1997 Lake Stevens Survey: The Warmwater Fish Community after Implementation of a Minimum Length Limit on Largemouth and Smallmouth Bass

Lake Stevens is a deep (maximum depth = 45.7 m), moderate size (surface area = 433 ha) body of water located approximately 6 km east of the City of Everett. It is the largest natural recreational lake in Snohomish County. Lake Stevens is fed by Stitch Creek from the south and Lundeen and Kokanee (or Mitchell) Creeks from the north. Surface water exits the lake at the northeast corner, through Stevens Creek, eventually discharging into the Pilchuck River.

Because of its depth, Lake Stevens stratifies readily as surface water temperatures increase. In the past, during the warmer spring and summer months, the lake’s hypolimnion (the cold, deep layer of water in a stratified lake) became hypoxic - even anoxic, effectively reducing the amount of habitat hospitable to fishes and their prey. Furthermore, the low dissolved oxygen levels exacerbated the release of nutrients (phosphorous) from the lake bottom causing eutrophication and nuisance blue-green algal blooms (KCM 1992; KCM undated). To rectify the situation, the City of Lake Stevens and the Drainage Improvement District No. 8, with funding from the Washington Department of Ecology (WDE), began operating the world’s largest hypolimnetic aeration system in the northwest basin of the lake on May 19, 1994. The system uses compressed air to increase the dissolved oxygen content in the deepest part of the lake, thereby increasing the habitat available to fishes and their prey, while reducing the phosphorous load and occurrence and intensity of algal blooms (KCM undated).

In addition to its water quality problems, Lake Stevens has endured invasions by Eurasian watermilfoil (Myriophyllum spicatum) and a top-level predator, the smallmouth bass (Micropterus dolomieu). In 1994, Eurasian watermilfoil (EWM) was patchily distributed throughout the lake. However, a routine survey by WDE in 1997 showed that EWM had died back; in fact, all submersed aquatic vegetation in the lake was unhealthy, possibly due to disease or herbivory by insects (Parsons 1998). Sometime during the early 1980's, smallmouth bass were illegally introduced into Lake Stevens. The first record of the species was noted in 1985. By the late 1980's, smallmouth bass were fairly abundant in the lake and their growth was rapid [Curt Kraemer, Washington Department of Fish and Wildlife (WDFW), personal communication]. Although colonization by Eurasian watermilfoil has the potential for serious impacts at the lake, the introduction of smallmouth bass has, fortunately, benefitted the recreational fishery.

Given the expanding population of smallmouth bass in Lake Stevens, biologists from WDFW proposed a minimum length limit regulation in order to create a trophy fishery for the predator. In 1990, a new fishing rule was implemented which allows anglers to retain only one smallmouth bass or one largemouth bass (Micropterus salmoides) per day with a minimum length of 457 mm (18") total length. Little or no information exists regarding the resident fish community of Lake Stevens after implementation of the minimum length rule. Therefore, in an effort to assess the warmwater fishery of the lake, as well as to monitor the success of the restoration plan, personnel from WDFW’s Warmwater Enhancement Program conducted a fisheries survey at Lake Stevens in early fall 1997.