A Standardized Warmwater Fish Survey and Roving Creel Survey of Lake Cassidy

Lake Cassidy is a small (48 surface hectares; 125 acres), shallow (?7 meters), seasonally eutrophic body of water located north of Lake Stevens and three miles east of Marysville in Snohomish County (Figure 1).  The lake is fed by Little Martha Lake and forms the headwater of Catherine Creek which drains into the Pilchuck River.

Water quality in Lake Cassidy is characterized by thermal stratification and hypoxia in the hypolimnion during the late summer (Figures 2 and 3).  Although algal production appears to contribute significantly to microbial respiration and subsequent hypoxia in the hypolimnion, much of the productivity of Lake Cassidy probably results from littoral macrophyte growth and decomposition (Downen et al. 1999).  Over 65 percent of the shoreline to the two-meter bathymetric contour is densely vegetated with yellow water lily (Nuphar polysepalum), coontail (Ceratophyllum demersum), and bulrush (Scirpus sp.; Downen et al. 1999). The remaining shoreline is moderately vegetated with these and other aquatic plant species.

Lake Cassidy's shallow basin, low altitude, productivity and largely undeveloped shoreline provide adequate habitat for warmwater fish species, despite the poor water quality that occurs in late summer.  The popularity of this warmwater fishery led to a 1982 survey of the warmwater community by the Washington Department of Game (WDG).  Populations of largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus), and pumpkinseed sunfish
(Lepomis gibbosus) demonstrated slow growth and poor condition.

In 1984, a slot limit was imposed on largemouth bass to increase recruitment to larger size classes.  Downen et al. (1999) reports that growth rates for largemouth bass began improving throughout the 1980s.  In 1998, the Washington Department of Fish and Wildlife (WDFW) Warmwater Enhancement Program conducted the first standardized warmwater survey (for methods, see Bonar et al. 2000) to detect changes in community structure, growth and condition of warmwater fish and form a basis for other management options that might increase warmwater fishing opportunities in the lake (Downen et al. 1999).  Growth rates of largemouth bass, yellow perch, and black crappie improved from the 1982 survey, though proportional stock densities (PSDs) and numbers of stock size fish in the sample remained low.  Based on these results, Downen et al. (1999) made the following management recommendations: destratify lake with aerator, control aquatic vegetation, and change the slot limit for largemouth bass to improve size structure.  In 2000, WDFW adjusted the slot length for largemouth bass from 12-15 to 12-17 inches (5 fish limit; no more than one fish over 17 inches may be retained).

As early as the 1930s, there was considerable interest in the crappie fishery at Lake Cassidy.  In 1938, 938 fishermen caught 2135 fish, of which 79% were black crappie (WDFW, unpublished data).  Three major changes have occurred to the fish community since that time: (1) numbers of native cutthroat and coho have declined, (2) rainbow trout are planted annually to provide a trout fishery and (3) the yellow perch population has grown, and may have partially supplanted black crappie.  A 1993 creel survey of 128 anglers on Lake Cassidy showed the catch of 128 fish was predominantly black crappie (39%) with the remainder split evenly between largemouth bass
(21%), rainbow trout (20%), and yellow perch (18%; Curt Kraemer, WDFW, unpublished data).  In 1999, black crappie comprised only 4% of the population by number; 5% by weight (Downen et al. 1999).  From 2001-2003, the WDFW Warmwater Enhancement Program attempted to improve the crappie fishing on Lake Cassidy by stocking fry and adults.

Given the investment by the WDFW to enhance the crappie fishery at Lake Cassidy, we conducted a warmwater survey during spring 2011 to assess the relative abundance, growth, and condition of black crappie to inform future management decisions.  Size structure, stock density indices, and relative weights of largemouth bass were used to evaluate whether changes to slot regulations have had any impact on the population.  Second, we conducted a creel survey during the summer 2011 to characterize the largemouth bass, yellow perch, and crappie fisheries in terms of effort and catch rates and draw comparisons to a 1993 creel survey (Curt Kraemer, WDFW, unpublished data).