A giant ‘bait ball’ of anchovy, with two humpback whales approaching on the lower right.
Photo: Liz Vernand via GrindTV

Massive anchovy swarms off the coast of California have kept marine mammals and their observers busy for the past couple of months. It’s not so much that there are more anchovy than usual, it’s that there are more anchovy gathered in one place.

According to this article, anchovy movement can be due to a number of factors – plentiful plankton, mild temperatures – and this year, the anchovy stars aligned over Monterey Bay. Their presence, telegraphed far and wide via whale song, has set off a feeding frenzy of seals, whales, dolphins, and the press.

Northern anchovy
Photo: Monterey Bay Aquarium

Anchovies and other small fish are known as ‘bait fish’ or ‘forage fish’, and form a key element in the marine food chain for mammals and the larger fish that humans prefer to see on their dinner plates. Some have recommended that humans switch away from the larger fish, which are being hunted by vast fishing fleets, to these smaller forage fish for human consumption.

Currently, we fish bait fish for use as feed to the other animals we prefer to eat – pigs, chickens, salmon. The ratio of forage fish feed to salmon, however, is around 5:1. Not very efficient. But the smaller fish, which tend to be oily, just aren’t popular for human consumption.

Anyway, the whales do exactly what human fishermen when they come across a bounty like this – they keep fishing until they’re full, or the fish are gone.

Here’s a very cool short clip, created by Robert Hodgin for the Auckland Museum, of how a bait ball works (in this case, sardines).