Background:
Lake Pleasant has historically been regarded as one of the premier largemouth bass fisheries in the state. However, over the past 15 years, the quality of the largemouth bass fishery has decreased, resulting in low angler satisfaction and a general concern for the health of the fishery. The leading viewpoint regarding this decline is that the recent invasion of striped bass may be responsible, in part, for the shift in size structure through competition for resources and predation. Striped bass initially entered the Central Arizona Project (CAP) canal system as eggs or larvae, entrained in Colorado River water pumped in from Lake Havasu. Preliminary results of a recent evaluation of the Lake Pleasant fishery indicate that the striped bass fishery is expanding. Lake Pleasant anglers are extremely concerned that the striped bass population has become established and will eventually out-compete the favored largemouth bass and white bass fisheries by effectively eliminating the primary prey source, threadfin shad.

Location:
Lake Pleasant is located approximately 25 miles northwest of Phoenix in Maricopa and Yavapai counties and covers nearly 10,000 acres. The CAP system is connected to Lake Pleasant through intake and outtake structures located in the New Waddell Dam forebay.

Approach:
This 3-year study, beginning in January of 2004, has 3 primary goals: 1) Evaluate the striped bass population in the CAP canal system and its contribution to the Lake Pleasant population, 2) Determine reproductive success and recruitment of striped bass in Lake Pleasant, including seasonal migrational spawning movements and habitat preferences, and 3) Determine energetic demands of striped bass, white bass, and largemouth bass in Lake Pleasant to assess their effect on the primary prey source (threadfin shad), and evaluate the potential impacts of a secondary prey source in the lake.

Adults, larvae, and eggs in the canal upstream of Lake Pleasant are sampled by boat electrofishing and setting larval drift nets. Quarterly sampling of the predator (largemouth bass, striped bass, white bass) and prey (threadfin shad, sunfish) populations in Lake Pleasant is conducted by gill netting and electroshocking. Stomachs and otoliths are collected and analyzed to determine food habits and age. Larval sampling in tributaries and throughout the reservoir is conducted during spring and enables detection of in-lake striped bass reproduction. Radio tagging and subsequent tracking of adult striped bass indicates seasonal migrational patterns and habitat use.

Benefits:
This study will determine if striped bass are reproducing in Lake Pleasant, or whether the CAP canal system is acting as a seed source for the reservoir population. Energetic requirements of striped bass in Lake Pleasant will be determined, allowing prediction of future population growth. This information will indicate how the presence of an additional predator (striped bass) will impact the current sportfish fishery, including white bass and largemouth bass, as well as the primary prey source in the system, threadfin shad. Management strategies will be developed with the goal of minimizing the negative impact striped bass may have on the existing fishery.

For more information contact:
Bill Stewart, Arizona Game and Fish Department, 5000 W. Carefree Highway Phoenix, AZ 85086-5000 .
Phone: (623) 236-7368 E-mail: bstewart@azgfd.gov

Marianne Meding, Arizona Game and Fish Department, 5000 W. Carefree Highway Phoenix, AZ 85086-5000 .
Phone: (623) 236-7672 E-mail: mmeding@azgfd.gov

Diana Rogers, Arizona Game and Fish Department, 5000 W. Carefree Highway Phoenix, AZ 85086-5000 .
Phone: (623) 236-7664 E-mail: drogers@azgfd.gov