. CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/238956 doi: bioRxiv preprint first posted online Dec. 23, 2017; 3 Abstract 30 Sea turtles are a keystone species and are highly sensitive to changes in their environment, 31 making them excellent environmental indicators. In light of environmental and climate changes, 32 species are increasingly threatened by pollution, changes in ocean health, habitat alteration, and 33 plastic ingestion. There may be additional health related threats and understanding these threats is 34 key in directing future management and conservation efforts, particularly for severely reduced 35 sea turtle populations. Hawksbill turtles (Eretmochelys imbricata) are critically endangered, with 36 those in the eastern Pacific Ocean (Mexico-Peru) considered one of the most threatened sea turtle 37 populations in the world. This study establishes baseline health parameters in hematology and 38blood biochemistry as well as tested for heavy metals and persitent organic pollutants in eastern 39Pacific hawksbills at a primary nesting colony located in a mangrove estuary. Whereas 40 hematology and biochemistry results are consistent with healthy populations of other species of 41 sea turtles, we identified differences in packed cell volume, heterophils and lympohcyte counts, 42and glucose when comparing our data to other adult hawksbill analysis (1), (2), (3). Our analysis 43 of heavy metal contamination revealed a mean blood level of 0.245 ppm of arsenic, 0.045 ppm of 44 lead, and 0.008 ppm of mercury. Blood levels of persistent organic pollutants were below the 45 laboratory detection limit for all turtles. Our results suggest that differences in the feeding 46 ecology of eastern Pacific hawksbills in mangrove estuaries may make them less likely to 47 accumulate persistent organic pollutants and heavy metals in their blood. These baseline data on 48 blood values in hawksbills nesting within a mangrove estuary in the eastern Pacific offer 49 important guidance for health assessments of the species in the wild and in clinical rehabilitation 50 facilities, and underscore the importance of preventing contamination from point and non-point 51 sources in mangrove estuaries, which represent primary habitat to hawksbills and myriad other 52 marine species in the eastern Pacific Ocean. 53