Using Side‐Scan Sonar and N‐Mixture Modeling to Estimate Atlantic Sturgeon Spawning Migration Abundance

Abstract

Understanding the relationship between number of spawners and recruitment is essential for managing fish populations. Atlantic Sturgeon Acipenser oxyrinchus (ATS) are endangered anadromous fish inhabiting the rivers, estuaries, and marine environments along the Atlantic coast of North America. Atlantic Sturgeon are periodic life history strategists that exhibit both spring and fall spawning migrations. Traditional capture–mark–recapture techniques can be used to estimate spawning run abundance but are resource intensive and potentially stressful on migrating individuals. Noninvasive methods, such as side‐scan sonar, can be a less stressful alternative to estimating abundance. We sampled the uppermost portion of the Savannah River, USA, over 50 occasions from August to November 2017 using side‐scan sonar. Bayesian N‐mixture modeling was used to estimate spawner abundance and covariate effects based on spatially and temporally replicated count data obtained from sonar recordings. We detected at least one ATS on each sampling occasion and estimated a maximum daily spawner abundance between 35 and 55 individuals (95% credible interval) within the sampled area during the 2017 fall spawning season. Maximum discharge significantly affected ATS detection, and site average maximum depth significantly affected ATS abundance. Our results suggest that side‐scan sonar can be used as an alternative to traditional mark–recapture techniques for spawner abundance estimation. Routine sampling by using our methods will efficiently produce spawning run estimates and provide insight regarding the effects of environmental covariates on spawner abundance seasonally.

Effects of Hurricane Michael on Gulf Sturgeon in the Apalachicola River system, Florida

“…Furthermore, our reader's skill and experience in sonar image interpretation and our use of the same reader over time also likely contributed to the accuracy of the index counts. We are currently working to evaluate this monitoring approach in other Gulf Sturgeon systems; the results presented here add to a growing body of literature demonstrating the successful application of side‐scan sonar to enumerate large‐bodied sturgeons (Flowers and Hightower 2015; Hughes et al 2018; Vine et al 2019; Andrews et al 2020; Bunch 2020).…”

“…Nonetheless, the detection probability associated with the use of side-scan sonar to enumerate large-bodied sturgeons during nonmigratory periods in other large river systems has been estimated by other authors and is both relatively high (i.e., range = 0.78-0.84) and precise (95% CIs range from 0.69 to 0.90; Flowers and Hightower 2015;Hughes et al 2018). Vine et al (2019) estimated a lower detection probability during sturgeon migratory periods, yet counts remained similarly precise across replicates.…”

“…These estimates were derived from post hoc analyses of several types of data, including mark-recapture modeling, side-scan sonar counts, and acoustic telemetry. here add a growing body of literature demonstrating the successful application of side-scan sonar to enumerate large-bodied sturgeons (Flowers and Hightower 2015;Hughes et al 2018;Vine et al 2019;Andrews et al 2020;Bunch 2020). Surprisingly, despite the high mortality of adults, we observed a very strong age-1 year-class during the summer after Hurricane Michael (Figure 7), which confirms that young-of-the-year (age-0) fish that were present in fall 2018 survived the storm.…”

Monitoring fish using imaging sonar: Capacity, challenges and future perspective

“…Mark and recapture sampling is a standard method to estimate fish population or migrating run size (Hughes et al, 2018). Numerous reports have shown that side‐scan sonar can achieve comparable accuracy to the abundance estimates from the mark and recapture sampling method but takes much less effort (Fleming et al, 2018; Hughes et al, 2018; Vine et al, 2019). For example, Hughes et al (2018) found that side‐scan sonar yielded a narrower 95% confidence interval for white sturgeon abundance estimates with 75% fewer sampling days than the mark and recapture approach.…”

Effects of Training on Side-Scan Sonar Use as a Fish Survey Tool: A Case Study of Alligator Gar

“…First applied to assess aquatic habitat features in rivers Litts 2008, 2010), its use has expanded to serving as a fisheries survey instrument. Bollinger and Kline (2017) used SSS to successfully derive biomass estimates of fishes utilizing artificial reefs in the Gulf of Mexico, and Fleming et al (2018) and Vine et al (2019) used SSS to estimate the abundance and distribution of adult (i.e., > 1 m total length [TL]) alligator gar Atractosteus spatula and Atlantic sturgeon Acipenser oxyrinchus, respectively. The authors of these studies noted significant increases in the efficiency, versatility, and affordability of SSS when compared to more traditional fisheries sampling methods, indicating a likelihood for continued growth in use of the technology by management agencies.…”