Proceedings of the 18th Working Meeting of the Crocodile Specialist ...

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These levels of exploitation seriously imperilled wild populations along its whole range. Consequently, Mexico imposed a ban to commercial hunting of wild individuals in 1970, which is in place up to date. Also in response to that situation, the species was included in the ESA as Endangered in 1970. At that time, this measure reinforced Mexico’s policy for the recovery of the species. In order to complement these actions, the Mexican government, in conjunction with NGOs and national institutions, promoted the installation of captive rearing programs, meant to serve as reservoirs for potential reintroduction or restocking programs. In addition, many Natural Protected Areas have been decreed in Mexico in the last two decades, and this has significantly increased the species area and habitat under protection. These continuing actions sowed the seed for the recovery of this crocodile that recent field evidence is demonstrating. 3. Field study results Field surveys included ten States of Mexico, summing up 63 localities. So far, 40 new localities have been recorded, for a total of 105 (IUCN had cited only 40 of those previously reported). From the total known (historic) localities, the COPAN Project visited a sample of 21.9% of these, and persistence of the species in all of them was recorded. In addition, 24 localities were surveyed for habitat quality for the species, and from these 57% were evaluated by the COPAN field team as with habitat apt for C. moreletii. According to reports of these surveys, self-consumption fishing and cattle raising appear to mildly affect the species, while urban development and industry are the least compatible activities. Agricultural areas have historically altered crocodile habitat in Mexico, and this factor was taken into account as will be explained later. 4. Abundance and population structure Abundance indices obtained by COPAN were moderate in most areas, with a single surprising case of 38 ind./Km, which was not taken into account for further analyses as it represents an obviously outlying value (see Figure 2). Averaging of abundance indices reported resulted in 5.76 ind./Km and a wide interval of confidence (0.31 to 10.16 ind./Km). But as data did not show a statistically normal distribution, the average and SD were discarded for further work. Besides, as arithmetical averaging does not reflect actual frequencies of values, from the same database the Mode was then calculated, and resulted in 3 ind./Km. Also, a general index of abundance could be calculated as total individuals seen / total Km surveyed in the more than 60 localities in Mexico. This exercise gave a figure of 3.16 ind./Km. As this overall index for Mexico was very close to the Mode, and much lower than the average, it was used for further calculations, in order to keep a precautionary approach. Based on COPAN results, a working estimation of wild population size for C. moreletii in Mexico was conducted, though it is recognized that periodic updating may improve the analyses we report here. 257
individuals/km 40 35 30 25 20 15 10 Figure 2: Abundance indices for C. moreletii as registered for 63 localities in Mexico The 3.16 ind./Km abundance index obtained for C. moreletii in Mexico is comparable to those known for other crocodile species considered as of lesser concern, in terms of potential extinction, within the IUCN context (see Table 1.). Species Country Index Year C. porosus Malaysia 1 – 3 ind./Km 1998 C. palustris India 2.8 ind./Km 2002 C.acutus Honduras 2 ind./Km 2002 C. novaeguineae Indonesia 2 – 2.1 ind./Km 2003 A.mississipiensis USA 0.3 – 4.7 ind./Km 2003 C. moreletii Mexico 3.16 ind./Km 2004 Table 1. Relative abundance indices for several crocodilian species not considered as endangered Sources of data for Table 1: C. porosus (Ross, 1998); C. palustris (Vyas and Vyas, 2002); C. acutus (Cerrato, 2002); C. novaeguineae (Kurniati y Manolis, 2003); A. mississipiensis (Mazzotti et al., 2003); C. moreletii (COPAN, 2004). Regarding population structure, the analyses relied on the composite sample for all the area surveyed. It was found that adults represented 19% of the total sample reported by the COPAN from Mexican territory. Also, a 1.55:1 male:female sex proportion, was found. A high proportion of Class I (
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