Cooperative foraging between artisanal fishermen and bottlenose dolphins
Dolphin cognitive abilities could be underestimated because they don´t have a precision manipulation organ like our hands or fine motor abilities, so they are very limited for tool use.
Even without hands and fine motor skills dolphins have very complex society with very complex social structure and different cultures.
Dolphins evolved big brains to develop higher cognitive abilities that they need to manage their complex social life and their complex language.
Dolphins have very complex social structure that varies from one population to other with cultural differences even between simpatric populations of the same species. Dolphins have a huge variability in lot of behaviors and social structure between and within groups that also are transmitted culturally.
Dolphins have a huge variety of hunting tactics which are learned and transmitted culturally between generations. Bottlenose dolphins have an even greater variability in their tactics not only between populations but also individual dolphins uses various tactics that evolve over short times. I´m going to resume some dolphin tactics.
First a very widely used tactic used by various offshore species including common dolphins, bottlenose dolphins, spinner dolphins, pantropical spotted dolphins, false orcas and probably more species for herding big schools of small fish. they use sound pulses to herd them to the surface and them surround them and use sound walls and bubble walls to herd them in a tight formation and then they take turns to feed while other dolphins continue herding the school. Orcas have a variation of that tactic without sound pulses and bubbles but with showing their white belly to the herrings and using tail flaps to stunt them.
Bottlenose dolphins (tursiops truncatus) has a lot of variations of this tactic that includes to herd the school of fish against a barrier that could be the shore, a bay or a ship. Some pods uses fishing nets as barriers so those fishing ships has higher catch but their nets receive heavy damage. Bottlenose dolphins who specialize in such tactics rarely get tangled in nets but fisherman usually shot at them and/or uses explosives to attract them.
An extreme and elaborated variation of this tactic is used in Laguna in Brazil. There there is a pod of bottlenose dolphins (tursiops truncatus) who help fisherman. Dolphins herd mullets to the muddy shore where fisherman are waiting with their hand nets. The dolphins made signals indicating fisherman when and where to throw the nets to catch fish. It is all directed by the dolphins and they have a code of signals with movements to tell the fisherman when and where to trow the nets.
Dolphins herd a school of mullets or other fish to the deep channel in the entrance of the lagoon or one of the others 10–12 sites they use to collaborate with fisherman. Then dolphins make a signal indicating that the process is going to start so the fisherman locate themselves in a line in the shallow water. After that the dolphin make signals indicating where is going to herd the school so the fisherman locates themselves according to dolphin signals.
Then a dolphin herds a small school of fish toward the fisherman and signals to them and the fisherman trow the nets to the area the dolphin signaled. Part of the school is caught in the net. The rest of the school is caught up between the nets and the dolphins so they are easy prey for them.
After that dolphins make signals indicating where is going to herd the next school of fish and respites the process. Finally a dolphin raises its tail vertically making a signal to indicate they run out of fish and the end of the process.
The code its passed between generations in both humans and dolphins since at least 1850 when the town was created and by Indians before. This code is a closed language that allow dolphins to tell the fisherman where the fish are and how big is the school and how fast they move and when and where to trow the nets. Female dolphins comes with their calf to teach them the signals.
If dolphins heard the school of fishes against a line of fishermen and signal them when to throw the nets, the fishes would´t be allowed to reach the part of the beach that is too shallow for the dolphins and since those kind of nets traps only a fraction of the fishes, the rest of them would be easier to trap to the dolphins. They are caught up between the nets and the dolphins so they cannot go anywhere
http://www.scielo.br/scielo.php?...
That dolphin pod is divided in 2 subgroups. The ones who help fisherman and the ones who don´t. Both groups are separated most of the times. Dolphins that help fisherman not only forage together they also rest together and socialize together they rarely join the other group. Except for one dolphin who associates with both groups. He is the reason why the 2 subgroups are not totally isolated. He was present in every rare occasion when the 2 groups joined.
https://journals.plos.org/ploson...
There are cultural and language differences between subgroups. There is evidence that both subgroups whistle differently, there are specific whistles that only dolphins of the subgroup that help humans uses, and they uses them when forage with humans, that whistles are not signature whistles.
