( CNN ) -- Who ordered the anchovies ? That 's what beach-goers may be asking after a huge swarm of the oily fish descended on the shallow waters of La Jolla Shores , California , this week . `` It is rare to see so many anchovy abutting the surf zone , '' said Professor Dave Checkley of the Scripps Institution of Oceanography ( SIO ) . `` More usually , schools are seen hundreds of yards to many miles offshore . '' The surf zone is the area in which waves break on shore and humans normally swim . Schools of anchovy can range from hundreds to millions of fish , said Checkley , who gave this school `` a very rough estimate '' of between 1 million and 100 million anchovies . Anchovy influx leads to shark run in . `` In my approximately 30 years at the SIO starting in 1970 , I 've not seen this before , '' Checkley said . Changing ocean temperatures may be the cause of the anchovy influx . The North Pacific is currently transitioning into a cooler state , which is favorable to anchovies , said Checkley . He added that , while this particular phenomenon is unusual , anchovy populations naturally fluctuate on the scale of decades . Scientists were n't the only one taking note of the army of anchovies . The California sea lion , which preys on the small fish , seemed `` happy as a clam , '' Checkley said . `` Human beach-goers and surfers similarly [ were happy ] , enjoying a rare sight of an abundance of schooling fish within easy swimming distance , '' said Checkley . `` For those able to snorkel among the anchovy , it is a wonderful experience ... fish , fish , fish ! '' By Wednesday , the school had departed the surf zone near La Jolla Shores . According to Checkley , the anchovies could have moved farther offshore just as easily as they could have slid along the coast to the north or south . 30 mesmerizing underwater photos . Swimmer bitten by great white shark off California beach . Awe-inspiring animal migrations that send people flocking .
Millions of anchovies swarmed the surf off La Jolla Shores , Ca . No school this large has been so close in 30 years . Comment: