One of the most vexing problems posed by the widespread introduction of rainbow trout in the American West has been their propensity to hybridize with the natives. Take for example, the westslope cutthroat of the northern Rockies. Once the most widespread cutthroat subspecies, their range has been dramatically reduced in the last century due to the introduction of rainbows. Just how far it has shrunk, though, is a matter of some contention. According to the criteria applied by the U.S. Fish and Wildlife Service, a fish can still be considered a Westslope cutthroat even if it has a small amount of rainbow trout DNA (say from a great-grandparent). Such fish still occupy about 20 percent of their original range.
|Westslope cutthroat native range|
Interbreeding between slightly hybridized westslopes and their unpolluted cousins might alleviate these problems. But it would also create new ones. There are the biological issues, of course—some studies for example suggest hybrid fish are less fit. But maybe more importantly, it raises a host of legal issues.
The Endangered Species Act passed by Congress in 1973 did not include any guidelines on hybrids. Thus, when the issue arose in the 1980s, Department of Interior lawyers concluded that hybrids could not be protected under the act. It seemed a reasonable decision, at least for a few years. But when new technology gave us the ability to sequence DNA, it became apparent that hybridization was far more common than anybody had previously thought. Certain wolves (which had a little coyote DNA) and other listed species were thrown into legal limbo.
|A likely hybrid westslope-rainbow trout|
After a brief period of struggle, the lawyers threw in the towel. Hybridization would have to be handled on a case-by-case basis, they concluded, since hybridization was “more properly a biological issue than a legal one.”
I wonder whether it isn’t also an issue of human values and psychology. Are we really so concerned about purebred westslope cutthroats because hybrids may be less fit or because biodiversity may be associated with ecosystem stability? Or do untainted westslopes somehow appeal to our thirst for the prelapsarian, the rare, or some other innate urge?