Historically, acoustic telemetry studies tracking movement of aquatic organisms have lacked rigorous, long-term evaluations of detection range. The purpose of the present study was to identify potential sources of variability in long-term acoustic telemetry data, focusing specifically on environmental variability. The study was conducted for 15 mo in Gray's Reef National Marine Sanctuary, Georgia, USA, using 2 submersible Vemco VR2W hydrophone receivers and 2 stationary range test transmitters (controls). Tag detections (±1 SE) decreased from 54.2 ± 2.5 to 11.4 ± 0.5 detections d −1 as transmission distance increased from 100 to 300 m. Detections varied seasonally (likely due to stratification), with the direction of flood and ebb tidal currents (12.4 h cycle), and with tidal current speed (6.2 h cycle). Tides explained up to 92% of the short-term variability in hourly detection data. Detections also increased or decreased during episodic weather events depending on the season and type of event. These results suggest that stationary control tags are useful for characterizing variability in sound transmission in open water marine acoustic telemetry studies.

Atlantic sturgeon Acipenser oxyrinchus oxyrinchus were listed as 5 distinct population segments under the US Endangered Species Act in 2012. At that time, only 2 abundance estimates of the Atlantic sturgeon population were available: one from commercial fisheries landings in the Hudson River ending in 1995 and one from mark-recapture research in the Altamaha River, Georgia, in 2004 and2005. In 2013, we verified spawning in the York River, Virginia, system and initiated a multiple-year mark-recapture study focusing on spawning-run abundance. We used a Schumacher-Eschmeyer model and Program CAPTURE to produce estimates of annual spawning abundances from 2013 to 2018. The Schumacher-Eschmeyer estimates of spawning-run abundance with 95% confidence intervals from 2013 to 2018 were 75 (31−190), 157 (115−244), 184 (150−238), 222 (137−576), 212 (157−328), and 145 (89−381), respectively. Because Atlantic sturgeon do not spawn every year, the trends in estimates do not suggest a recovering or declining population, but rather variability in proportions of the adult population that return to spawn each year. The estimates produced in Program CAPTURE using M 0 (null), M t (Chao M t and Darroch), M h (Chao M h and Jackknife), and M th (Chao M th ) models all produced similarly reliable estimates. The models that consider a behavioral response to initial capture (M b , M bh , and M tb ) failed to produce reliable estimates for these data, likely because as an endangered species, the dataset for Atlantic sturgeon was sparse. The Jackknife equation (model M h ) was the most precise every year with reliable accuracy and therefore is recommended.

A sex ratio is one of the most basic demographic estimates produced because it is easy to collect and provides deeper insight into population dynamics for the species under consideration. For inconsistently or intermittently breeding species, the breeding sex ratio (BSR) and adult sex ratio (ASR), both reported as the proportion of males, can be quite different. The entire adult population of some wide-ranging species may never be present and capable of being sampled in the same time and place. We explore equations to indirectly estimate ASRs and annual abundance estimates from annual surveys of BSRs. We sampled Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) from 2013 through 2019 and implanted acoustic transmitters during those sampling periods. The BSRs calculated during capture from 2015 through 2019 were 0.65, 0.75, 0.69, 0.75, and 0.64 each year. Relying on telemetry detections from the lowest potential spawning region, the expected BSRs in the same years were 0.64, 0.74, 0.67, 0.69, and 0.60, suggesting telemetry is a reliable and passive way to estimate BSR. The BSRs were used to indirectly estimate ASR to be approximately 0.51 (95% confidence limits of 0.43-0.58). Estimates of annual abundance derived through sex ratios matched previously published mark-recapture estimates of the same breeding population, but provide additional detail on abundances of each sex. For populations where BSR is more accessible, ASR and abundance estimates can be estimated with capture data and acoustic telemetry.

Survival estimates of animal populations provide managers with critical information on productivity, population stability, and demography. Telemetry-based survival estimates can be obtained remotely. The Atlantic sturgeon Acipenser oxyrinchus oxyrinchus is a wide-ranging species whose populations overlap along the East Coast of North America, complicating survival estimation. The objective of this study was to estimate apparent annual survival of the York River population using a Cormack-Jolly-Seber model. In this study, 36 males and 24 females were telemetered and monitored between 2013 and 2019. We considered the fit of a variety of models, selecting the best fit using Akaike’s information criterion. The optimal model estimated survival in seasonal increments and detection probability by sex in monthly increments. Five transmitters failed to leave the river and another 3 stopped being detected within 21 mo, but of those, recapturing fish confirmed 2 had been lost and 3 were technological failures (12.8% of 39 recaptured). Apparent adult annual survival was estimated to be 99.2% (95% CL: 97.9-99.7%). Addressing sex-specific detection probability and failed transmitters while including a length covariate for each individual produced higher survival estimates than previously reported studies of Atlantic sturgeon. Four males and one female appear to have died, with the location of last detection for 4 of the suspected mortalities in shipping channels near the mouth of the Chesapeake Bay, suggesting managers should focus on this area of increased risk. Such high survival estimates of the adult stage suggest Atlantic sturgeon survival may be more similar to other long-lived, late-maturing animal species than to most other short-lived fish species.