By Ana Helena Bevilacqua
Everything started in 2007, when a São Paulo girl left her hometown to live on the Amazon. The main objectives were to get a master’s degree, study freshwater fish physiology, get to know the forest, learn how to fish, and to spread her wings. She achieved all of these things, fishing abilities left to be desired…
The master’s project fieldwork required long periods of time spent in the Amazon’s countryside, collecting fish, doing experiments, meeting people, learning the local customs, and living intensely with the forest and its traditions. And in the middle of this ocean of new experiences, a passion for the anecdotes told by fishers arose!
At the time, the stories were not the goal of the study, but they quickly became a personal goal. Long, late afternoons were spent together with fishermen and their families, with many kids, dogs and, for sure, a good cup of sweet, fresh coffee, a local tradition not to be missed!
From these relaxed chats, was born ideas for a future PhD. Until this point, the PhD was merely a faint idea since the master’s degree needed to be finished first. As time passed, the fieldwork was finished, the master’s degree was defended, and the will to continue the talks was only increasing. But what was next?
But there, a PhD topic had already been mapped out: human ecology of small-scale fishers!
And so, the migration to the marine sciences happened as naturally as those long conversations on the riverbank. Giving way to more targeted conversations, accompanied with only clipboard, paper, pencil, and a huge salt-water ocean ahead.
The perfect life: go to the beach to spend all day talking with fishers! This is all that I wanted! But, there was more to this, I had an ultimate goal, so the conversations were not uncommitted and light. There were questions to be answered, a methodology to be followed, and something to be done. After all, it was PhD fieldwork!
The goal of my PhD was to understand a little more about the small-scale fishers from the northeast coast of Brazil, and communicate traditional fishers’ knowledge to the scientific community. Basically what I wanted to do was to combine the fishers’ stories with traditional knowledge of marine sciences, and show that this knowledge can fill the gaps in scientific information in areas with limited data available. This information from local fishers could be used in sculpting local management plans and public policies. However, this first required me to prove that there is knowledge and truthful information behind the fishers’ anecdotes.
I needed to compare the information provided in the fishers’ stories with the information from scientific literature, which I did using a marine ecosystem virtual model. This virtual model tries to represent all ecological relationships that exist in the real ecosystem, such as growth, reproduction, and predation. For this, I built two models: one based on scientific information and another one based on my conversations, and then compared the two!
For this ecosystem model I used free software called Ecopath with Ecosim, which is a computational program where we can insert all the information of a real environment and to create a virtual one. This software was created by Villy Christensen and Daniel Pauly in 1992, at the Institute for the Ocean and Fisheries (ex-Fisheries Centre), in the University of British Columbia, in Canada, and is constantly being enhanced. The program I use is based on energy balance equations that define the natural dynamics present in the marine environment and the ecological interactions that occur there. In other words, all energy available is cycled between all species, and is responsible for organismal growth and reproduction. For this, we use information about how much food predators require and compare this to production rates of the prey. The program is able to create an “ecological snapshot” about what is happening in that environmental (if you want know more about this software, go to ecopath.org).
For the construction of a virtual marine ecosystem (or freshwater, if you prefer), we must define the area, insert all species or groups of species, include information about the diet of each organism, determine the predators, how much food each one needs per day and growth rates. Of course we also must include the fisheries, by vessel type and gear.
After this, the software can use the biological interactions to create a trophic web of who eats whom, just like the diagram below. The advantage of this model is that in addition to creating an easy visualization ecosystem, we can change fishing pressure on target species, and also include the by-catch (common expression in fisheries science to define the species that was caught unintentionally).
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| This food web was created using Ecopath with Ecosim software, using only the fishers’ information. The color indicates the trophic level: in red are the producers at the bottom of the ecosystem (seaweeds, phytoplankton, and detritus), and blue is the highest trophic level, represented by predators (shark, dolphin and large pelagic). The circle size represent the biomass (amount of individuals or weight of each group) and the lines represent the links between each group. |
