Earth & Sky

The following individuals were interviewed for today’s show. Our thanks to:

Dr. John Rinne
Research Fish Biologist
Rocky Mountain Research Station
U.S. Forest Service

Status of Spikedace in the Verde River, 1999: Implications for Management and Research by John N. Rinne, USDA Forest Service Rocky Mountain Research Station, Flagstaff, AZ. Published in Hydrology and Water Resources in Arizona and the Southwest Proceedings of the 1999 Meetings of the Hydrology Section, vol. 29, Arizona-Nevada Academy of Sciences.

Author’s Notes
The following article was written for American Currents, a quarterly publication of the North American Native Fishes Association. Reprinted here with permission.

Habitat Improvement and Native Fish Loss: The Upper Verde River Fish Mystery

Beneath the flowing waters of a tranquil stream lies a deceptively complex aquatic ecosystem. All the parts that make up this environment – biologic, geologic, and hydrologic – are closely intertwined. Tweak one aspect of this system, and the result can be a cascade of unexpected events.

Take the upper Verde River, a mere 30 miles of desert stream in Arizona that has scientists scratching their heads. Conventional wisdom dictated that restoring the streams riparian habitat – the areas along the streambanks – would improve stream conditions, making the waters healthier for native fishes. But instead of seeing a rebound, the population of native fishes has plummeted.

Caught in the center of these confusing events is a small minnow, about 2 to 3 inches long. The Spikedace (Meda fulgida), a Federally Threatened fish species, is endemic to the Gila River Basin of Arizona and New Mexico. Its a silvery fish with an olive-gray to brownish back, with vertical black specks along the sides. Spikedace feed primarily on aquatic insects, as well as terrestrial insects that get caught in the water current. A genetically distinct population of Spikedace lives in the upper Verde, along with five other native fish species.

In 1994, scientists at the U.S. Forest Services Rocky Mountain Research Station in Flagstaff, Arizona, began a systematic survey of the fish fauna in the upper Verde, studying the populations of native fishes including the threatened Spikedace, as well as introduced fish species like Smallmouth Bass and Green Sunfish. They did this by monitoring these fish populations at seven established sites. One of the scientists involved in that study is John Rinne, a fisheries biologist at the research station. The reason we started this study was to define fish community structure and how it changes relative to biotic and abiotic factors. Flooding was the primary abiotic factor, instream physical habitat was another. The biological [biotic factor], then would be the non-native fishes. So we started the study, but we saw that oh! this one fish blinked out.

That one fish species that blinked out was the Spikedace. In the first year of the survey, 1994, 428 spikedace were caught. The next year, 72 were taken, followed by a rebound in 1996 with 140 Spikedace. Then the fish numbers took a nosedive. In 1997, 1998, 1999, and 2000 no Spikedace could be found at any of the seven routinely monitored sites. So Rinne and his colleagues started what they called their Spikedace chase, looking at other sites in the upper Verde. They found about 12 fish in 1997, half as many the following year, and only one spikedace in 1999. This startling trend in Spikedace numbers was reflected in the other native fish numbers as well – they were all in a precipitous decline. But not the non-native fish. They, on the other hand, were doing quite well.

The downturn in Spikedace and other native fishes in the upper Verde happened to coincide with efforts to restore habitat along the rivers edge. Since the 1890s, livestock grazing had been established along the banks of the Verde. In other parts of the country, livestock grazing along streams had been implicated in degrading aquatic habitat. The lack of vegetation from constant grazing, and destruction of ground-cover that had been trampled over by cattle and sheep, had greatly increased erosion and sedimentation in many streams. Excessive nutrient runoff from livestock waste had polluted the water, making it unfit for many kinds of aquatic life. Therefore, by removing livestock and restoring the stream bank vegetation to approximate pre-grazing conditions, land managers and scientists thought they were doing the right thing.

Despite the riparian restoration, the upper Verde today is not the same place it was 120 years ago. As people settled the area, they brought with them the familiar trappings of their lives back East. One such activity was sports fishing – not just the sport, they brought their favorite sportsfish too. Smallmouth Bass, Green Sunfish, and Channel Catfish were among some of the new arrivals to the upper Verde. And these fish changed the biological character of the river.

The riparian habitat restoration that had been initiated in 1997 changed the stream. It was now 30% to 50% deeper, and 50% narrower. And the fish had responded to these new conditions. Data from subsequent fish surveys indicated an overall decline in all fish species. However, the non-native fish were much more abundant than the natives. One possible reason? Predation, said Rinne, pointing to data collected on one of the natives, the Desert Sucker. Of 167 Desert Suckers, 130 of them were adults. There were very few young-of-year or babies. Thats a problem. So if you’re a smaller fish out there, youre not doing well. And why is that? Maybe they’re getting eaten. We know there are Smallmouth Bass in there, and theyre predatory, and Green Sunfish too, so were beginning to look at predation by non-native fishes as one of the big factors causing the marked decline in native fishes in the upper Verde River.

This theory was reflected in the survey data as well. Of the six native fishes, it was the three smaller ones, Longfin Dace, Speckled Dace, and Spikedace that were declining the most, suggesting that the little fish were being overwhelmingly preyed upon at all life stages by the larger non-native fish.

There was a third major player to consider in the dynamics of the upper Verde: the hydrology of the stream. Research has shown that many desert fishes depend on ecological disturbances for their survival. At one small stream in south-central Arizona that had been studied for about 25 years, said Rinne, some years, certain fish species are very very abundant and typically, its after a flood. And then, a year or two later, you cant find any of these same fish species. Therefore, there may be some innate, or something inherent within Spikedace that may be a survival tendency, they come and go.

If a flooding event somehow brought about large numbers of native fishes, perhaps by creating ideal spawning conditions or by flushing out the non-native fishes, that could explain the large numbers of Spikedace seen in 1996 in the upper Verde. The batch of 96 had been preceded by a small flooding event. Since then, no large water flows had occurred in the upper Verde. So, were the Spikedace and other native fishes undergoing a natural decline in response to the lack of flooding? Would there be a surge in their populations when the next flood occurred?

But first, what causes the population explosion in some native fishes after a flood? Different desert fishes have different substrate requirements for spawning and egg development. During a flood, the rapid flow of water invigorates the ecosystem, resorting different types of substrate – sand, gravel, pebbles, cobbles, boulders – to create new spawning habitat for different fish species. Its a process that John Rinne refers to as disturbance.

Said Rinne, I’ve got a hypothesis based on some of the data we have collected in different streams in the arid Southwest … these native species are perhaps disturbance species, that is, they’ve done well through the eons of time, clear back in the Pleistocene, in disturbance. We as human beings don’t like to be disturbed, but native fish may indeed count on disturbance to make their living. There may be more disturbance species out here in the West than what we would have for a Mississippi fauna. So if you begin to remove a system from being a disturbance type system, maybe the non-native fishes can gain an advantage, and that is what were working on right now. We dont know that for sure.

Perhaps a combination of factors were responsible for the low numbers of Spikedace and other natives in the upper Verde: they were undergoing a natural decline in the absence of flooding, but it was a decline further exacerbated by a change in habitat that favored non-native fish. Historically,continued Rinne, Spikedace probably fluctuated extremely with alternating cycles of drought, flood, and other disturbance events. They do that currently, but the problem is that now we have superimposed a lot of management and other anthropogenic influences on top of these natural events, and it makes it tough for a species to sustain themselves. How much can they withstand? A parallel: look at your own personal health. Can you take the stress, take the high blood pressure, the high cholesterol levels … how many different negatively-impacting factors can your body withstand before you just dont make it? You tolerate some of those things, and compensate, but once you get too many things imposed upon you, its very difficult to basically sustain life.

One way to truly restore the upper Verde to its original condition is to get rid of the non-native fish, a very daunting task even for just 30 miles of stream. Its not like a terrestrial system with plants where you just go out there and cut em and remove em and thats it. The fish can move around, they can hide. The most powerful technique is to use a fish toxin to remove the non-native fish (native fish would be collected prior to treatment and held in a safe place, then returned later to the stream after the toxin had cleared out). But its very difficult to get all those fish out because you have backwater vegetation where fish toxins never get to. You also have areas where there is underflow … fish toxin never gets there. Rinne and colleagues also looked at electrofishing, a method that involves passing a low current into the water to stun the fish, bringing them to the surface for easy capture. They tested the efficiency of this method at three test sites. The results were both discouraging and encouraging. First, it was impossible to remove all non-native fish because of dense instream aquatic vegetation. Furthermore, removing Smallmouth Bass, for instance, simply resulted in increased numbers of Green Sunfish, another predatory species. However, the good news was that native fishes did respond by increasing recruitment (numbers of young) each year.

Another strategy for keeping Spikedace and other native fishes around is to increase their numbers, or at least set aside habitat specifically for them. In the large Colorado River, fish species like the Humpback Chub, Bonytail Chub, and Razorback Sucker still swim in the wild thanks to captive propagation efforts. Said Rinne, if for some reason we get flow [from a flooding event] and sizable numbers [of Spikedace], certainly more than we have now, we better try to hold the species and be ready to rear it in refugiums until we can figure out what to do …. We need to look at some of these tributary streams on the Verde River or the feasibility of creating side channel refugia on-site for propagating and holding stocks there. Getting Spikedace stocks from another river in the Gila River Basin, though, is not an option because the upper Verde Spikedace is genetically distinct from other Spikedace populations in other parts of the Gila River Basin.

A mere 30 miles of stream has turned out to be more complicated than anyone ever imagined. Scientists and land use managers from the U.S. Forest Service, Arizona Game and Fish Department, and the U.S. Fish and Wildlife Service have not given up on the Spikedace and other native fishes of the upper Verde. They are continuing to study the complicated dynamics of this system, and looking at other ways to save the native fish. Meanwhile, another threat is looming over the horizon. As human populations at the headwaters of the upper Verde increase, so does the demand for water. Studies have indicated that if the upper Verde is tapped as a source of water to quench the thirst of future desert towns, the river could run dry at least 2 out of every 30 years. No water, no fish. And so it will continue, the constant tug-of-war between the needs of an increasing human population and dwindling wildlife habitat ….

(Include this table in article)
Data from the following publication:
Status of Spikedace in the Verde River, 1999: Implications for Management and Research
by John N. Rinne, USDA Forest Service Rocky Mountain Research Station, Flagstaff, AZ.
Published in Hydrology and Water Resources in Arizona and the Southwest Proceedings of the 1999 Meetings of the Hydrology Section, vol. 29, Arizona-Nevada Academy of Sciences.

Table showing data on fish community at seven sampling sites in the upper Verde River, 1994-2000.
1994 1995 1996
1997 1998 1999 2000
NATIVE SPECIES
Longfin Dace 1319 12 282
21 13 2 1
Desert Sucker 2644 328 471 231
126 167 137
Sonora Sucker 1810 322 654 240
125 118 197
Roundtail Chub 776 341 259
50 64 25 20
Spikedace 428 72 140
0 0 0 0
Speckled Dace 171 25 68
1 12 2 7

NONNATIVE SPECIES
Yellow Bullhead 31 29 9
40 33 15 22
Common Carp 23 6 13
19 9 4 15
Red Shiner 1473 97 275
1238 1047 545 1594
Channel Catfish 5 2 0
1 0 0 0
Mosquitofish 0 0 0
3 6 59 227
Flathead Catfish 0 1 1
1 1 0 0
Green Sunfish 4 29 6
8 21 49 95
Smallmouth Bass 14 10 32 35
66 104 48
Fathead Minnow 7 0 0
0 0 0 1
Total Fish 8750 1274 2210 2288
1523 1090 2364
Percentage Native 82 86 85
19 22 29 15

Acknowledgments: Special thanks to Dr. John Rinne, research fisheries biologist at the Rocky Mountain Research Station (U.S. Forest Service) at Flagstaff, Arizona, for his time and patience in explaining the upper Verde native fish situation to me, for providing us with the latest (2000) data on the fish surveys, and contributing the fish photographs in this article. I?m also grateful to Chris Scharpf (editor, American Currents) for his thoughtful review of the initial draft of this article and for providing some basic information about Spikedace.

Article Copyright: Shireen Gonzaga, 2001.