From spring to fall, when herring are in large schools in coastal and offshore waters, they are food for diving birds like cormorants, gannets, some duck species, guillemots, and auklets.  When some of the very agile and fast divers, like the auklets and guillemots, attack a school of herring from the sides and underneath, the herring try to defend themselves by forming a “herring ball” or “bait ball’. Hundreds of herring form one big roiling body of fish as each fish tries to take protection in the center of the mass. The unlucky fish on the outside of the ball are easily caught by attacking birds and other predators.

Other marine animals take advantage of or create herring balls. Less agile and capable birds like gulls profit as the herring balls are driven to the surface. Sea lions, dolphins, and whales can also join the feeding frenzy. Often involving hundreds of birds, these feeding frenzies can be spotted from a great distance, in turn attracting other prey such as eagles and humans.


Cormorants, guillemots, auklets and other diving birds feed on herring. Photo: Mark Wunsch


Friday, January 24, 2014