I’ve been remiss in reading Greg Laden’s blog, though it’s familiar to plenty of other science bloggers. However, after reading a couple recent posts of his that showed up on Research Blogging (which I think anyone with an interest in science should sign up for) I think I’m going to have to start reading his stuff on a regular basis. He has a very interesting post on how culture develops on islands that has plenty of allusions to prehistoric peoples who once lived on Georges Bank (back before the Ice Age glaciers finished melting and it was still above water). However, what really got me was his most recent Research Blogging post on finding predators by paying attention to their prey.
He uses the example of urban birds scattering from a tree occupied by a hawk, which got me thinking about the marine applications of this concept. Then it occurred to me that they’re all around. Both recreational and commercial fishermen use the presence and behavior of prey species such as menhaden and anchovies to determine whether a given area is a good fishing spot. If you see a lot of schooling fish, stick around. If they start bunching up, scattering, or jumping out of the water, it’s time to throw a line in. Odds are just below that layer of panicked baitfish is a hungry school of stripers or bluefish (or dogfish for that matter). This concept is so dependable that fishermen have developed ways of manipulating it. Modern industrial tuna fishing is accomplished by setting out “fish aggregating devices,” a fancy term for flotsam and jetsam floating at the surface in the middle of the ocean. Smaller fish in the open ocean will take whatever cover they can find, which in turn brings the predators. Tuna fishermen then set their nets around the whole shebang, catching prey and predator alike in a process that is both a clever use of ecology and horrendous for the environment (I can’t link to David’s post enough).
Paying attention to prey behavior also has useful field (and survival) applications. I recall a time when I was snorkeling with my father in the Florida Keys over some seagrass flats, and suddenly all the fish and crabs that had been frolicking around us were gone. I don’t even remember seeing them leave, just that they suddenly disappeared. At this point I’d had enough of a biological background to know that something had scared them, and both of us were overcome with a feeling of being watched. We never saw what must have been swimming just out of view, but somehow the other potential prey species picked up on it.
So in conclusion, if you’re looking for predators, whether as a meal, for research, or just to avoid becoming a meal yourself, pay attention to the prey.