Estimating Population Abundance with a Mixture of Physical Capture and PIT Tag Antenna Detection Data

The inclusion of passive interrogation antenna (PIA) detection data has promise to increase precision of population abundance estimates (Nˆ ). However, encounter probabilities are often higher for PIAs than for physical capture. If the difference is not accounted for, Nˆ may be biased. Using simulations, we estimated the magnitude of bias resulting from mixed capture and detection probabilities and evaluated potential solutions for removing the bias for closed capture models. Mixing physical capture and PIA detections (pdet) resulted in negative biases in Nˆ . However, using an individual covariate to model differences removed bias and improved precision. From a case study of fish making spawning migrations across a stream-wide PIA (pdet ≤ 0.9), the coefficient of variation (CV) of Nˆ declined 39%–82% when PIA data were included, and there was a dramatic reduction in time to detect a significant change in Nˆ . For a second case study, with modest pdet (≤0.2) using smaller PIAs, CV (Nˆ ) declined 4%–18%. Our method is applicable for estimating abundance for any situation where data are collected with methods having different capture–detection probabilities

The Strayed Reveller, No. 8

The eighth issue of The Strayed Reveller.https://scholarworks.sfasu.edu/reveller/1007/thumbnail.jp

Abundance, Standing Stock Biomass and species Composition of Zooplankton in Lake Sakakawea, ND and Uptake of Dissolved Organic Carbon (DOC) by Daphnia pulex

Zooplankton were collected biweekly from mid-May through mid-October, 1993, from the upper, middle and lower reaches of Lake Sakakawea, ND. Zooplankton were also collected at 2 km and 20 km below Garrison Dam on the Missouri River. To detect spatial and temporal differences in zooplankton abundance and biomass, an analysis of variance was performed on Log10-transformed data. Sixty-two zooplankton species were identified from the 408 samples collected from Lake Sakakawea and its tailwaters, including 12 Copepoda, 19 Branchiopoda and 31 Rotifera. Mean annual zooplankton abundance was greatest at Van Hook Arm (216.2/l; n = 65; CV= 75.6%), and at White Earth (205.7 /l; n = 66; CV= 81.5%). Abundance was lowest at Wolf Creek near Garrison Dam (65.8/1), and also the least variable (n = 66; CV= 34.8%). Rotifers were the most abundant taxa at Van Hook Arm and White Earth (Polyarthra vulgaris, Keratel/a quadrata and Synchaeta spp.), while copepods (mainly nauplii) were the most abundant taxa at Wolf Creek. Abundance tended to be greatest at the nearshore stations. Mean annual standing stock biomass was greatest at Van Hook Arm (229.3 μg dry weight DW/l; CV= 78.2%), followed by White Earth (145.0 μg DW/l; CV= 61.8%) and Wolf Creek (122.1 μg DW/l; CV= 89.7%) Copepods and branchiopods (mainly daphnids) made up nearly equal fra\u3c\u27tions of the mean annual biomass at Wolf Creek and White Earth. Branchiopods were clearly the predominant component of the total biomass at Van Hook Ann. Annual mean zooplankton abundance 2 km below Garrison Dam was 40.3/l (n = 105; CV= 58.7%) and 33.1/l (n = 105; CV= 73.5%) 20 km below the dam. Zooplankton abundance was greater at the 2 km site than at the 20 km site from July through midOctober. Zooplankton abundance tended to be greatest at 130 0 and 210 0 hr at the 2 km station, but abundance was greatest at 0300 and 0600 hr at the 20 km station. A 1:1 relationship existed between total zooplankton abundance above and 2 km below Garrison Dam (n = 11; r2 = 0.7832; p = 0.0001), which suggests that zooplankters were removed from Lake Sakakawea in direct proportion to their abundance above the dam. Total branchiopod biomass above the dam explained most of the variation in total biomass below the dam (n = 35; r2 = 0.2818; p = 0.0010). Time of day at which samples were taken as a second variable increased the R2 of this model to 0.3551 (p = 0.0006), which suggests that variation in total biomass in the tailrace is explained mainly by quantity and diel vulnerability to entrainment of large bodied branchiopods. Export of total zooplankton biomass from Lake Sakakawea was greatest in the spring and early summer (1000-4000 kg DW/day). Export rates dropped to 631.4 kg DW/day by mid-July and fluctuated between 400 and 2000 kg DW/day throughout the rest of the summer. Exports stabilized at 400 to 1000 kg DW/day during September and October. The total annual export of zooplankton biomass was 589.0 t DW. Concentrations of DOC in Lake Sakakawea and its tail waters did not differ along the longitudinal axis of the system, but temporal differences existed. Dissolved organic carbon increased from a mean of 3.3 ppm on June 16 to 4.5 ppm on July 8 and remained above 4.0 ppm through September 18. To determine if Daphnia pulex utilize DOC as a potential food source, live adult D. pulex were exposed to four levels of radiolabelled DOC (n = 10 each in 5.0, 9.8, 25. 9 and 45.8 ppm DO14C) for 1 hr. As a control, freshly killed daphnids were exposed to the same levels of DO14C to correct for any passive absorption or bacterial uptake of DO14C. Radioactivity of the live groups was measured after they were allowed to evacuated their digestive tracts for 30 min. The radioactivity of the waste products was also measured, as was that of the dead (control) groups. Daphnids that were allowed to feed in radiolabelled DOC always had greater radioactivity than either the dead (control) daphnids or unexposed daphnids (p≤ 0.0026). The resulting radioactivity was greatest in the 25.9 ppm and 45.8 ppm groups (83.7 CPM/individual [CV= 43. 2%] and 71.8 CPM/individual [CV= 54.5%], respectively). The radioactivity of the waste products was always much higher than that of the daphnids themselves. Results of this experiment suggest that uptake of DOC by daphnids is possible, but assimilation of DOC by daphnids is probably low