Modeling and mapping isotopic patterns in the Northwest Atlantic derived from loggerhead sea turtles

Abstract

Abstract. Stable isotope analysis can be used to infer geospatial linkages of highly migratory species.Identifying foraging grounds of marine organisms from their isotopic signatures is becoming de rigueur as it has been with terrestrial organisms. Sea turtles are being increasingly studied using a combination of satellite telemetry and stable isotope analysis; these studies along with those from other charismatic, highly vagile, and widely distributed species (e.g., tuna, billfish, sharks, dolphins, whales) have the potential to yield large datasets to develop methodologies to decipher migratory pathways in the marine realm. We collected tissue samples (epidermis and red blood cells) for carbon (d 13 C) and nitrogen (d 15 N) stable isotope analysis from 214 individual loggerheads (Caretta caretta) in the Northwest Atlantic Ocean (NWA). We used discriminant function analysis (DFA) to examine how well d 13 C and d 15 N classify loggerhead foraging areas. The DFA model was derived from isotopic signatures of 58 loggerheads equipped with satellite tags to identify foraging locations. We assessed model accuracy with the remaining 156 untracked loggerheads that were captured at their foraging locations. The DFA model correctly identified the foraging ground of 93.0% of individuals with a probability greater than 66.7%. The results of the external validation (1) confirm that assignment models based on tracked loggerheads in the NWA are robust and (2) provide the first independent evidence supporting the use of these models for migratory marine organisms. Additionally, we used these data to generate loggerhead-specific d 13 C and d 15 N isoscapes, the first for a predator in the Atlantic Ocean. We found a latitudinal trend of

Age and size at maturation- and adult-stage duration for loggerhead sea turtles in the western North Atlantic

“…The variability observed in the current study is perhaps not surprising, as freshwater turtle population studies have revealed sex-specific, temporally varying growth patterns and maturation schedules, in addition to differences between geographically adjacent populations that diverge only somewhat in habitat and forage type (Gibbons 1967;Gibbons et al 1981;Frazer et al 1991a, b;Snover et al 2015). In comparison, movements and habitat use for the loggerhead sea turtle population considered in the current study encompass much of the North Atlantic Ocean basin (Bolten 2003;Ceriani et al 2014). Within this large region, dichotomies in migration and foraging strategies have been observed for both juveniles (McClellan and Read 2007;Mansfield et al 2009) and adults (Reich et al 2009) and individuals appear to exhibit a degree of consistency in resource use at different life stages (Avens et al 2003;McClellan et al 2010;Vander Zanden et al 2010).…”

“…Episodic increases in bottom water temperature in the Mid-Atlantic Bight (MAB) during the time period from 1958 to 2007 were recently found to correspond with significantly reduced growth and increased mortality for the surfclam (Spisula solidissima) population, particularly on the inner shelf (Narváez et al 2015). Given that the MAB provides important foraging habitat for large neritic juvenile and adult loggerhead sea turtles (Arendt et al 2012;Griffin et al 2013;Ceriani et al 2014), the potential for linkages between temperature changes, benthic productivity, and loggerhead growth dynamics merits further investigation.…”

Opportunism on the High Seas: Foraging Ecology of Olive Ridley Turtles in the Eastern Pacific Ocean

“…The isotopic data generated in this study adds to the growing body of work describing stable isotope baseline data for marine organisms in the eastern Pacific Ocean (Arthur et al, 2008;Olson et al, 2010;Ruiz-Cooley and Gerrodette, 2012;. A natural future direction would be to estimate marine isoscapes across taxa and trophic levels to provide a systematic framework for stable isotope ecological applications, as well as empirical studies of trophic dynamics (Somes et al, 2010;Ceriani et al, 2014;Vander Zanden et al, 2015;Magozzi et al, 2017;Kurle and McWhorter, 2017). A central repository of stable isotope data for sea turtles would support the advancement of this field and reduce duplication of efforts (Pauli, 2017).…”

Carry-over effects and foraging ground dynamics of a major loggerhead breeding aggregation

“…Thus, stable isotope ratios function as intrinsic markers that reflect the isotopic composition of the environment (location and food web) where the tissues were synthesized (Hobson and Norris 2008). Because geographic variation in stable isotope ratios in marine systems has been described only at very coarse scales (e.g., McMahon et al 2013), isotopic approaches have been validated with telemetry in several marine species such as sea birds (Jaeger et al 2010;González-Solís et al 2011) and sea turtles (e.g., Ceriani et al 2012Ceriani et al , 2014bPajuelo et al 2012b;Seminoff et al 2012).…”