What Fish Gonads Tell Us About Overfishing

In 2005, CI’s Marine Management Area Science (MMAS) program began a pioneer effort to characterize the reproductive cycles of several threatened and commercially-important fish species in northeastern Brazil’s Abrolhos Bank. The study was recently published in the journal Scientia Marina. Here, Matheus Freitas researcher at the Museu de História Natural Capão da Imbuia in Paraná, Brazil and lead author of the paper explains what they found.

CI’s work to establish “no-take zones” in the waters off Brazil’s Abrolhos region has led to dramatic increases in fish stocks, improving the lives and livelihoods of local communities — and it is important to understand just what bred that success in order to sustain it. One goal of our study was to map the breeding seasons of commercial and endangered species, as well as to find the locations of their major spawning sites. To access the biological materials we needed for our research, we realized we would have to buy fish, as much of the fish caught in Abrolhos is for export to European and North American markets. We soon established a system where I would buy fish at the local fishing port, remove their gonads and stomachs at the lab and resell the fish at the market.

Altogether we analyzed 3,528 fish from eight species selected for the study. By observing factors such as consistency, size and color of gonads, we were able to identify the minimum size at which each species is able to reproduce. We also found that many fish are caught before reaching reproductive maturity, a reality that poses serious threats to the long-term productivity of the local fishery.

In order to ensure protection, we must determine the exact locations where spawning of these species takes place. We are continuing to work in the region to identify these sites; in the meantime, we must use existing knowledge to support measures to protect stocks, including regulations which restrict fishing to certain seasons and only allow fish over a certain size to be caught.

The local community was a key partner in the research study. We interviewed experienced fishermen, who were called to share their knowledge of fish reproduction. The results of the study and its possible impact on fisheries management were also discussed with the community at subsequent meetings. We conducted several lectures and are now in the process of preparing educational materials to disseminate the key recommendations coming out of the research with community stakeholders involved in fishery activities. This is what we call “science to action” — transforming information into knowledge that can contribute effectively to social and environmental conservation efforts in Abrolhos.

The success of this initiative is due to its collaborative, grassroots nature, involving participants from more than a dozen institutions, including governments, NGOs, universities, sponsors and local Brazilian communities. I am especially grateful to the Conservation Leadership Programme and CI staff in the region.

Matheus Freitas is a Ph.D. student at the Federal University of Paraná and a researcher at the Museu de História Natural Capão da Imbuia. Read the paper here or learn about a similar study conducted several years ago on Coiba Island, a former penal colony off the coast of Panama.


  1. CaitlinK says

    This morning I read a news story on Reuters.com about the continued overfishing of Bluefin tuna. It states that at current rates the Atlantic breeding population will be eliminated within three years, and that the average size of a mature fish has more than halved since the 1990s resulting in fewer offspring per adult fish. I am wondering if Conservation International is or will be getting involved in this issue. I find the continued fishing of Bluefin tuna to be appalling, and am saddened that many people do not even know about the issue.


  2. Molly Bergen says

    Hi Caitlin – thanks for your question. Among our other marine protection efforts, CI is working with governments and partner NGOs to improve high-seas policies, which will regulate fisheries on the global commons and prevent further declines in fish stocks. To learn more about overfishing and how you can take action, check out these insights from CI Science Advisor Dr. Bryan Wallace: https://blog.conservation.org/2010/08/bryan-wallace-discusses-declining-fisheries/.

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