photo credit: The giant tambaqui (Colossoma macropomum) in Manaus Fish Market, Brazil. Photo by: Thorke Østergaard.opomum)
A fruit in the flooded Amazon falls from a tree and plops in the water. Before it can even sink to the floor, a 60-pound monster fish with a voracious appetite gobbles it. Nearly a week later—and miles away—the fish expels its waste, including seeds from the fruit eaten long ago and far away. One fortunate seed floats to a particularly suitable spot and germinates. Many years later the new fruit tree is thriving, while the same monster-fish returns from time-to-time, waiting for another meal to drop from the sky. This process is known as seed-dispersal, and while researchers have studied the seed-dispersal capacity of such species as birds, bats, monkeys, and rodents, one type of animal is often overlooked: fish. Jill T. Anderson, a post-doctoral associate at Duke University, however is one of a few researchers who have begun to connect the dots between massive fruit-eating Amazonian fish, such as the weighty tambaqui (Colossoma macropomum), and the diversity and health of the Amazon rainforest. Unfortunately just as researchers are uncovering the importance of these fish, the fish themselves are vanishing in many parts of the Amazon due to unregulated and overfishing.
The seed dispersal activities of many animals is essential for the Amazon and other forests, because, as Anderson explains: “plants rely on the seed dispersal activities of these animals (i.e. birds, bats, monkeys, tapirs, rodents, and fish) to move seeds away from the mother tree to good sites for germination […] For pioneer species like Cecropia (a genus of tree that we studied), seeds might need light gaps to germinate—that is, seeds might have very specific requirements for germination.”
A tambaqui with a radiotelemetry device. Photo courtesy of: Jill Anderson.
In a 2009 study Anderson and her colleagues studied two species of frugivorous fish—the tambaqui and the pirapitinga (both known as pacus)—in Peru. Picking through over a million seeds, they documented 44 species of seeds, including 36 from trees and lianas, from the guts of 195 individual fish.
“But,” she says, “it is likely that [tambaqui] disperse seeds of many more species in different locations. For example, Michael Goulding [from the] Wildlife Conservation Society has done beautiful work, documenting a diverse array of species in the diet of Colossoma macropomum (and other fruit-eating fishes) in Brazil.”
A paper published by Anderson and other researchers this year outlines that the tambaqui are truly long-distance dispersers.
“In our study, fish can carry seeds up to 5.5 kilometers, although it is likely that larger (older) fish can disperse seeds much farther than that,” says Anderson. The older the fish, according to research, the more effective it is at dispersing seeds
“Previous studies of ours, and our colleagues, have shown that younger fish consume fewer fruits and disperse fewer viable seeds,” explains Anderson adding that “in this study, our models indicate that smaller (younger) fish do not disperse seeds as far as larger (older) fish.”
Of course, this finding has implications for conservation, since older fish are vanishing from ecosystems due to overexploitation by locals.
Radiotelemetry crew following a fish. Photo courtesy of: Jill Anderson.
“[Tambaqui] is very commercially important. The population size of this species has decreased by up to 90% in some parts of its range over the past several decades because of overfishing. Fish is the primary source of protein for human populations throughout the Amazon, so it is not surprising that people would overfish a massively large fruit-eater,” Anderson says.
While humans likely have fished for tambaquis and other pacus for millennia, rising populations in the Amazon and increasingly easy access to once impenetrable places have pushed big fruit-eating fish into treacherous territory. Even if these species don’t vanish altogether, a significant drop in the population or a loss of older individuals has the potential of impacting the diversity and abundance of the Amazon rainforest.
Neither the tambaqui, the pirapitinga, nor any of the pacu-like species have yet been evaluated by the IUCN Red List, the main authority behind extinction threats.
Footnotes:
1) CITATION: Banack, S. A., M. H. Horn and A. Gawlicka (2002) Disperser- vs. establishment limited distribution of a riparian fig tree (Ficus insipida) in a Costa Rican tropical rain forest. Biotropica 34(2): 232-243.]
2) CITATON: Isaac and Ruffino ML (1996) Population dynamics of tambaqui, Colossoma macropomum Cuvier, in the Lower Amazon, Brazil. Fisheries Management and Ecology 3:315?333)
CITATIONS FOR ARTICLE:
Anderson, J.T., T. Nuttle, J. Saldaña Rojas, T. Pendergast, A. Flecker. 2011. Extremely long-distance seed dispersal by an overfished Amazonian frugivore. Proceedings of the Royal Society of London B. doi:10.1098/rspb.2011.0155.
Anderson, J.T., J. Saldaña Rojas, A.S. Flecker, 2009. High quality seed dispersal by Amazonian fruit-eating fishes. Oecologia. 161: 279-290
STAR FISH & SEAFOOD FOOTNOTE:
Our Tambaqui — closely related to the pacu fish — is farm raised in the clean waters of the Amazon, in the state of Rondônia, Brazil. Omnivorous, no fish meal or fish oil is needed for feeding. Our suppliers farm achieved the Best Aquaculture Practices (BAP) label, likely making our Tambaqui the first sustainably farmed in the world. Tambaqui ribs- also referred to as pacu ribs- are ideal alternatives for non-beef or chicken consumers in seafood, specialty, BBQ and Fried wings restaurants.
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