Joseph E. Hightower

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.

Nature‐like fishways are engineered to be low maintenance, aesthetically pleasing, and able to pass a diversity of species. However, evaluations of nature‐like fishways are limited, especially on large rivers and for anadromous species. Therefore, we studied a nature‐like “rock arch rapids” rock ramp fishway constructed in 2012 at the most downstream of three locks and dams (LDs) on the Cape Fear River, North Carolina. We evaluated upstream fish passage effectiveness and time until passage through the LD‐1 (river kilometer [rkm] 97) fishway and via locking procedures at LD‐2 (rkm 149) and LD‐3 (rkm 186) from March to early July for three consecutive years, 2013–2015. We used stationary acoustic telemetry receivers to evaluate tagged anadromous American Shad Alosa sapidissima and Striped Bass Morone saxatilis and introduced potamodromous Flathead Catfish Pylodictis olivaris. For American Shad, raw upstream passage efficiency at the LD‐1 fishway was similar to that for LD passage via locking procedures in this and previous studies (53–65%), but passage rates were considerably lower for Striped Bass (19–25%). Duration downstream prior to upstream passage averaged 14.7 d for American Shad (SD = 10.2) and 11.6 d for Striped Bass (SD = 17.1). The raw upstream passage efficiency of Flathead Catfish at LD‐1 was variable (13–80%), and certain individuals passed multiple times in a season and spent extended durations downstream prior to passage (mean = 17.4 d; SD = 20.8), potentially foraging. The rock arch rapids LD‐1 fishway passed each species upstream in all years, but anadromous fish passage was delayed for some individuals and the fishway did not meet predetermined success criteria (80% passage efficiency), indicating that design modifications may be necessary to improve overall effectiveness.

We developed an integrated tagging model to estimate mortality rates and run sizes of Albemarle Sound – Roanoke River striped bass (Morone saxatilis), including (i) a multistate component for telemetered fish with a high reward external tag; (ii) tag return components for fish with a low reward external or PIT tag; and (iii) catch-at-age data. Total annual instantaneous mortality was 1.08 for resident (458–899 mm total length, TL) and 0.45 for anadromous (≥900 mm TL) individuals. Annual instantaneous natural mortality was higher for resident (0.70) than for anadromous (0.21) fish due to high summer mortality in Albemarle Sound. Natural mortality for residents was substantially higher than currently assumed for stock assessment. Monthly fishing mortality from multiple sectors (including catch-and-release) corresponded to seasonal periods of legal harvest. Run size estimates were 499 000–715 000. Results and simulation suggest increasing sample size for the multistate component increases accuracy and precision of annual estimates and low reward tags are valuable for estimating monthly fishing mortality rates among sectors. Our results suggest that integrated tagging models can produce seasonal and annual mortality estimates needed for stock assessment and management.

We simulated and evaluated multistate capture–recapture models to estimate mortality rates using telemetry data. Four field designs were considered: (A) fixed receivers to estimate total instantaneous mortality (Z), (B) manual searches to estimate instantaneous fishing (F) and natural (M) mortality, (C) fixed receivers combined with external high‐reward tags to estimate F and M, and (D) manual searches combined with external high‐reward tags to estimate M and fishing mortality rates associated with harvest (F_h) and catch‐and‐release death (F_cr) as well as the probability of death due to catch and release (α). Estimates generally appeared to be unbiased for a simulated study with five periods and releases of telemetered fish at the start of periods 1–4. Compared to estimating Z, larger sample sizes are needed to achieve reliable estimates of component rates (F and M). Estimates of component rates were more precise when that source of mortality was directly observed (M in design B, F in design C). The field design using fixed receivers and high‐reward tags should be especially useful in practice, because manual searches are not required to estimate F and M. Multistate models are useful for clarifying the connection between field observations and ecological processes. Reliable estimates of mortality rates, coupled with information on behavior, habitat use, and movement, make telemetry a highly valuable tool for improving fisheries management and stock assessment.