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An important component of any conservation project is evaluation and assessment. This has rarely been done in sea turtle conservation projects, as the time lag for the impacts of management procedures to be seen is on the scale of decades, and there is a limited number of long-term projects in existence. In the case of the black turtle project, we have more than 20 years of data, thus facilitating the opportunity to assess whether the black turtle project is achieving its conservation goals in Michoacán. We utilized a threat reduction assessment
(TRA; Salafsky & Margoluis 1999). This approach employs the degree to which threats are reduced as an index of success. The TRA applied to the black turtle project is based on three key assumptions. First, the turtle population decline is human-induced. Second, all threats to black turtle survival in Michoacán can be identified and ranked in terms of their scale, intensity of impact, and urgency. Third, changes in all threats can be measured or at least estimated. Although the geographic range of the black turtle is extensive (Alvarado & Figueroa 1992), the project's conservation activities and associated TRA were focused on the nesting area in Michoacán (15 beaches along 60 km of coastline).

The threats to the black turtle in Michoacán were listed by Cliffton et al. (1982) as being: illegal and legal harvest of adult turtles (commercial and subsistence), egg poaching (commercial and subsistence) and destruction and degradation of nesting habitat.

Adult harvest: In 1980 a local fishing cooperative was granted a legal quota of 250 male black turtles per month throughout the nesting season (September - December). At the same time members of several fishing cooperatives from Michoacán were poaching black turtles (mainly using shark gillnets set in front or near nesting beaches) to be sold to intermediaries who smuggled them to Sonora and Sinaloa for meat consumption (Alvarado & Figueroa 1987). It was estimated that about 2,000 females and 1,000 male black turtles were illegally taken in Michoacán every year between 1979 and 1982 (Cliffton et al. 1982; Alvarado & Figueroa 1987). In addition it is estimated that in the same period an average of 150 black turtles were poached annually in Michoacán for subsistence purposes (Cliffton pers. comm. 1983). The reduction of this class of threats includes the elimination of the quota system for capture of turtles, and enforcing legislation against the illegal capture of adults.

Table 1. Threat reduction assessment (TRA) for the black turtle population nesting in Michoacán (1982?1999 assessment period). 100% reduction of these threats involves eliminating the quota system for capture of turtles, eliminating illegal commercial take of adult turtles, eliminating all subsistence take of turtles, eliminating all commercial and subsistence egg poaching, eliminating the risk of touristic commercial development and stopping construction and deforestation on nesting beaches.

Egg poaching: In the early 1970s approximately 70,000 eggs were poached each night during the nesting season at Colola and an additional 10,000 to 20,000 from Maruata (Cliffton et al . 1982). This egg harvest, approaching 100%, was continued until 1980 when armed protection of Colola and Maruata began. Beach surveys during the nesting season indicated that between 1979 and 1982, 35 - 45% of black turtle nests were poached every season at Colola and Maruata (Alvarado & Figueroa 1987). An estimated 20% of poached nests were used for local consumption and the remainder sold by local people to regional smugglers. The reduction of this class of threats includes the elimination of all take (illegal and legal) of eggs from nesting beaches.

Habitat degradation: The main potential threat for the nesting habitat registered in 1982 was the loss and deterioration of nesting habitat to commercial touristic development, dwelling construction and deforestation of areas adjacent to nesting beaches, especially Colola and Maruata. Reduction of this threat includes the elimination of risk associated with development and stopping construction or deforestation on nesting beaches.

Activities to counter these threats include beach and offshore patrolling and roadblocks to control adult poaching, lobbying to declare Colola and Maruata a protected area for the conservation of sea turtles and to ban any take of turtles, beach protection of nests and hatchlings, and community work (Alvarado & Figueroa 1991).

In 1985 the black turtle quota system in Michoacán was cancelled, and in 1986 Colola and Maruata were declared a natural reserve area. Between 1982 and 1989 turtle and nest poaching rate in Michoacán showed a steady decline. Since then the poaching rate has remained similar from year to year. From 1989 to 1999 field enforcement activities have not registered any commercial take in Michoacán and subsistence take was low. Early morning ground beach surveys in the main nesting beaches indicated that since 1989 an average of 12 nesting turtles (range = 8 - 18) were taken every season, while roughly 80 - 90 % of nests were protected every season in beach hatcheries and natural nest sites. Although commercial tourism development in the nesting area has remained incipient, construction of human dwellings has increased since 1982 especially in Maruata. We estimated that up to 1999 about 15% of nesting habitat has been lost.

We have calculated a threat reduction index, whereby the actual threat reduction expressed as a percentage of total potential threat reduction (Margoluis & Salafsky 1998) is presented. Using the threats identified above, we ranked each threat according to three criteria:

1) Area, which refers to the percentage of the breeding area in Michoacán that the threat affects,

2) Intensity, which refers to the impact of the threat on a smaller geographical scale (specific places within the breeding area in Michoacán), and

3) Urgency, which refers to the immediacy of the threat.

Following Salafsky and Margoluis (1999) the total number of threats (n) was assigned as the score of the highest ranking threat in each category (Table 1). The next highest-ranked threat in each category was assigned the score n ? 1. The lowest ranked threat was assigned the score 1. The three criteria rankings for each threat were summed to obtain the total ranking (Table 1). Next, the degree to which each threat was reduced at the date of the most recent nesting season (1999) was determined, based on the definitions given in Table 1. The reduction in threat is expressed as the percent change in the original threat identified at the start of the project. To calculate the final threat reduction index score, the individual reduction scores for all threats were summed. This value was divided by the sum of the total rankings and multiplied by 100 (Table 1).

The TRA Index obtained (82.4%, Table 1) suggests a relatively high level of success of the activities of the project in Michoacán to mitigate major threats. Nevertheless, if we utilize the nesting numbers at Colola (main nesting beach; Figure 1) as an indicator of the condition of the breeding population, the project has failed in its main goal: the recovery of the population to historical levels. However, it is noteworthy that:

1) the nesting numbers (Figure 1) have not substantially declined since 1983 and;

2) within the context of the well-established and pronounced interannual variation in numbers of nests demonstrated at green turtle (Chelonia mydas) rookeries, nest totals in 1995 and 1997 suggest possible cause for optimism.

Figure 1. Number of nesting black turtle females per year in Colola, Michoacán, México

TRA measures threat reduction, therefore, the validity of TRA scores in estimating project success depends on whether project goals are directly related to the reduction of threats. For the Michoacán project, the resultant TRA score indicated a considerable success in the reduction of threats in the nesting area. However this reduction did not result in the recovery of the nesting population, suggesting that nesting female numbers were affected by additional threats not considered in the TRA analysis (or that nesting numbers were also affected by non-human induced factors). The decline of the nesting numbers is likely to be the result of the impact of human activities outside the geographical area of the project. If we consider the black turtle as a metapopulation which uses a series of habitats at different life stages, the nesting area in Michoacán is perhaps the major habitat "source" assuring a level of recruitment into the breeding ranks. Therefore, the main achievement of the project in Michoacán is to have provided safe conditions in Michoacán for breeding, nesting, and hatchling production. Unfortunately, at least some of the developmental-feeding habitats are "sinks" where according to the dramatic decline of the nesting numbers the rate of capture of adults and juveniles is outweighing the recruitment rate. For instance, in Baja California, perhaps the most important feeding-developmental area for the black turtle, the mortality rate (due to direct and indirect take of adults and juveniles) has been estimated to be greater than 10,000 turtles annually (Nichols 2000). Therefore, it is obvious that the protection of the nesting population in Michoacán is not enough to offset the harvest rate in feeding areas. If we incorporate the threat of direct and indirect capture of black turtles in Baja California into the TRA analysis the original score of 80.2% is reduced to 61.8% (giving the threat of direct and indirect capture in Baja California the highest ranking).

Although TRA application to evaluate success (or failure) of sea turtle conservation projects needs to be further refined and tested in other projects, its utilization in assessing the Michoacán project was a useful tool for measuring and monitoring how efficient project activities are in the mitigation of major threats. Furthermore, TRA was useful in indicating the possible existence of unknown threats that demand attention. We suggest that other projects with long term datasets should consider the utility of the TRA in assessing the success or limitation of their management techniques.

Acknowledgements: We thank Ouissem Drif, Matthew Godfrey and Wallace J. Nicholls who reviewed and greatly improved a previous version of the manuscript. The black turtle conservation project in Michoacán is supported by the US Fish and Wildlife Service.

ALVARADO, J. & A. FIGUEROA. 1987. The ecological recovery of sea turtles of Michoacán, México. Special attention: the black turtle, Chelonia agassizii. Final Report 1986-1987 submitted to U.S.F.W.S. and W.W.F. - U.S.

ALVARADO, J. & A. FIGUEROA. 1991. Recovery of the black turtle in Michoacán, México: an integrated conservation approach. Marine Turtle Newsletter 53: 1 - 3.

ALVARADO, J. & A. FIGUEROA. 1992. Recapturas post-anidatorias de hembras de tortuga marina negra (Chelonia agassizii) marcadas en Michoacán, México. Biotropica 24(4): 560 - 566.

CLIFFTON, K., D. O. CORNEJO & R. S. FELGER. 1982. Sea turtles of the Pacific Coast of México. In: K. Bjorndal (Ed.). Biology and Conservation of Sea Turtles. Smithsonian Institution Press, Washington, D.C. pp. 199 - 209.

MARGOLUIS, R. & N. SALAFSKY. 1998. Measures of Success: Designing, Managing, and Monitoring Conservation and Development Projects. Island Press, Washington, D.C.

NATIONAL MARINE FISHERIES SERVICE & U.S. FISH AND WILDLIFE SERVICE. 1998. Recovery Plan for U.S. Pacific Populations of the East Pacific Green Turtle (Chelonia mydas). National Marine Fisheries Service, Silver Spring, MD.

NICHOLS, W. J. 2000. Biology and conservation of sea turtles in Baja California, México. Doctoral dissertation. Wildlife and Fisheries Science. University of Arizona, Tucson.

SALAFSKY, N. & R. MARGOLUIS. 1999. Threat reduction assessment: a practical and cost-effective approach to evaluating conservation and development projects. Conservation Biology 13 (4): 830 - 841.