Twenty-six years of green turtle nesting at Tortuguero, Costa Rica: An encouraging trend

The green turtle (Chelonia mydas) population that nests at Tortuguero, Cost a Rica, is the largest in the Atlantic by at least an order of magnitude. S urveys to monitor the nesting activity on the northern 18 km of the 36-km b each were initiated in 1971 and extended to the entire beach in 1986. Front the survey data, we estimated the total number of nesting emergences on th e northern 18 km for each year from 1971 through 1996. Evaluation of the tr end in nesting emergences indicated a relatively consistent increase from 1 971 to the mid-1980s, constant or perhaps decreasing nesting during the lat e 1980s, and then resumption of an upward trend in the 1990s. Evaluation of trends in sea turtle nesting populations requires many years of data becau se of the large degree of annual variation in nesting numbers The trends re ported in this study must be evaluated with caution for several reasons. Fi rst, if the the mean number of nests deposited by each female each year (cl utch frequency) varies significantly among years, changes in the number of nesting emergences among years could reflect changes in the number of nesti ng females, clutch frequency, or both. Second, we only assessed the trend i n one segment of the population (mature females), which may or may not repr esent the trend of the entire green turtle population and which, because of late maturity, may not reflect changes in juvenile mortality for many year s. Third, survey frequency, and thus confidence in annual estimates varied among years. The upward population trend must be assessed from the perspect ive of the catastrophic decline that the Caribbean green turtle populations have experienced since the arrival of Europeans. If careful management is continued in Costa Rica and adopted throughout the region,the collapse of t he Caribbean green turtle populations-which seemed imminent in the 1950s-ca n be avoided.