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Context:
A recent study was conducted & it raised the concerns about the effect of marine heat waves (MHWs) on Arctic & Subarctic marine mammals.

These heat waves are creating problems for both short term & long term problems like deaths, lower birth rates, & higher risks of disease among these marine animals.

What are Marine Heat Waves (MHWs)?

• When ocean temperatures rise 3-4 degrees Celsius above the average for at least five days.
• Then it is called Marine heatwave. These heat waves can last from several days to even years & can cover large areas of the ocean.
• The Arctic Ocean is expected to be a future hotspot for these heat waves.

What are the Impact on Marine Mammals

The study found that marine mammals in the Arctic and Subarctic are facing serious problems because of these heat waves. The effects include:

• Increased Deaths: Many marine mammals, including whales and seals, have had higher death rates during times of extreme warmth.
• Lower Birth Rates: Marine mammals are finding it harder to have babies & raise healthy offspring. The heat waves are affecting their ability to reproduce.
• Higher Risk of Disease: Warmer waters make it easier for diseases, like harmful algae blooms, to spread, affecting the health of marine mammals.

What are the Effects on Specific Species :

• Whales and Dolphins: Species like narwhals and bowhead whales are especially at risk. These animals have thick layers of fat, called blubber.
• It helps them to stay warm in cold waters.
• But they also make it harder for them to cool down in warmer water. This makes it hard for them to adjust to rising ocean temperatures.
• Other Marine Mammals: Humpback whales & fin whales have suffered higher death rates after heat waves in the Gulf of Alaska (2014-2016).

• Some species are also moving farther south to find cooler waters. It is putting them at greater risk of getting caught in fishing gear.

What are the Examples of Specific Events ?

• Polar Bear Death: A polar bear was reported to have died from avian influenza in 2024, probably after eating infected marine birds.
• This shows how diseases can spread among Arctic animals because of warmer temperatures.
• Seal Deaths: Ice-seals, like the spotted seal, have been greatly affected by the warm conditions in the northern Bering and Chukchi seas.
• High death rates & poor health of seal pups were seen, as they struggled to survive in the warmer environment.

What are the Wider Effects on the Ecosystem ?

• Marine heat waves are not only hurting mammals.
• The study also found that the effects reach across many different species, from plankton to fish and seabirds.
• For example, the warmer waters can lead to toxic algae blooms, which also harm marine mammals and other wildlife.

What is algal bloom ?

• An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in fresh water or marine water systems.
• It is recognized by the discoloration in the water from the algae's pigments.
• Global warming + polluted runoff = greater risk of algae outbreaks.

Source: DTE