MONITORING THE DISTRIBUTION, ABUNDANCE AND BREEDING AREAS OF CAIMAN-CROCODILUS CROCODILUS AND MELANOSUCHUS-NIGER IN THE ANAVILHANAS ARCHIPELAGO, CENTRAL AMAZONIA, BRAZIL

Caiman crocodilus crocodilus and Melanosuchus niger occur throughout m ost of the Anavilhanas Archipelago, located in the lower Rio Negro, Ce ntral Amazonia. The observed densities of these species vary from 0 to 58 per km of shoreline and 0 to 8 per km of shoreline, respectively. Multiple regression analysis indicated that the temperature difference between the water and the air, and water depth affected the observed density of C. crocodilus during spotlight surveys in the Archipelago. Percentage illumination by the moon, cloud cover, frequency of occurre nce of grass, and food availability did not significantly affect the o bserved density of C. crocodilus. Nine hatchling groups of M. Niger th at hatched in 1992 were found on islands near the north bank of the Ri o Negro, and 15 of 20 hatchlings groups of C. crocodilus were found cl oser to the south bank, indicating a tendency for separation of nestin g areas. Discriminant function analysis indicated that water depth and presence of grass were correlated with the occurrence of hatchling gr oups. Melanosuchus niger hatchling groups occurred in areas with deepe r water and more grass than those of C. crocodilus. This study showed that surveying hatchling groups in the Anavilhanas Archipelago is more efficient than surveying for subadults and adults, which, by itself, can give false impressions about the suitability of areas for conserva tion of breeding populations of these species.