9334 - Laserfiche WebLink

Home Browse Search

WILLIS, MURPHY, AND GUY REVIEWS IN FISHERIES SCIENCE PSD would be higher because females would be more abundant at that time. Mero and Willis (1992) used experimental gill nets to obtain monthly samples of walleyes and saugers (Stizostedion canadense) in Lake Sakakawea, North Dakota. Both PSD and RSD-P were highest in spring and fall and lowest during summer samples. We are aware of no work concerning seasonal patterns in size structure for eoldwater fishes. B. GEAR-RELATED BIASES Size-related biases in data also can result from gear selectivity. Reynolds and Simpson (1978) reported that electrofishing was progressively more effective as the length of largemouth bass increased. However, Reynolds (1983) noted that the overestimation was slight when only stock-length (200 mm) fish were- considered. Electrofishing also underestimates the size structure of bluegill (Reynolds and Simpson, 1978) and smallmouth bass (Milewski and Willis, 1991) populations. Laarman and Ryekman (1982) found that trap nets were selective for larger sizes of rock bass (Ambloplites rupestris), walleye, black crappie (Pomoxis nigromaculatus), bluegill, yellow perch (Perca flavescens), and pumpkinseed (Lepomis gibbosus). They did not find significant size selectivity for smallmouth bass and white sucker (Catostomus commersona). Mesh-size selectivity of gill nets causes small fish to be less effectively sampled than larger fish (Hamley, 1975). Thus, size structure is likely overestimated for most fishes that are effectively sampled with gill nets. However, biases in length frequency due to mesh-size efficiency (i.e., the length range of fish effectively sampled by a particular mesh size) of gill nets will vary depending on the complement of mesh sizes chosen to sample a fish population (Willis et al., 1984). Size structure is underestimated for most species of fish collected by cove rotenone sampling (Rayne et al., 1967). However, that bias is probably due to the typical late summer sampling time for the technique. Larger individuals of many species are no longer near shore during Iate summer. Barwick (1984) showed that more representative samples would be collected in May than in August. Bayley and Austen (1988) reported that retrieval efficiencies for marked fish increased with length for both rotenone and detonating cord in ponds and cove enclosures. Thus, the typical underestimation in size structure during cove samples in Late summer is likely due to fish behavior and movement patterns. Use of angler-collected data for making management decisions is becoming more popular and prevalent (Guthrie et ai., 1991). Again, length-related biases must be considered before interpretation of any type of length-frequency data, including stock density indices. Data from bass tournaments are a readily available source of information (Shupe, 1978; Durocher, 1978; Van Rom and Birehfield, 1981; Chapman and Fish, 1983; Duttweiler, 1985; Willis and Hartmann, 1986; Dolman, 1991). Gabelhouse and Willis (1986) found that tournament anglers in Kansas selected for larger sizes of largemouth bass; stock density indices calculated from angler- collected data were overestimated compared to electrofishing samples. Angler diaries also have proven to be a useful technique fox collecting fisheries data (Green eE al., 1984). Ebbers (1987) reported that largemouth bass data supplied by anglers 210