Compiling the most extensive photo-identification dataset for large marine mammals, a team of 75 scientists tracked populations of North Pacific humpback whales from 2002 to 2021.
In their study, titled "Bellwethers of change: population modeling of North Pacific humpback whales from 2002 through 2021 Reveals shift from recovery to climate response" published in Royal Society Open Science, researchers found that the 20% decline of humpback whales is attributed to marine heatwave and projects a troubled future for these majestic marine mammals.
Humpback Whales Face Climate Threats Post-Whaling Success
The North Pacific humpback whale population steadily increased after the cessation of commercial whaling in 1976, showcasing successful conservation efforts until 2012.
However, the last decade witnessed a sharp decline in whale numbers, notably coinciding with a substantial marine heatwave known as the blob, which emerged in 2013 and persisted until 2016, likely a consequence of global warming.
Now, the team of scientists utilized artificial intelligence (AI) to identify whales from images of their unique tails, amassing over 200,000 sightings of more than 33,000 individuals.
Initially, the humpback population was expected to reach a natural carrying capacity, but instead, a significant decline occurred. From 2012 to 2021, the number of humpbacks dropped by 20%, with a more pronounced 34% decline for those wintering in Hawaii.
The unprecedented marine heatwave from 2014 to 2016 caused severe temperature anomalies, disrupting the marine ecosystem and impacting humpback prey availability. The study estimates that around 7,000 whales likely starved to death during this period.
Ted Cheeseman from Southern Cross University warns that without addressing global climate change causes, future marine heatwaves could reduce ocean productivity worldwide, affecting not only humpback whales but indicating broader ocean health issues crucial for human dependence.
The abrupt decline in humpback numbers points to a significant disruption in the oceans. The extreme marine heatwave potentially lowered the carrying capacity threshold for humpbacks, impacting their ability to adapt. This decline extends beyond whales, affecting various marine species and even commercial fisheries.
The projection of increased global marine heatwaves by the Intergovernmental Panel on Climate Change raises concerns about the future health of the oceans.
READ ALSO: Humpback Whale Seen Seemingly Frozen in 'Handstand' Pose; Experts Explain Surreal Behavior [WATCH]
Recurrent Marine Heatwaves off California's Coast and Their Ecological Impacts
Off California's coast in the last decade, recurrent marine heatwaves, characterized by abnormally high ocean temperatures, have sparked investigations into their origins and impact on marine ecosystems.
Marine heatwaves are gauged by sea surface temperature anomalies, with a 1-degree Celsius anomaly indicating a heatwave and 2-3 degrees Celsius signifying a more severe event covering 500 to 2000 kilometers across the Pacific.
The formation of these heatwaves involves the North Pacific High generating southward winds, typically cooling the ocean through evaporation. Weakened winds, linked to warmer subtropical temperatures, thin the mixed layer, facilitating easier heating and contributing to the occurrence of marine heatwaves.
Key events in recent years include "The Blob" in 2014-2016, a localized heatwave in 2018 around Southern California, and "Blob 2.0" in 2019, each impacting fish populations, migration patterns, and food availability, affecting species such as sharks, tuna, and red crabs.
The complex interplay of these events brings surprises and challenges for California's ocean ecosystems, underlining the ongoing need for observation and assessment.
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