The counts and distance data sets were analyzed using procedures
in package unmarked (Fiske and Chandler 2011) in
program R (R Development Core Team 2009). For both analytical
methods, we assumed that we correctly identified targets
classified as sturgeon, although additional sturgeon were
assumed to be present but not identifiable from a particular
side-scan image. Count data were analyzed in unmarked using
the pcount procedure, based on the N-mixture framework proposed
by Royle (2004). The general form of the N-mixture
model for site abundance is