Wednesday, August 09, 2006

Where have all the glass eels gone? Nobody knows.

Glass eelComplexity in the Field
By J.B. Ruhl
Post 1: Seeing the Bigger Picture

The American eel, known as the glass eel because of its translucent body, spawns and hatches somewhere in the relatively calm waters of the Sargasso Sea in the mid-Atlantic ocean — nobody knows exactly where. The hatchlings — flat, leaf-shaped larvae — ride the currents of the Gulf Stream as their bodies grow compact and snakelike to about the size of an earthworm. Along the way, eels hop off the current to make their way to freshwater rivers flowing into the ocean from Florida’s Atlantic coast all the way to Nova Scotia. The eels grow larger in the river ecosystems, where they had been for long considered “baitfish” by American fishermen. Europeans, however, have a penchant for smoked eel, and starting in the 1960s live eels were heavily fished from American rivers and shipped live to Europe for smoking.

In recent years, however, the eels have been scarce to the point of nonexistent in many rivers. Eel fishermen blame dams, and others blame overfishing. But some researchers believe the juvenile eels are being stranded in the ocean as melting ice caps in polar regions have changed salinity levels of the Atlantic waters, which in turn alters Gulf Stream current dynamics. The currents are driven by a “conveyor belt” mechanism, known as the meridional overturning circulation, that depends on salinity to keep it running: as water from the warm Gulf moves northward, it evaporates moisture to the colder atmosphere, which increases the ocean water salinity and thus its density; the denser water sinks and flows back southward, where the cycle begins anew. But increased ice melt flow from the Arctic ice caps feeds more freshwater into the northern Atlantic. See Ruth Curry and Cecilie Mauritzen, Dilution of Northern North Atlantic Ocean in Recent Decades, 308 SCIENCE 1772 (2005); Walter Munk, Ocean Freshening, Sea Level Rising, 300 SCIENCE 2041 (2003). This in turn counteracts some of the evaporation effects, keeping salinity levels stable and thus interfering with the density sinking effect necessary to drive the “conveyor belt.” See Richard A. Kerr, Sea Change in the Atlantic, 303 SCIENCE 35 (2004).

Researchers surmise that the mysterious decline of the American eel could be the result of a slowing or redirection of the Gulf Stream as the salinity-dependent flow regime is interrupted, which could prevent the juvenile eels from finding or reaching their freshwater river habitat. See Thierry Wirth and Louis Bernatchez, Decline of North Atlantic Eels: A Fatal Synergy?, PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON (2003). Other researchers have found similar shifting of ocean species distributions as a result of water temperature changes, with potentially profound impacts on species interactions. See Allison L. Perry et al., Climate Change and Distribution Shifts in Marine Fishes, 308 SCIENCE 1912 (2005).

What does this have to do with law? Two things. First, the conventional response to species decline in natural resources law has been to look for culprits like dams and overfishing. To be sure, those have caused a lot of damage on their own. But sometimes that’s just too easy. Without a thorough grounding in the ecological context within which species decline is taking place — i.e., in the case of the eels, the complex ocean current system — law (and politics) may completely miss the bigger picture of causation and potential solutions. Of course, the second point is that effective legal solutions often have nothing to do with the problem law is trying to address. If the researchers are right about the eel, no amount of regulation of dams or fishing is going to save the eels. That’s not to say we don’t need to manage dams and fishing appropriately, just that, for the eels at least, we’ll get little bang for the buck at this juncture.

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