I just finished two days of fish work on the Virgin River near Mesquite, Nevada. The purpose of the trip is to monitor for blue tilapia, a highly invasive fish that recently found in Lake Mead after escaping from a fish farm. With the current drought and low snowpack in the Utah headwaters, the Virgin is very low this year. The river dries up in the Virgin River Gorge in Arizona but several large springs near Beaver Dam, Arizona feed the river into Nevada. Normally the river is silty and turbid, but when the only water in the river is from the springs, it runs clear. The lowest site that we checked, actually had no water and was dry sand. One of the good things about drought, is that it keeps the bad guys from moving around. Furthermore, the lower lake elevation means the invasive fish have longer distances to go before they can impact native fish areas.
In natural conditions of low water, the native fish would crowd into the few deep pools and near the springs. Currently, these pools still exist but they are crowded with invasive fish including large catfish, carp, and bass. These predatory fish may eat the smaller native fish that are concentrated in the pools. They also eat the limited food in the pools, utilize the dissolved oxygen in the pools, and even physically crowd out the native fish. Furthermore, we also found that the large spines on the catfish wound and injure the larger native fish. One foot-long flannelmouth sucker we saw yesterday had a dime sized wound in its flank from a channel catfish and another flannelmouth had a fresh wound to one of its fins.
The good news is that we didn’t find any tilapia. The better news is that on Tuesday we found a woundfin. We pulled a seine haul with several hundred red shiner minnows just like all the other seine hauls. As we looked for native fish amongst the flopping minnows, a silvery torpedo-shaped fish caught my eye. I picked it up and examined it closely. I asked the fish expert next to me “What the heck is this?” He looked and his eyes got big. “Woundfin!” He filled a bucket with river water, we put the fish in, finished counting the other fish, took some photos and released the fish back into the river. This is the first woundfin found in that area in six years.
Woundfin are one of the rarest and most endangered fish in the United States. It was listed as an endangered species in 1970 and, like several other endangered western fish, probably only escaped extinction due to the captive breeding program at Dexter National Fish Hatchery in New Mexico. A few thousand fish are released in the Virgin every year. The are marked with a bit of fluorescent plastic injected under their skin to show that they are hatchery fish. The color and location of the dye change to indicate the year. The one we had found had no dye so it was possibly born in the river and not in captivity. Wild or captive bred, it was a great find.
We also found another woundfin higher up in the river today just below a diversion dam. This one had the elastomer dye that showed it was in the group of fish released in Arizona in November 2006. This fish had made it downstream, past a dam, across the state line, and managed not to get sucked into the irrigation works that take almost all of the flow of the river. This is the first woundfin in this section of river in two years.
This woundfin picture I took upstream in Arizona in December 2006 about a quarter mile downstream of where the fish were released a few weeks earlier. You can see the green dye near the dorsal fin.