February 26, 2026 — Each spring, humpback whales start to feed off the coast of California and Oregon on dense schools of anchovies, sardines and krill—prey sustained by cool, nutrient-rich water that seasonal winds draw up from the deep ocean.
That process, known as coastal upwelling, turns the California Current into one of the most productive marine ecosystems in the world, giving whales a chance to rebuild the energy reserves they depleted during months of fasting in their winter breeding grounds in Mexico.
But according to a new study published on Wednesday in the scientific journal, PLOS Climate, rising ocean temperatures are shrinking and redefining this critical foraging habitat, putting the humpbacks at greater risk of entanglement in fishing gear.
Marine heatwaves weaken upwelling, reducing the amount of cold, nutrient-rich water reaching the surface. That, in turn, reduces offshore krill blooms. Humpbacks then begin to move inshore, where other prey, like anchovies and sardines tend to swarm. There, they are more likely to overlap with dangerous fishing activity and fixed gear, like Dungeness crab traps.