Starving sea lion pups have been washing up on Southern California beaches at an alarming rate, and no one can seem to figure out why. Roughly 1,100 pups have been rescued and placed into local rehabilitation centers, and last week NOAA declared the strandings an "Unusual Mortality Event". Pups that are being rescued are coming in weighing about half of what they should.
The rate of strandings resembles what can be seen during an El Nino evvent, however, the area hasn't seen an El Nino event in years. The last major El Nino event was in 1997-1998.
The best guess is that something is causing the sea lions' food source (mainly sardines and anchovies) to move or disappear, making it harder for the young pups to find food. Without an indication as to why the pups are washing ashore, it's anyone's guess as to how long these strandings will continue.