Colorado State University Researcher's Detective Work Uncovers Clues To Save West's Endangered Fish

May 22, 1997

FORT COLLINS--A Colorado State University researcher's uncanny ability to identify young fish smaller than the tip of a pencil is helping to restore populations of endangered fish in Colorado and the West.

Relying on keen eyesight, a microscope and 30 years of experience, Darrel Snyder is one of a handful of people in the world who can identify days-old fish so small most people wouldn't see them darting around rocks at the edge of a stream.

Snyder and his associates already have identified the larvae of endangered fish in reaches of the Upper Colorado River Basin where they were not previously thought to reproduce. This signals the possibility that other spawning sites of endangered fish may exist but have gone undetected.

The researcher's knack for identifying fish provides state and federal fishery management agencies with important clues useful in efforts to monitor and bolster populations of endangered razorback sucker, Colorado squawfish, bonytail and humpback chub in the upper basin. The basin stretches from the high mountains of Wyoming and Colorado, through Utah and New Mexico, to Lee's Ferry below Lake Powell in Arizona.

"Everything we need to know about the survival of these threatened species begins when the fish are days old," said Snyder, a fish larvae taxonomist at Colorado State's Larval Fish Laboratory. "Without that knowledge, it's difficult to predict where they have the best chance for survival or analyze what kind of habitat is ideal for producing offspring."

The Colorado State researcher helped prove that razorback sucker are reproducing in parts of the Green River in Utah where they previously weren't known to spawn. Snyder also has confirmed a small population of Colorado squawfish are successfully reproducing in the Gunnison River in Western Colorado. It was the first time squawfish larvae were discovered upstream of the Redlands Dam between Grand Junction and Delta, a discovery that points to the likely success of a recently installed fish ladder to which allows migrating adults passage to swim around the dam to spawn upstream.

Snyder likens his work to that of a detective. State and federal fish management agencies send the lab tens of thousands of larval and early juvenile fish each year in samples collected from upper basin rivers and tributaries in Colorado and Utah. Then, Snyder and his assistants begin the tedious process of sorting the tiny fish into smaller lots by species with the help of microscopes.

"It's a lot like trying to solve a crime," said Snyder, who estimates he's seen millions of young fish through the lens of a microscope. "You look for the clues and piece them all together to come up with the answer. Sometimes, the answer is elusive."

To the untrained eye, fish larvae resemble pale white tadpoles ranging between one-eighth inch and one inch in length and lack the many distinctive features that make identification of adult fish easy. An additional challenge is that larvae of one species can look strikingly similar to different species at various stages of development. In order to identify fish larvae accurately, Snyder must know what each species looks like at every stage of growth--which means hundreds of different possibilities.

Another difficulty is the limited references available to identify fish larvae. Snyder estimates that only one-quarter of North America's freshwater fish species have been adequately described as larvae for identification purposes. Due in part to the efforts of Snyder and his associates, nearly two-thirds of the fish larvae in Colorado have been described.

In the case of fish larvae identification, Snyder looks for a variety of clues such as pigmentation, the number of muscular body segments, position of various physical structures, overall size and skeletal development. By analyzing those features, Snyder can differentiate between a recently hatched razorback sucker and its close relative--the flannelmouth sucker--with ease. When specimens are too similar or damaged to make visual identification, researchers sometimes turn to DNA analysis for a definitive answer.

"When all else fails, I just look for their name tags," Snyder jokes.

The lab's efforts at Colorado State are an important part of the Colorado River Recovery Program, a 15-year project directed by the U.S. Fish and Wildlife Service and state agencies in Colorado, Wyoming and Utah. The program aims to restore declining populations of fish native to the Upper Colorado River Basin.

Over the past 60 years, the number of many native fish in the upper basin has dropped dramatically, largely due to the introduction of non-native sport fish and changes in habitat caused by dams.

Snyder said past research focused only on how adult fish fared in these waters. With the revelation of criteria to identify fish larvae, the focus shifted toward work on early life stages. Researchers now are better able to monitor where reproduction takes place and investigate how changes in habitat, water quality, or non-native fish affect larvae and juveniles.

Research at the larval lab has showed that many factors influence the survival rates of young fish, such as the availability of backwaters in rivers, water temperature, dissolved oxygen levels, food supply, and predation by other fish. That's where Snyder fits in.

"Darrel can identify fish for us at these early ages, which is key to helping us understand their development, habitat requirements and survival," said Robert Muth, director of the Larval Fish Lab. "A large part of the research we do to help these endangered fish couldn't be done without his expertise."

Researchers from many parts of the United States and Canada consult with Snyder or send him specimens for identification, verification and sometimes formal description. He's described the larvae of many fish, including four of North America's seven sturgeon species.

The lab, one of the few in the world that focuses on identifying freshwater fish at early stages of life, was established in 1978. Once fish are identified, most preserved specimens are counted, measured and stored for future study or reference. Over 3 million fish are in storage.

Some specimens are dissected to study food habits. Small ear bones--called otoliths--are removed from other fish to determine age, growth rates and probable spawning dates based on the bones' daily growth rings, which are similar to the annual rings of trees. Larval Fish Laboratory researchers and students also study fish behavior, determine the effects of toxic chemicals and electric currents on fish, track adult fish migration patterns with radiotelemetry and conduct other field and laboratory research related primarily to endangered species.

Colorado State University

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