Protecting diversity in Gila trout
By Brian Hickerson
There wasn’t much know about the genetics of the five remaining wild Gila trout populations when they were officially placed on the endangered species list in 1975, according to the Gila Trout Recovery Plan. All five populations residing in separate small creeks in the Gila Wilderness of New Mexico were believed to be pure-strain Gila trout. A sixth population was found in Whiskey Creek in 1992, but this addition was short lived.
In 1996 and 1997, following some genetic surveys of the relict populations, the populations in McKenna Creek and Iron Creek were found to be hybrids of Gila trout and rainbow trout, according to the recovery plan. This meant that two of the six relict populations were not recognized under the Endangered Species Act listing.
Gila trout can easily hybridize with introduced rainbow trout. Hybridization with Gila trout can result in the dilution of thousands of years of genes unique to the Gila trout. In fact, hybridization with non-native rainbow trout is one of the main reasons why Gila trout were eliminated from much of their original range.
In order to prevent distinct lineages of Gila trout from being wiped out forever, the Gila Trout Recovery Team has developed a plan to stock Gila trout from different lineages in different locations. This way, if one population was extirpated, those genes would not disappear.
The loss of an entire lineage is a very real scenario, as was demonstrated in the 1989 Divide fire in New Mexico, where one of the relict lineages, known as the Main Diamond Creek, was extirpated from the stream in which it originated in the wild. Due to the Main Diamond Creek lineage being replicated in several other streams, officials were able to reintroduce fish from the replicated populations back into Main Diamond Creek.
Thanks to the replication of the different relict lineages in different streams, a single catastrophic event like a wildfire is unlikely to eliminate thousands of years of genetic diversity. Currently all four of the relict lineages – Spruce Creek, Main Diamond Creek, Whiskey Creek, and South Diamond Creek – have at least one replicate population in the wild.
Main Story: Gila trout return home to southeastern Arizona