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On 17 March 2010, the Draft Bi-National Recovery Plan for the Kemp’s Ridley Sea Turtle (Lepidochelys kempii) was released for public review and comment (the final plan was released in September 2011: <http://www.nmfs.noaa.gov/pr/pdfs/recovery/ kempsridley_revision2.pdf>). It showed that the outlook for recovery of the Kemp's ridley population was promising, based on demographic model projections made by the recovery team (see Caillouet 2010). However, the oil spill changed that outlook (Crowder & Heppell 2011), even though its actual impacts have not been fully evaluated. Oil spill-related Kemp’s ridley strandings occurred, and efforts were made to retrieve them; those that were still alive were cleaned, rehabilitated, and later released (<http:// www.nmfs.noaa.gov/pr/health/oilspill>). Evaluation of impacts of the oil spill and dispersants on the Kemp's ridley population will be ongoing, perhaps for many years. Further demographic modeling (Heppell et al. 2005, 2007; Crowder & Heppell 2011) could be essential to this evaluation, but the models, parameter estimates, and data time series must be updated and improved Caillouet (2010). Consideration also must be given to strandings that may have been related to shrimping in the northeastern Gulf of Mexico, prior to the temporary U.S. moratorium imposed on shrimping there in 2010.

Fortunately, four decades of conservation efforts and research laid a strong foundation for comparison of Kemp's ridley population status before and after the oil spill (TEWG 1998, 2000; Heppell et al. 2005, 2007; Crowder & Heppell 2011). Recent use of “what if?” demographic modeling suggested long-term detrimental effects on the Kemp’s ridley recovery trajectory (Crowder & Heppell 2011).

Reports by Gladys Porter Zoo, Brownsville, Texas (e.g., Peña 2010 and a similar 2009 report presented by Patrick Burchfield, Gladys Porter Zoo) and postings on the National Park Service’s Padre Island National Seashore web site (<http://www.nps.gov/pais/naturescience/kridley.htm>) showed substantial reductions in annual counts of nests (clutches laid) and hatchlings released in Tamaulipas, Mexico and Texas in 2010 as compared to 2009. For nesting beaches in Tamaulipas, there was a 37% reduction in nests and a 33.6% reduction in hatchlings in 2010 (Table 1). However, average number of hatchlings per nest in 2010 was 54 as compared to 52 in 2009.

Based on time series graphs, annual nests and hatchlings on Texas beaches were lower in 2010 than in 2009 (<http://www.nps.gov/pais/naturescience/kridley.htm>). Were these declines in Tamaulipas and Texas caused by impacts of the oil and dispersants, or by other influences? Part of the answer to this question will depend on whether the levels of effort directed toward counting nests, protecting eggs, and producing hatchlings in Tamaulipas and Texas in 2010 were the same, higher, or lower than in 2009. Counts of nests and hatchlings during the 2011 and subsequent nesting seasons in Tamaulipas and Texas will be very important in answering this question.

Assuming that levels of effort directed toward counting nests and hatchlings in Tamaulipas and Texas did not decline from 2009 to 2010, what then caused the substantial drops in nests and hatchlings in 2010? The oil spill occurred in the northeastern Gulf at the onset of the 2010 nesting season in the western Gulf, but nesting beaches in the western Gulf did not appear to be impacted. Therefore, for the oil spill to have reduced nesting in 2010, it would have had to kill large numbers of nesters directly or indirectly (e.g., by killing or tainting their prey), provide barriers preventing them from reaching nesting beaches in the western Gulf, or otherwise interfere with their ability to navigate to nesting beaches (see Putman et al. 2010). Alternatively, the decline in 2010 could represent a natural, alternate- year nesting oscillation, unrelated to the oil spill, or differences in environmental variables (e.g., temperature) during the nesting seasons of 2009 and 2010. Perhaps results from the 2011 nesting season will help answer such questions.

The oil spill could have had differential impacts on various life stages of Kemp’s ridley, thereby altering the population’s age structure and creating a potentially long-lasting and recognizable demographic mark. It might be recognizable in 2011 and in years to come. For example, the drop in hatchlings released in 2010 could make the 2010 cohort recognizable over many years. If this cohort can be followed over the years (e.g. by modeling its location in annual age structure), it could provide useful data for estimating age as sexual maturity, and perhaps other population vital statistics.

Any life stage-specific impacts of the oil spill likely would have been influenced by temporal-spatial distributions of the life stages in relation to temporal-spatial distribution of oil and dispersants (Collard & Ogren 1990; Putman et al. 2010). A “before spill-after spill” comparison of size distributions, or age distributions derived by transforming size to age using somatic growth curves, might reveal life stage-specific impacts if they occurred. There are many potential sources of information on sizes of Kemp’s ridleys in the population, including the Sea Turtle Stranding and Salvage Network (STSSN), conservation programs on nesting beaches, in-water studies, and by-catch investigations.

Table 1. Registered nests and hatchlings released on beaches in Tamaulipas in 2009 and 2010 (data from Gladys Porter Zoo annual reports for 2009 and 2010).

If age structure of the population was significantly altered by the oil spill or dispersants, Kemp’s ridley recovery could be delayed (Crowder and Heppell 2011), by reducing population momentum and altering reproductive value of the population (Heppell et al. 2007; Caillouet 2010). Continued cooperation and collaboration among research groups in universities, government agencies, and non-government organizations in assessing and comparing (pre- and post-spill) annual size distributions and age structure will be essential to evaluating impacts of the oil spill. Investigators should provide public access to collected data, to encourage and facilitate independent assessments.


BJORNDAL, K.A., B.W. BOWEN, M. CHALOUPKA, L.B. CROWDER, S.S. HEPPELL, C.M. JONES, M.E. LUTCAVAGE, D. POLICANSKY, A.R. SOLOW & B.E. WITHERINGTON. 2011. Better science needed for restoration in the Gulf of Mexico. Science 331:537-538.

CAILLOUET, C.W. Jr. 2010. Editorial: Demographic modeling & threats analysis in the draft 2nd revision of the bi-national recovery plan for the Kemp’s ridley sea turtle (Lepidochelys kempii). Marine Turtle Newsletter 128:1-6.

COLLARD, S.B. & L.H. OGREN. 1990. Dispersal scenarios for pelagic post-hatchlings sea turtles. Bulletin of Marine Science 47:233-243.

CROWDER, L. & S. HEPPELL. 2011. The decline and rise of a sea turtle: how Kemp’s ridleys are recovering in the Gulf of Mexico. Solutions 2:67-73.

HEPPELL, S.S., P.M. BURCHFIELD & L.J. PEÑA. 2007. Kemp’s ridley recovery: how far have we come, and where are we headed? In: P.T. Plotkin (Ed.). Biology and Conservation of Ridley Sea Turtles. Baltimore: The John’s Hopkins University Press, pp. 325-335.

HEPPELL, S.S., D.T. CROUSE, L.B. CROWDER, S.P. EPPERLY, W. GABRIEL, T.R. HENWOOD, R. MÁRQUEZ & N.B. THOMPSON. 2005. A population model to estimate recovery time, population size, and management impacts on Kemp’s ridley sea turtles. Chelonian Conservation & Biology 4:767-773.

PEÑA, L.J. 2010. Report on the Mexico/United States of America population restoration project for the Kemp’s ridley sea turtle, Lepidochelys kempii, on the coasts of Tamaulipas, Mexico 2010. Gladys Porter Zoo, Brownsville, Texas, 12 pp.

PUTMAN, N.F., T.J. SHAY & K.J. LOHMANN. 2010. Is the geographic distribution of nesting in the Kemp’s ridley turtle shaped by the migratory needs of offspring? Integrative and Comparative Biology 50: 305-314.

TURTLE EXPERT WORKING GROUP (TEWG). 1998. An assessment of the Kemp’s ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) sea turtle populations in the western north Atlantic. NOAA Technical Memorandum NMFS-SEFSC-409, 96 pp.

TURTLE EXPERT WORKING GROUP (TEWG). 2000. Assessment update for the Kemp’s ridley and loggerhead sea turtle populations in the western north Atlantic. NOAA Technical Memorandum NMFS- SEFSC-444, 115 pp.