Movement of Paddlefish once past a lock‐and‐dam structure on the Alabama River

Abstract

Movement of fish past dams can be facilitated by dedicated fish passage structures, navigational locks, and crested spillways, with the efficacy of a passage structure depending strongly on the nature of the systems (height of the dam, flow rate, etc.) and the fish's behavior and swimming capability. However, once past a dam whether by the use of a mitigation structure or due to active translocation, fish encounter a different habitat upstream versus in the tailrace, potentially affecting their ability to continue their upstream migration. Here we had two objectives: First, we determined whether Paddlefish Polyodon spathula that successfully passed a structure continued on their upstream migration. Because assuring passage by tagged fish required that we move fish past the dam, our second objective was to determine whether translocated fish exhibited fallback behavior (downstream drift or movement post‐release that would compromise their continued migration). We used both active and passive telemetry to quantify post‐passage movements of tagged and translocated Paddlefish. Fish translocated above Claiborne Lock and Dam (CLD) exhibited up‐river movements once translocated and exhibited no fallback (i.e., downstream movement with delayed or no continuation upstream). Timing of movement relative to spawning periods did not influence initial fish movement or the likelihood of reaching the next upstream dam (Millers Ferry Lock and Dam; MFLD, approx. 100 river km upstream) within the first 30‐days of observation, but more fish tagged and released during the early pre‐spawning period made it within 4.83 km of MFLD (the location of our closest receiver below MFLD) than did fish from pre‐spawning or spawning periods. Fish released above CLD had a lower probability of being subsequently detected downstream of their release sites compared to fish released below CLD. Our findings support that Paddlefish will continue their upstream migration once past a structure despite changes in habitat.