Diets of spectacled and black Caiman in the Anavilhanas Archipelago, Central Amazonia, Brazil

Abstract

Stomach contents were collected from 213 Caiman crocodilus with snout-vent lengths (SVL) between 15 cm and 115 cm, and 25 Melanosuchus niger with SVLs from 15 cm to 95 cm, in the Anavilhanas Archipelago, Rio Negro, Central Amazonia. The prey types consumed by the two species were generally similar. However, fish were common in the diet of C. crocodilus but absent from the M. niger. Snails (Pomacea) occurred in 24% of stomachs of M. niger, but in only 2% of C. crocodilus. The mean mass of food and the mean proportion of fish consumed increased, while the mean proportion Of terrestrial invertebrates decreased significantly with the size class of C. crocodilus. The mean proportion of molluscs consumed increased significantly with the size class of M. niger, but there was no relationship between the mean mass of food or the mean proportion of other prey categories and size class in this species. However, the sample included only subadults. The mean size of all prey consumed, and of fish, increased significantly with size of C. crocodilus. However, there was no relationship between the mean size of prey in the categories terrestrial invertebrates, shrimps, or crabs, and the size of C. crocodilus. The mean size of all prey consumed was positively related to the size of M. niger. The mean mass of food consumed by C. crocodilus varied with the water body type (lake or canal), but there was no effect of season as indexed by the water level of the Rio Negro. Seasonal variation in the proportion of fish, terrestrial invertebrates, and shrimps consumed by C. crocodilus differed among water body types. Empty stomachs occurred in 24% of the C. crocodilus and 20% of the M. niger. Individuals with food in the stomach had eaten small volumes, suggesting that the caiman are unlikely to impact fisheries in the region.