By Carson Jeffres, Gislene Torrente Vilara, Jansen Zuanon
Seeds are often thought of as a start that will eventually grow into something larger than it originally started. In this case, the seed was a seed grant from UC Davis Global Affairs to develop a collaborative project with international partners working with a migratory fish along the southern coast of Brazil. The fish, tainha (Mugil liza), is a migratory mullet that supports an artisanal fishery and provides a sustainable protein source for local communities along the southern Brazilian coast. As with many fisheries around the world, an industrial fishery has entered the scene, and increased extraction, coupled with climate change and habitat degradation, resulted in declining populations and increased regulation and curtailment of the fishery. This is a story common to migratory fish across the globe.
Despite the importance of this fishery, very little is known about the life history of this important species. This is where the UC Davis Global Affairs Seed Grant comes in. In 2022, we were selected for a collaborative project with the Universidade Federal de São Paulo Instituto do Mar. We were tasked with using a novel technique using istopes in eye lenses and trace metals in otoliths (ear bones) of the fish to let them tell us their life histories and help fill in the blanks in their life history. Our hope is to better manage this species of critical importance to coastal communities along the southern coast of Brazil.
In collaboration with Dr. Gislene Torrente Vilara and Dr. Jansen Zuanon, we traveled some 670 miles (1077 km) along the coast, talking with fishermen about what they understand about the life histories of the tainha and collecting fish tissues and environmental samples along the way.
Similar to salmon in the north Pacific, we know that tainha are born in one location, migrate as juveniles, then return as adults to spawn where they were born, but little is known about the details. Like any good story, every person tells it a bit differently. Where the fish are born (in the Atlantic Ocean off the coast of Brazil), where the larvae then go (like a snowflake, each story is a bit different), then how they migrate up the coast, reproduce then start the process all over again (yet another snowflake). In this case, the samples we collected on this seed project told a story very similar to that of the fishermen.
Using isotopic analysis of the various layers of the eye lenses and trace metal analysis of the otoliths we found truth in many of the stories. These fish exhibit a variety of life history strategies and appear to utilize a large number of estuaries during their northerly migration to the spawning grounds in the Atlantic Ocean off the Brazilian Coast. These results highlight the importance of protecting the habitats of not just a single location, but throughout the migratory corridor. Like most migratory fish, any weak link in the circle of life can result in declining populations and associated challenges to the ways of life of the people that rely on them.
For those of us living in California, this story is similar to the plight of the Chinook salmon and the current closure of the commercial and recreational fishery and the resulting economic impact to the communities that rely on the fish. Like the tainha, California Chinook salmon rely on a diversity of habitats, and any weak link in the chain of their incredible journey can result in reduced populations that impact everything from tribal communities, fishermen, farmers, cities to all the people that rely on the health of the rivers and ocean. The tainha and the salmon may be the canary in the coal mine telling us that we need to do better.
Through this process, we have met many amazing people who invited us in for lunch, let us stay at their houses, and told us their stories. During this seed grant, we have learned quite a bit, but, as in any good science project that tries to guide resource management, we are humbled by all that we don’t know. We hope that this seed of information will grow into a larger collaborative project that will help better tell the story of this important fish and how we can better protect them into the future. We are very grateful for UC Davis Global Affairs, Universidade Federal de São Paulo Instituto do Mar, the students at LaFama and UC Davis Center for Watershed Science, and especially to the fishermen who were willing to let us into their lives and tell us their stories to help this seed grow.
Dr. Carson Jeffres is a Senior Researcher at the UC Davis Center for Watershed Science. Dr. Gislene Torrente Vilara is a Professor of Marine Sciences at Universidade Federal de São Paulo, Santos, Brazil. Dr. Jansen Zuanon is a Senior Visiting Professor Universidade Santa Cecilia, Santos, Brazil and a retired Senior Researcher at Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil
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