Whales divided: how adults and calves use Hervey Bay differently

If you go whalewatching in Hervey Bay after mid-September, you may notice that there is a calf in nearly every pod you see. Mothers with calves are typically the last to arrive in the bay, and they may be the group that benefits most from the shallow, protected waters near Fraser Island.

Our research on the East Australia population of humpback whales allows us to ask questions about long-term trends in behavior and habitat use within the area. Using sighting data collected by our research team from 2004 – 2016, we looked at whether pods with a calf preferred different areas of the bay compared to pods without a calf. As it turns out, mothers with calves do show a preference for an place just inside the U-shaped coastline of Fraser Island, known colloquially by whalewatch operators as “the pocket”. Pods without a calf show an opposite preference for waters a bit farther offshore.

Although depth and distance to shore do not vary much throughout the bay due to the overall shallow waters and the U-shape of the coastline, mothers may prefer that area because it might be the most protected from rougher weather conditions. They may also use it as a place to avoid pursuing males and competition pods. Pods that do not have a calf may prefer the area slightly farther out of the pocket if they are seeking mating or socializing opportunities from other adults or subadults.

The study provides a baseline to compare future observations of whale distribution within the Hervey Bay area, particularly as this population continues to coexist with human activities in the bay including recreational boating, commercial whalewatching, and swim-with-whales tourism.

Pod types in Hervey Bay

In an earlier post, we mentioned the recent appearance of mothers with calves in Hervey Bay. Humpback whales do not all migrate at the same time; rather, multiple group types will be predominantly seen at different points throughout the migration.

The earliest pulse of whales to arrive in Hervey Bay is sub-adult whales; meaning whales that are sexually mature but have not yet reached their full size. Sub-adults in this area seem particularly curious about the vessels, and the early portion of the season is well known for “mugging” events where the whales approach the vessel. Later in the season, mothers and calves begin to migrate through the area, and the sub-adults continue their migration toward their Antarctic feeding grounds. Mothers with calves tend to stay in the tropical breeding areas longer than the sub-adults, likely to allow the calf more time to build up its muscles and blubber layer before beginning the migration southward. The protected waters on the westward side of Fraser Island provide a safe, sheltered stopover for these mothers to rest and nurse their calves.

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Are the whales jumping for joy in Hervey Bay?

Breaching, or jumping out of the water, is a behavior that the PWF researchers in Hervey Bay and in Maui observe frequently. A commonly asked question is “Why do whales breach”? The short answer is that no one knows a single cause for this behavior; however, there are a number of theories about what drives such impressive whale acrobatics.

One possibility is that the whales breach just for fun, similar to humans and other terrestrial mammals when they are excited or playing. Another option is that they use breaching and other surface activity as a way of communicating to other whales. If you’ve ever been close to a breaching whale, you know that the sound is astonishing. The sound is also quite loud underwater and may be used to communicate the whale’s location or activity level to other whales in the distance. It has also been suggested that whales breach to deter predators or other perceived threats.

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Fluke-Up Feeding in Hawaiian Waters

In the past few weeks our office has received numerous calls from concerned citizens about seeing a whale in distress.  The whale observed is spending long periods of time at the surface with its flukes extended above the water’s surface.  Some have conjectured that it is a whale using its tail flukes to sail; others have suggested it is attempting to cool down using its tail as a thermoregulatory device.

We believe a different hypothesis to be true.  The whale with the extended flukes is most likely a female humpback with a newborn calf. The mother is resting while still allowing her calf access to her mammary glands (located near the posterior portion of her body some 6-8 feet from her flukes).  By extending her tail into the air she is able to keep her body relatively close to the surface, allowing her to rest while minimizing dive depths for her young calf.  The calf is then able to nurse at will and expend less energy.

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Mother-calf pairs in Hervey Bay

There has been a change in the size and composition of humpback whale groups sighted within Hervey Bay as the season progresses. In the first weeks of August, yearlings (one-year old whales) and sub-adults (immature individuals of both gender) were mainly found in the bay. This is the time where you are more likely to be mugged by whales. By late August, mature females come in the area, followed by mature males and their songs can be heard throughout the bay. In mid-to-late season, i.e. September to October, the majority of groups sighted are mother-calf pairs as they tend to be the last groups to migrate south to the Antarctic feeding grounds.

Hervey Bay is a shallow and protected bay in Australia, which provides an ideal temporary stop-over for mother humpback whales to care for their offspring during the southern migration. Using photo-identification, we know that some mother-calf pairs may stay more than a week within the bay.

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