The best performing N-mixture model used a negative binomial
distribution for abundance and included river as a covariate
(Table 1). There was negligible support for a Poisson
distribution for abundance (with or without zero inflation) ormodels without river-specific estimates. Estimated abundance
varied substantially among sites and rivers, the highest
observed and estimated counts being for the Pee Dee and Edisto
rivers (Table 2; Figure 3). The Pee Dee River had the highest
estimated abundance for a single river (1,944) and
comprised a large fraction of estimated total abundance for the
Carolina DPS (Table 2). The selected model appeared to be
adequate based on a goodness-of-fit test (Figure 4). The data
do appear to be overdispersed, with estimated dispersion
a > 0, at 0.13.