Overview
Since I first learned about the River Continuum Concept (RCC) in college, I have been intrigued by its ability to predict the longitudinal distributions of primary consumers based on how basal resources (e.g. algae, detritus) aggregate and change along the fluvial continuum. In 2010, as a postdoc in Kirk Winemiller's lab at Texas A&M University (TAMU), I received a Coypu Foundation grant that would allow me to lead a team to test the predictive power of this theory outside of the northern temperate streams where it was originally developed. I particularly wanted to examine how the ecomorphologically diverse assemblages of herbivorous and detritivorous fishes in Neotropical rivers might change or adhere to RCC predictions.
Few Neotropical rivers are ecologically intact and easily accessible along their entire length, but in 2010 the Interoceanic Highway was near complete and it folowed the Arazá-Inambari River in southern Peru from its confluence with the Madre de Dios River at 200 m elevation to its source at 4,300 m. The Arazá-Inambari is part of the Madeira River basin, the largest and most biodiverse tributary of the Amazon, making it ideal for our study. My primary collaborators on this project were river ecologist Katie Roach (then a PhD student at TAMU), macroinvertebrate ecologist Dean Jacobsen (from the University of Copenhagen), and fish biologist Vanessa Meza-Vargas (then a biologist at the Museum of the University of San Marcos in Lima, Peru; MUSM). Also joining us in the field were fellow ichthyologists Don Taphorn (retired Curator of Fishes at MCNG) and José Birindelli (then finishing a PhD at the Museum of Zoology at the University of São Paulo; MZUSP), my friend David Brooks (an artist focusing on environmental issues), and fish biologists Hernan Ortega (Curator of Fishes at MUSM), Max Hidalgo and Rosemary Argomedo (both from MUSM).
Most of the team departed from Lima in trucks on 14 July and headed south along the Pacific Coast. We took a few days to reach Cusco, collecting in Pacific drainages along the way where we collected only Basilichthys (or pejerry), a silverside common along the Pacific Coast of South America. Dean Jacobsen met us in Cusco, then we crossed over a 4,700 m pass in the Andes Mountains before starting our decent into the Arazá-Inambari watershed. We started collecting water, algal and macroinvertebrate data at the source of the Arazá-Inambari, but did not encounter any fish until approximately 2,600 m elevation, where we collected only a single native Astroblepus species and the non-native rainbow trout (Oncorhynchus mykiss). Fish diversity increased as we decended in elevation, reaching a maximum in lowland streams between Puerto Maldonado and the Bolivian/Brazilian/Peruvian border town of Iñapari.
For a week of sampling in the lower Inambari River we were joined by my friend and New York Times jornalist Clay Risen, and friends Mark Dion, Juan Valadez and Brian Booth (all artists who focus on environmental issues). Mark, Juan, Brian, and David spent over 58 person/hours fishing with hook and line but, unfortunately, the lower Inambari was heavily impacted by in-stream mining dredges and shore-based mining operations. Only three fish were caught: two catfishes and one stingray. Clay Risen wrote a Smithsonian Magazine article based on his observations during this trip entitled A Mega-Dam Dilemma in the Amazon. Results of our examination of the RCC were published in the Journal of Biogeography. Specimens collected during this trip are now cataloged at AUM, ROM and MUSM (field number prefix PER10), where they continue to benefit ichthyological research. Published papers that have already benefited from material collected during this trip include the following:
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1. A group photo before departing Lima. 2. Vanessa casting her net in a Pacific Coast river. 3. Pacific slope of the Andes Mountains, which is an arid desert because of the Andes' rain shadow. 4. Greener slopes nearer the Amazon Basin. 5. Don filters water at the source of the Arazá-Inambari while Vanessa collects macroinvertebrates in a Surber Sampler. 6. Katie collecting water chemistry and nutrient data on the tailgate. 7. Rolling stones in search of fishes. 8. Dean's kit for collecting and sorting macroinvertebrates. 9. A stonefly nymph (Plecoptera: Perlidae). 10. Our homemade electrofisher. 11. Non-native rainbow trout (Oncorhynchus mykiss). 12. Native naked suckermouth catfishes (Astroblepidae: Astroblepus). 13. Photographing specimens with Don and José. 14. Katie and Dean work along the banks of the upper Inambari. 15. Setting gill-nets in a lower channel of the Inambari. 16. Mouth of Parodon buckleyi (Parodontidae), a surface-scraping algivore. 17. Spatuloricaria cf. puganensis, an invertivorous species of suckermouth armored catfish (Loricariidae). 18. Turbid waters of a stream being mined for gold entering the clear waters of an intact Andean stream. 19. Wide flood plains of the lower Inambari. 20. Photographing a South American darter (Crenuchidae: Characidium) with Don. 21. Katie, David, Vanessa and José at a lowland stream near Puerto Maldonado. 22. A male whiptail cat (Loricariidae: Loricaria) carrying a raft of eggs. 23. The unfinished Interoceanic Highway bridge across the Madre de Dios River at Puerto Maldonado. 24. Orienting Juan, Clay, Mark and Brian to the geography around Puerto Maldonado. 25. Processing specimens for nutrient analysis as we boat upriver. 26. Don, Juan and I haul a bag-seine in from a backwater of the lower Inambari River. 27. Contents of the bag-seine. 28. An ocellated freshwater stingray (Potamotrygonidae: Potamotrygon motoro) caught by our boat captain Rogelio. 29. Chowtime on the banks of the Inambari. 30. One of hundreds of placer mining operations in the lower Inambari River. 31. Our team at the end of the river trip. 32. Sorting and identifying specimens back in Lima, with new Andean hats. 33. Giving a presentation on loricariid jaw morphometrics to biologists at the Museum of San Marcos in Lima.
Fishes
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1. Aphyocharax sp., 2. Astyanax cf. bimaculatus, 3. Brachychalcinus hummus, 4. Charax caudimaculatus, 5. Creagrutus sp., 6. Hemibrycon inambari, 7. Hyphessobrycon pando, 8. Moenkhausia collettii, 9. Paragoniates alburnus, 10. Tyttocharax tamboensis, 11. Chilodus fritillus, 12. Characidium sp., 13. Corydoras weitzmani, 14. Platyurosternarchus macrostoma, 15. Sternarchorhynchus sp., 16. Ernstichthys megistius, 17. Ancistrus marcapatae, 18. Centromochlus perugiae, 19. Apistogramma rubrolineata, 20. Crenicara latruncularium.
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Sponsors
2010 Elevational Transect of the Arazá-Inambari Watershed, Peru
Work
This fieldwork was sponsored by the Coypu Foundation and The Aquatic Critter Inc.