Summary
Diel and spring/summer space-use and feeding patterns were investigated in an assemblage dominated by five fish species occupying the offshore waters of Lake Opinicon, a shallow mesotrophic lake in southeastern Ontario. We assessed fish distribution and diel movement in May and July through the use of gill nets set at various depths in 1.5–7.0 m depth contour zones, supplemented by observations of fish reaction to the nets.
Methodology
Lake Opinicon is a shallow (maximum depth < 11 m), 787 ha mesotrophic lake that does not stratify in summer. The offshore fish assemblage consists of bluegill, Lepomis macrochira, black crappie, Pomoxis nigromaculatus, yellow perch, Perca flavescens, alewife, Alosa pseudoharengus, golden shiner, Notemigonus crysoleucas, and small numbers of brook silversides, Labidesthes sicculus, brown bullhead, Ictalurus nebulosus, northern pike, Esox lucius, largemouth bass, Micropterus salmoides, and smallmouth bass, Micropterus dolomieu (Keast 1977, 1978, 1984). Occasionally, pumpkinseeds, Lepomis gibbosa, and rock bass, Ambloplites rupestris, are also found in offshore areas. The alewife, a non-native species in Lake Opinicon, first colonized the lake in 1964 (Keast & Harker 1977).
The study was carried out in 1985 at Cow Island Bay, which contains a narrow littoral zone that slopes gradually towards a central basin with a depth of 7 m (see Fig. 1 in Keast & Harker 1977). The study site was one of only two deeper basins in Lake Opinicon over half of which is less than 5 m in depth (Curran et al. 1947). The shallow portion supports a diversity of macrophytes, dominated by Potamogeton spp., Ceratophyllum demersum, Vallisneria americana, Najas flexilis, and N. guadalupensis. Stands of Myriophyllum spicatum are found at 2.5-3.5 m depth (Keast 1984). Little vegetation occurs beyond 3.5 m depth in this lake.