Gulf Sturgeon
Gulf Sturgeon Annual Recruitment
AG Fox | NQ Hancock | JA Marbury| AJ Kaeser | DL Peterson
The Gulf sturgeon (Acipenser oxyrinchus desotoi) is an anadromous fish found in drainages of the Gulf coast from Louisiana to Florida and is federally listed as threatened under the Endangered Species Act. Estimates of abundance of adult Gulf sturgeon from several studies have been reported, but direct quantification of juvenile abundance has not been attempted—although such information regarding annual recruitment and juvenile population trends is critical. Our objectives were to quantify recruitment of Gulf sturgeon in the Apalachicola River in Florida by estimating age-1 juvenile abundance and to investigate their survival. During May–August in 2013–2018, we used entanglement gear to conduct a mark-recapture assessment of juvenile Gulf sturgeon. Using Huggins closed population models, we estimated that the Apalachicola River produces 28–210 age-1 juveniles annually (mean: 70 individuals [standard deviation 69.4]). Acoustic telemetry data collected from a subset of age-1 fish indicate that the study area was closed during sampling. We conservatively estimated overwinter survival on the basis of detections and recapture of age-2+ fish acoustically tagged at age 1. Survival varied among years from 33% to 90%. These results indicate that direct estimates of recruitment of Gulf sturgeon to age 1 are feasible, but it is difficult to determine whether this population is recruitment limited without similar data for other populations of Gulf sturgeon. DOI: 10.7755/FB.119.4.4
Our work on juvenile Gulf Sturgeon continues, with several ongoing studies into survival, fall-spawning, and the drivers of annual recruitment.
Effects of Hurricane Michael on Gulf Sturgeon
BT Dula | AJ Kaeser | MJ D'Ercole | CA Jennings | AG Fox
Gulf Sturgeon Acipenser oxyrinchus desotoi populations have undergone substantial declines since the start of the 20th century due to overfishing and habitat loss. A predicted increase in the frequency of major hurricanes, driven by climate change, presents an additional but poorly characterized threat to Gulf Sturgeon populations. In October 2018, Category 5 Hurricane Michael made landfall 40 km west of the Apalachicola River, causing a hypoxic event and an ensuing fish kill that included Gulf Sturgeon. We used acoustic telemetry, mark-recapture, and side-scan sonar data to examine migration behavior, and estimate Gulf Sturgeon abundance, mortality, and annual recruitment in the system before and after the storm. Within two days of landfall, we observed an early and rapid emigration response among tagged adults residing in lower portions of the river system, coinciding with declining dissolved oxygen levels; migration behavior returned to normal by the subsequent spring. The hurricane caused an acute mass mortality event – mortality of Gulf Sturgeon in October 2018 was 4–5 times greater than previous years. Several other independent metrics also indicate a major decline in Gulf Sturgeon abundance after the hurricane. Juvenile recruitment to age-1 post-storm was greater than five of the previous six years, indicating the hurricane did not cause a year class failure. These findings suggest that major hurricanes can impact the structure and abundance of Gulf Sturgeon populations, yet elements of resiliency including survival – facilitated by early emigration and refugia – and enhanced recruitment may aid in population recovery following such disturbances. DOI: 10.1002/tafs.10384
