Movement, Microhabitat, Exploitation, and Management of Gulf of Mexico Sturgeon, Apalachicola River, Florida

Abstract

Gulf of Mexico sturgeon (Acipenser oxyrhynchus desotoi) in the Apalachicola River, Florida were tagged with radiotelemetry transmitters and conventional external tags from 1982 to 1984 to determine population size, movement, and exploitation rate, and identify the specific microhabitat for this subspecies. The population estimate for sturgeon larger than 450 mm in the upper river was 282 (181-645) fish in 1983. During summer, these sturgeon concentrated in the tailwater basin below Jim Woodruff Lock and Dam (JWLD). This summer microhabitat was characterized by a mean depth of 8.4 m (6.0-12.0 m; SD 1.3) and a mean velocity of 64.1 cm/second (60.0-90.0 cm/ second; SD 6.8). Sturgeon tagged in May-June and recaptured during July and September experienced weight losses between 4 and 15%. Fifteen of 17 radio-tagged fish migrated downstream from JWLD over a 40-day period (October-November) as the water temperature in late fall dropped to 18 C. All 15 fish entered the Brothers River and were located in areas that have a mean depth of 11.0 m (8.0-18.0 m; SD 1.9) and a velocity of 60.2 cm/second (58.0-75.0 cm/second; SD 1.8). Sturgeon vacated the Brothers River after an average of 12 days (mid-November) and proceeded downstream into either Apalachicola Bay or the Gulf of Mexico. The two largest sturgeon over-wintered below JWLD, demonstrating the capability for extended freshwater residency. In early April 1984, radio-tagged sturgeon were observed at the mouth of the Apalachicola River in Apalachicola Bay grouping before commencing upstream movement. On April 16, the first sturgeon was located back below JWLD. By July, all 13 sturgeon that migrated out of the river in fall 1983 were located back at JWLD, occupying the same summer microhabitat as the previous summer. Forty-three percent of the fish tagged in 1982 were recaptured during 1983 and all 13 radio-tagged fish returned from saltwater in 1984 to the Apalachicola River, indicating a strong homestream tendency. The estimated exploitation rate was 9.5%—mostly from incidental catches in shrimp trawls. Depth and velocity greatly influenced the river microhabitat selection by the sturgeon in the summer and fall.