American Eel and Other Fishes of the Colorado

1 • The National Hydrography Dataset’s Watershed Boundaries, that we use extensively, includes barrier islands, and so, fishes in bays and estuaries, as well as the outer coast are included. Thus many of the 649 species known from “Texas” are only in the bays and inshore Gulf of Mexico. • The reason for “about 282” is that it’s hard to draw the line freshwater/marine line, and new species are still being discovered and described. • All species shown here are known from “freshwater” of Texas • Thus the Colorado has a bit more than 1/3 of the state’s total freshwater fish diversity 2 • Our Fishes of Texas database is described at the top • It is based entirely (so far, but that will soon change) on less colorful preserved specimens like those on our own collection’s shelves (shown in part on left), but color is not as important as is the simple fact that the specimens were preserved and deposited in the world’s Natural History Collections where they last for a very long time. • Note little difference between specimens collected 130 and 10 years ago. • Museums have always been very careful to preserve not only specimens, but also the original data about their collection. • The specimens and data together thus can tell us a lot about the history of fish communities in our state than we’d otherwise not know. • And, because we can inspect specimens any time, we can be sure we know exactly what species we are talking about, and not be plagued by uncertainty of written identifications. • Mis-identifications of fish species are common, even in museums, but if we have specimens, past errors can usually be corrected. • Our database extends back to Collections made in the 1850s to present. • Not unexpectedly, old specimens are relatively scarce, but starting 70 or so years ago, Texas was being pretty thoroughly sampled by biologists who were preserving their specimens in natural history collections. 3 We’ve invested a lot of work in this database 1. systematically compiling the data from all museums we can find that have TX specimens, we 1. reformat and import it into the database, and since nobody had GPS’s back then, 2. manually figure out, one by one, the latitude/longitude of all of the places where they were collected, 3. find “outliers”, and check those specimens to be sure they’re not mis- identified, and 4. finally, we use computer modeling of distributions to help fill in blanks between collections. 2. Then we spend a lot of time programming the web interface to provide the information to the world. It’s a massive, and never-ending task, but we’ve made good progress. 4 Our website can easily extract a list of all species known from different geographies: the whole state, any county, or any major river basin or sub-basins within them. The Colorado has 105 freshwater fishes. And, our checklists include info about how certain we are about this list, marking “suspect” records, and telling the user how many records we have of each species in the selected area. We also flag non-native species. Unfortunately, 25% of the Colorado’s fish fauna is not native. 5 The data are then easily mapped. Dot size increases with number of collections at a place (zoom in to see each). Gray marks native range. Green = specimens we’ve examined ourselves. Blue = those for which we see no reason not to trust original identifications. Yellow and red dots are those we’ve flagged as likely to be incorrectly located or mis- identified, but we have yet to examine the specimens. The Blacktail Shiner is one of the state’s most common and widely distributed minnows, native to all of Texas’ major river basins except the Río Grande, where it was introduced. There are relatively few other species so well collected. The other species here is another minnow, but one that has yet to be described by scientists. It has a small range in the Colorado River’s San Saba sub-basin. 6 This endangered species is found in only one spring in Menard County, but for many years (1950s – 80s) it was well studied. In the 1960’s it was found to be threatened by hybridization with the common Mosquitofish. A rock dam isolated the springhead from downstream reaches, but it was breaking down allowing Mosquitofish to enter the springhead. That problem was rectified by the Hubbs lab repairing the dam in 1970s and follow-up studies demonstrated that hybridization decreased. About 10 years ago the dam was noted to be failing again. 8 years ago, when last inspected by qualified ichthyologists, pure individuals still were found in the spring head. FWS offered to assist the landowner with repairs to the dam, but apparently negotiations were never finalized and I’m told there have been no official follow-up visits to assess the species’ status. 7 Despite the name “Guadalupe Bass”, most of the range of this popular sport fish is in the Colorado basin. 8 There’s a long, ongoing, and successful history of recovery efforts for this once endangered but also sport fishing species by TPWD, and I’d refer anyone interested to the brand new Conservation Plan they just released. 9 Naked Goby, native to the Texas coast, was discovered in the Upper Colorado about 10 years ago, and has been apparently expanding and showing up in other basins since then. At least in the Colorado, it appears restricted to extremely altered (high sediment loads over gravel) that few other fishes utilize. We don’t know what its impact will be. However, it is in the same general area as Greenthroat Darter, a Texas endemic of conservation concern, with which it might interact if it continues expanding. 10 The Río Grande Cichlid (or Perch), native to that basin has been expanding for many years. It clearly interacts with native sunfishes and many other species, likely to the detriment of the natives. Sharpnose Shiner was listed as endangered by USFWS a few years ago. Critical habitat was designated in the Brazos. Close relatives of this species have been extensively studied elsewhere (does the endangered Rio Grande Silvery Minnow ring any bells?). Their eggs drift downstream and if they end up in a reservoir before hatching, they die. Dams and the related habitat fragmentation were likely a primary contributor to endangerment of this species for the same reason. The listing mentions specimens from the Colorado in the early 1940s, but dismissed them as introduced. When we were checking specimen ids at the Smithsonian we examined some specimens of a relative of this species collected in Austin in 1882 and determined them to be mis-identified – they looked a lot like Sharpnose Shiner, but we couldn’t be absolutely sure. FWS funded us to look deeper, and after checking thousands of specimens in many jars of relatives of Sharpnose, we ended up with more records of this species or a close relative from the Colorado that ranged from 1882 into the early 1970s. We still can’t say for sure that these are Notropis oxyrhynchus, but if not, they are a close relative that was never described scientifically. Unfortunately, whatever it was, it looks to be now almost certainly extinct. 11 Our large, now well normalized, database now allows us to start getting into rigorous statistical analyses of temporal trends. The left-most graphs depict temporal trends in what can be described as detectability or “relative abundance or common-ness” (on the Y or vertical axis) controlled for a constant amount of sampling in each of the variable time intervals (earliest to most recent left to right) on the horizontal axis. Higher values indicate more frequent detection of the species. So, for Sharpnose, as sampling effort is held relatively constant, observation of the species has become more rare over time. Obviously, very different things are going on with these two species, but at least these two trends are exactly what we expected. While Sharpnose Shiner has been becoming increasingly rare over time in the two basins where it occurs or occurred, the Cichlid is becoming relatively more frequently collected as it has steadily expands into its new non-native range. We’re in the process of refining these analyses and improving statistical power. The results look very promising at this preliminary stage. We hope that by doing such analyses for all species, we might discover worrisome, but still undetected trends in other species early, and thus be better able to address them via appropriate management. 12 Our large geospatial database also allows us produce Species Distribution Models. We started doing this when the methodology was quite new, but it’s now very well established in Ecology. I won’t get into the details, but will show you how to read these – the model basically fills in the gaps between specimens by using basic environmental data and the specimen records to computing a probability of finding a species in every kilometer of stream. These are simply heat maps – red hottest (> 90% of finding it) and yellow is essentially a coin toss (50%), with white being < 50%. When we first produced these models, we were skeptical about their value in practice, so came up with a basic way to empirically test them. 13 We looked for a relatively large watershed that had never been sampled. The James River, a Llano River tributary just below Mason, fit the bill. It’s also sparsely populated and so relatively un-impacted by humans. We used all of our models for the Colorado River basin species to predict the fish community that we would expect to find in the James River basin.

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