The ocean is going silent.

Blue whales,the gentle leviathans that swim in all but one of the world’s oceans,are the singers of the underwater world.

Their groans,whistles and clicks are famously so soothing that they count as white noise,and they may even have a pho-ne-tic alphabet.

These haunting melodies aren’t just for fun – these giants do so to socialise,get around and differentiate friend from foe.

But researchers have revealed that blue whales are singing less and less as they’re simply too hungry to do so.

Scientists have used underwater hydrophones – an aquatic version of microphones – to monitor and record their vocalisations off the coast of Monterey Bay, California.

Blue whales are among the largest animals in the world (Picture: Getty Images/iStockphoto)

The Monterey Bay Aquarium Research Institute found that the beats are singing 40% less than they once did six years ago.

Over this period,the temperatures in the ocean have been cranked up by major heat waves,causing toxic algae to bloom that kill krill and anchovies.

Both are the main diet of blue whales,the study said.

John Ryan,a biological oceanographer at the institute,told the National Geographic: ‘When you really break it down,it’s like trying to sing while you’re starving.

‘They were spending all their time just trying to find food.’

Humpback whales have a more diverse diet of krill,plankton and schooling fish,so their song frequency didn’t change amid the heatwave.

The mammals have to use a lot of energy to gulp krill to eat (Picture: Getty Images)

Over the six-year study,a pool of warm water officially dubbed ‘the blob’ drifted into the Bering Sea and Gulf of Alaska.

The blob warmed the ocean by 2.5°C,far more than El Niño,a natural climate pattern linked to warmer conditions in the Pacific Ocean,could.

The 2,000-mile-wide blob caused a record-breaking outbreak of toxic algae so severe that it shut down crab fisheries,starved seabirds and killed plankton.

As krill vanished from the seas,the blue whales scattered and had to spend all their energy searching for food rather than singing.

The scientist said this suggests the mammals not only ate less but also mated less,given they vocalise low-frequency D calls when they do.

The researchers said that the blue whales’ acoustics are a warning for what’s to come as climate change cranks the planet’s thermostat up.

Warmer temperatures in the ocean can lead to rising sea levels (Picture: Mario Tama/Getty Images)

Sea surface temperatures broke records last year,with a quarter of the oceans experiencing once-rare marine heat waves. These warmer oceans cause rising sea levels,bleaching coral reefs and more intense hurricanes.

Sea basins absorb 90% of the excess heat trapped in the atmosphere from greenhouse gases,which are emitted by burning fossil fuels.

Dr Judith Brown,projects director at Blue Marine Foundation,which supports governments to protect marine areas,described whale song as a ‘truly eerily beautiful sound’.

‘We know that 90% of global fish stocks are overfished – a harsh reality that threatens marine ecosystems,’ she told Metro.

‘Blue whales rely on krill to survive,and fishing krill,a species from the bottom of the food chain,occurs annually around Antarctica. This year,more than 620,000 tonnes of krill were taken in just a few months.

‘High fishing pressure likely results in limited krill availability for whales. So it’s no surprise that whales struggling to find sufficient food may no longer “sing”.’