A common method for estimating absolute abundance of
fish species is mark–recapture; however, there are drawbacks
to these studies, including cost and potential harm to the study
species. The endangered status of sturgeon limits the sampling
methods researchers can employ because extra care must be
taken when sampling and handling specimens (Damon-Randall
et al. 2010; Kahn and Mohead 2010). Hydroacoustics provides
a nonintrusive method for sampling endangered species.
Sturgeon and related Paddlefish Polyodon spathula have been
identified as potentially suitable targets for hydroacoustic studies
(Nealson and Brundage 2007; Bergman 2011; Nelson et al.
2013). Side-scan sonar is a relatively old hydroacoustic technology
that has been used increasingly in fisheries studies in
recent years (Kaeser and Litts 2008; Foote 2009). In a previous
paper, we described a procedure to rapidly survey sturgeon
populations using side-scan sonar and occupancy modeling
approaches (Flowers and Hightower 2013). We reexamine
those data here, with a goal of estimating Atlantic Sturgeon
abundance in the Carolina DPS. Large body size, including a
maximum length of over 3 m (Gross et al. 2002) and distinctive
shape make this species an ideal hydroacoustic target.
This anadromous species, spends large amounts of time
feeding and migrating in marine environments, using freshwater
rivers for spawning and a summer dormant period (ASSRT
2007). During summer, Atlantic Sturgeon may aggregate in
lower portions of rivers, often in deep holes near the freshwater–saltwater
interface, although locations vary with river
characteristics and flow conditions (Moser and Ross 1995;
Collins et al. 2000).
Sturgeon density can be obtained from counts based on
side-scan images and the length and width of the survey transect.
These counts can be analyzed with an N-mixture model
(Royle 2004) that uses a distribution, such as a Poisson, to simulate
abundance and binomial distribution to simulate detection.
Count data can also be analyzed using distance sampling
methods (Buckland et al. 2001; Royle et al. 2004) based on
the distance on side-scan images from sturgeon to the survey
transect. We compare results from the various data types and
models and provide abundance estimates for Atlantic Sturgeon
recovery planning.