study lends support to the role that Hervey Bay is a comprehensive stopover where whales of differing demographic groups not only rest but also undergo active and social behaviours. By contrast, dominated by calf-groups, the research shows Moreton Bay fulfils more of a utilitarian role, primarily for lactating females involved in maternal care.

The 2021 whale season provided an opportunity for Mayaud and his colleagues at Griffith University’s Southern Ocean Persistent Organic Pollutants Program to explore those whale populations and work out the roles and relative importance of the two bays to the broader humpback whale network.

“Because Hervey Bay has been extensively studied and well-documented as a stopover for the past couple of decades, it serves as an appropriate benchmark for us to compare Moreton Bay with,” says Mayaud.

The researchers looked at overall population structures, behaviours and distribution

patterns, and whale condition — were they well-fed or skinny?

Mayaud says all whales in both bays were resting, not feeding.  Hervey Bay was a mixture of whales of all ages and both sexes, but Moreton Bay was a largely mums and calves, he adds. Juveniles were also spotted socialising in Hervey, but not Moreton.

“Hervey Bay felt like a playground, where the whales were socially interacting with one another, and were genuinely curious about the research vessel, whereas Moreton Bay seemed more like a much-needed pit-stop,” he said.

“And this was reflected within our results. We found Hervey Bay had a more equal proportion of pod groupings while Moreton Bay was heavily dominated by calf-groups.”

These results have significance for conservation, including management of recreational vessel impact.

Whales get disturbed or even hit by boats in both bays.  “Particularly in Moreton Bay,” says Mayaud, “and there is also the disturbance from recreational boaties. Moreton Bay is a popular destination for recreational boating. The majority of registered recreational vessels in Queensland are within the Brisbane maritime region, and so it does experience a lot of on water presence and when there’s mothers and calve trying to rest, that can cause some issues.”

“Given the potential significance of this finding in terms of how it could impact the conservation status of the bay, it’s important that we understand the functional roles of stopovers because they give us a holistic perspective of population dynamics and connectivity,” says Mayaud.

Climate change also intrudes here, through its effects on the entire marine food chain. The zooplankton on which humpback whales feed  in the southern and Antarctic oceans, depend on phytoplankton. Both face major impacts from global heating. Reductions in krill populations will reduce the ability of whales to store enough energy for their annual migrations.

“And as climate change worsens, we might see an increasing use of the Moreton Bay by mums and calves needing to use the bay more often to rest, if they’re migrating in lower body condition” Mayaud says. “Which puts them at risk of other anthropogenic impacts like vessel strike.”

More research is needed, says Mayaud, to work out whether Moreton Bay is a facultative stopover (i.e., one mother-calf pairs only use, based on their current energy needs), rather than a socially-learned stopover like Hervey Bay, where a core subgroup of humpback whales repeatedly returned year after year.

Comprehensive observations and mapping of whale activities appear in PLOS One.

Where did that whale come from?