Sea lions on the Sardine Run: the ocean's most charming thieves
On the Sardine Run, the California sea lion hunts the same schools as the striped marlin and steals its prey: across more than 5,000 attacks filmed off Baja California Sur, sea lions reduced how often marlin attacked and caught fish [1]. Curiously, with humpback whales it's the opposite: when sea lions are around, whales feed 23% more often [2].
If you've swum with sea lions in La Paz, you remember them playing and blowing bubbles. In open water, during the Sardine Run, you see their other side: fast, clever and very opportunistic hunters.
What the cameras saw
A team of scientists filmed sea lions and striped marlin underwater attacking schools of fish in the southern California Current System, off the Baja California Peninsula. They recorded more than 5,000 individual attacks on 13 schools of different species and sizes [1].
The result: sea lions practiced kleptoparasitism, meaning they stole prey from marlin hunts, and they also reduced how often marlin attacked and caught fish through sheer competition [1].
Marlin's rivals, whales' allies
In Monterey Bay, California, using 46 video tags on humpback whales, scientists found that when sea lions were around, whales fed 23% more often and spent 16% less time between lunges. The authors think sea lions help concentrate the fish [2].
So the same animal can be a nuisance to one predator and a help to another. In the ocean, alliances depend on who eats what, and how.
When the sea warms up
Sea lions feel ocean changes right away. During the 2015 El Niño, at the San Benito archipelago (Baja California), their total abundance dropped 52% and pups 61.7% compared to 2014; pups averaged 8.7 kg instead of 9.9 kg, and mothers had to forage farther out in oceanic waters [3]. Read what the 2026 super El Niño means.
Want to swim with them in calmer conditions? Read swimming with sea lions in La Paz.
Experience it with Keabelmet
Frequently asked questions
Do sea lions eat sardines?
Yes, they hunt the same schools as striped marlin during the Sardine Run [1].
Do sea lions steal from marlin?
Yes. A study of more than 5,000 filmed attacks found they steal prey and reduce marlin attacks and captures [1].
How does El Niño affect sea lions?
During the 2015 El Niño at San Benito, their abundance fell 52% and pups 61.7%, and pups were born lighter [3].
Scientific sources
The wildlife, season and geography facts in this article come from these publications. The [n] citations in the text link here.
- Hansen, M. J., Kurvers, R. H. J. M., Licht, M., Häge, J., Pacher, K., Dhellemmes, F., Trillmich, F., Elorriaga-Verplancken, F. R. & Krause, J. (2023). California sea lions interfere with striped marlin hunting behaviour in multi-species predator aggregations. Philosophical Transactions of the Royal Society B 378(1878): 20220103. doi.org/10.1098/rstb.2022.0103
- Krylova, A., Blawas, A. M., Fahlbusch, J. A., Calambokidis, J., Clayton, H., Friedlaender, A. S., et al. (2026). Increases in foraging performance of humpback whales in multi-predator feeding aggregations with California sea lions. Philosophical Transactions of the Royal Society B 381(1961): 20250344. doi.org/10.1098/rstb.2025.0344
- Elorriaga-Verplancken, F. R., Sierra-Rodríguez, G. E., Rosales-Nanduca, H., Acevedo-Whitehouse, K. & Sandoval-Sierra, J. (2016). Impact of the 2015 El Niño-Southern Oscillation on the abundance and foraging habits of Guadalupe fur seals and California sea lions from the San Benito Archipelago, Mexico. PLOS ONE 11(5): e0155034. doi.org/10.1371/journal.pone.0155034
