Stripers Under The Microscope Lake Pleasant Arizona
Arizona trophy bass lake suffers from growth pains
By Lee Allen
BASS Times, Nov. 2004
PHOENIX, Ariz. ? Lake Pleasant experienced what biologists often refer to as "new lake vigor," beginning about a decade ago when dam renovations more than tripled the surface acreage of this central Arizona fishery.
Largemouth bass flourished inside the newly flooded cover and nutrient-rich waters. So, too, did white bass and striped bass, the latter migrating through the aqueducts of the Central Arizona Project (CAP) via the Colorado River.
The "vigor" has since subsided. In fact, biologists are now concerned because Pleasant's productivity has now fallen below pre-expansion conditions and the decline has shown no sign of slowing down.
Scott Bryan, a research biologist with the Arizona Game and Fish Department, recently wrapped up the field survey portion of a five year lake study. The comments he made several years ago now seem prophetic: "With the new lake syndrome over, productivity has leveled off and the size and number of bass is reverting to pre-dam conditions. Catching big fish won't be as easy as it was five years ago, and we expect that trend to continue."
Not only has Pleasant's downward spiral continued, according to Bryan and others, it has escalated.
Overall catch rates have decreased from .44 fish per hour (before the new dam was built in 1992), dropping to .32 fish per hour in 2003.
A variety of reasons may be behind the disturbing trend, none of them totally responsible but all of them contributing to the decline. "We haven't found any smoking guns so far," admitted Bryan, after four years of study and eight separate visits by both the gillnet team and the electrofishing squad. While data is still being analyzed and creel surveys will be conducted through the end of this year before the final report is written, some facts are already becoming apparent.
"Gamefish are spawning in sufficient numbers to populate the lake," Bryan said.
"The problem comes after the spawn. There are so many predators here and very little cover for fry to hide in. The trouble isn't in the reproductive cycle, but in keeping fish around long enough to recruit them into the catchable population."
Researchers have also discovered that even though the water flowing in from the CAP is healthy, its richness is not being distributed over the entire reservoir. The new dam dwarfs the old Waddell Dam, once one of the largest multiple arch dams in the world. The original structure was left intact and now acts as a baffle that keeps nutrients from spreading to the rest of the lake. "It's just a guess ? and an expensive one at that ? but if we could blow up the old dam, or move the intake structure to redistribute incoming nutrients, fish throughout the lake would benefit," said Bryan.
Bass clubs and tournament fishermen have worried from the beginning about the striped bass that began to show up in Pleasant through the CAP canals. Stripers today are reported as large as 20 pounds or more ? eating machines by any definition.
Before the lake was reconfigured, not one striper showed up in the state's sampling work. Ten years later, they're now common. "This used to be one of the top bass fishing lakes in the West. Now numbers are going down and fish are becoming smaller. We don't want what happened at Lake Powell to happen here," said Arizona Bass Club member Troy Bell.
There's no doubt that a striped bass population has become established inside Lake Pleasant. Biologist Marianne Medina is just beginning a three year study on this large predator and its impact alongside a largemouth bass population.
"We've got to figure out how to manage striped bass while maintaining the lake as a premier largemouth fishery. Stripers are schooling fish, pelagic in nature, that live and forage in open water, while largemouth bass are generally loners that hang around shore structure. They live in different types of habitat and, according to existing literature, should be able to co-exist."
Other factors contributing to the declining largemouth population include an abundant white bass population that joins the stripers and crappie in competing for threadfin shad forage; interrupted reproductive success caused by anglers who "sight fish" the clear waters for spawning bass, and the simple fact that Lake Pleasant, located a mere 20 miles north of metropolitan Phoenix, has become one of the most visited regional parks in the state, accommodating nearly 150,000 anglers who tally an estimated 528,000 angling hours per year. A check of creels and livewells shows approximately 150,000 fish are caught annually and one out of five largemouth bass take a trip home with the angler for supper.
In the halcyon days, tournaments frequently resulted in five fish limits that exceeded 40 pounds and 6- and 7-pound fish were routinely culled. "Catch-and-release anglers smart enough to figure out an ever changing bite pattern routinely caught and freed up to 100 quality bass a day," said Rory Aiken, an information officer with the Arizona Game and Fish Department.
"Tournament bags are considerably lighter than they have been and, as far as competition numbers go, a lot of little fish are being caught," said Mike Johnson, president of the Arizona BASS Federation, which represents two dozen BASS-affiliated clubs throughout the state.
"Although I don't think the lake will ever be as good as it's been in the recent past, this could be an awesome fishery again.
"Anglers need to start working more closely with Game and Fish to ensure the future health of this lake and return trophy bass to the water."