Seasonal variation in the phenology of Atlantic tarpon in the Florida Keys: migration, occupancy, repeatability, and management implications

Abstract

Atlantic tarpon Megalops atlanticus are important mesopredators in the western Atlantic Ocean, and the focus of a popular recreational fishery that targets them throughout their annual migration in the Gulf of Mexico and southeastern USA. Using 4 years of acoustic telemetry data, we quantified the seasonal variation in phenology of arrival and departure, and occupancy for subadult and adult M. atlanticus in the Florida Keys, USA. While detection profiles of subadult M. atlanticus (n = 11) varied in residency and dispersal patterns, all adult M. atlanticus detection profiles (n = 47) exhibited seasonal residency. The median spring-summer residence period of adult M. atlanticus ranged from 40 to 60 d, with a mean of 51 d across years. At the individual level, repeatability in the timing of arrival and duration were high across years, suggesting that photoperiod may be an important migratory cue. Further, the repeatability in the timing of arrival to the Florida Keys for individuals was not associated with sea surface temperature (SST). At the population level, residency corresponded with the spawning season, with the majority of adult M. atlanticus arriving in April once SST reached 26°C, and then departing in June (27-29°C). Highest occupancy probabilities for adult M. atlanticus occurred in May (26-28°C) and lowest between August and October. Large aggregations of M. atlanticus that occur during the spawning season (April-June) are potentially vulnerable to the effects of habitat degradation and angling-related mortality and behavioral changes. These data on M. atlanticus phenology provide insights for implementing science-based strategic management plans.