Every year, blue whales—the largest animals on Earth—make a spectacular appearance off the coast of San Diego, drawing thousands of visitors hoping to glimpse these majestic giants. Last year was an exceptional season, with a phenomenal 308 blue whale sightings aboard our vessels. This abundance was fueled by favorable ocean conditions that supported dense krill populations, the primary food source for blue whales.
However, this year, the blue whale season has been notably slower, with sightings down significantly for all operators in the area, and our crew spotting about 47 so far this season. So, what’s behind this sharp decline? Our naturalists, backed by their expertise and experience, share insights that explain this change through the lens of oceanography, ecology, and broader environmental factors.
Ocean Conditions and Climate Variability: The Big Picture
Greg McCormack, a former NOAA Education Specialist with years of experience studying the West Coast marine environment, points to shifts in oceanographic patterns as the core reason behind fewer blue whales this season.
“Over the past few years, we experienced several La Niña events—periods of cooler-than-average sea surface temperatures—which tend to increase nutrient upwelling along the California coast,” Greg explains. “This cooler water, rich in nutrients, stimulates primary productivity, leading to abundant krill, the main food source for blue whales.”
Last year, these cool-water conditions created an ideal environment for krill blooms, supporting an exceptional blue whale season. In contrast, this year has marked a transition out of La Niña conditions, possibly moving into El Niño-neutral or warming phases, accompanied by a developing marine heatwave.
“Warmer water suppresses upwelling, reducing nutrient availability and lowering krill abundance. Blue whales are krill specialists, so without dense krill swarms, they may shift their foraging effort elsewhere—often farther offshore or northward—following the food,” Greg says.
He also notes that larger climate cycles such as the Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO), combined with persistent high-pressure ridges like the “Ridiculously Resilient Ridge,” have further blocked storm systems and reduced wind-driven upwelling. These disruptions have led to broader ecosystem instability evidenced by marine heatwaves, kelp forest collapses, and nutritional stress in other marine species.
Food Availability and Krill Behavior
Olivia Tran, a naturalist with a focus on marine biology, underscores the critical role of krill availability for blue whale presence:
“One of the possible reasons as to why blue whale abundance is so different this year is quite likely due to the lack of krill. Blue whales eat about 4-6 tons of krill per day! They are highly food motivated and follow wherever the food is. Krill generally does not like warmer water temperatures, which could be the large contributing factor to limited blue whale sightings this season.”
Alison, another seasoned naturalist, adds an economic and ecological dimension to this story:
“Our ocean water temperatures are averaging 5 to 7° warmer than usual this time of year. But the big difference this year is that commercial krill fishermen have extended their catch range farther into Antarctic waters. Krill fishing hasn’t been as productive or lucrative, so fishermen are pushing further south to meet public demand for krill oil, which is prized for its bioavailable omega-3s.”
This expanded krill fishing pressure in Antarctic waters could be influencing krill availability along the California coast as well, further contributing to the reduced prey base for blue whales locally.
Takeaways: A Dynamic Ocean Environment and the Future of Blue Whale Sightings
The slower blue whale season in San Diego this year is not a permanent trend but a reflection of dynamic ocean conditions linked to climate variability and ecosystem changes. As Greg McCormack reminds us, “Blue whale presence is not guaranteed—it’s a gift from a healthy, functioning ocean.”
The interplay of warming waters, disrupted upwelling, reduced krill abundance, and expanded commercial krill fishing all combine to influence where blue whales choose to forage each season. While we may see fewer blue whales close to San Diego this year, the ocean’s cycles will continue to shift, and hopefully, future seasons will bring these incredible animals back in full force.
In the meantime, San Diego Whale Watch continues to monitor and share these changing marine patterns with our guests, celebrating the complexity and beauty of our ocean ecosystem.