1998 Twin Lakes (Gissburg Ponds) Survey: Assessment and Comparison of the Warmwater Fish Communities in Two Small, Heavily Fished Ponds

Twin Lakes (Snohomish County), aka Gissburg ponds, located north of Marysville, were formed from two borrow pits created during the construction of Interstate-5 in the 1960’s. These large (total surface area = 7 ha), moderately deep ponds (maximum depth = 9 m and 5.5 m, north and south, respectively) are somewhat rectangular in shape and nearly equal in size (Figure 1). Connected by a shallow canal, Twin Lakes are fed by a spring from below the north pond and drained by a small ephemeral stream at the southeast corner of the south pond. These ponds form the focus of Twin Lakes County Park which is bordered by Interstate-5 on the east and agricultural lands to the south and west.

No water quality problems have, as yet, been identified for the ponds. However, data regarding lake productivity and seasonal temperature and dissolved oxygen concentrations are currently unavailable. During an October 1994 fisheries study, Bonar et al. (1995) found dissolved oxygen concentrations above 5 mg/L throughout the water column in both ponds. During this study they also estimated aquatic macrophyte volumes in each of the ponds as 2% for the north pond and 27% for the south pond.

The county park is used for a variety of recreational activities including swimming, canoeing, model boat racing, and fishing. Although no formal creel survey data exists for Twin Lakes, this water body receives heavy fishing pressure for stocked populations of rainbow trout (Oncorhynchus mykiss), channel catfish (Ictalurus punctatus), and naturalized centrarchid populations of largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus), and pumpkinseed sunfish (Lepomis gibbosus). The Washington Department of Fish and Wildlife (WDFW) stocks between 8,000 and 10,000 legal-size rainbow trout in four equal plants in March, April, May, and June, annually. The WDFW also stocks between 500 and 1,000 channel catfish each year.

In fall 1994, Bonar et al. (1995) examined growth and survival of channel catfish over a fifteen month period in the north and south pond as part of a larger study including several Washington lakes. Growth of channel catfish in the north and south ponds was high with instantaneous growth rates of 2.1 and 2.2, respectively. Survival was 3.2% and 21.8%, respectively. The largemouth bass during this study were characterized by fewer fish in larger size classes relative to numerous smaller stock length fish. Largemouth bass in all size classes exhibited high relative weight (Wr) values suggesting competition was low and forage abundant.

Twin Lakes were selected for a warmwater fishery stock assessment by the WDFW due to the presence of warmwater populations, the absence of native salmonid populations, and due to the accessibility and popularity of these ponds with anglers. During early fall 1998, personnel from the WDFW Warmwater Enhancement Program surveyed the ponds in order to evaluate species composition, abundance, growth, size structure, and condition of fish in the north and south pond. We compared fish communities of each pond and discussed our results in context of earlier observations of Bonar et al. (1995).