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Individual study: Intensive beach management improves nesting success of olive ridley turtle Lepidochelys olivacea, Playa Cuixmala, Jalisco, Mexico

Published source details

García A., Ceballos G. & Adaya R. (2003) Intensive beach management as an improved sea turtle conservation strategy in Mexico. Biological Conservation, 113, 253-261

Summary

The main strategies for sea turtle conservation in Mexico include bans on exploitation of turtles and eggs, and the protection of nesting beaches. However, here, as in many other countries, there is a lack of funds for sea turtle conservation. Insufficient beach protection and inadequate management of nests moved to hatcheries result in poor overall success of conservation programmes. In this study, the potential of intensive beach management is investigated. This includes intensive beach patrolling and nest re-burial to avoid natural- and human-induced nest losses.

Study site: Playa Cuixmala is a 3 km long beach with seasonal variation in width (30 to 70 m). The beach has been protected as an olive ridley turtle Lepidochelys olivacea turtle nesting sanctuary since 1986 and prior to 1988, poaching was common place. Beach erosion is caused by high tides during hurricanes and storms and can reduce beach area by 70%. Nest losses are high because the hurricanes coincide with the turtle nesting season. Data were collected from July 1988 to March 1997, encompassing nine annual breeding seasons (July to March).

Beach protection: The two points of access were controlled to protect against poaching.

Nest location: Beach patrols were conducted at 3 hour intervals throughout the night from 22:00 to 07:00 to locate turtle tracks and, therefore, nests. Because of the regularity of patrols and the small beach length, nests were transported to the hatchery and reburied within 3 hours of oviposition.

Nest reburial: After nests were found, they were carefully excavated, eggs were collected, numbered, clutch size recorded, and transported in clean plastic bags to the beach hatchery on foot. The hatchery was located in a well drained area lacking vegetation and shade. The hatchery was 10 x 35 x 2.5 m and covered with woven fabric and wire mosquito meshes. The edges of the frame was buried 0.5 m.

Mosquito mesh tubes were placed around each nest to prevent hatchlings from escaping. Hatchlings from each nest were then counted, and immediately released by putting them on the sand next to the sea. Two days after the emergence of hatchlings from a nest, the remainder of the nest was opened to count the hatched, non-hatched and infected eggs, and to obtain a total count of dead and live hatchlings for the nest.

Poaching: The number of poached nests was compared to the number of all nests on the beach.

Hatching success: The hatching success of nests reburied in enclosures and nests left in-situ was compared. In August 1990 (n = 32), July 1991 (n = 80), and October 1994 (n = 18), nests found in the field were alternately allocated to: i) removal to hatchery, and ii) left in-situ. At the end of the experiment, the number of surviving and destroyed (by erosion or predators) nests was recorded. For surviving nests, hatching success was calculated by dividing the number of hatched eggs by the total number of eggs in the nest.

Sex ratios: In October 1994, the temperature inside all 18 nests was monitored twice a day (06:00 and 14:00 h) using Thermocouples (Bailey Instruments, model BAT-12, with 0.1 °C resolution) during the incubation period. Upon hatching, the sex ratios of 20 randomly selected hatchlings from each removed and in-situ nest was compared.

Contribution of Cuixmala: The nesting results were compared with all other protected beaches along the Jalisco coast (totalling 50 km of beach). Results were standardised as the average number of nests protected per km.


Poaching: Between July 1988 and March 1997, there were 2,418 nests protected and 141,548 hatchlings released on Playa Cuixmala. The number of nests increased from 20 nests in 1989 to 456 nests in 1996, with an annual average of 300 nests (± 127 SD). During the 1987/8 and 1988/9 breeding seasons when the beach was not intensively protected, over 90% of nests were poached, whereas in the next eight years with effective beach protection only two nests were poached (in 1990).

Hatching success: There were no nest losses due to beach erosion or predation in reburied nests, whereas only 56% (range 44-70%) of in-situ nests survived. There was no significant difference in hatching success between in-situ (66%) and hatchery (59%) nests, with higher hatching success in in-situ nests in 1991 and 1994, but lower success in 1990.

Sex ratios: The in-situ (30.5°C) and hatchery (30.6°C) nests experienced similar temperatures during the incubation period and, consequently, the sex ratio did not differ between in-situ and hatchery nests.

Contribution of Cuixmala: The relative contribution of the 3 km Cuixmala beach to the total 50 km of protected beaches on the Jalisco coast as a whole increased from 1989 to 1994. The proportion of all successful nests increased from 4 to 16% and the proportion of all hatchlings released increased from 3 to 18% of the regional totals. During this period, Cuixmala became the most important beach in relative terms (i.e. most hatchlings per km of beach) and the second most important beach in absolute terms (i.e. total number of hatchlings released) for sea turtle conservation in Jalisco.

Conclusions: Intensive beach management was very successful at Playa Cuixmala, which suggests that similar management on other small beaches or on the most productive parts of large beaches would be of considerable conservation benefit.


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