Annual Spawning Migrations of Adult Atlantic Sturgeon in the Altamaha River, Georgia

Abstract

The Atlantic Sturgeon Acipenser oxyrinchus has declined throughout its range, and the species is now protected under the U.S. Endangered Species Act. Information on the timing and extent of spawning migrations is essential for the development and implementation of effective management and recovery strategies, yet this information is lacking for most populations. The objectives of this study were to document and identify temporal and spatial patterns in the seasonal movements and spawning migrations of Atlantic Sturgeon in the South Atlantic distinct population segment. A stationary array of acoustic receivers was used to monitor the movements of 45 adults in the Altamaha River system, Georgia, from April 2011 through March 2014. Telemetry data revealed that putative adult spawners exhibited two distinct patterns of upriver migration: a spring two‐step migration and a fall one‐step migration. During the spring two‐step migration, the adults appeared to stage in the upper Altamaha during the spring and early summer, before migrating to suspected spawning habitats in the Ocmulgee and Oconee tributaries during the fall. During the fall one‐step migration, fish entered the system in late summer and migrated directly upriver to suspected spawning habitats in the Ocmulgee and Oconee tributaries. Regardless of which pattern was used during the upstream migration, all fish returned downstream and left the system by early January. Although direct evidence of spawning has not yet been obtained, the telemetry and environmental data provide strong circumstantial evidence that Atlantic Sturgeon spawning in the Altamaha population occurs only during the fall months when water temperatures are less than 25°C. These findings further illustrate the clinal variation in the life history of Atlantic Sturgeon and highlight the need to manage the species as distinct population segments with regionally specific recovery goals. Received March 23, 2016; accepted September 25, 2016

Movement and Out‐Migration of Juvenile Atlantic Sturgeon in Georgia, USA

“…Across all three rivers in this study, 30.4% of tagged Atlantic Sturgeon were detected outside of their natal river after completing their transition to the MMJ stage during the winter after tagging (Table ). Given that Ingram and Peterson () found that spawning occurs from October to December in the Altamaha River, the results of this study suggest that RRJs began their initial transition to MMJs during the winter and early spring months immediately after reaching age 2. In all three study rivers, age‐1 RRJs dispersed downstream in their natal estuary during the winter.…”

“…Because tagged fish are only detected when they come within range of a receiver, it is not possible to ascertain whether an individual's lack of detections indicates mortality. Based on recaptures of transmittered fish in this and other studies from our research group (Ingram and Peterson ), surgical incisions healed completely within 1 month of capture. Of the 92 total fish tagged across 3 years in this study, 15 (16.3%) were last detected less than 1 month after being tagged.…”

“…). In southern rivers (e.g., the Altamaha River in Georgia), spawning only occurs in the fall (Ingram and Peterson ). Preferred spawning habitat is typically found in areas with strong currents and rocky substrate (Gilbert ).…”

Using Side‐Scan Sonar and N‐Mixture Modeling to Estimate Atlantic Sturgeon Spawning Migration Abundance

“…; Kahn et al. ; Ingram and Peterson ); therefore, only fish measured to be greater than or equal to this length were considered ATS. We also observed shadows created by marks in the sonar and looked for determining features of ATS (i.e., heterocercal tail, dorsal fin), but when estimating length for each sturgeon we measured the actual mark created by the sonar rather than the shadow produced by the mark (Flowers and Hightower , ).…”

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“…In northern populations, spawning occurs in the spring (Bain, 1997), whereas the results of recent studies indicate that at least some central and southern populations spawn in the fall (Hager et al, 2014;Smith et al, 2015;Ingram and Peterson, 2016). During the first several years of life, the young fish, known as river-resident juveniles (RRJs), occupy estuarine habitats near the freshwater-saltwater interface.…”