Health and nutrition of loggerhead sea turtles (Caretta caretta) in the southeastern United States

Abstract

Loggerhead sea turtles (Caretta caretta) are opportunistic carnivores that feed primarily on benthic invertebrates and fish. Sea turtle rehabilitation requires provision of a species‐specific, balanced diet that supplies nutrition similar to that of a wild diet; this can be challenging because free‐ranging loggerheads’ diets vary depending on their life stage and geographic location, with predominant prey species dictated by local availability. The goal of this study was to better understand the nutritional needs of subadult and adult loggerheads in rehabilitation. This was accomplished by conducting a retrospective survey of stomach contents identified during gross necropsy of 153 deceased loggerheads that stranded in coastal Georgia, USA. A total of 288 different forage items were identified; the most frequently observed prey items belong to the subphylum Crustacea (N = 131), followed by bony fish (Osteichthyes; N = 45), gastropod mollusks (N = 40), bivalve mollusks (N = 23), and Atlantic horseshoe crabs (Limulus polyphemus; N = 15). The proportions of certain prey items differed significantly with turtle size; adult turtles ate proportionately more gastropods (p = 0.001), and subadults ate proportionately more fish (p = 0.01). Stomach contents information was used to determine common local prey items (blue crab, cannonball jellyfish, horseshoe crab, whelk), which were evaluated for nutritional content. Additionally, we compared hematology and plasma biochemistry profiles (including proteins, trace minerals, and vitamins) between four cohorts of loggerhead turtles, including free‐ranging subadults and adults, nesting females, and loggerheads undergoing rehabilitation. This information was applied to inform a regionally specific, formulated diet for tube feeding, and a supplement containing vitamins and minerals for captive loggerheads, to more closely approximate the nutritional content of their natural diet. Assessing the regional and temporal variability in loggerhead diets is an important component in their effective conservation because resultant data can be used to help understand the impacts of environmental perturbations on benthic food webs.

Fine-scale intraspecific niche partitioning in a highly mobile, marine megafauna species: implications for ecology and conservation

“…for use in isotopic mixing models) do not exist from the study site. Prior studies of gut contents from stranded loggerheads on the Atlantic coast of the southeastern United States indicated that subadults might primarily consume fish before switching to a gastropod-dominated diet as adults [ 91 , 92 ]. However, existing isotopic forage item data from the Gulf of Mexico [ 93 ] suggest that most fishes' δ 15 N is higher (mean = 10.64 ± 2.36 ‰ s.d.)…”

Capture vulnerability of sea turtles on recreational fishing piers

“…Additionally, although the genetic origin of juvenile green turtles captured on the pier is unknown, green turtle nesting has increased exponentially in Florida in recent years (Ceriani et al, 2019) while loggerhead nesting has remained stable (Ceriani et al, 2019) and Kemp’s ridley nesting appears to have declined (Caillouet et al, 2018; Gallaway et al, 2016). Capture of Kemp’s ridleys and loggerheads on recreational fishing piers may not be unexpected considering that the bait typically used by recreational anglers (e.g., fish, shrimp) are known diet items of these species (Molter et al, 2021; Ramirez et al, 2020; Shaver, 1991). However, capture of green turtles on the NAV pier was unexpected as juvenile green turtles in neritic habitats are generally considered herbivores (Williams et al, 2014).…”