Amazon Megafish Migration

In this project Ecologists Without Borders is partnering with two researchers in building our understanding of long distance fish migration of large fish in the Amazon basin. Jens Hegg, a PhD Candidate at University of Idaho, and Tommaso Giarrizzo of the Federal University of Pará, Brazil, are the first research team to utilize new isotopic techniques to uncover details of the migration of three species of goliath catfish (genus Brachyplatystoma) two of which span the length of the Amazon basin from the estuary to the Andes foothills. In addition the project is exploring the use of these isotopic techniques to understand the movement of IUCN Redlisted sawfish, which make unexplained upriver movements into the Xingu River basin and are often killed after becoming entangled in fishing nets.

This project is in the planning and funding stages, with a crowdfunding effort currently underway on Experiment.com.  This funding effort will cover travel costs associated with planning a more comprehensive study and collecting initial samples, as well as providing an important public awareness and science communication role.  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.

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 last year 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. Sawfish sample collection will provide a small, preliminary dataset to explore the feasibility of recovering microchemistry from rostral tooth bands.

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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