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Walleye in the Desert: Feast or Famine?
 
Apache Lake.Background:
For the past 25 years, Arizona Game and Fish Department (AZGFD) has stocked walleye in three Salt River reservoirs with the goal of developing a productive walleye fishery in central Arizona. Maintaining a walleye fishery in Arizona's low elevation, warm water reservoirs is challenging for managers since this cool-water species is more typically found in northern U.S. and Canadian lakes. In 2000, AZGFD Research Branch initiated a three-year study that ended June of 2003 to evaluate walleye populations in the three reservoirs and develop management strategies with goals of providing a more satisfying walleye angling experience.

Location:
Saguaro, Canyon and Apache lakes are water storage and hydropower reservoirs located east of Phoenix along the Salt River. Apache Lake located furthest upstream of the three reservoirs, approximately 65 miles east of Phoenix, and is the largest and deepest of the three reservoirs. Canyon Lake, the smallest of the three reservoirs, is located downstream of Apache Lake, approximately 50 miles east of Phoenix. Finally, Saguaro Lake, shallowest of the three reservoirs, is approximately 40 miles east of Phoenix. All three reservoirs experience high recreational use, with Saguaro receiving the heaviest use due to its proximity to Phoenix.

Approach:
Walleye being removed from gillnet.During the study we monitored fish abundance, primary productivity, zooplankton, and water quality. From these data we determined the age and growth of walleye, what food they eat, the level of walleye condition or health, success of previous walleye stockings, and success of walleye spawning in the Salt River reservoirs. With this information, managers can assess the status of the fishery and detect significant changes comparing current findings with long-term records collected by regional managers.

Our findings indicate walleye in the Salt River reservoirs live to approximately 6 - 7 years of age, and reach up to 13 inches by the end of their first year, and 21 inches by the end of their third year of growth, after which growth slows dramatically. Walleye diet consists primarily of threadfin shad, as they tend to avoid eating spiny-rayed fish such as bass and catfish. Although sexually mature walleye were collected there was no evidence of successful walleye reproduction in these reservoirs. Consequently, continued stockings will be required to maintain the walleye fishery in the future.

Walleye are one of the three most abundant large-bodied fish in these reservoirs along with yellow bass and channel catfish. Summertime is stressful for walleye because the reservoirs stratify and the fish are restricted to a narrow band of tolerable habitat with overlying water being too hot to enter without experiencing considerable energy demands or even death, and underlying water not having enough dissolved oxygen for respiration. Consequently walleye exhibit lower condition during summer because, less food is available, and more energy is required to forage for, capture and digest food. Furthermore, other fish species are also compressed into this band, and the walleye must compete with them for space and food. Winter conditions in Arizona are similar to those during summer at northern latitudes. During this period, temperatures are optimal for growth, food is abundant, and walleye condition is high.

Because a majority of nutrients entering the reservoirs originate upstream in the Salt River watershed, nutrients are filtered by each reservoir as the water flows downstream from Apache, through Canyon to Saguaro Lake. Consequently, Apache Lake receives the highest amount of nutrients, and Saguaro, the lowest. Walleye condition reflects this nutrient trickle-down effect with Apache Lake walleye having the highest condition and growth rates, and Saguaro Lake having the lowest.

Walleye in Saguaro, Canyon and Apache Lakes generally have higher condition than their counterparts in northern Arizona lakes and reservoirs. These differences may be a function of the lower productivity of northern lakes, and warmer year-round temperatures of the Salt River reservoirs.

Benefits:
Findings from this study enable managers to effectively stock and manage walleye in the Salt River reservoirs, thereby providing a unique angling experience to the state. Furthermore, study findings enable managers to confidently age walleye to assess growth and status of the walleye fishery in these low elevation reservoirs.

For more information contact:
Marianne Meding, Arizona Game and Fish Department, 5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7672 Email: mmeding@gf.state.az.us

Diana Rogers, Arizona Game and Fish Department, 5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (602)789-3664 Email: drogers@gf.state.az.us
 
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