Even as their numbers decline, the habit of tiny fish such as sardines to form into tightly packed "bait balls" keeps them super easy to catch, which puts them at risk of collapse and means active conservation such as catch limits is crucial for their survival. In fact, we might want to halve the number caught each year, says a new report from a 13-scientist panel funded by the Lenfest Foundation, called "Little Fish, Big Impact." The report found that as fishing for these little guys increases -- they're used in animal feed, as bait, and as food for aquaculture -- they get no more difficult to catch because they naturally form really tight schools called bait balls. You've probably seen these things in nature documentaries such as Planet Earth (and the photo above) -- the massive school of fish packed so tight they appear to move as one being. Well, they do that regardless of dwindling population numbers, and it's incredibly easy to throw a net around that bait ball and catch the whole school. That makes these fish populations vulnerable to collapse, the report found: "Fishermen might therefore be able to scoop up large numbers of forage fish during a natural population decline, greatly compounding that decline."
Overfishing of anchovies and their ilk hasn't always been a problem, because there's not a great consumer market for the little fish, but as The New York Times points out in its coverage of the study, thanks to their increased use in agriculture and aquaculture the fish "now account for 37 percent, by weight, of all fish harvested worldwide, up from about 8 percent half a century ago." Because they're so easy to catch quickly, the fisheries face a distinct risk of collapse, and that means a domino effect for the rest of the ecosystem. "The Task Force found that the only fishing strategies that reliably prevented a decline in dependent predators were those that limited fishing to half the conventional rate," the study says.