Movement patterns of juvenile Atlantic tarpon (Megalops atlanticus) in Brewers Bay, St. Thomas US Virgin Islands

Abstract

\n Background Atlantic tarpon (Megalops atlanticus) are a highly migratory species ranging along continental and insular coastlines of the Atlantic Ocean. Due to their importance to regional recreational and sport fisheries, research has been focused on large-scale movement patterns of reproductively active adults in areas where they are of high economic value. As a consequence, geographically restricted focus on adults has left significant gaps in our understanding of tarpon biology and their movements, especially for juveniles in remote locations where they are common. Our study focused on small-scale patterns of movement and habitat use of juvenile and subadult tarpon using acoustic telemetry in a small bay in St. Thomas, U. S. Virgin Islands. Results Four juvenile tarpon (80 – 95 cm FL) were tracked from September 2015 to February 2018, while an additional eight juveniles (61 – 94 cm FL) left the study area shortly after tagging and were not included in analysis. The four resident tarpon had >78% residency and average activity space of 0.76 km2 (range = 0.08-1.17 km2) within Brewers Bay (1.8km2). Their vertical distribution was <18 m depth with occasional movements to deeper water. Activity was greater during day compared to night, with peaks during crepuscular periods. During the day tarpon used different parts of the bay with consistent overlap around the St. Thomas airport runway and at night tarpon typically remained in a small shallow lagoon. However, when temperatures in the lagoon exceeded 30 °C, tarpon moved to cooler, deeper waters outside the lagoon. Conclusion Our results, although limited to only four resident fish, provides new baseline data on the movement ecology of juvenile Atlantic tarpon. We showed that juvenile tarpon had high residency within a small bay and relatively stable non-overlapping daytime home ranges, except when seasonally abundant food sources were present. Fine-scale acoustic tracking for over a year showed the effects of extreme environmental conditions on tarpon movement and habitat use. These observations highlight the need for more extensive studies of juvenile and subadult tarpon across a broader range of their distribution, and compare the similarities and differences in behavior among various size classes of individuals from small juveniles to reproductively mature adults.