You'd think fish, of all creatures, would be smart enough to go with the flow.
I was telling a group of fifth-graders about the amazing migrations of spawning herring and shad, how they used to climb the tributary rivers of the Chesapeake Bay, bucking the spring runoff for hundreds of miles, thrashing all the way from the ocean to upstate New York and the foothills of Virginia's Blue Ridge Mountains.
The kids were intrigued, and glad to learn that Maryland, Virginia and Pennsylvania are breaching and bypassing dozens of dams in hopes of restoring the historic runs. But one girl had a question: Why did those fish spend so much time and energy swimming upstream? If she were a fish, she'd go with the current.
I explained that anadromous, or upstream-running, species seem drawn back to the waters in which they were born; the fish are imprinted from birth to follow cues as subtle as a few molecules of a given stream's organic "odor," wafted far downstream.
Over geologic time, adaptations have occurred -- from feeding strategies to the density of their eggs -- that enhance reproduction in the fishes' natal waters.
Upstream there is more safety and protection and less stress on the young; while downstream, in the oceans, food is more abundant and there is room to grow big.
Some fish in the bay's vast, six-state drainage basin do go with the flow. Eels, which inhabit virtually every creek in the watershed, are catadromous. In autumn, after feeding for a decade or more, they run downstream, to join with eels from all over the Eastern seaboard, spawning in the Sargasso Sea. But they are the exception.
From striped bass and relict sturgeon, to American and hickory shad, alewife and blueback herring, white and yellow perch, the watershed's fishes seem overwhelmingly wont to struggle annually against gravity and currents.
Though the behavior works to perpetuate the species, you still wonder: What is the percentage in a journey that, for shad and herring, consumes two to three months of every year, and is so arduous that a large percentage die at journey's end?
Perhaps the beginnings of the answer lie in realizing that nature never is doing just one thing.
By ignoring that fact, we often create environmental disruption. We straighten a river to maximize drainage, unmindful of the wetlands in its bends. Or we enlarge a sewage plant to clean up the water, only to find the air dirtier and the traffic thicker, from all the new building stimulated by the improved sewer.
So it is that the bay's anadromous fishes are doing more than one thing. By swimming upstream, they not only follow the prime directive of their own species -- to reproduce and perpetuate itself -- but also serve larger purposes of the watershed itself.
It sounds curious to speak of the bay's drainage basin almost as if it were animate; yet as ecologists increasingly probe the complex inter-relationships that bind and regulate natural systems, the lines between animate and inanimate seem to blur.
In a recent paper called "How Watersheds Work," which I'd recommend to anyone teaching about the bay, Nick Carter, a Maryland Department of Natural Resources biologist, considers how anadromous fishes help solve a fundamental problem of the watershed.
The upstream portions of drainage basins, Carter notes, are constantly shedding water. How do they stop this process from eventually eroding all their vital soils downstream, leaving a wasteland?
A big part of the solution lies in each stream drainage area's vegetation, soil microbes, insects and other species. They retard runoff, and recycle and re-use vital minerals and nutrients with supreme efficiency before those substances can be washed downstream.
Then there are the anadromous fishes, which to the watershed are more than just fish; they help supply the stuff of life.
They are a mechanism to harvest the abundant energy of oceanic plankton (itself fed by nutrients washed from the land). Then, the fish return it hundreds of miles upstream, transferring the energy back to its birthplace as they die and decompose or are eaten by otters, minnows and great blue herons.
So it is that as fish run upstream -- what for them is a hassle -- it serves larger purposes: the ordering and organizing process that runs like a common thread through all of life.
To test this cosmic theory in practice, another bay biologist, Dr. Greg Garman of Virginia Commonwealth University in Richmond, has spent the past few years examining a sub-watershed of the James River down to the level of the carbon atoms in a blueback herring. In particular, he used the ratio of two isotopes of carbon (C-12 and C-13) found in living matter. Creatures from different habitats -- salt marshes, forests, fresh water -- exhibit unique ratios.
Sure enough, during the spring herring run he was able to identify a uniquely oceanic carbon "signature" among the little stream's herring; also to trace its passage into the flesh of local predators -- evidence of a seasonal subsidy of marine energy, ferried far upriver by the fish.
The impact, while significant, must have been far greater when the runs of anadromous fish were closer to their historical abundance. We can only marvel at what that might have been like. In 1777, a single day of netting at Mount Vernon on the Potomac caught half a million shad and herring for George Washington's crews.
In colonial times, the James River supplied so many shad that the harvest "amounted to half a hog crop for the entire population of the basin," according to a Virginia fish commission report.
On the Susquehanna River, the spring arrival of shad and herring more than once marked an end to winter famine for settlers throughout Pennsylvania and New York. The carcasses and eggs and young of such legions of fish, before over-harvesting, pollution and dams so diminished them, must have profoundly enriched the upper watershed of the bay with nutrients and minerals.
Just as this ocean-to-stream recycling was a mission of anadromous fish, some ecologists have speculated, only half-jokingly, that we humans may have a similar role. What if our real destiny is to dig and drill and mine, unearthing the planet's buried stores of energy -- coal, oil, gas, phosphate fertilizer -- and putting it back into circulation through our lust for generating power and running automobiles and factories?
The resulting global warming and ozone holes may do us in; but the planet, the biosphere, will have renewed, rich sources of energy available, and do quite well, thank you.
Of course, that supposes we are as simple as shad, uncomprehendingly following urges to thrash upstream again and again until we die.
We can laugh, can't we? We would never find our cars and our air conditioning so compelling.
For a copy of "How Watersheds Work," call Nick Carter at (410) 974-5780.