Ancient DNA Analysis and Stable Isotope Ecology of Sea Turtles (Cheloniidae) from the Gold Rush-era (1850s) Eastern Pacific Ocean

Cyler Conrad,Marie Labonte,Michael Stoyka,Jeffrey A Seminoff,Emily Lena Jones,Laura Pagès Barceló,Brian M Kemp,Calandra Turner Tomaszewicz,Allen Pastron,Kale Bruner

doi:10.5334/oq.41

Abstract

Historical and archaeological evidence documents the importation of sea turtles from the eastern Pacific Ocean (Baja California) to California during the Gold Rush (1848–1855) and through the end of 19th century, but it is unknown whether these 19th century sea turtles foraged in similar ways to their modern counterparts. To identify the species of two Gold Rush-era sea turtle specimens recovered from archaeological deposits in San Francisco, California, we first analyze ancient DNA (aDNA). We then analyze carbon (δ13Ccol), nitrogen (δ15N), and hydrogen (δD) stable isotopes of bone collagen and carbon (δ13Cap) and oxygen (δ18Oap) stable isotopes of bone apatite to test if eastern Pacific sea turtle diets have changed over the past 160 years. Ancient DNA confirms that both archaeological specimens are green sea turtles (Chelonia mydas). The stable isotope values from the 19th-century specimens are statistically indistinguishable from the modern comparatives in both δ13Ccoland δ15N, suggesting that green sea turtle dietary intake has remained relatively unchanged since the 1850s. However, the values are unclear for δD and δ18Oapand require additional research. Social Media: Ancient DNA and isotopic analysis of 1850s sea turtles suggest stability in sea turtle foraging through time despite environmental changes.

Highlights

From the 1960s through the 1980s sea turtle (Cheloniidae) populations in the Eastern Pacific, especially those of green sea turtles (Chelonia mydas), declined in abundance to the point of near extinction (Cliffton et al 1982; Delgado-Trejo and Alvarado-Diaz 2012; Early-Capistrán et al 2017; P lotkin et al 2012; Seminoff et al 2012a)
As habitat change contributes to declining sea turtle abundance today (Hawkes et al 2009; Saba 2012) and known sea surface temperature changes have occurred since the mid-19th century in the eastern Pacific Ocean (Douglas 1980), it is possible that changes in turtle diet, reflecting the habitat and sea surface temperature changes, contributed to sea turtle population declines in the 20th century
Ancient DNA Both CA-SFR-186H and CA-SFR-195H specimens were identified as green sea turtles (Chelonia mydas) based on COI sequence (Table 1)

Summary

Introduction

From the 1960s through the 1980s sea turtle (Cheloniidae) populations in the Eastern Pacific, especially those of green sea turtles (Chelonia mydas), declined in abundance to the point of near extinction (Cliffton et al 1982; Delgado-Trejo and Alvarado-Diaz 2012; Early-Capistrán et al 2017; P lotkin et al 2012; Seminoff et al 2012a). As habitat change contributes to declining sea turtle abundance today (Hawkes et al 2009; Saba 2012) and known sea surface temperature changes have occurred since the mid-19th century in the eastern Pacific Ocean (Douglas 1980), it is possible that changes in turtle diet, reflecting the habitat and sea surface temperature changes, contributed to sea turtle population declines in the 20th century Research on this this topic has likely not occurred previously for two logistical reasons: a lack of credibly-dated historic zoological and zooarchaeological specimens; and difficulties in determining the correct taxon of those specimens, those from archaeological sites.

Methods

Results

Discussion

Conclusion