Fish movements before, during, and after restoration of tidal flow through culverts in two southern Florida <scp>USA</scp> mangrove creeks

Abstract Many coastal roads lack adequate passageways for water to flow under them in tidal creeks. Ecosystem connectivity can be restored to upstream areas by installing new or larger culverts to improve flow. This study quantified movements of hardhead catfish ( Ariopsis felis ), grey snapper ( Lutjanus griseus ), and common snook ( Centropomus undecimalis ) before, during, and after restoration both upstream and downstream of a mangrove restoration site in southern Florida, USA. Fishes were tracked using acoustic telemetry with surgically implanted transmitters and an array of data loggers. There were few changes in movements on both short timescales (i.e., days) in response to specific events, and over longer timescales (i.e., weeks or months) during the pre‐ versus post‐restoration periods. Hardhead catfish and grey snapper both experienced 1–2 day changes in movement patterns coinciding with extreme hot and cold temperatures but almost no changes in response to discrete construction events. Grey snapper exhibited the largest deviation from their normal behaviour during Hurricane Ian, whereas hardhead catfish maintained regular movement patterns. Only 4% of fish conclusively passed through the new culverts including three hardhead catfish, and one snook. Grey snapper did not pass through culverts, but did use a larger activity space after restoration was completed, especially in habitats immediately downstream of restored flow. Practical Implication: Results demonstrate that downstream benefits to hydrological restoration can outweigh the upstream benefits for some organisms and can be used to justify conservation projects.