Information and current status of sea turtle populations and their breeding environments in Mexico
Of the eight species of sea turtles known in the world, seven inhabit Mexican beaches and two of them, the Kemp's ridley (Lepidochelys kempi) and the black turtle (Chelonia agassizii), occur exclusively on these beaches. The Kikila turtle ( Natator depressus ) is the only one that does not nest in Mexico and its distribution is restricted to the coasts of Australia. In Mexico, several sandy beaches along the Pacific, Gulf of Mexico, and the Caribbean Sea offer ideal nesting sites for females, with optimal humidity and temperature conditions for this phase of their development.
For the protection and study of turtles, the nesting process is one of the most important periods because it is when the greatest efforts are made to prevent the nests from being plundered and the females from being captured. From June to September, the females leave the sea to go to the same beaches where they were born to deposit their eggs in nests dug in the sand. After this process the females return to the sea, so the clutches lack parental care.
The incubation period ranges from 45 to 60 days and, in each clutch (which depending on the species can be from 2 to 8 per season) they deposit between 60 to 100 eggs. During their development and on the journey from the nest to the sea, the hatchlings are easy prey for predators such as seagulls, crabs, dogs, and raccoons that feed on them. In their juvenile stage, at the age of 2 or 3 years, they move towards lagoons, estuaries, and bays where they find optimal conditions for growth. The natural mortality rate of sea turtles is high during the first stages of life, so it is considered that out of every one hundred hatchlings, only one or two reach adulthood.
However, the reduction of sea turtle populations throughout their global distribution is mainly due to anthropogenic factors with a long history. Apart from the excessive direct fishing that was practiced until recent times, other factors include the plundering of nests, the incidental capture of juveniles and adults in shrimp nets, the alteration or destruction of their nesting habitats, and poorly planned urban and tourist development and the increasing pollution of the seas. As a result, some sea turtle populations have virtually disappeared. This situation has led to the declaration of all sea turtle species as threatened or endangered.
It is estimated that only one out of every one hundred sea turtle hatchlings reaches adulthood. This situation has led to the declaration of sea turtles as threatened or endangered.
In Mexico, it was in the early 1960s when sea turtle capture intensified, as their skin replaced that of the crocodile, the shell and meat were industrially processed, and large quantities of eggs were collected and sold in markets in Mexico City, Guadalajara, Mazatlán, Oaxaca and Acapulco. In 1972, the then Secretary of Commerce declared a ban on sea turtle capture, and a year later the purchase and sale of eggs was prohibited.
In 1986, 16 beaches were decreed as Reserve Zones and Refuge Sites for the nesting, reproduction and development of sea turtle species: Isla Contoy, in Quintana Roo; Rancho Nuevo, in Tamaulipas; Ría Lagartos, in Yucatán; Ceuta and Verde Camacho, in Sinaloa; Mismaloya, Teopa and Cuitzmala, in Jalisco; Colóla, Mexiquillo and Maruata, in Michoacán; Piedra de Tlacoyunque and Tierra Colorada, in Guerrero; Escobilla and Chacahua, in Oaxaca; and Puerto Arista, in Chiapas.
In June 1990, a total ban went into effect for an indefinite period of time to prohibit the capture and commercialization of sea turtles, as well as the products and byproducts derived from them.
Because they are highly migratory species, sea turtles are also a resource that is shared geographically among several countries. The lack of effective regional management plans for these species can sometimes conflict and even nullify costly conservation efforts. For example, in early 1993, the United States threatened to impose a trade embargo on Mexico's shrimp exports, arguing that there was a high rate of sea turtle bycatch in this fishery. In response to this situation, a series of preliminary evaluations were carried out on the Mexican coasts and as a preventive measure, the official gazette of February 25 of that year established that the use of sea turtle excluder devices (det's) was mandatory in the Mexican Gulf and the Caribbean Sea.
Prior to the installation of these devices, technicians, fishermen, and trawlers from the Mexican shrimp fleet were trained. However, reports recently published by U.S. non-governmental organizations show that the U.S. fishing sector has not complied with the legal provisions established in the United States for the protection of these chelonians. The U.S. Endangered Species Coalition states that the cause of the turtle mortality is related to the failure of the U.S. fishing industry to comply with the legal provisions established in the United States for the protection of these marine turtles.
Effective regional management plans are required for the conservation of sea turtles from their early life stages.
Sea turtle conservation efforts should be focused on the factors that have the greatest impact on the decline of sea turtle populations in each region. Accordingly, the strategy for more organized and efficient management should promote and consolidate national, regional, and international collaboration agreements to distribute the commitment to conservation in an equitable manner.
By Jacinta Ramírez, Sources: CONABIO, the first issue of its bi-monthly bulletin Biodiversitas.