Amazon Megafish Migration

In this project Ecologists Without Borders is partnering with three researchers in building our understanding of long distance fish migration of large fish in the Amazon basin. Jens Hegg, at University of Idaho, and two Brazilian researchers, Tommaso Giarrizzo of the Federal University of Pará, and Jorge Nunes of the Federal University of Maranhão. Hegg and Giarrizzo are the first research team to utilize cutting edge isotopic techniques to reconstruct the details of the migration of three species of goliath catfish (genus Brachyplatystoma). In two of these species the migration spans the length of the Amazon basin from the estuary to the Andes foothills (nearly the width of the continental United States), making this the longest but known freshwater migration but the least understood. In addition the project is exploring the use of similar isotopic techniques to understand the movement of IUCN Redlisted sawfish, which make unexplained upriver movements and are often killed after becoming entangled in fishing nets.

A planning and initial sample collection expedition was successfully funded for this project on Experiment.com.  The crowdfunding effort raised $5,664, doubling the funding goal and winning a competition for fish-related projects which garnered an additional $1,500. This funding effort covered travel costs to meet collaborators and present research at the Brazilian Ichthyological Society Conference in Porto Seguro, Bahia; followed by further sample collection and collaboration meetings in Belém, Pará (at the mouth of the Amazon River) and São Luis, Maranhão. Ecologists Without Borders will provide logistical support, funding management, and volunteer support as appropriate, with a growing role as the project expands.

 

Background

Two species of Amazonian goliath catfish make one of the longest migrations on earth, from the Amazon estuary to the Andes foothills. This is as long as a road trip from Seattle to Miami, via Chicago, yet we know very little about how they make this trip. These species (B. rousseauxii and B. vaillanti, commonly known in Portuguese as dourada and pirimutaba), as well as other members of the genus, are apex predators in the largest channels of the Amazon basin and the only species that requires the entire length of the Amazon basin to complete it’s lifecycle. They also make up the largest commercial fishery in the Amazon basin.

 Sawfish, related to sharks and rays, are listed as Critically Endangered worldwide. In the lower Amazon River, sawfish are often caught accidentally in fishing nets. Aside from their decline, very little is known about the ecology of these species. Like megafishes worldwide, the long distance movements of both goliath catfish and sawfish make them particularly vulnerable.

 

project significance

Understanding the details of catfish and sawfish migrations are vitally important for Amazon conservation and its fishing economy. Dams are being built in the headwaters of many Amazon tributaries that could block this migration, and both dourada and pirimutaba have been shown to be overfished. Fish passage is poorly understood in this system and the current dams block adult upstream migration, while the reservoirs created likely impede the free floating larva from washing downstream to rearing ereas in the estuary. We need only look to the story of salmon to see how dams and overfishing might affect these catfish. 

Sawfish, despite being critically endangered, lack almost all understanding of their movements. They normally inhabit shallow, brackish, coastal waters but make movements in an out of freshwater that are poorly understood. Using chemical histories recorded in the teeth of their “saw” (called a rostrum) we hope to reconstruct when and where they move into freshwater. This information is invaluable for our understanding of their ecology, as well as for finding ways to protect them from becoming intangled in nets.  

In both cases modern isotopic chemistry gives ecologists incredible tools to understand these types of migrations. Using the chemistry trapped in the hard parts of fish (sawfish teeth or catfish ear bones) we can reconstruct with incredible precision the movements of individual fish. This data can help direct conservation strategies. 

We have proven this is possible in the Amazon, with a paper published in PLOS One, and further research will help us to understand these incredible migratory movements in greater detail. This, in turn, will inform conservation strategies in the future.

 

project goals

The best conservation strategies take into account the natural variation in migration within the population. We currently have very little understanding of this for either species. Chemical analysis of the movements of many fish help us build an understanding of the whole population.

 

To complete this project we will collect sawfish rostral teeth and catfish ear bones from fish captured by fisherman. The details of the study design are still being planned but we hope to focus our efforts on a single population of catfish, which have recently been found to home to their natal river, to minimize the unknowns of movement within a basin as large as the Amazon.

Our most recent expedition revealed that sawfish rostrum are often saved by fisherman, despite laws against their capture and sale. This is due to their value in Asia and to a lesser degree as a spiritual items within some local variants 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. We have identified a preliminary sample-set of rostral teeth from research collections of sawfish rostra in the Amazon region of Pará, as well as from Maranhão state. These samples will allow us to begin reconstructing chemical signatures in these fish for the first time and, with some luck, reconstructing their movements into fresh water as well as their growth and age.  

Our samples will be analyzed in the United States for age, as well as for strontium isotopes and trace elements using cutting-edge techniques at Washington State University and University of Idaho.

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