World Status, Exploitation and Trade - WIDECAST

COSTA RICANesting numbers The Hawksbill is far less abundant at Tortuguero thanC. mydas ; from 1955 to 1983, 2A6 nesting individuals were tagged in thenorthernmost 8 km at Tortuguero (i.e. miles 0-4), compared with 20 982C. mydas at the same site during the same period, although monitoring didnot take place during the peak Hawksbill nesting period (tagging was onlycarried out during the Green Turtle nesting season) (Bjorndal et al. . 1985);only 12 remigrant Eretmochelys were recorded in this period. Moreconsistent efforts were made to count from 1976 onwards, and these figuresare given in Table 45.Trends in nesting numbers Carr and Stancyk (1975) cite evidence of aconsiderable decrease in density of nesting females at Tortuguero since1956: in the period 1956-59, 3.7 Eretmochelys were tagged per patrol-hourper mile (= 2.3 per patrol-hour per km) in nightly patrols of the study areaat Tortuguero (miles 0-4); in 1970-73, 0.97 per patrol-hour per mile (= 0.60per patrol-hour per km) were tagged at the same site. Bjorndal et al.(1985) stated that the data before 1972 could not be used because ofdiffering methodology, but that from 1972 onwards beach coverage had beenreliable, and the data showed no consistent trend in the number ofHawksbills seen in the patrolled area during the period 1972-83, or in thenumber of nests recorded during July, August and September beach surveys,suggesting that the population may have stabilised. However, Bjorndal laterpointed out ( in litt . 24 July 1988) that the counts prior to 1976 wereunreliable and that if the data from 1976 to 1987 were considered (Table 45)a significant decline was apparent (Pearson's r = -0.757, p = 0.0044). Inaddition Bjorndal et al. (1985) noted a slow though steady and statisticallyhighly significant decline (slope = -0.15; p = 0.0005, Spearman rankcorrelation) in carapace length of nesting females over the period 1955-77,suggesting that the population is not demographic ally stable.Nesting season Carr et al. (1966) state that the nesting season atTortuguero is essentially May to November. Systematic observations wereonly made during the Chelonia mydas nesting season but they considered atthe time that peak nesting was probably in May and June prior to theC. mydas season; Bjorndal et al. (1985) also report a significant increasein nesting activity in October immediately after the C. mydas season.Foraging sities Bjorndal et al. (1985) report that the Caribbean coast ispoor in what is generally considered Eretmochelys habitat. They state thatIt is not clear whether any of the Hawksbills that nest at Tortuguero areresident in Costa Rican waters, although there is a record of a female takennear Puerto Limdn south of Tortuguero one year after being tagged whilenesting (i.e. almost certainly in a non-nesting year); the best coral reefhabitat on the coast is at Cahuita south of Puerto Lim6n, and Eretmochelysis known to occur there (Wells, 1988a), although whether year-round or notis unclear. Carr et al (1982), however, state that concentrations ofmature Hawksbills are found foraging on Tortuguero Bank, two patches of rocklying c . 1 km off the mouth of the Tortuguero River, throughout the year,though especially in late spring. They also note that immature Hawksbillsof all post "lost year" sizes are found off southern Costa Rica between Moln(just north of Puerto Lim6n) and the Nicaraguan border.Migration Bjorndal et al. (1985) report nine international tagrecoveries; eight of these have come from the region of the Miskito Cays andother shallow banks off the coast of Nicaragua and Honduras, the majorfeeding ground of the Tortuguero Green Turtles, and one was taken nearColon, Panama. There is no information on migration in the Pacificpopulation.148