No abstract

Largemouth bass (Micropterus salmoides) and northern pike (Esox lucius) are top predators in the food chain in most aquatic environments that they occupy; however, limited information exists on species interactions in the northern reaches of largemouth bass distribution. We investigated the seasonal food habits of allopatric and sympatric assemblages of largemouth bass and northern pike in six interior lakes within Voyageurs National Park, Minnesota. Percentages of empty stomachs were variable for largemouth bass (38-54%) and northern pike (34.7-66.7%). Fishes (mainly yellow perch, Perca flavescens) comprised greater than 60% (mean percent mass, MPM) of the northern pike diet during all seasons in both allopatric and sympatric assemblages. Aquatic insects (primarily Odonata and Hemiptera) were important in the diets of largemouth bass in all communities (0.0-79.7 MPM). Although largemouth bass were observed in the diet of northern pike, largemouth bass apparently did not prey on northern pike. Seasonal differences were observed in the proportion of aquatic insects (P = 0.010) and fishes (P = 0.023) in the diets of northern pike and largemouth bass. Based on three food categories, jackknifed classifications correctly classified 77 and 92% of northern pike and largemouth bass values, respectively. Percent resource overlap values were biologically significant (greater than 60%) during at least one season in each sympatric assemblage, suggesting some diet overlap.

No abstract

This study examined the use of antifungal chemicals at nonstandard treatment concentrations or treatment intervals during the incubation of eyed eggs of rainbow trout Oncorhynchus mykiss until hatch in vertically stacked incubation trays. Daily chemical treatments of 500, 1,000, and 1,667 mg of commercial formalin (containing 37% formaldehyde)/L for 15 min and a nonchemical, dead-egg-removal control were included in three trials. The second and third trials added a true control (no antifungal measures) and the third trial also incorporated a treatment of formalin at 1,667 mg/L for 15 min every other day. In these three trials, formalin at 1,000 or 1,667 mg/L daily or 1,667 mg/L every other day significantly improved egg survival to hatch relative to the other treatments and completely controlled fungal growth. A fourth trial evaluated treatments of formalin at 750 mg/L for 15 min daily or every other day, hydrogen peroxide at 500 mg/ L for 15 min daily or every other day, and control groups for both treatments. Egg survival to hatch was significantly different among the treatments; the daily 750-mg/L formalin treatment produced the greatest number of hatched fry, followed by the treatment with 750 mg/L formalin every other day, the dead-egg-removal control, and daily hydrogen peroxide treatment. Survival in the every-other-day hydrogen peroxide treatment and the true control could only be estimated because of extreme fungal growth, and was substantially less than the other treatments. Only daily 750 mg/L formalin treatments and dead egg removal completely controlled fungal growth. To adequately control fungus and maximize egg survival, either daily 15-min treatments of formalin at concentrations of at least 750 mg/L or every-otherday treatments of formalin at 1,667 mg/L are recommended.

When creel survey methods such as noncontact aerial designs are applied to large water bodies, they are often biased because of scheduling difficulties and flight reductions made to reduce cost. An aerial creel survey has been used to estimate fishing pressure on South Dakota's Missouri River reservoirs since 1975. We compared fishing pressure estimates from aerial and bus route designs and examined the effect of count frequency on variance and point estimates. A total of 71,400 (observed and unadjusted) and 94,298 angler-hours were estimated on Lake Francis Case during June 2000 by use of the aerial and bus route methods, respectively. Aerial boat and shoreline fishing pressure estimates were 65,845 angler-hours (95% confidence interval [CI] ¼ 25,770) and 5,554 angler-hours (95% CI ¼ 62,436), respectively. Bus route boat and shore fishing pressure estimates were 82,671 angler-hours (95% CI ¼ 614,878) and 11,627 angler-hours (95% CI ¼ 66,618), respectively. Analyses indicated that reservoir zone, day type, and type of fishing were significant main effects (P , 0.001), which supported spatial and temporal stratification in the sampling design. Within-strata comparisons of fishing pressure estimates from the two surveys did not reveal any significant differences (0.09 , P , 0.99). Although the bus route method led to 22,898 more angler-hours of fishing pressure than the aerial method, the bus route method estimated total fishing pressure with higher precision because the day-to-day variation in fishing pressure estimates was comparatively lower than that of the aerial estimates. The aerial and bus route methods both estimated shoreline fishing pressure with lower confidence than for boat fishing pressure; this was probably the result of overall low shoreline fishing pressure and high day-to-day shoreline fishing pressure variability. Bootstrap analysis and nonlinear regression indicated breakpoints in variance estimates between six and seven counts for both survey methods. Therefore, a minimum of eight counts per month was required to produce stable variance and point estimates with an acceptable level of confidence for either survey design.