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.

Nursing is commonly observed here in Hervey Bay, and occasionally the mothers exhibit an interesting “fluke up” posture while feeding their calves. This behavior is characterized by the mother sticking her tail flukes out of the water and pointing her head downwards. While the mother is stationary in this posture, the calf will dive down to nurse and then pop up to the surface repeatedly for quick breaths of air. Eventually, as with the sub-adults, the mothers and calves will leave the area to continue their migration. It is important for the mother to return to the feeding grounds to replenish her energy stores lost from nursing as well as to properly wean her calf and teach it to feed on its own.

After the bulk of the mothers and calves have left the bay, mature whales will make up the majority of the latest pods in the season. These are whales that remained in the breeding areas the longest, for example, adult males trying to ensure the best chances of mating.

There are interesting trade-offs to consider in such a large scale migration where whales travel away from their feeding grounds, and these trade-offs affect whales differently depending on their sex, age, and reproductive status.

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.

Young calves may have a completely separate motivation for breaching. As more mother and calf pairs enter Hervey Bay, researchers and whalewatch passengers alike can’t help but to notice the awkward jumps of young calves. These calves are trying to imitate what the larger whales are doing with mixed success. Breaching calves are entertaining to watch, but there has been recent research suggesting that through repeated breaching, humpback whale calves increase the amount of myoglobin in their muscles. Myoglobin is a protein that binds iron and oxygen, and high concentrations of myoglobin can improve the diving ability of marine mammals.

There are a variety of possible explanations for why whales breach, but it is most likely that whales do not breach for any single reason, but rather do this behavior for a number of reasons that serve different functions throughout the seasons and over the course of their lives.

Written by Eilidh Milligan

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.

While it is rare to see a female displaying this resting/nursing posture in Hawaii, it is not without precedent.  PWF researchers have observed this feeding behavior in over three dozen female humpback whales off east Australia since 1984.  It appears to be a socially transmitted behavior: initially just a few whales employed this resting and feeding posture, and over the past 20 years we have seen a steady increase of females displaying this behavior. We refer to it as “fluke-up feeding”, or “tail-up feeding”, and once an animal employs this method, they then tend to repeat the behavior with subsequent calves.

The gestation period for humpback whales is between 10 and 12 months, and they have only one calf at a time. A whale has never been seen with two live young, but there are records from the whaling days of a pregnant whale with two fetuses. Humpback whale calves observed in Hawaii are both conceived and born in the Hawaii region. Surprisingly, there is little firsthand evidence of birthing. Scientists have observed newborn calves with their dorsal fin still folded flat against the back and fetal folds along the body. There have also been reports of a placenta being recovered while floating at the surface of the water.

A recent finding by Murdoch University Cetacean Research Unit in West Australia reveals nursing occurs at an average depth of 16 feet.  Most calves nurse throughout the day, and spend 30% of their time nursing in a 24-hour period.  Although most calves nurse opportunistically throughout the day, some females only nurse their calves during the morning hours, and others nurse only at night. Humpback whales have two nipples which, when nursing, will protrude through the mammary slit. To nurse, the calf curls a specially shaped tongue around the nipple and the thick, fatty milk is reflexively squirted into the calf’s mouth. Humpback whale calves drink many gallons of milk per day, which allows them to grow quickly. Newborn humpback whales average 12-14 feet in length and weigh upward of two tons. Lactation continues for 10-11 months and once the calf has weaned, it has little contact with its mother.

There is no need to be alarmed at the sight of a whale with its tail extended for long periods of time: the animal is neither injured nor in harm’s way.  In this case it is a mother who has figured out a novel way to feed her calf while resting and conserving her energetic resources for the long journey back to the northern feeding grounds.

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.

Mother-calf pairs have the strongest and more lasting bond within humpback whales. The calf will stay with its mother for about a year until it is weaned. During that time, it will feed on a fat rich milk to put on weight very quickly and be able to migrate to the feeding grounds with its mother.

As in many mammal species, calves can be full of energy, performing many surface activities, such as breaching, while their mother is travelling slowly or even resting at the surface, which is often referred as “logging” given that from a distance a whale can look like a floating log at the surface. When calves are very active to the delight of passengers and researchers alike, one question often comes to mind: “where do they get all that energy?”

During their stop-over in the bay, calves also get more opportunities to learn how to behave by mimicking their mother’s actions, like “pec slapping” and breaching for example. Both mother and calf may participate at the same time, making it a priceless photo if you get the shot.

Being able to observe whales in their natural habitat, especially mother-calf pair interactions, is a real privilege. I am always in awe to witness such a strong bond and how gentle mothers can be toward their calves despite their size. They touch one another with their flippers and at times you may be lucky enough to observe a calf swimming on top of its mother’s head and being gently lifted by her rostrum (upper jaw or snout).

Calves swim very closely to their mothers, especially in the early stages of their life, for protection from predators such as killer whales. Whales that were attacked by killer whales and survived often bear distinctive “rake” marks on their flukes.

Some mothers appear more protective of their calves, staying away from a vessel. Others, on the other hand, are more relaxed and will approach a vessel with their calves.

Mothers are also very protective of their calves in the presence of one or several escorts, often swimming between her calf and escort(s), as she may be harassed by the escort exhibiting vigorous and aggressive behavior such as head lunges. If more than one escort is present, the individual defending the position closest to the female is often referred to as the “primary escort” and the others as “secondary escorts.”

After a stop-over in Hervey Bay, mother-calf pairs with or without escort(s) will continue their south migration to Antarctica. Mothers will look after their calves for almost a year. At that point in time, the calves now called “yearlings”, will become independent while on the feeding grounds or in route to the breeding grounds. Some may even accompany their mothers back to the breeding grounds. Once there, they would have completed their first round migration, one of many to come throughout their lifetime.