A recent study by the University of Queensland’s School of the Environment has found that humpback whales (Megaptera novaeangliae) off the country’s eastern coast were less stressed and healthier generally in the first year of the Covid-19 pandemic.
There were fewer people in the ocean at this time. Stress is as bad for animals as for humans, suppressing growth, immune system function and reproduction. It affects species as varied as marine iguanas and ring-tailed lemurs.
The silence of the pandemic
The team of researchers operated from the Moreton Bay Research Station. Dr Jake Linsky led them. They went out in small boats and used darts to obtain blubber and skin samples from whales off North Stradbroke Island, 19 miles (30 km) from Brisbane. This is the second largest sand island in the world. The Aboriginal name for it is Minjerribah, while locals call it Straddy.
The research appeared on 5 June 2024 in the journal Marine Environmental Research. It echoed the findings of a study by scientists from Boston’s New England Aquarium soon after the 11 September 2001 terrorist attacks. At the time, two teams of them were at sea in the Bay of Fundy on Canada’s Atlantic coast.
Originally, the researchers’ aim was to develop pregnancy tests and other ways to study whale reproduction. But after the attacks, commercial planes and ships ceased activity. The lack of sound led to fewer stress hormones being found in the faeces of North Atlantic right whales (Eubalaena glacialis) in the next few weeks. Blood samples could also be used but were much harder to collect. A couple of years later, the whales’ stress had returned to normal.
Stress can also go the other way as it did during the Second World War. Fewer whales were being harpooned then, but cortisol rose, probably due to people being louder. Cortisol also increases with water temperature: climate change stresses whales. This affects even the largest animal that ever lived, the blue whale (Balaenoptera musculus). Melting sea ice reduces the population of krill, on which blue whales feed.
A measure of health
Whales around Australia are protected, first by the Whale Protection Act 1980 and then by the Environment Protection and Biodiversity Conservation Act 1999. Dr Linsky’s people examined humpback whales as they migrated and bred in 2020 and 2021. They tracked whale health, size and energy. There was a great deal less of the stress hormone cortisol in 2021 than 2020.
Dr Linsky explained that this might be down to a number of reasons. One possible reason for whales being healthier was that they were eating fewer man-made pollutants. Polychlorinated biphenyls are one such example.
The noise problem
Ships hitting whales is one of the leading causes of their mortality, but their noise also causes problems. Human-caused noise has increased by a massive amount in the last century; international legislation considers it a pollutant. Sight is much less important underwater than on land; lower than 330 ft (100 m), 99% of light entering the water has been absorbed. As a result, sea life has developed other senses, with sound being one of the most important. Whales are extremely sensitive to noise as they navigate and communicate over huge patches of ocean.
Anything that makes communication more difficult will affect creatures. Human doings mean whales act like people in a crowded bar: they talk louder, stay closer together and keep conversation simple. Sans humans, whales can hear each other over around 1.4 miles (2.3 km). Otherwise, they can only hear something closer to 650 ft.
A good example of the impact of man-made noise on whales comes from navy sonar. Whales are pretty damn loud, with their calls being more than 180 dB, louder than a jet taking off. Sonar, however, is worse, being over 200 dB. This causes embolism — blocked blood vessels — in beaked whales when they ascend rapidly to avoid the pulses. This might be lethal. Or there is the low hum of container ships that drowns out whales’ calls so thoroughly that some fall silent.
Auditory stress
Auditory stress strikes many more sea animals than just whales: fish, seals, squid and even creatures as simple as oysters. Outboard motors sometimes cause damselfish to not flee the scent of predators. Loud noises might lead to deformities in scallops, thus reducing their chance of survival. Noise also drives Arctic cod from their feeding grounds and scatters schools of tuna. Seismic airguns see use for ocean mapping and in oil and gas exploration; they can kill the tiny zooplankton that are at the very bottom of the ocean food chain.
In the words of Michelle Fournet, an acoustic ecologist at New York’s Cornell University: “Almost all life underwater relies on sound. … [A] a lot of very vital functions are compromised when it gets too noisy”. If things are quieter: “You’re afforded much richer language and the ability to convey more information in that exchange”.
From hunting to conservation
Eastern Australian humpback whales were once valued only when they were dead, for their oil and bones (baleen). Export of whale products was, in fact, Australia’s first primary industry. Now, humpbacks gain appreciation while alive, both ecologically and economically. They came close to extinction in the 60s but then attracted considerable efforts at conservation. Their number has risen from slightly more than 100 in 1963, when whaling ended, to about 8,000 in 2006. Their recovery from whaling was one of the best ever.
Dr Linsky commented that humpback whales’ health is a good indicator of the entire Antarctic marine ecosystem’s health. He believes that further research is called for to determine how healthy whales are, but human activity surely plays a major role. He spoke of the “remarkable ability to adapt to changes in their environment” of Eastern Australian humpback whales, but insisted that humans’ adverse effects should be limited so whales “continue to thrive in our rapidly changing oceans”.
