Warming oceans drive Humpbacks into fishing gear

Climate-driven changes to ocean conditions are increasing the risk of humpback whales becoming entangled in fishing gear along the US west coast, according to new research in PLOS Climate.

Fishing gear, like gillnets and traps, can entangle whales – injuring and killing them. Formal reports show an overall increase in entanglements: in 2014, there were fewer than 10 annual reported incidents involving humpbacks, but that number rose to 31 in 2024.

Scientists have previously struggled to determine what is driving this. Entanglements are notoriously difficult to monitor, and humpback whale populations have rebounded following the end of commercial whaling, providing simply a greater number of whales who could be susceptible to entanglement. 

But this new study suggests that population growth alone does not explain the trend. 

Humpback whales feed on the US west coast, near California and Oregon, on schools of anchovies, sardines and krill – prey that is reliant on cool, nutrient rich water that is drawn up from the deep ocean through coastal upwelling.

However, rising ocean temperatures and recurring marine heatwaves are disrupting that system.

When warm surface waters suppress upwelling, offshore krill populations decline sharply. The whales’ preferred cool-water feeding habitat subsequently shrinks in a process known as “habitat compression.” This in turn forces them into a smaller area closer to shore.