Fishers and ecosystem modeling

One of the goals that Ana established for her PhD is to understand a little more about the small-scale fishers from Brazilian northeastern coast, bringing their knowledge closer to the academic science. She intended to do that by combining fishers’ knowledge in marine sciences with published literature, showing that fishers could help fill gaps in scientific information.  She has just achieved this goal by publishing her most recent study, which is described below. Ana knows that filling such gaps with alternative methods is especially relevant in data poor places, where such knowledge could be used to base management plans and public policies.

Ana used information she got from fishers and information from the literature to build two marine ecosystem virtual models: one based on scientific information and another one based on conversations with fishers. The models were built in the free software Ecopath with Ecosim, which is nothing more than a computational program where we insert the information we have of a real aquatic environment to get a more detailed and complete virtual environment. This software was created by Villy Christensen and Daniel Pauly in 1992, at the Institute for the Ocean and Fisheries (former Fisheries Centre), at the University of British Columbia (Canada), and is continually updated and enhanced. This program is based on energy balance equations that define the natural dynamic present in the marine environment and the ecological interactions that occur there (for more information about Ecopath: www.ecopath.org).

To build an ecosystem model it is necessary to define the area, add the species or groups of species, insert information about the diet of these species, determine their predators, their dietary intake per day and their growth rate, not forgetting to insert the fisheries, by vessel type and gear. From that information, the software builds the biological interactions and creates a trophic web, just like the diagram below. Besides providing an easy visualization of the ecosystem, the software shows the effects of putting fishing pressure on certain target species, including the consequences of fisheries on by-catch (a common expression in fisheries science to define fish caught unintentionally). By doing so, one can “predict” how the ecosystem would react to an increase or decrease in fishing pressure, restriction of certain gears, creation of no-take zones or even a total ban of fishing. That gives us some direction to plan the consequences of adopting or not specific conservation actions.

What is really interesting about Ana’s study is that the model she built totally based on fishers’ information was almost the same of the scientific one! This is to say that fishers have knowledge similar to science on some issues. For instance, fishers were able to provide information on total and modal weight of the species, their most frequent predators and their diet items.

Of course, fishers don’t know everything! For instance, fishers had trouble answering about the average lifetime of fish species and had difficulties estimating the growth rates for non-pelagic species. Apparently it was easier for them to know such details for species they see on the surface. Besides, familiarity is possibly a strong predictor of the accuracy of the answers provided by the fishers, as they mostly provided answers that regarded their most commonly caught species. Again, they could provide only qualitative information on stock size, a topic that is also hotly debated among scientists as well. It seems like some issues still remain a mystery for all, fishers and scientists alike.

What Ana’s study comes to show is that perhaps filling some of the scientific gaps in marine science with fishers’ knowledge is not a far-fetched dream after all.... Besides, interviewing fishers is cheaper and faster in comparison to scientific research. Some, like Ana, would even say that it is more fun too! 

By Ana Helena.