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

A species may partition its realized ecological niche along bionomic and/or scenopoetic axes due to intraspecific competition for limited resources. How partitioning manifests depends on resource needs and availability by and for the partitioning groups. Here we demonstrate the utility of analyzing short- and long-term stable carbon and nitrogen isotope ratios from imperiled marine megafauna to elucidate realized niche partitioning in these species. We captured 113 loggerhead (Caretta caretta) sea turtles at a high-use area near Crystal River, Florida, between 2016–2022, comprising 53 subadults, 10 adult males, and 50 adult females. Isotopic analyses indicated that loggerheads partition their realized ecological niche by life stage, along a scenopoetic axis. Most adults likely forage and reside in shallow areas of the study site, with most subadults displaying habitat switching between deeper locations to forage and shallower locations to rest. Some subadults, like adults, also forage a..., Capture surveys for sea turtles were conducted in the coastal waters of the Florida Big Bend between the mouths of the Crystal and Homosassa Rivers in Citrus County, Florida. Surveys were conducted approximately bi-monthly between January 2016 and February 2022 dependent on logistics and boating conditions (see Table S1). Sea turtles were spotted opportunistically from a vessel and captured using the “rodeo” method. Sighting and capture GPS locations were recorded using a Garmin GPSMAP. Captured turtles were brought on board the vessel and checked for Inconel flipper tags and passive integrated transponders (PIT). Tag numbers were recorded when already present and new flipper (National Band and Tag Company, Style 681) and PIT tags (Biomark, GPT12) were applied in the absence of old tags. Standard (nuchal notch to caudal tip) and minimum (nuchal notch to caudal notch) lengths were measured from each carapace using a tape measure (curved carapace length, CCL) and calipers (straight carapa...,