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Adam G. Fox

Publications and source records attributed to Adam G. Fox.

5 recordsLinked to original sources
USGS2026

Seasonal and annual survival of acoustically tagged juvenile Gulf sturgeon in the Apalachicola River, Florida, USA

Gulf sturgeon Acipenser desotoi are anadromous fish that have undergone major population declines throughout their range. Habitat alteration and previous overharvest in commercial fisheries led to the species being listed as ‘threatened’ under the US Endangered Species Act in 1991. An accurate understanding of population dynamics, including survival, is necessary for monitoring population trends and recovery. Juvenile Gulf sturgeon are migratory within their natal river system; their survival is not well-studied, but their over-winter occupation of more saline habitat has been identified as a potential bottleneck to juvenile survival. Therefore, we estimated over-winter and annual survival of juvenile Gulf sturgeon in the Apalachicola River system (Florida, USA) using Cormack-Jolly-Seber models informed by acoustic telemetry data from 2014-2023. Seasonal apparent survival estimates ranged from 0.96 in the fall to 0.99 in the spring. Contrary to our expectation, results indicated that survival was high across all seasons with no notable difference in over-winter survival compared to other periods. We also estimated apparent annual survival to be 0.76 for juvenile Gulf sturgeon in the system. These findings suggest that over-winter juvenile mortality is not a major bottleneck to Gulf sturgeon population recovery within the Apalachicola River.

Florida↗
USGS2026

Climate change and water quality influence on juvenile Atlantic sturgeon aggregation in the Altamaha River, Georgia

In the summer, juvenile Atlantic sturgeon ( Acipenser oxyrinchus oxyrinchus ) are vulnerable to extreme water quality conditions (i.e., temperature, dissolved oxygen [DO], and salinity) in the estuaries they inhabit. The effects of climate change on Atlantic sturgeon are largely unknown, but it may exacerbate these water quality issues. We used a 20-year dataset from the Altamaha River estuary, Georgia, USA to fit negative binomial mixed-effects models describing the relationship between water quality and catch per net hour of juvenile Atlantic sturgeon. Water temperature and DO were significant positive predictors of catch; salinity and sampling year were significant negative predictors. The interaction between temperature and DO was also significant. Water temperature, salinity, and year were significant in explaining variability in catch. Our modeling results suggest that response to water quality depends on fish age. Next, we used global climate projections to construct future climate scenarios incorporating warming water and increased salinity. By coupling these predictions with catch models, we forecast juvenile Atlantic sturgeon catch as a proxy for distribution. Water temperature increases of 1–5 °C led to predicted catch increases of 5–24%, although this result may be influenced by aggregation behavior or sampling limitations at high temperatures. Salinity increases of 1–2 ppt led to 9–17% decreases in catch, suggesting that saltwater intrusion may limit future Atlantic sturgeon estuarine habitat availability. Our study combines a long-term dataset with a robust statistical modeling approach to offer some of the first insights into future climate change effects on juvenile Atlantic sturgeon’s southern nursery habitats.

Georgia↗
USGS2021

Regional-scale variability in the movement ecology of marine fishes revealed by an integrative acoustic tracking network

Marine fish movement plays a critical role in ecosystem functioning and is increasingly studied with acoustic telemetry. Traditionally, this research has focused on single species and small spatial scales. However, integrated tracking networks, such as the Integrated Tracking of Aquatic Animals in the Gulf of Mexico (iTAG) network, are building the capacity to monitor multiple species over larger spatial scales. We conducted a synthesis of passive acoustic monitoring data for 29 species (889 transmitters), ranging from large top predators to small consumers, monitored along the west coast of Florida, USA, over 3 yr (2016-2018). Space use was highly variable, with some groups using all monitored areas and others using only the area where they were tagged. The most extensive space use was found for Atlantic tarpon Megalops atlanticus and bull sharks Carcharhinus leucas . Individual detection patterns clustered into 4 groups, ranging from occasionally detected long-distance movers to frequently detected juvenile or adult residents. Synchronized, alongshore, long-distance movements were found for Atlantic tarpon, cobia Rachycentron canadum , and several elasmobranch species. These movements were predominantly northbound in spring and southbound in fall. Detections of top predators were highest in summer, except for nearshore Tampa Bay where the most detections occurred in fall, coinciding with large red drum Sciaenops ocellatus spawning aggregations. We discuss the future of collaborative telemetry research, including current limitations and potential solutions to maximize its impact for understanding movement ecology, conducting ecosystem monitoring, and supporting fisheries management.

Marine Ecology Progress Series↗