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Globally distributed, highly migratory marine megafauna present serious challenges to designing effective conservation strategies that target specific habitats and threats to population persistence.

Marine turtles exhibit several characteristics that make multiple population levels, life-history traits, and stages potentially appropriate targets for conservation (Wallace et al., 2010), including distinct feeding and breeding areas for adults, geographically separated ontogenetic habitats, and complex population structures (Bowen & Karl, 2007). Different threats that operate on various spatial scales can differentially affect the same marine turtle population, warranting distinct conservation actions. Although the International Union for the Conservation of Nature (IUCN) Red List provides conservation status assessments for marine turtle species at a global level, these listings belie regional variations in population sizes and trends (Wallace et al., 2010). This discrepancy has led the IUCN/SSC Marine Turtle Specialist Group (MTSG) to advocate for regional assessments at several scales below the species level that have been defined as biologically discrete population units (Seminoff & Shanker, 2008).

In a new paper, Bass, Anderson & De Silva (2011) applied the Key Biodiversity Area (KBA) approach to marine turtle nesting sites in Melanesia. As KBAs originally were developed for terrestrial species, highly migratory, widespread marine species, such as marine turtles, are questionable candidates for the KBA approach because their mere presence can trigger KBA status, despite the relative lack of importance of that area to the species' survival (Edgar et al. 2008). Perhaps unsurprisingly, then, Bass et al.'s (2011) initial application of generic KBA thresholds based on presence of IUCN Red List of Threatened Species Critically Endangered and Endangered species generated extremely high numbers of marine turtle KBAs within the region, a result that was far too inclusive for meaningful conservation. However, the authors then adjusted the thresholds to be more biologically relevant for marine turtle nesting distributions, and generated a subsequent list of KBAs that prioritized for established nesting sites with consistently higher numbers of nesting females.

This underscores that the most significant issue for the KBA approach to taxa like marine turtles is the population-level context of the analysis. Bass et al.'s (2011) identification of KBAs within Management Units (MUs), or separate breeding populations defined primarily by genetic distinctiveness (Moritz, 1994) that are considered functionally independent (i.e. exhibit distinct demographic processes) was of critical importance. MUs are recognized as logical targets for conservation efforts, so identifying KBAs within MU boundaries makes the process more applicable to informing existing conservation strategies in the broader Melanesia region. The lessons learned for migratory marine species KBA identification are the need to interpret criteria in the relevant population context, and to calibrate thresholds appropriately to generate meaningful recommendations.

Along the lines of delineation of marine turtle population segments, Wallace et al. (2010) recently introduced a multi-scaled, nested envelope framework for organizing marine turtle populations below the level of species but above the level of individual nesting populations, termed Regional Management Units (RMUs). RMUs integrate information from nesting sites, genetics, tag returns, satellite telemetry and other data to identify geographically defined and biologically discrete population segments for all marine turtle species. As such, these RMUs spatially integrate sufficient information to account for complexities in marine turtle population structures, and thus provide a flexible, dynamic framework for evaluating threats, highlighting data gaps, and assessing conservation status of marine turtles (Wallace et al. 2010).

The Bass et al. (2011) study is important particularly because it focuses attention on conservation priorities below the species level at biologically appropriate scales (i.e. nesting site and MUs), and thus it has potential for application to other regions. We recommend that future iterations of marine turtle KBAs use RMUs as the geographical and biological frame of reference within which KBAs should be identified. Further, feasibility of marine turtle KBAs in aggregation areas for feeding, breeding and ontogenetic life stages should be explored. The key is to account for population complexities and connectivity among sites and within regions. While much work remains, Bass et al. (2011) have made important progress in tailoring a data-driven, science-based prioritization framework (KBAs) to a widespread, migratory marine taxon.

References

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  2. References
  • Bass, D., Anderson, P. & De Silva, N. (2011). Applying thresholds to identify key biodiversity areas for marine turtles in Melanesia. Anim. Conserv. 14, 111.
  • Bowen, B.W. & Karl, S.A. (2007). Population genetics and phylogeography of sea turtles. Mol. Ecol. 16, 48864907.
  • Edgar, G.J., Langhammer, P., Allen, G., Brooks, T., Brodie, J., Crosse, W., De Silva, N., Fishpool, L.D.C., Foster, M., Knox, D.H., McCosker, J.E., McManus, R., Millar, A.J.K. & Mugo, R. (2008). Key biodiversity areas as globally significant target sites for the conservation of marine biological diversity. Aquat. Conserv.: Mar. Freshw. Ecosyst. 18, 969983.
  • Moritz, C. (1994). Defining ‘evolutionary significant units’ for conservation. Trends Ecol. Evol. 9, 373375.
  • Seminoff, J.A. & Shanker, K. (2008). Marine turtles and IUCN Red Listing: a review of the process, the pitfalls, and novel assessment approaches. J. Exp. Mar. Biol. Ecol. 356, 5268.
  • Wallace, B.P., DiMatteo, A.D., Hurley, B.J., Finkbeiner, E.M., Bolten, A.B., Chaloupka, M.Y., Hutchinson, B.J., Abreu-Grobois, F.A., Amorocho, D., Bjorndal, K.A., Bourjea, J., Bowen, B.W., Briseño-Dueñas, R., Casale, P., Choudhury, B.C., Costa, A., Dutton, P.H., Fallabrino, A., Girard, A., Girondot, M., Godfrey, M.H., Hamann, M., López-Mendilaharsu, M., Marcovaldi, M.A., Mortimer, J.A., Musick, J.A., Nel, R., Pilcher, N.J., Seminoff, J.A., Troëng, S., Witherington, B. & Mast, R.B. (2010). Regional Management Units for marine turtles: a novel framework for prioritizing conservation and research across multiple scales. PLoS One 5, e15465 (Online DOI: DOI: 10.1371/journal.pone.0015465).