was not well described by the half-normal distribution (or any
other alternative), but the half-normal did account for the low
detections at ranges greater than 20 m. Detections probably
decreased at the far edge of the swath because acoustic shadows
would have been outside the sonar image field-of-view.
Detections increased gradually at distances of 8–20 m off the
transect, perhaps because the more gradual angle relative to
the sonar provided a clearer acoustic shadow for identification.
Abundance estimates from the distance model were quite similar
to those of the N-mixture model, the Carolina DPS estimate
being 1,823 (Table 2; Figure 3). The preferred distance model
was supported by the goodness-of-fit test (Figure 4). The
data do appear to be overdispersed, with estimated dispersion
a > 0, at 0.274.