Whale Stranding

When 230 pilot whales recently became stranded on ocean beach, tasmania, rescuers immediately jumped into action - and so did the scientific community. this horrible event provided researchers with an opportunity to research a species so rarely encountered in the wild, and to seek answers to the mystery of why whales and other cetaceans become stranded in the first place.

Data collected included visual observations such as scars on the males which were likely received while fighting with each other during the mating season, to physical samples such as stomach contents to understand where they have been, if they have been feeding, and what they have been feeding on. Skin samples alone can contain a wealth of knowledge on the sex and age composition of the pod, as well as their overall health, while also providing genetic information to help researchers figure out if there is a relationship between these whales and those that have stranded in the past, or may do so in the future.

"It gives us an opportunity to work out things about how their family groups are structured — but we can also look at the animals themselves… We can work out, essentially, how these animals are living at sea and what sort of community they actually have out there," - Dr. David Hocking

While David Hocking, the senior curator of vertebrate zoology and palaeontology for the Tasmanian Museum and Art Gallery, was collecting data from the whales that did not survive, he was also receiving phone calls from around the world as fellow scientists requested specific observations and samples be taken. One group of researchers from the US specifically asked that a brain be collected to assist them in their studies investigating if brain injuries may contribute to strandings.

Because the sad fact of it is we simply do not know for sure why mass whale stranding happen!

If this is a field of science you may be interested in pursuing one day (and if so, go you!) the first thing you need to know is how whales find their way around. Whales (like bats) navigate via echolocation, by first sending out sound waves and then interpreting the echo that returns to them. A fatty structure in their forehead known as a ‘melon’ acts as a sort of sound beam, helping them focus the high frequency, short duration echolocation clicks they send out. As the sound bounces off nearby objects and returns to them, sound receptors in their jawbone conduct sound vibrations to the middle ear and help them perceive the world around them.

So, what are some of the prevailing hypotheses for what causes mass whale strandings?

FEEDING

For pilot whales, like those stranded in Tassie, echolocation is perfect for helping them find prey in the dark water they usually hunt (swimming as deep as 1000m down). But, there is a theory that when they can’t find enough food in their usual hunting grounds they will approach the cold, food-rich ocean currents that flow close to shore. Once they swim into the shallow waters along the coast it may become too difficult for them to swim back out. Echolocation does not work as effectively in shallow waters as it does in the open ocean and the wide, gently sloping coastlines may confuse them. This was not the first time pilot whales have stranded at the Ocean Beach, earning it the title of ‘whale trap’. In fact, exactly 2 years prior to this stranding we witnessed Australia’s largest-ever documented cetacean stranding when 470 pilot whales became stranded in the exact same location. Prof Karen Stockin, an expert on cetacean strandings at Massey University in New Zealand, told The Guardian “The tide comes in and out very quickly and you can get caught out,” she said. “If you’re a pilot whale foraging and are distracted, you can get caught. That’s why we refer to these places as whale traps.”

noise pollution

Humans are now adding so much noise to the oceanic soundscape through shipping, boating, and exploration that it’s interfering with the ability of animals to hear the specific sounds they need to listen to. Scientists have linked some strandings that have occurred in the past to sonar from ships interrupting the ability of whales to echolocate and determine their surroundings, and some may even stop using echolocation altogether while in the presence of anthropogenic (man-made) noise.

SICKNESS and injury

Not only does all this extra noise prove to be majorly annoying, but there is also evidence to show that noise pollution can actually physically hurt whales. Loud and sudden sounds from human activity may frighten the whales so badly that they flee towards the surface, resulting in injuries like damaged blood vessels or decompression sickness, and results in an animal who simply finds it too hard to swim anymore. One study which found gas bubbles in the livers of stranded cetaceans lead to a study investigating the relationship between the amount of energy used by cetaceans during a normal dive vs an escape dive and concluded that the extra physical exertion can lead to tissue damage.

LOYALTY

This is the truly heartbreaking part. Whales are known for having especially strong social bonds, and may become trapped on mass as whales follow a sick or injured pod leader into the perilous shallow waters, or refuse to leave frightened family who find themselves trapped. After the 2020 stranding event at Ocean Beach, Prof. Karen Stockin told the Washington Post:

“These animals are constantly communicating, it’s like a distress call. So even when you got some animals successfully into deeper waters, it’s not uncommon for them to turn tail and come straight back in.”

1986 beached whales in Flinders Bay. Photo by Bahnfrend. Used under CC BY-SA 3.0

We can’t imagine how horrible it would be to stumble across a cetacean in need, can you? We know your first instinct would be to run to the animal and try to help them because that is what we would want to do! But remember - the animal (or animals) will be frightened and stressed and the last thing you want to do is add to that - sadly, you may be more of a hindrance than a help! (Also, it’s against the law.) But if you are really keen, especially if you live near a well-known ‘whale trap’, you could take advantage of the few organisations that run training programs that will allow you to become a licensed rescuer. Click here to find out when the next ORRCA training workshops will be held in NSW, QLD and WA.

The most important thing to remember is that if you find a stranded whale your first step is to alert the authorities. Click here to find the correct number to call (it’s different for every state) to save to your contacts.

What you know now

• Strandings can provide researchers a chance to learn more about species that are rarely encountered in the wild

• Data collected goes beyond why they strand, it also helps to build a bigger picture of how they live their lives

• When whales strand members of the global scientific community work together to gather data and build knowledge

• Whales use echolocation to navigate and hunt and this can be impacted by noise pollution or unfamiliar environments

• The exact cause of strandings is unknown though there are some prevailing hypotheses

References

Gas-bubble lesions in stranded cetaceans

Morphology of the odontocete melon and its implications for acoustic function

Stomach contents of long-finned pilot whales, Globicephala melas mass-stranded in Tasmania

Swimming and diving energetics in dolphins: a stroke-by-stroke analysis for predicting the cost of flight responses in wild odontocetes

Tasmanian museum team helping research to understand whale strandings

Tasmania’s whale stranding: what caused it and can it be stopped in the future?

Why Do Whales Strand Themselves?

Underwater noise pollution is risking the lives of whales and dolphins