The giant otter (Pteronura brasiliensis) is a large predator inhabiting South American freshwater ecosystems. Known for its size and social nature, this species is at the top of its aquatic food chain. Understanding its diet reveals how this mustelid thrives, highlighting its adaptations for hunting.
Primary Prey
Fish make up over 90% of the giant otter’s diet. These opportunistic hunters target diverse fish species based on local availability. Common fish include cichlids, perch, characins like piranhas, and various catfish. A study in Amazonian Brazil found fish in all giant otter fecal samples, with cichlids and perch in 97% and characins in 86% of samples.
Beyond fish, giant otters supplement their diet with other aquatic and semi-aquatic animals. They consume crustaceans like crabs and prawns, frogs, snakes, and even small caimans. They have also been observed preying on turtles and anacondas. These supplementary items become more significant when fish populations are scarce.
Hunting Strategies
Giant otters use effective strategies to find food, often working cooperatively within family groups. They are agile and swift in water, using streamlined bodies and webbed feet to pursue prey. Their keen underwater vision spots fish in clear waters, while sensitive vibrissae (whiskers) detect subtle changes in water pressure, enabling them to locate prey even in murky conditions.
Cooperative hunting is a distinguishing behavior, where groups herd fish into shallow waters or against riverbanks, making capture easier. Once prey is cornered, otters use their jaws and teeth to grasp and consume it quickly. Smaller fish are often eaten immediately in the water, while larger catches are brought to the shore. Underwater chases involve lunges and twists, allowing them to capture targets efficiently.
Dietary Adaptations and Influences
The giant otter’s diet is influenced by environmental factors, particularly seasonal changes and habitat types. During the wet season, rising water levels disperse fish into flooded forest areas, requiring otters to expand foraging ranges. In the dry season, fish concentrate in shrinking pools, making them easier to catch. Diet composition and prey size can differ between river channels and oxbow lakes, reflecting variations in prey availability.
Giant otters possess specialized dentition, capable of crushing fish bones, scales, and spines. Their high metabolic rate requires a substantial daily food intake; an adult can consume 2.8 to 4 kilograms (6 to 9 pounds) of food per day, up to 10-20% of their body weight. This high energy demand drives their continuous hunting and shapes feeding behaviors.