1998 Lake Hummel Survey: The Largemouth Bass-Bluegill Community of a Eutrophic, Island Lake

Lake Hummel is a small (surface area = 15 ha), shallow (maximum depth = 3 meters), productive, lowland lake (elevation = 30 meters) located on Lopez Island (San Juan County). Sedimentary and metamorphic materials characterize basin geology and the drainage area of the lake is small (less than two square kilometers). Two ephemeral, poorly channeled outlet drain the lake intermittently to the north and to the southeast, and one small intermittent stream enters the lake on the west side (Figure 1).

A dense, extensive aquatic plant community suggests these waters are highly productive. The littoral zone is dominated by coontail (Ceratophyllum demersum), extending to 2 meters deep and choking much of the lake in summer months. Most of the shore is lined with common cattail (Typha latifolia) and bulrush (Scirpus sp.). Yellow water lily (Nuphar sp.) occurs extensively along the south side of the lake, and semi-terrestrial reed canary grass (Phalaris arundinacia) and nightshade (Solanum sp.) encroach along much of the lake margin (Jenifer Parsons, Washington Department of Ecology, unpublished data). Frequent blooms of green and blue-green algae, occurring regularly in Lake Hummel since the 1960’s, provide further evidence of high primary productivity and possible system enrichment. Attempts to control algae with copper sulfate treatments have had only short-term effects on standing crops and biologists have concluded that the only long term solution to overproduction is to identify and reduce nutrient inputs into the lake [Washington Department of Fish and Wildlife (WDFW) Files, unpublished data).

Water quality data for Lake Hummel with regard to phosphorus, clorophyll a, and dissolved oxygen is currently limited or unavailable. However, the lake’s small size, shallow depth, restricted drainage area, and sedimentary geology predispose it to eutrophication (Hern et al. 1981, Wetzel 1983). Agricultural land use and septic systems are likely to contribute additional nutrients resulting in high productivity by aquatic macrophytes and algae. Eutrophication impacts the fish community of Lake Hummel directly since plant and algae production and subsequent decomposition result in summer and fall oxygen depletion. Low dissolved oxygen concentrations have been identified in Lake Hummel as a major stressor to trout populations and a possible cause of winter fish kills occurring in the lake (WDFW, Lake Hummel Files, unpublished data).

Washington Department of Fish and Wildlife files suggest that there were no native sportfish in the lake prior to the first introductions of rainbow trout (Oncorhynchus mykiss) in the 1930’s. As part of a standard trout management program, Lake Hummel was rehabilitated with the piscicide, rotenone, in 1936, 1948, 1962, 1972, and 1979. During these rehabilitations common carp (Cyprinus carpio), black crappie (Pomoxis nigromaculatus), largemouth bass (Micropterus salmoides), and brown bullhead (Ameiurus nebulosus) were routinely removed from the lake to enhance trout stocking and subsequent production. Interest in managing Lake Hummel for warmwater species began to develop in the 1970’s due to the ability of these species to tolerate environmental conditions in the lake and due to the intensive management required to maintain quality trout populations under conditions they were poorly adapted to. In the early 1980’s the WDFW, then acting as the Washington Department of Game (WDG) stocked bluegill (Lepomis macrochirus) and largemouth bass into the lake, and began stocking channel catfish (Ictalarus punctatus) on a regular schedule. Preliminary follow up surveys in 1981 and 1982 indicated that intermediate sized bluegill had become too numerous and that growth rates of both largemouth bass and bluegill were slow. However, biologists believed the fish community would achieve balance when enough largemouth bass became large enough to begin cropping the bluegill population, thus relieving competition at lower trophic levels. Due to local interest in establishing suitable fisheries in Lake Hummel, and the predisposition of lake conditions to warmwater species, the Department of Fish and Wildlife (WDFW) Warmwater Enhancement Program conducted a stock assessment in early fall of 1998. We assessed the growth, condition, and balance of the largemouth bass-bluegill community in Lake Hummel.