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

Frontiers in Marine Science

Steven D. Gaines¹  Lindsey E. Peavey¹  Karen E. Arthur²  Brian N. Popp²  Robert L. Pitman³  Jeffrey A. Seminoff³  Shaleyla Kelez⁴ 

[1] Bren School of Environmental Science and Management, University of California, Santa Barbara, Santa Barbara, CA, United States;Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI, United States;National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA, United States;ecOceanica, Lima, Peru;

关键词: amino acid compound specific isotope analysis;    niche area;    trophic position;    oceanic food webs;    olive ridley;    Lepidochelys olivacea;   

DOI  :  10.3389/fmars.2017.00348

来源: DOAJ

【 摘 要 】

Stable isotopic compositions in animal tissues have been widely used to gain insight into trophic dynamics, especially of mobile aquatic predators whose behavior and dietary preferences are difficult to directly measure. Olive ridley sea turtles (Lepidochelys olivacea) range across >3 million km2 of the tropical and subtropical eastern Pacific Ocean and their trophic ecology in open ocean areas has not yet been adequately described. Individuals feed within biogeographic regions where varying nutrient cycling regimes result in phytoplankton with distinct δ13C and δ15N values that are assimilated by the turtles. We sampled 346 turtles at-sea between 2003 and 2009 and used bulk tissue (n = 346) and amino acid compound specific isotope analysis (AA-CSIA, n = 31) to empirically support the conventional understanding that olive ridleys are omnivores. Bulk δ15N values did not significantly vary with carapace length, a proxy for age, or with putative sex of adults. We therefore hypothesize that trophic position (TP) does not vary across age or sex. In line with other isotopic studies of this biogeographic scale in the same region, we observed a trend of bulk tissue 15N enrichment with increasing latitude. Using AA-CSIA to account for δ15N baseline shifts among food webs (space), we estimated the TP of adult foragers using two methods. We found that across their eastern Pacific range, olive ridley δ13C and δ15N niche area varied, but median TP of adults remained constant (~3.1). Using a two-amino acid TP estimation method, we detected a small but notable elevation of TP for olive ridleys on the Costa Rica Dome. This study underscores the value of large-scale in-water olive ridley sea turtle research across oceanic foraging habitats to confirm or challenge anecdotal understanding of trophic roles, susceptibility to environmental change, and critical habitats. Further, it improves our understanding of why this species is now abundant in the eastern Pacific Ocean. A prey generalist with plenty of suitable foraging habitat can recover from the brink of extinction despite the presence of major threats. However, such foraging characteristics may require dynamic open ocean management approaches to meet conservation objectives if threats persist and/or increase.

【 授权许可】

Unknown