Global conservation priorities for marine turtles

Abstract

Where conservation resources are limited and conservation targets are diverse, robust yet flexible priority-setting frameworks are vital. Priority-setting is especially important for geographically widespread species with distinct populations subject to multiple threats that operate on different spatial and temporal scales. Marine turtles are widely distributed and exhibit intra-specific variations in population sizes and trends, as well as reproduction and morphology. However, current global extinction risk assessment frameworks do not assess conservation status of spatially and biologically distinct marine turtle Regional Management Units (RMUs), and thus do not capture variations in population trends, impacts of threats, or necessary conservation actions across individual populations. To address this issue, we developed a new assessment framework that allowed us to evaluate, compare and organize marine turtle RMUs according to status and threats criteria. Because conservation priorities can vary widely (i.e. from avoiding imminent extinction to maintaining long-term monitoring efforts) we developed a "conservation priorities portfolio" system using categories of paired risk and threats scores for all RMUs (n = 58). We performed these assessments and rankings globally, by species, by ocean basin, and by recognized geopolitical bodies to identify patterns in risk, threats, and data gaps at different scales. This process resulted in characterization of risk and threats to all marine turtle RMUs, including identification of the world's 11 most endangered marine turtle RMUs based on highest risk and threats scores. This system also highlighted important gaps in available information that is crucial for accurate conservation assessments. Overall, this priority-setting framework can provide guidance for research and conservation priorities at multiple relevant scales, and should serve as a model for conservation status assessments and priority-setting for widespread, long-lived taxa.

Figure 1. Conservation priority portfolio approach to displaying and interpreting paired risk (i.e. population viability characteristics) and threats scores (i.e., direct and indirect anthropogenic impacts), for marine turtle RMUs (see Table S3 for RMU codes).

The four categories are: High risk-High threats, High risk-Low threats, Low risk-Low threats, Low risk-High threats; see Methods for more details on portfolio categories. RMUs were also classified as critical data needs if data uncertainty indices for both risk and threats ≥1 (denoting high uncertainty). Vertical and horizontal bars associated with each paired score represent the data uncertainty index; RMU IDs in red denote critical data needs (see Methods for details on how this was calculated). Where multiple RMUs have identical scores, RMU IDs are listed together, separated by commas. NOTE: C. mydas, Northeast Indian Ocean RMU was not plotted due to excessive data deficient scores.

Figure 2. Conservation priority portfolio categories for RMUs of each marine turtle species.

(A) loggerheads (Caretta caretta), (B) green turtles (Chelonia mydas), (C) leatherbacks (Dermochelys coriacea, (D) hawskbills (Eretmochelys imbricata), (E) Kemp's ridleys (Lepidochelys kempii), (F) olive ridleys (Lepidochelys olivacea), (G) flatbacks (Natator depressus). RMUs were classified as critical data needs if the data uncertainty indices for both risk and threats ≥1 (denoting high uncertainty), and are outlined in red. Hatched areas represent spatial overlaps between RMUs. The brown area in Fig. 2B highlights an overlap of four RMUs, while the grey area in Fig. 2B represents the C. mydas Northeast Indian Ocean RMU, which had excessive data deficient scores and was not included in overall calculations and categorization.

Figure 3. Risk (i.e. population viability) scores (A) and threats (i.e. direct and indirect anthropogenic impacts) scores (B) with data uncertainty indices by ocean basin.

Symbols bordered in red are scores with accompanying data uncertainty indices that exceed 1 (see Methods for details). Refer to Table S3 for list of RMU IDs. NOTE: C. mydas Northeast Indian Ocean RMU was not plotted due to excessive data deficient scores.

Figure 4. Conservation status assessments of marine turtle RMUs in regions recognized by the IUCN Marine Turtle Specialist Group (MTSG).

(A) number of RMUs that occur within MTSG regions; (B) most prevalent conservation priority portfolio category (see Methods and Fig. 1 for descriptions) for RMUs that occur within each region.