The first large school of anchovies was sighted in early July off Scripps Pier in La Jolla. The video that Scripps made of this anchovy “aggregation” went viral (www.youtube.com/watch?v=XvxIdkhsoqU ), with more than 4 million hits and counting. Scripps scientists estimated the school had more than a billion fish in it. A week later, the large schools appeared off Ocean Beach and Sunset Cliffs, easily spotted from shore by the presence of large numbers of diving birds and dolphins.
David Checkley, Scripps Institute of Oceanography biological oceanographer, said this is something they have not seen in years. He and his colleagues are hesitant to point to a definitive explanation. They do have a number of clues, however. Scientists know that anchovy and sardine populations do have a cyclical nature that is tied to changes in water temperature. What scientists call the “pacific decadal oscillation” (PDO) is a type of long-term El Nino that causes ocean temperature changes over decades, as opposed to El Niño/La Niña’s short-term effects. As the ocean temperature decreases, the anchovy population increases and the sardine population decreases. As the ocean temperature rises over decades, the opposite happens. PDO seems to have a cycle that takes about 50 to 75 years to complete.
Checkley points to the P.D.O. as a possible causation for the increase in anchovy schools. He also notes that because anchovies prefer cooler water, they do sometimes aggregate near shore after winds have blown up colder water from the deep, a process known as “upwelling.” This could also figure into it.
These huge conglomerations of fish are often referred to as “bait balls” by fisherman, and word is out that the fishing is firing. It is hard to find a spot along the pier with everyone from Imperial Beach to Los Angeles trying to catch a little piece of the action. Most people are not after the actual anchovies but the larger fish that feed on the anchovies. These anchovies, known as the northern anchovy (Engraulis mordax), do not grow much more than 25 centimeters, but the fish that eat them grow much larger. Large numbers of predatory bonita and mackerel are being caught off the Ocean Beach Pier.
For a few lucky fishermen, there are some elusive yellowtail, dorado, and barracuda to be caught. Some fishermen, however, are content to simply catch the small anchovy, claiming that fried and eaten whole, it is a delicacy.
This anchovy is the same that you might eat on your pizza. But Scripps scientists point out that the anchovy supply comes not from the Pacific but from huge anchovy fisheries off the West Coast of Africa.
Scientists say we might see this phenomenon again for many more years to come. Then again, we might not. The mysteries of the sea are just that — mysteries. If you want to appreciate one of these enigmas firsthand, head out to the beach and look for all the birds the point to the spot where billions of small anchovies are struggling to stay alive in our wild and beautiful backyard — the Pacific Ocean
— Jorge Valcarcel is a local freelance journalist who contributes to the San Diego Community Newspaper Group.