Amazon Megafish Migration

The Amazon Megafish Migration Project offers opportunities for EcoWB volunteers to contribute to important basic research and conservation of large, migratory fish in the Amazon River and the nearby coast. Over the next few years, EcoWB will solicit volunteers to assist U.S. and Brazilian researchers in varying capacities on the project.

Scientific research and data are essential to efforts to conserve the Earth’s unique ecosystems. The Amazon River basin, covering nearly 3 million square miles, or roughly 36% of the South American continent, supports an incredibly diverse biological community, unlike any other. The Amazon basin is also inextricably linked to the ocean into which it flows, and several large fish species use this area of river-to-ocean transition to complete their life-cycle. Sadly, the river basin, and the Amazon coast are both under renewed development pressure. To prevent its degradation and the accompanying loss of biodiversity, it is important that we know which species are at risk and how they interact with other components of the environment. In this EcoWB-sponsored project, Dr. Jens Hegg of the University of Idaho is partnering with two Brazilian researchers – Dr. Tommaso Giarrizzo of the Federal University of Pará, and Jorge Nunes of the Federal University of Maranhão – to monitor and describe the long distance migration patterns of several species of large-bodied fish in the Amazon basin.

Given the size of its catchment and its geomorphological and hydrological complexity, it’s not surprising that the Amazon River is home to so many fish species. The life histories and ecological requirements of the majority of these species, including several that grow to exceptionally large sizes over the course of their lives, are poorly understood. The researchers on this project have already made important contributions to our knowledge of the extensive migrations of several large-bodied species of fish whose life histories include significant portions of time spent moving in and between diverse habitats of the Amazon River. Jens and Tommaso were the first scientists to describe the individual movements of three species of “goliath” catfish (genus Brachyplatystoma) which make the world’s longest, and least understood, freshwater migration across the Amazon basin. The team is currently focused on two other species that grow to large sizes and that exhibit protracted, yet largely undocumented, movements across salinity gradients at the mouth of the river and along the Amazon coast. One of these is the Largetooth sawfish, a rarely encountered species that is Redlisted by the lUCN. Although the extent and timing of sawfish migrations and the environmental factors that cue and govern them are largely unknown, they can be deduced from the reports of fishermen and the remains of juvenile and adult sawfish that died after becoming entangled in their nets.

In a recent expedition to the lower Amazon River, we discovered that fishermen often save the rostra and teeth of sawfish, despite laws against their capture and sale. Sawfish rostra and teeth are valued as collector items and to a lesser degree as spiritual totems by local practitioners of Umbanda, the Afro-Brazilian religion. Further, the largest sawfish rostral teeth are often polished for sale as spurs for cockfighting, several of which we have discovered for sale at Ver-o-Peso market in Belém.

This project will also investigate the movements of Atlantic tarpon, another large-bodied species of fish that move back and forth between saltwater and freshwater in the lower Amazon River. Because tarpon are highly sought after by fishermen, their forays into and out of saltwater is a well-known aspect of their life history. Nevertheless, the extent and frequency of their migrations and the conditions that trigger them in the Amazon region and across their range are poorly understood.

In this phase of the Amazon Megafish Migration project, a binational team of researchers will use the isotopic and trace-element chemistry of hard parts (otoliths, rostral teeth, and scales) collected from Largetooth sawfish and Atlantic tarpon to reconstruct their movements, age, and rate of growth across different life stages, habitats, and seasons. Information gleaned from these calcified structures, and the chemical signatures they contain, will help us understand the basic migration ecology of these fish. This information is critical in order to assess their vulnerability to habitat loss, fishing, and other human activities. We are currently seeking additional project grant funding and donations from various sources. After funding has been secured, a series of field trips will be initiated to collect samples, interview fishermen, and perform the requisite analyses.

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