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.

Depredation rates and spatial overlap between Great Hammerheads and Tarpon in a recreational fishing hot spot

“…The data presented herein, in conjunction with the findings reported by Griffin et al. (2022a), demonstrate the repeated return of mature Tarpon to the same prespawning aggregation site in the Florida Keys. Although depredation causes direct mortality to individuals, there could also be sublethal behavioral consequences that affect the aggregation and the broader Tarpon population.…”

“…Beginning in May 2016, Tarpon were targeted on conventional spinning or fly-fishing gear and tagged internally with a coded acoustic transmitter (Model V16; 69 kHz; tag delay = 60-120 s; Innovasea) throughout the Florida Keys, coastal Florida, Georgia, and South Carolina as part of a study examining broadscale migratory patterns (Griffin et al 2018(Griffin et al , 2022a. A detailed description of the tagging procedure was provided by Griffin et al (2018).…”

“…In the spring, many adult Tarpon migrate to the Florida Keys from the Gulf of Mexico and southeastern U.S. Atlantic coasts (Griffin et al 2018;Luo et al 2020), forming large coastal prespawning aggregations. These migrations generally occur from April to June, when sea surface temperatures are between 26°C and 28°C (Griffin et al 2022a), and the majority of females complete spawning by July (Crabtree et al 1997). Prespawning aggregations are often the target of intense recreational fishing pressure since they occur close to shore, often in channels and passes (Sargeant 1991;Crabtree et al 1992).…”

Predator–prey landscapes of large sharks and game fishes in the Florida Keys

“…While both tarpon and permit are considered natural prey for these shark species (A. J. Adams, unpublished data; Castro, 2010; Roemer et al, 2016), recreational angling has exacerbated predation events when fish are exposed to capture stress, including extended fight times (Ault et al, 2007; Guindon, 2011). A common time for anglers to target both tarpon and permit in the Florida Keys is before and during spawning events when they aggregate in large schools ranging from hundreds to thousands of individuals in the spring and summer (tarpon: Luo et al, 2020; Griffin et al, 2022; permit: Brownscombe, Griffin, Morley, et al, 2019). Indeed, Holder et al (2020) documented that depredation rates of angled permit by bull and great hammerhead ( Sphyrna mokarran ) sharks exceeded 30%–50% of hooked fish at certain sites, and, most troubling, depredation rates were particularly high at permit spawning aggregation sites.…”

Globally coordinated acoustic aquatic animal tracking reveals unexpected, ecologically important movements across oceans, lakes and rivers

“…New movement data suggest a small proportion of individuals migrate between the Florida Keys northward as far as Virginia Beach, USA, distances far beyond those expected. One relatively small male (119 cm fork length) tagged in the Florida Keys in May 2017 was later detected in the near‐shore waters off Ocean City, Maryland, USA in July 2018, over 2000 km from where it was caught (Griffin et al 2022, Fig. 4e).…”