9488 - Laserfiche WebLink

Home Browse Search

"a.. -- Comparing predation rates between predatory species is complicated by the different rates of satiation in experiments with larger prey and the variation in test duration (see Table 4). Also, in the bluegill test, the predators appeared to be unusually uninterested in the prey, pOfmibly due to shock from handling before the experiment. This test will be repeated in 2004. Instantaneous predation rates (number of razorback larvae consumed/predator/hour) account for variations in test duration. Predation rates varied from 0.015 for bullfrog tadpoles to 0.455 for adult rainbow trout (Table 6). Mortality in control tanks was insignificant: it occurred in 6 of 29 control tanks (a total of 580 larvae), with a total of7 deaths. Thus mean mortality in controls was 1.03% ~ 0.46 SE). All hut one dead larvae were <15 mm. In mixed-prey experiments (channel catfish, largemouth bass, bluegill), the fathead. minnows used at the beginning of the experiment were the same size as the razorback suckers (separate variance t-tests: p :;:: 0.1; Table 7). Surviving prey were also not significantly different in size, ,suggesting that the predators were not size-selective for the prey sizes they were presented with. Table 7. Size of prey (x :t SE) in mixed-prey tanks with predators at beginning and end of experiments. Separate variance t-tests compare differences in size by prey species. NM = Not measured. All Prey Surviving Prey Beginning of experiment End of experiment (mm) (mm) Razorback Fathead Razorback Fathead Predator sucker minnow su cker minnow Bluegill 35.0:t 0.9 36.8 :t 0.5 NM NM n=8 n=8 t=1.79; df=10.6;p=0.1O Channel 41.7:t 0.7 41.6:t 0.6 44.7:t 1.2 42.3 :I: 0.6 catfish n=30 n=30 n=l1 n=25 t=-0.11; df=55.2;p=0.92 t=-1.8, df=15.5; p=0.09 Largemouth bass 39.4:t 0.6 n=30 40.2 :to.6 n=29 40.6 :t 0~6 n=19 41.9:1: 0.6 n=15 t=0.87, df=56.4,p=0.39 t=1.56, df=31,p=0.13 21