Age and growth of early‐life‐stage Atlantic tarpon (Megalops atlanticus) from the northcentral Gulf of Mexico

Abstract

Age and growth of early‐life‐stage Atlantic tarpon Megalops atlanticus collected from Mississippi coastal waters in the northcentral Gulf of Mexico (GOM) are described using otolith microstructure analysis. Tarpon leptocephali (n = 95, 16.0—27.8 mm standard length, LS) collected from June throughOctober 2013—2018, ranged in age from 22 to 43 days (mean = 30.9 ± 0.5 days). Leptocephalus somatic growth rates ranged 0.46—1.24 mm day−1 (mean = 0.76 ± 0.02 mm day−1), and leptocephalus otolith growth rates ranged 1.78—3.97 μm day−1 (mean = 2.58 ± 0.04 μm day−1). Growth rates were inversely correlated to leptocephalus age, indicating the shrinkage phase associated with leptocephalus metamorphosis. Juvenile tarpon (n = 358, 50—359 mm fork length, LF) were collected from August through December 2007—2018. Juveniles exhibited a positive allometric relationship (adjusted R2 = 0.99, P < 0.001) between length and mass. The age of 100 juveniles (71—277 mm LF) ranged from 76 to 174 days. Juvenile growth rate was estimated as 1.56 ± 0.11 mm day−1. Significant (P < 0.001) linear relationships were found between juvenile age and otolith metrics, including otolith mass (R2 = 0.81) and radius (R2 = 0.68). Evaluation of the backcalculated hatch dates suggests that specimens in the collection hatched from late May through mid‐September with slight peaks during July and August. A Rao's Spacing Test of Uniformity indicates the presence of significant lunar periodicity in leptocephalus hatch dates (n = 95, U = 250.1, P < 0.05), with 50% of the leptocephali hatched within 5 days (before or after) of the full moon. This study fills critical gaps in the scientific knowledge of tarpon and provides estimates of early‐life‐history metrics for an iconic game fish at the northernmost extent of its GOM range.

The effects of temperature and salinity on the blood chemistry and survival of juvenile Atlantic tarponMegalops atlanticus

“…Wild juvenile tarpon ( n = 50) were collected from Mississippi Sound tidal sloughs in September and October 2020 using monofilament cast nets (0.9–3.0 m radius, 0.9–1.6 cm mesh). Salinity in these habitats is variable and known to range from <1 to >30 ppt (Graham et al ., 2021). The specimens were immediately placed in a 45 l holding container with aerated water from the collection sites, transferred to an aquaculture facility located at the University of Southern Mississippi, Gulf Coast Research Laboratory, then transported to Mississippi State University's South Farm Aquaculture Facility for experimentation.…”

Effects of nocturnal illumination on fitness-related traits of the New Zealand common triplefin (Forsterygion lapillum)

“…Some fish spawn on a seasonal or daily (circadian) rhythm, using changes in light:dark ratios and temperature to initiate development to sexual maturity and reproduction (Koger et al, 1999). Both seasonal and lunar cycles may influence reproductive timing concurrently (Bushnell et al, 2010, Graham et al, 2021. Some fish spawn year-round in regions where environmental conditions remain relatively consistent but still rely upon environmental cues to trigger reproduction at optimal times (Taylor, 1984).…”