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

AbstractObjectiveGulf 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.MethodsWe 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.ResultWithin 2 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 four to five times greater than that in previous years. Several other independent metrics also indicate a major decline in Gulf Sturgeon abundance after the hurricane. Juvenile recruitment to age 1 after the storm was >5 of the previous 6 years, indicating the hurricane did not cause a year‐class failure.ConclusionThese 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.