Not too long ago the ol’ sister-ship blog posted about the growing Save the Krill movement, which aims to turn at least some conservation resources towards a species that occupies a more basal position in the marine food web. This makes a lot of sense. As a fan and researcher of sharks, my own bias tends to give me more of a “top-down” ecological worldview, and certainly top predators are important regulators of ecosystems. That said, without something to eat all those big charismatic predators are just going to starve to death regardless of how much conservation effort heads their way. This is why it’s important for conservationists to make sure not to neglect the “bottom-up” worldview.
A link from a comment in the post on Southern Fried Science lead me to the Herring Alliance. Formed of a conglomeration of national and Northeast-based environmental groups and fishing interests, this organization looks almost exactly like what a conservation organization should be, complete with an impressive involvement of commercial fishermen. So what is it about herring that has brought together groups that normally can’t agree to protect other species?
Ecologically, herring are like the krill of shallow, temperate waters. Everything eats on them, and the migrations and local movements of several important predators are determined by the movements of these forage fish. The problem with living in shallow surface waters is that the species is much closer to the influences and depredations of well, us. Added to this is the fact that the river herring species (blueback, alewife, and American shad) are anadromous, meaning that they depend on being able to travel up and down rivers in order to breed. Dams are probably the biggest anthropogenic problems for herring upriver, but rivers also happen to be very popular places to put cities, which historically has lead to habitat degradation. Even out at sea herring cannot escape their human predators: poorly-regulated drift-net fishing for the totally marine Atlantic herring has been cited as a cause of dramatic declines in both seagoing and anadromous species.
So when you admire that great white leaping out of the water on the Discovery Channel, think about that seal it’s eating, then think about the herring and other forage species that feed the seal. Without those herring, there wouldn’t be any seals to sustain their predators, so the mighty Carcharodon carcharias depends just as much on the presence and survival of herring as species like the spiny dogfish that directly prey on the little fish.
For those interested in learning more about how scientists and starving grad students alike try to determine the comings and goings of river herring, here’s another shameless plug for my labmate’s blog The Endolymph.