LAKE POWELL Wayne Gustaveson had been working for years to convince people that what the game fish in Lake Powell needed most was more food on the table.
A single forage fish was simply not enough to feed all those mouths, he argued. But not everyone agreed. So the lake was left with the threadfin shad as its main source of food.
A few years back he got his new fish albeit quite by accident. Gizzard shad were "accidentally" released into a lake that was linked to Lake Powell by the San Juan River.
Last fall, during a gill-net survey, aquatic technicians found an abundance of gizzard shad, the secondary forage fish Gustaveson had been asking for to feed striped bass, as well as largemouth and smallmouth bass, walleye and even crappie.
Each fall biologists canvas the entire 2,000-mile shoreline of this red-rock playground examining trends in fish size, health and population densities. Five years ago Gustaveson, Utah Division of Wildlife Resources fisheries project manager for Lake Powell, found what he called a mixed blessing in the San Juan arm.
"It was either July or August when we found the first gizzard shad in the upper stretch near the inflow above Copper Canyon into Mike's Canyon. That was in 2000," he said.
Two summers later biologists found them throughout the San Juan River arm of Lake Powell. By 2003 gizzard shad showed up in surveys throughout the lake from Good Hope Bay near Bullfrog Marina in the north to Waheap Bay near the Glen Canyon Dam.
"In 2004, we found good numbers of fish in our surveys. This year the gizzard shad population is taking up nearly 27 percent of the biomass," Gustaveson said as he examined some of the netted shad lined up along the back deck of the trawler used to establish camp and a miniature lab on the lake.
The netting results in 2005 along the San Juan arm were high. Of the 437 fish collected during the two-day sample, 177 were gizzard shad.
Gustaveson explained that the gizzard shad were introduced into the San Juan through Morgan Lake near Shiprock, N.M., when largemouth bass were stocked from a federal hatchery in Texas. The shad were mixed in with the game fish. When the lake spilled over into the San Juan River during spring runoff, the shad had their opening and slowly worked their way west into Lake Powell.
"We did not know they were in the river until we started checking and found them five years ago," Gustaveson said. "The gizzards had been established in Morgan for nearly four years before anyone started to look for them elsewhere. No one looked for them before that time. Navajo reservation biologists are in charge of the reservoir. It was so far from us we had no idea what was going on."
Last fall, technicians pulled in 10 different species of fish, including three- and six-pound stripers, two-pound smallmouth bass, largemouth bass, young crappie, sunfish, walleye, catfish, shad, carp, and a rare find, flannel mouth suckers, native to the Colorado River drainage.
"We look at the adult population and see how it changes from year to year. If we go to the same spot at the same time each year we can tell if we get a big catch one year and small catch the next year that our population is changing somewhat," Gustaveson explained. "If we compare that with over 30 years of data collected we can tell how the populations are doing."
The nets were set along rocky points in both shallow and deep water for two consecutive nights. Each net is 100 feet long and 6 feet deep. Four panels of monofilament mesh with openings ranging from three-quarters of an inch to 2 inches collect a balanced sample of both small and large fish.
The nets were anchored on shore and then stretched out to their full length. A weight was attached on the end with a floating marker. Once settled, the net conforms to the contour of the shore and lake bottom. Depending on water depth the net may fall 20 to 60 feet.
Technicians collected more fish than they anticipated in the two-day survey. The nets were left in place overnight. During the day fish see the nets and avoid them. At night, as they cruise the shallow shoreline and rocky structure, they are more likely to get caught in the nets.
"Most of the fish at Lake Powell are structure-oriented, and they will be within 6 feet of the bottom during the evening so we are more likely to catch the fish we are after with this technique," Gustaveson said.
After each net was pulled and the fish plucked from the twisted monofilament snare the nets were reset into the water for a second sampling the following morning. Then each fish was separated by species for processing. Stripers overflowed one bucket while crappie, catfish, green sunfish and walleye filled another. Smallmouth and largemouth bass filled yet another bucket. The fish were counted, body scales were taken for aging studies and digestive systems opened and examined for content.
It was a tedious process that took several hours. In the end, the results were very encouraging. Not only does Lake Powell now have another forage base for its prized game fish, but also the fish themselves will no longer have to deal with the feast-and-famine pattern they have had to contend with when threadfin shad populations are low.
"The very biggest change is in smallmouth bass. They used to be small, numerous, hungry and extremely catchable," Gustaveson said. "You could catch hundreds a day, the size was not great, but you could always catch fish. Now, with the increased forage fish, the biggest change is that it is not easy anymore. You have to work to catch fish. So when you fix a reservoir so that it is more in the favor of the fish, anglers suffer. When fish are hungry anglers are in charge."
But, when anglers do catch fish they are likely to be larger and healthier.
"Absolutely," said Gustaveson. "The quality has gone up and the quantity is still really good."
The biggest smallmouth handled during the netting effort tipped the scales at just over 2 pounds. The smallmouth composed nearly one-fourth of the total number of fish sampled in the two-day collection.
The benefits of a second, unscheduled forage fish have added many advantages to Lake Powell. With the gizzard shad there is now more food to go around. The cornerstone forage of the lake is still the threadfin shad. However, at maturity this fish may reach only 5 to 6 inches in length, well within the diet of even of the largest striped bass predator.
The gizzard shad, on the other hand, are only in the forage game for the first two years of their lives. They will reach 5 inches by their second year, and by age 5 as seen from those collected during the sampling effort they can reach 17 inches and more at maturity. That puts them well beyond the reach of any predator in the lake.
The upside to their larger size is that they will likely increase the size of the largest striped bass because they can forage on a greater number of larger gizzard shad for a longer period of time. Instead of seeking out large carp that may be in shallow water and be too difficult for larger stripers to enter, the larger gizzard shad will stay in the same general area as the stripers. It is not unlikely that new state records for stripers, smallmouth, largemouth bass and other sport fish could be set at Lake Powell.
Compared to threadfin shad, gizzard shad like onshore areas. The bigger fish are more likely to be caught in the gill nets and so their numbers are overestimated. In the overall scheme the threadfin shad are estimated at 75 percent vs. 25 percent for the gizzard shad. Because the large adult gizzard shad, like the 17-inch ones collected on this trip, have no predators they showed up in disproportionate numbers in the fall surveys.Comment on this story
Even though biologists were encouraged with what they collected in the gill nets throughout the lake, there were other indicators that the lake will shift again.
With so many large striped bass, Gustaveson feels the fishery is at its peak again and a decline is coming.
"The threadfin are going to have a periodic collapse in their population. At that point these large gizzard shad that we are finding will still be there and still provide good forage and hold the other game fish over until the threadfin can come back," Gustaveson said."The boom-and-bust period with the stripers may be over. Right now though they are producing on a tremendous rate, and hopefully there will be enough shad to reduce any impact."
Deseret Morning News outdoors editor Ray Grass contributed to this report.