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Most sample sex ratios for Kemp’s ridley life stages are female- biased (Coyne & Landry 2007; Shaver & Wibbels 2007; Wibbels 2007). Manipulative conservation methods no doubt contributed to these female-biased sex ratios. The epicenter of Kemp’s ridley nesting, discovered in 1947, is a stretch of beach near Rancho Nuevo, Tamaulipas, in the western Gulf of Mexico (Hildebrand 1963; Heppell et al. 2007). Prior to 1963, nestings in small numbers were documented elsewhere on the Gulf of Mexico coast of Mexico and on Padre Island, Texas (Hildebrand 1963). Based on simulations of Kemp’s ridley hatchling dispersal, Putman et al. (2010) concluded that Rancho Nuevo is the most favorable region of the Gulf of Mexico with regard to conditions that facilitate hatchling migration to foraging grounds. However, as the Kemp’s ridley population increased, nestings also increased to the south and north of Rancho Nuevo (Caillouet 1999; NMFS et al. 2011).

Beginning in 1966, the Mexican government’s Kemp’s ridley conservation efforts restored annual hatchling production at Rancho Nuevo by protecting nesters and relocating clutches to artificial nest cavities within fenced corrals (Heppell et al. 2007; NMFS et al. 2011). Using similar methods, annual hatchling production at Rancho Nuevo was increased through a cooperative Mexico-U.S. program which began in 1978 and continues to this day. This cooperative program also led to reintroduction of Kemp’s ridley nesting to Padre Island National Seashore (PAIS) near Corpus Christi, Texas (Shaver & Wibbels 2007; <http://www.nps.gov/pais/naturescience/kridley.htm>). During the late 1980s and early 1990s, U.S. regulations were implemented requiring turtle excluder devices (TEDs) in shrimp trawls, and use of TEDs reduced mortality in neritic life stages (Yaninek 1995; Epperly 2003; NMFS et al. 2011). All of these conservation efforts, coupled with declining shrimping effort in the Gulf of Mexico (TEWG 1998, 2000; Caillouet et al. 2008; Caillouet 2010; Nance et al. 2010; NMFS et al. 2011), contributed to the post-1985 exponential increase in the Kemp’s ridley population (Heppell et al. 2007; Caillouet 2010). Conservation efforts on beaches in Tamaulipas and Padre Island National Seashore were carried out in ways that deliberately favored production of female-biased hatchling sex ratios (Coyne & Landry

2007; Shaver & Wibbels 2007; Wibbels 2007). However, this should not predispose clutches left in situ where laid to be female-biased.

Determining sex ratios of newly emerged hatchlings is essential to any search for male-producing nesting beaches. The natural sex ratios of hatchlings produced from clutches left in situ at Rancho Nuevo appear to be female-biased (Wibbels 2007); this provides a baseline for comparison with sex ratios of hatchlings produced in clutches left in situ on beaches north of Tamaulipas. Mrosovsky & Godfrey (2010) emphasized that the most reliable method for determining sex of hatchlings is histology of gonads, which requires sacrificing hatchlings. The U.S. Endangered Species Act of 1973 as amended (ESA; <http://www.fws.gov/endangered/esa-library/pdf/ESAall.pdf>) prohibits killing of threatened or endangered species, but allows exceptions for purposes of scientific research. However, as long as Kemp’s ridley remains endangered, it may be unlikely that permits will be issued to allow sacrifice of large numbers of hatchlings for histological examination of gonads. Currently federal government policy requires translocation of all clutches laid and found on the upper Texas coast to PAIS for incubation; this precludes leaving these clutches in situ.


To determine whether Kemp’s ridley nesting beaches north of Tamaulipas naturally produce male-dominated hatchling sex ratios, some clutches could be left in situ where laid, and conditions could be monitored to determine incubation temperatures to which they were exposed. This could provide valuable hatchling sex-ratio and temperature data. However, if such a study is objectionable, reasonable alternatives might suffice. Researchers could wait until Kemp’s ridley is delisted (NMFS et al. 2011) before conducting such studies. By then, annual nestings of Kemp’s ridleys to the north of Tamaulipas probably will have increased considerably, providing larger samples of clutches and hatchlings. It is highly likely that the Kemp’s ridley population will recover and be delisted before global warming and accompanying sea level rise become serious threats to existing nesting beaches, thus providing ample time to conduct the research. In the interim, given that pivotal temperature is known for Kemp’s ridley (Shaver et al. 1988; Shaver & Wibbels 2007; Wibbels 2007), researchers could monitor physical characteristics (including sand temperatures) of beaches north of Tamaulipas, and use them to predict Kemp’s ridley hatchling sex ratios.

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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.

CAILLOUET, C.W., JR., R.A. HART & J.M. NANCE. 2008. Growth overfishing in the brown shrimp fishery of Texas, Louisiana, and adjoining Gulf of Mexico EEZ. Fisheries Research 92:289–302.

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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: In: P.T. Plotkin (Ed.). Biology and Conservation of Ridley Sea Turtles. Baltimore: The John’s Hopkins University Press. pp. 325-335.

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