9588 - Laserfiche WebLink

Home Browse Search

of recapture occasions (e.g., minimum of 5) are needed to detect differences in capture probabilities among groups of animals in the same population. We also explain much individual heterogeneity by including the covariate TL in other analyses. Survival and finite population rate of change models.-Jolly-Seber type models (recaptures only and Pradel's survival and population rate of change models) in program MARK (Cormack 1964; Jolly 1965; Seber 1965; Pradel 1996; White and Burnham 1999) were used to estimate apparent survival (1991 to 1999) and population rates of change (x,,1991 to 2003), respectively, for Colorado pikeminnow captured in the Green River Basin. Apparent survival rates (S) are the joint probability of a fish surviving from one year to the next and remaining in the population available for capture. In other words, estimates from these models do not distinguish a fish that died in the study area from one that survived and moved from the study reach to an unsampled reach. Because of that, survival rates obtained from ISMP data are likely conservative (low) because capture data were gathered from reaches that represent only about 23% of the basin. Thus, Colorado pikeminnow that move out of reaches sampled by ISMP and are never recaptured would be treated as mortalities. These models are also not able to distinguish if fish that were previously captured were able to avoid subsequent recapture by some behavioral change mechanism. Such a behavioral change would result in reduced capture probability and lower apparent survival rates. Assuming that no behavioral change occurred, survival rates obtained from 2000-2003 during abundance estimation sampling likely approached true survival, because nearly all the Green River Basin habitat where Colorado pikeminnow likely occurred was sampled. The goal of survival analyses was to determine if a composite, and perhaps conservative, survival rate from 1991 to 1999 was different than survival in the 2000 to 23