As a hunting community, dolphins and fishermen in southern Brazil are increasing their catch quotas. A study describes how humans benefit from animals and vice versa. However, the rare symbiosis is currently in acute danger.
Scientists have gained new insights into the hunting behavior of dolphins. Dolphins on the southern Brazilian coast are actively influencing their behavior to cooperate with human fishermen in fish hunting. This was announced by the Max Planck Institute for Animal Behavior in Constance, which was involved in the study. Not only humans, but also the dolphins benefit from the common hunt.
Dolphins - so-called bottlenose dolphins - drive schools of mullets in front of them off the Brazilian coast of the city of Laguna. This increases the number of fish in the water for a short time and signals the fishermen standing in the water where to cast their nets. The researchers have now been able to prove that the dolphins actively control this behavior. "Fishermen were known to observe the behavior of dolphins to determine when to cast their nets," said Fabio Daura-Jorge, a researcher at the University of Santa Catarina, Brazil. "But we didn't know that the dolphins actively coordinate their behavior with the fishermen."
Both dolphins and humans benefit from this hunting tradition, which has been practiced for around 140 years. The researchers found that the dolphins benefit from a 13 percent higher survival rate compared to their lonely hunting counterparts. The fishermen, in turn, catch around four times more fish than without the marine mammals. The researchers emphasized that the cooperative behavior of the dolphins is not genetically determined. Rather, it is a peculiarity of the dolphin population at Laguna. Both dolphins and humans would pass on their knowledge to subsequent generations.
However, model calculations show that the cooperation between dolphins and humans is at risk. The number of fish in the region has declined sharply in recent years. The coastal population is also less interested in learning the special hunting technique.
"Our calculations show that if current developments continue, the cooperation could become uninteresting for either the dolphins or the fishermen," explained Daura-Jorge. In order to preserve the cooperation between dolphins and humans, it is necessary to better understand the reasons for the decline in mullets and to promote sustainable fishing.
For the study, researchers from Brazil and from the Max Planck Institute observed the behavior of the fishermen and dolphins for around 15 years. She also used drones and underwater photography.
