Coupling acoustic tracking with conventional tag returns to estimate mortality for a coastal flatfish with high rates of emigration

Abstract

The addition of acoustic telemetry to conventional tagging studies can generate direct estimates of mortality and movement rates to inform fisheries management. We applied a combined telemetry and tag-return design to southern flounder (Paralichthys lethostigma), a coastal flatfish that demonstrates limited movements within estuarine habitats coupled with extensive ontogenetic migrations that present unique challenges for estimating mortality rates. The fates of acoustically and conventionally tagged fish were followed during 2014–2016 to estimate annual rates of fishing mortality (F), natural mortality (M), and estuarine emigration (E). Multistate models estimated southern flounder annual F for each of the 3 years at two spatial scales (New River estuary F = 0.49–1.61; North Carolina coast F = 0.36–0.72). Annual rates of emigration were high (E = 1.06–1.67), and direct estimation of this source of loss considerably improved mortality estimates. The model estimated natural mortality as a constant annual rate (M = 0.84), which was similar in magnitude to life-history-based estimates for similar age groups. By accounting for unique behavioral attributes in the study design, the application of multistate tagging models provided robust estimates of mortality and emigration rates for a valuable coastal fishery resource that will inform future efforts to achieve yield and conservation goals.

Using Acoustic Telemetry to Estimate Weakfish Survival Rates along the U.S. East Coast

“…For detailed methods, refer to Manderson et al (2014) for the Navesink River, New Jersey, and Turnure et al (2015aTurnure et al ( , 2015b for Great Bay, New Jersey. Array placement and estuarine site descriptions for Delaware Bay are provided by Kilfoil et al (2017), those for the New River of North Carolina are provided by Scheffel et al (2020), and those across multiple receiver arrays deployed from Florida to Maine are provided by research groups participating in the Atlantic Cooperative Telemetry Network Web site based at Delaware State University (www.theactnetwork.com). Our methods are primarily focused on NCSU-telemetered Weakfish in Delaware Bay, the New River, and Bogue Sound, and any major methodological differences between NCSU efforts and the Navesink River and Great Bay studies are highlighted (Table 1).…”

“…(), those for the New River of North Carolina are provided by Scheffel et al. (), and those across multiple receiver arrays deployed from Florida to Maine are provided by research groups participating in the Atlantic Cooperative Telemetry Network Web site based at Delaware State University (http://www.theactnetwork.com). Our methods are primarily focused on NCSU‐telemetered Weakfish in Delaware Bay, the New River, and Bogue Sound, and any major methodological differences between NCSU efforts and the Navesink River and Great Bay studies are highlighted (Table ).…”

“…New River Weakfish were tracked with a 76‐receiver array in 2014 (Scheffel et al. ), and Delaware Bay Weakfish were tracked with an approximately 54‐receiver array (Kilfoil et al. ).…”

“…Delaware Bay fish were captured using hook and line or beach seining (27-× 1.8-m seine with 25-mm mesh). New River Weakfish were tracked with a 76-receiver array in 2014 (Scheffel et al 2020), and Delaware Bay Weakfish were tracked with an approximately 54-receiver array (Kilfoil et al 2017). Of all NCSU-released fish, only 12 New River Weakfish were tagged with a single, 63.5mm-long, wire-core internal anchor tag (FM-95W; Floy Tag and Manufacturing, Inc., Seattle).…”

“…If all fish had received high-reward external tags, additional information regarding catch-and-release and fishing mortalities could have been acquired (Kerns et al 2016; Hightower and Harris 2017), a condition that was only applicable to some of our telemetered Weakfish. Many of our study estuaries were spatially large and had porous gates, which did not give us the ability to confidently assign a fate for 21% of all released fish that disappeared within the array; therefore, we were unable to confidently subtract emigration from φ to estimate true survival (Scheffel et al 2020). In addition, emigration was consistent in spring and fall time periods, so it was not possible to choose φ estimates from time periods with no emigration to estimate emigration by difference from φ with emigration.…”