Sunday, July 14, 2013

Sardine Cyclone


While in California during Independence Day week, I had the opportunity to visit the Monterey Aquarium with my parents and sister. The first thing we saw was the Open Ocean exhibit feeding. That day they were feeding the sea turtle and the sardines. It turns out feeding the sardines is really exciting, and feeding the sea turtle is really boring (you couldn't see her munch her lettuce at the top of the tank very easily). It's also very fitting -- the aquarium is on Cannery Road in an old sardine cannery!

The sardines normally swim together in a school in the bottom of the tank. When it's feeding time, food flakes are dumped in the tank. Slowly the flakes sink down to where the sardines are. When one sardine finally notices a flake, it starts moving upwards, and whole school swirls to the top of the tank to have better access to the food. After the food is gone, the sardines swirl back down to the bottom of the tank (pictured).

Group Think

Sardines travel in schools, and benefit from being in a group. While the feeding was going on, our "guide" to the Open Ocean (i.e. the employee who had the mike) explained some of the benefits of being in a school:

  1. Protection from predators. It's more difficult for a predator to focus on one sardine when it's swimming around with hundreds of others than if it was by itself. 
  2. More chances to mate. What better way to find another sardine then to be in a group of sardines?
  3. Foraging success. When one sardine notices food and starts swimming upwards, the others follow. They didn't need to spot the food themselves in order to know that it was there. They just followed the pack. Rising to the surface to feed highlights another trade-off sardines face: safety vs. food. They are much more likely to be successfully hunted near the surface, so they only swim up there when there is actually food to be found. 

The Aftermath of the Feeding

What happens when a sardine doesn't get the message that the food is gone and is left behind when the rest swirl to the bottom of the tank? Apparently, it freaks out and doesn't know what to do on its own, so it swims around randomly. It's a sardine after all; its instincts are tuned to schooling behavior.

In addition, something else interesting happens: the mahi-mahi gets some lunch. Oh, didn't I mention? The Open Ocean exhibit has sardines and their predators in the tank together, just like in the wild! Because they are all hand fed on a schedule, the predators (like mahi-mahi) don't normally hunt the sardines for food. But when a sardine gets left behind in the swirl to the depths of the tank, the pickings are too easy, and the hunt too fun to resist.

A sardine did get left behind that day, and the mahi-mahi glowed yellow and green from the excitement of the hunt and an easy mid-morning snack.

Related Discussions at Economonomics:
The Sheep Cyclone (with video)
Influence, Chapter 4: Sheep Cyclone Redux (halfway down the post)