Fishing with dolphins

By Leila Lemos, Ph.D. Student, Department of Fisheries and Wildlife, OSU

Hello everybody! I am Leila Lemos, a new member of the GEMM Lab. I am from Rio de Janeiro, Brazil, and moved to Corvallis just 2 months ago where I am now taking classes at OSU. Although I have not yet travelled around Oregon to see my surroundings I am loving the fall colors! We don’t have all of this yellow/orange/red in our Brazilian trees; it’s amazing! The green of the pines also enchanted me. What a beautiful place! However, I confess that I do miss being close to the ocean, so I am looking forward to being based in Newport next year. So, since I cannot see the ocean for now, let’s talk a bit about it and the dynamic cetaceans that live there.

My thesis will explore the impact of ocean noise on the physiology of gray whales, but I have not started my fieldwork yet. So for my first blog post I will discuss a unique interaction between bottlenose dolphins (Tursiops truncatus) and fisherman that occurs in the cities of Laguna, in the state of Santa Catarina, and Tramandaí and Imbé, in the state of Rio Grande so Sul, in southern Brazil. Unlike most relationships between fishermen and marine mammals, this interaction is mutually beneficial and both species appear to seek each other out. There are only three other places in the world where a similar interaction occurs: Mauritania, in the west coast of Africa; Myanmar, in the south coast of Asia; and in the east coast of Australia.

In the southern Brazil, dolphins and artisanal mullet fishermen have adapted their hunting strategies to perform a cooperative foraging strategy. Cast net fisherman wait for the dolphins to arrive and then observe their behavior. Only when a specific aggressive behavior pattern is observed do the fishermen enter the water with their nets. The dolphins move closer to the fishermen and begin rolling movements that trap fish close to the margin. The fishermen wait to throw their cast nets into the water until the dolphins perform specific and vigorous behaviors described by Simões-Lopes et al. (1998):

• the dolphin shows an arched back;
• the dolphin exposes its head and hits the surface with the throat;
• the dolphin moves rapidly, showing just the dorsal fin, producing a whirl;
• the dolphin slaps its tail against the surface.

This partnership is mutually beneficial. Dolphins use the disturbance caused by the net to separate the mullet school and trap individual prey. This method allows the dolphins to reduce escapees, capture more prey, and ultimately increase their net energy gain.

For fishermen, this cooperative association leads to greatly increased captures of mullet. The water in the southern coast of Brazil is too murky for the fishermen to see the schools and therefore know where to throw their net. By watching the behavior of the dolphins, the fisherman is able to throw his net at the exact time and location of the passing mullet shoal.

While this symbiotic relationship is remarkable, it is also hereditary in both humans and dolphins. The calves follow their mothers during the foraging events and learn the movements used in this cooperative behavior. Likewise, the fishermen learn their techniques from their relatives through observation. This cross-species interaction has created cultural ties of great socioeconomic value for both humans and dolphins. Furthermore, this unique relationship demonstrates how clever and adaptive both taxa are when it comes to capturing prey. Wouldn’t it be great if more teamwork like this were possible?

Here is a video that captures this amazing relationship:

Until next time and thanks for reading!

Bibliographic References:

Diário Catarinense, 2013. Interação entre golfinhos e pescadores em Laguna chama a atenção de produtores da BBC. Retrieved from http://diariocatarinense.clicrbs.com.br/sc/geral/noticia/2013/05/interacao-entre-golfinhos-e-pescadores-em-laguna-chama-a-atencao-de-produtores-da-bbc-4151948.html

Notícias UFSC, 2009. Especial pesquisa: UFSC estuda pesca cooperativa entre golfinhos e pescadores em Laguna. Retrieved from http://noticias.ufsc.br/2009/08/especial-pesquisa-ufsc-estuda-pesca-cooperativa-entre-golfinhos-e-pescadores-em-laguna/

Simões-Lopes, P.C., Fabián, M.E., Menegheti, J.O., 1998. Dolphin Interactions with the mullet artisanal fishing on southern Brazil: a qualitative and quantitative approach. Revta bras. Zool. 15(3), 709-726.