TexasHornshell_Salt_Randklev_Charles_DallasTX_24January2024_Reel4187.mp3

Charles Randklev [00:00:00] So, that's a really neat study.

Charles Randklev [00:00:04] So, and that actually started, again, around the same time that we initiated survey work in the Rio Grande.

Charles Randklev [00:00:10] At the time, a colleague of mine, Michael Hart, and I were sampling the lower Pecos with some students. And, Michael happened to get some river water in his mouth.

Charles Randklev [00:00:21] And I still remember to this day, you know, he kind of looked at me and said, "Man, this river is salty." And, and I was like, "That's, that's interesting."

Charles Randklev [00:00:28] And so, because mussels in general have a very low salinity tolerance. I mean, they are a freshwater organism.

Charles Randklev [00:00:34] And so, at that point, it kind of dawned on us that maybe the reason that Texas hornshell isn't doing well in some areas is because of issues with salinization.

Charles Randklev [00:00:44] And the Pecos is really interesting. There was a guy by the name of Artie Metcalf who used to be a professor over at the University of Texas in El Paso. And he had done a lot of work with Texas hornshell in the late 1960s.

Charles Randklev [00:00:57] And Dr. Metcalf had reported near Pandale, which is this small, little town like, if you blink, you'll miss it when you're driving. He had reported a massive population of Texas hornshell on that river in the late 1960s.

Charles Randklev [00:01:10] And we'd seen some of those collections in museums, not just in Texas, but outside of Texas, in some of the big national museums. And so, we knew that it was there and so, or had been there.

Charles Randklev [00:01:22] And so, the work that we had in the Pecos was to try to find that population. And we'd spent oh, man, about a week paddling that river looking for hornshell. And we found tons of, tons of shell, old shell, what we call subfossils, like shell that was reminiscent of a population that may have been there 30 or 40 years ago. And then we did find a couple of live individuals.

Charles Randklev [00:01:46] Then it was like the wheels started turning. We've got a salty river. Could this be one of the smoking guns in terms of a culprit for its decline?

Charles Randklev [00:01:53] And so, then that really was the genesis for a bunch of research looking at salinity tolerance, not just for adults, but also juveniles and then the larvae.

Charles Randklev [00:02:03] And what we've found since is that salinity is a problem in the Pecos. The system is actually kind of an enigma because the Pecos historically is naturally salty just kind of just because of some of the underlying geology.

Charles Randklev [00:02:17] But, it's been amplified over time.

Charles Randklev [00:02:20] And again, this gets at those water quantity issues, where we have reduced instream flows. We've got greater reliance on spring flows which have tapered over time. And so, we're not getting those freshwater inputs that you probably would have had 30 or 40 years ago.

Charles Randklev [00:02:35] And so, even in areas where we do find live individuals from time to time, the salinity is at concentrations that likely negatively affect reproduction, which is probably why we only found adults when we were sampling. And then in the upper part of the watershed - so this would be, say, above Independence Creek to the border with New Mexico - salinity concentrations can reach up to 30 parts per thousand.

Charles Randklev [00:03:00] So, that's like seawater is what we're talking about. And so, clearly that section of the river is, is no longer habitable for Texas hornshell.