2012 Fall Walleye Index Netting (FWIN) Surveys in Washington State

The walleye is a popular sport fish throughout the United States and represents an important recreational fishery in Washington. Management of walleye fisheries must include periodic standardized sampling, appropriate harvest regulations and exploitation by anglers in order to reduce negative impacts on other fish populations.

The Washington Department of Fish and Wildlife (WDFW) fisheries biologists, along with Spokane and Colville tribal fisheries biologists began monitoring important walleye populations in Washington in 2002 using Fall Walleye Index Netting (FWIN) methodologies. The FWIN methodologies were developed in Ontario, Canada as a means of monitoring a wide variety of biological parameters in walleye populations in a standardized fashion. Fisheries biologists from WDFW conduct FWIN surveys on five important walleye populations in eastern Washington (FIGURE 1) each fall, when water temperatures are 50â€"59°F, a range at which walleye are more equally distributed throughout lakes. Standardized sampling effort (i.e. nets set per lake) is based on lake size, or the minimum number of nets needed to collect 300 walleye (TABLE 1).

In 2012 walleye abundance in our FWIN waters was excellent. The average catch per unit effort (CPUE), for all lakes combined, was 18 walleye per net, and approximately 29 percent of the walleye collected from all lakes were over 16 inches. Length-at-age of walleye in Banks Lake, Moses Lake, Potholes Reservoir, and Scooteney Reservoir was above the statewide average with walleye reaching 16 inches by ageâ€"2. Length-at-age of walleye in Lake Roosevelt (FDR) was below average with most walleye reaching 16 inches by ageâ€"5. Anglers in search of walleye over 18 inches should visit Banks Lake, Moses Lake, and Potholes Reservoir (FIGURE 27).

We sample five lakes in eastern Washington each year during our FWIN sampling schedule (Scooteney Reservoir (Franklin County), Moses Lake (Grant County), Potholes Reservoir (Grant County), Banks Lake (Grant County) and Lake Roosevelt (Stevens County)) (Figure 1.). All fish in the FWIN surveys are collected with gill nets only. The FWIN gill nets have eight panels of differing mesh size from ½ inch to 4 inches, are 200 feet long and are designed to have a particular catch bias toward percids (walleye and perch). Nets are soaked for 21â€"24 hours overnight. The number of nets set per lake is based on the total surface area of the lake (Table 1.) so the effort per lake is comparable to other waters. Net set locations are randomly chosen so as not to bias the catch rates. Data collected from each fish includes: length (for size distribution) and weight, otoliths (for age and growth data), sex, sexual maturity, gonad weight (for reproductive potential) and fat weight (for condition factor).

We collect length and age data on all walleye which allow us to determine the size distribution of the population, the percentage of harvestable fish in the population and at what age walleye recruit to the fishery. Walleye ages are determined from otoliths, which provide a precise age estimate. Otoliths are fish ear bones, which have growth rings analogous to growth rings in a tree. Length and age data, when combined with abundance data, also help us determine if a change in regulations is necessary or if regulations are helping us meet our management goals.

Length and weight data, as well as relative abundance estimates, on other fish species are collected and presented but may not be an accurate representation of those populations. For instance, low numbers of largemouth bass and bluegill captured in a FWIN survey are not a cause for concern since these species are more effectively sampled using a boat electrofisher. In addition, length averages of smallmouth bass collected in gill nets tend to be higher than those collected via boat electrofishing and must be interpreted accordingly.

The average number of walleye collected per net gives fisheries managers an index of walleye population size. Throughout this report we report this as catch per unit effort (CPUE ± 80% confidence intervals). Abundance estimates, when examined over multiple years, reveal trends in populations and allow managers to make informed decisions on possible changes in angling regulations. Significant declines in abundance may signal a need for more restrictive regulations; whereas, increases in abundance, or stable populations at high abundance, may indicate the need for more liberal regulations.