By ALEC SMART
As winter cools the Southern Hemisphere, and ice extends over the Antarctic, whales move northwards to warmer waters, providing excellent opportunities to watch them migrate along the Australian coast.
Humpback Tail - credit: Pixabay
According to the Australian Government Dept of Agriculture, Water and Environment, “at least 45 species of whales, dolphins and porpoises are found in Australian waters including 10 large whales, 20 smaller whales, 14 dolphins and one porpoise.”
Whales, dolphins and porpoises are collectively known as cetaceans, from the scientific order of cetacea. The word was derived from the Latin ‘cetus’ which was adapted from Ancient Greek ‘ketus’, meaning ‘monster-sized fish’, although they are not fish but warm-blooded air breathing mammals. Divided into 86 species, cetaceans are exclusively marine-dwelling carnivores that give birth to live young.
Between May to November every year, several species of cetaceans pass Sydney during their north and southbound migrations along the east coast.
These include the baleen (their ‘teeth’ thin plates of strainers with frayed ends through which they filter plankton and small fish) and toothed whales (that eat mainly fish and squid, although some prey on other cetaceans and seals).
The whales are often accompanied by dolphins. Although most species of dolphins move between different feeding grounds, only a few migrate to follow the seasonal movement of their prey, and not the vast distances covered by some of the whales.
By mid-August, the last of the northbound whales head up the coast, while the first of the southbound return down to cooler waters, and they often pause to socialise as they pass one another. Around this time, whale-watching crews report that the whales get more curious about their vessels and often swim close to investigate, a phenomenon known as ‘mugging’.
During October-November, the tail end of the annual southward cetacean migration, the majority of whales are mothers and calves. They swim closer to shore to avoid predators, like orca, and because the calves are slower swimmers that need guidance.
Humpbacks 'bubble-herding’ - credit: Vivek Kumar/Unsplash
Humpback whales
The most common whale off Australia’s east coast is the humpback, moving back and forth between summer feeding waters in the Antarctic and their northern breeding grounds in the Coral Sea and mid-Pacific Ocean.
Along with grey whales, humpbacks are the furthest travelled of whales - some swim an annual round trip of 10,000km! During the northern migration, a lot of males ‘breach’ (leap out of) the ocean in displays of strength intended to impress the females.
With characteristic very long and bumpy fins (the bumps, up to 11, are called ‘tubercles’ and reduce drag in the water) and flutes (grooves) below their chin that enable better gulping of prey, humpbacks are typically covered in a mixture of hitchhikers - acorn and goose barnacles. These crusty arthropod often cause scarring on the skins of other whales as the huge creatures glide against each other.
There are approximately 80,000 humpback whales worldwide, the species now recovered from intensive slaughtering by humans that brought them to the edge of extinction until a 1966 moratorium on whaling. An estimated 30,000 of them travel up and down the east coast of Australia every year.
The eastern humpbacks that pass Sydney are a separate and distinct collection from those that migrate along Australia’s west coast every year (apart from a few females that exchanged pods), and the males have their own distinguishable group ‘song’ that they call to the females.
How long can a whale hold its breath?
Whales’ lung-to-body ratio is actually smaller than humans, but they have a significantly more efficient respiratory system that enables them to absorb as much as 90 percent of the oxygen in each intake of air – compared to around 5 percent for humans.
Pilot Whale - credit: Fitschen/Pixabay
Whilst descending, whales slow their heartbeat down significantly and blood can be diverted to vital organs from less important ones, facilitating longer, deeper dives.
The deepest divers are sperm whales, which regularly travel to depths of over 1000 metres to prey upon giant squid, requiring them to hold their breath for up to 90 minutes.
Humpbacks have been recorded remaining underwater for an hour, although usually they surface every five minutes for gulps of air.
Orcas seldom remain underwater over 15 minutes and need frequent breaths when hunting.
Whales and dolphins can’t breathe while they’re asleep, but they’re adept at snoozing parts of their brain while an active part enables them to stay afloat, breathe and watch for predators.
Herding fish in bubbles
Some whales, known as ‘herders’, employ group tactics to catch prey, with one diving below a school of fish and enshrouding them in ‘nets’ of spiralling bubbles released from its blowhole. Another whale will emit a loud noise below that panics the bubble-caught fish that causes them to swim upwards to escape. The group of whales will then form a circle and follow their prey, mouths agape, and swallow the now-trapped fish near the surface.
About dolphins
Dolphins are amongst the most intelligent creatures on Earth, with large brains capable of learning and remembering complicated tasks and the ability to plan ahead. They’re self-aware enough to recognise themselves in reflective surfaces, and experience happiness and grief whilst empathising with others. They develop complex social networks, communicate with their own sophisticated ‘language’ and cooperate in hunting, raising their young and defending themselves.
Dolphins are arguably the most athletic of marine creatures, capable of high leaps from the water utilising complicated twists and flips. These are done for a number of reasons - including having fun! – and sometimes performed in synchronicity as a group.
Dolphins - credit: Hamid Elbaz/Pexels
Whale Watching boat cruises around Sydney:
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