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During Turtle Expert Working Group (TEWG) deliberations and for several months thereafter, some of its members raised questions about changes made from time to time in the historical data on numbers of Kemp’s ridley (Lepidochelys kempii) nests laid at Rancho Nuevo, Tamaulipas, Mexico, and vicinity for years 1978-1995 (Turtle Expert Working Group 1998). Such changes were important to stage-based modeling, since changes in data resulted in different model-estimated rates of recovery, “post-1990” effect, stage-based mortality rates, and time required to achieve downlisting criteria specified in the Kemp’s ridley recovery plan (US Fish and Wildlife Service and National Marine Fisheries Service 1992).

Two recent articles in Marine Turtle Newsletter further demonstrate an unresolved problem of apparent changes in the historical record of numbers of nests at Rancho Nuevo (by “changes,” I am not referring to the expected updates made by adding new data each year). Marquez-M. et al.. (1996) presented a graph (their Figure 1) of numbers of nests at Rancho Nuevo for years 1966-1977 that appears quite different from that in Figure 2 of Márquez et al.. (1999) for the same period. Perhaps Figure 2 in Márquez et al. (1999) represents estimated numbers of nests for 1966-1977, while Figure 1 in Marquez-M. et al. (1996) represents actual counts for the same years, but if this is true the methods of estimation were not elaborated. It is also possible that Figure 2 in Márquez et al. (1999) represents corrections of Figure 1 in Marquez-M. (1996), but this was not mentioned in the later article. Although the stage-based model was not fitted to this earlier part of the data series (Turtle Expert Working Group 1998), it seems reasonable to question changes in historical data that appear without explanation, especially since the historical time series has been used repeatedly to gauge Kemp’s ridley population status and changes over the years.

Interestingly, Márquez et al. (1999) alluded to a similar problem with the estimated 40,000-turtle arribada in 1947, by saying “The methods of estimation have recently come into question.” Indeed, some TEWG members suggested that the methods used to estimate that arribada from the Andres Herrera film (Hildebrand 1963) be revisited to determine whether or not they were appropriate and the estimate correct. An image analysis of sequential frames in the Herrera film, supported by explicitly stated assumptions and methodology, might be a reasonable approach to re-estimating the size of that arribada. Frazer (1986) fitted a linear regression to logarithms of estimated numbers of Kemp’s ridleys that nested at Rancho Nuevo in years 1978-1985. When he extended the line backward to the late 1940s the number of nesters was around 3,000. Is it possible the 40,000-turtle arribada was grossly overestimated? Such questions are important in the contexts of current concerns about arribada estimation methodology (Valverde 1999) and Kemp’s ridley recovery goals (US Fish and Wildlife Service and National Marine Fisheries Service 1992).

Questioning changes in historical nesting data for Kemp’s ridley is not a trivial or academic pursuit. The methods used to generate the historical time series of nesting data are as important as the data themselves, especially when changes are made from time to time without explanation. Estimation of Kemp’s ridley population status, the effects of various management and recovery actions (e.g., enhancement of hatchling production through semi-artificial means, turtle excluder devices, etc.), and rates of population change are dependent in large part on these historical nesting data. Without a consistent data set it will be difficult if not impossible to evaluate relative merits of various management and recovery actions that led to reversal of the downward trend in Kemp’s ridley nest numbers after 1985. Such evaluation could be extremely important if the success with Kemp’s ridley becomes a model for recovery of other threatened or endangered sea turtle species.

FRAZER, N. B. 1986. Kemp’s decline: Special alarm or general concern? Marine Turtle Newsletter 37:5-7.

HILDEBRAND, H. H. 1963. Hallazgo del área de anidación de la tortuga marina “lora” Lepidochelys kempi (Garman), en la costa occidental del Golfo de México. Sobretiro de Ciencia, México 22:105-112.

MARQUEZ-M., R., R. A. BYLES, P. BURCHFIELD, M. SANCHEZ-P., J. DIAZ-f., M. A. CARRASCO-A., A. S. LEO-P., & M. C. JIMENEZ-O. 1996. Good news! Rising numbers of Kemp’s ridleys nest at Rancho Nuevo, Tamaulipas, México. Marine Turtle Newsletter 73:2-5.

MÁRQUEZ, R., J. DÍAZ, M. SÁNCHEZ, P. BURCHFIELD, A. LEO, M. CARRASCO, J. PEÑA, C. JIMÉNEZ & R. BRAVO. 1999. Results of the Kemp’s ridley nesting beach conservation efforts in Mexico. Marine Turtle Newsletter 85:2-4.

TURTLE EXPERT WORKING GROUP. 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.

US FISH AND WILDLIFE SERVICE AND NATIONAL MARINE FISHERIES SERVICE. 1992. Recovery plan for the Kemp’s ridley sea turtle (Lepidochelys kempii). National Marine Fisheries Service, St. Petersburg, Florida, 40 pp.

VALVERDE, R. A. 1999. Workshop on survey methodology on mass nesting beaches. Marine Turtle Newsletter 85:11.

Charles W. Caillouet, Jr. 6 Quintana Drive, Galveston, Texas 77554 USA (E-mail: Ccaillouet@aol.com)