Scientists and graduate students at the University of California, San Diego's Scripps Institution of Oceanography were shocked when a massive school of Northern anchovies invaded Scripps Pier near La Jolla, California.
"From a distance it looked like an oil slick ... and then you get up close and it's amazing," Scripps communications officer Robert Monroe said. "It's like watching the motion of a lava lamp."
The massive school contained some 10 million to 1 billion fish which, according to a press release from Scripps, scientists have not seen in the area in 30 years. The entire school reached about 10 feet deep and was around 1 mile long.
Scripps professor David Checkley noted that the school size was larger than usual.
Graduate students took advantage of the school by diving in to record the event and gather samples. At one point, a California sea lion as well as a leopard shark joined in on the action.
It's unclear why the school of anchovies came so close to shore, since they typically seek cooler water and the day's water temperature reached a warm 75 degrees. Checkley noted, however, that offshore waters in the area have been warming more rapidly than inshore waters, and that changing temperatures may be the reason for the unusual visit.
Live Science suggested that the coastal appearance could be due to Pacific Decadal Oscillation, a natural phenomenon that cools the ocean.
"It certainly is a mystery," Checkley said. "It may have something to do with the impending El Nino."
Regardless of the reason for the unusual behavior, Checkley insisted that the occurence is a natural phenomenon and does not indicate anything wrong with the ecosystem.