- In Cabo Verde, as in many low-income countries in Africa, the historical record of fish catch is incomplete, making it hard to know what’s been lost and what’s required to fully rebuild.
- In a new study, researchers interviewed fish workers to understand how catches have changed over the last five decades, finding evidence of a major decline in volume of catch and maximum size of key species.
- The study also shows that young fishers and fishmongers don’t fully realize the scale of the loss — a case of what scientists call “shifting baselines.”
- Fishing communities on the West African mainland tell a similar story of decline, pointing to the urgency of centering local knowledge when devising fisheries management and conservation policies.
In Cabo Verde, as in many low-income countries in Africa, the historical record of fish catch is incomplete, making it hard to know what’s been lost and what’s required to fully rebuild. In a new study, researchers used an old-fashioned workaround to understand how fish catches have changed over time: They tapped local knowledge, speaking to Cabo Verdeans up to 77 years old.
The study, recently published in the journal Marine Policy, indicates there’s been a “staggering decline” in fish stocks around Maio, one of the archipelagic nation’s 10 islands, since the 1970s, in terms of both volume of catch and maximum size of key species. The study also shows that young fishers and fishmongers don’t fully realize the scale of the loss — a case of what scientists call “shifting baselines.”
Younger people on Maio tend not to perceive the decline “because they don’t know what is the normal state of the environment, of the fishing and of the catch,” study lead author Thais Peixoto Macedo, a Ph.D. student at the Institute of Environmental Science and Technology in Barcelona, told Mongabay.
Cabo Verde lies in the Eastern Atlantic Ocean, some 570 kilometers (350 miles) west of Senegal on the African mainland. It’s considered part of West Africa, a region rich in marine resources but also threatened by intense fishing pressure. All of the key commercial species are overexploited or fully exploited in the Canary Current, a large marine ecosystem encompassing the waters of several West African nations, including Cabo Verde. As in other countries in the region, foreign interests dominate industrial and semi-industrial fishing in Cabo Verde, which was a Portuguese colony until 1975.
Maio is more than four times the size of Manhattan and has a population of just 6,330. It’s one of the most economically disadvantaged islands of Cabo Verde, and people there subsist largely from small-scale fishing.
Statistics on small-scale fishing in Maio were collected only from 1995. Macedo and her team’s analysis of that data shows a steady decline in total catch per fishing trip over the last three decades. However, that official data is incomplete, having only been collected at one beach.
To try to fill in the gaps, Macedo, who’s also a coordinator at the local nonprofit Maio Biodiversity Foundation, worked with a colleague there to interview more than 150 fishers and fishmongers. The jobs are divided along genders lines: Men generally fish by handline from 3-to-8-meter (10-to-26-foot) boats with outboard motors, while women process and sell the catch.
The researchers asked about work history — about half of the fishers had started the job between age 12 and 18 — and catch history, using a tape measure to estimate sizes and an identification guide to determine species. They then compared the results for older (at least 50), middle-aged, and young (below 30) interviewees.
The differences were pronounced. On their best-ever fishing day, the older fishers recalled having a median catch of 200 kilograms (440 pounds); the middle-aged group, 75 kg (165 lbs); and the young group, just 52 kg (115 lbs). Likewise, the size of the largest fish older fishers had ever caught was much bigger than for young fishers. For yellowfin tuna, used as an indicator species, one older person reported having caught a 2.1-m (7-ft) specimen weighing 129 kg (284 lbs), while the largest any young person had caught was a 1.85-m (6-ft) individual that weighed 70 kg (154 lbs).
Reconstructing historical data on the sizes of individual fish was an important part of the study, Macedo said, because smaller body size is used as an indicator of heavy fishing pressure. “That’s something that the official [landing] data doesn’t provide,” she said. “They don’t have information about the size. It’s another metric that shows the fishing pressure.”
While most fish workers on Maio agreed that local fish had declined in abundance, there were differences across age groups. Among the older set, 98.3% reported that fish abundance had declined, whereas just 76.5% of the young group did. That is, nearly a quarter of fish workers under 30 seemed to have lowered expectations of their marine environment — shifting baselines.
The interviewees most frequently cited semi-industrial purse seining as the main cause of the fish decline. Purse seining involves a boat lowering a large cylindrical net and cinching it together at the bottom, like a drawstring purse, to catch all that’s inside. Some semi-industrial vessels engage in illegal activities such as night-light fishing, which can attract large schools of fish and lead to overexploitation, and fishing in zones reserved for artisanal fishers or marine protected areas (MPAs), the small-scale fishers reported. In Cabo Verde, the MPAs are essentially paper parks, due to limited government capacity to enforce the rules, Macedo said.
The semi-industrial vessels, which the study says have caught “great amounts of small-pelagic fish since 1992,” are generally 8-20 m (26-66 ft) long and operate out of the main island of Santiago. They’re nominally owned by Cabo Verdeans, but many of the beneficial owners are in fact foreign, Macedo said.
Foreign-owned industrial vessels also work in Cabo Verdean waters, which cover an area larger than Texas, but Maio fishers rarely mentioned them as a threat, perhaps because they tend to operate further out at sea, the study suggests. The industrial vessels operate under fisheries agreements that have been criticized as leading to unsustainable exploitation, lacking in transparency and providing insufficient funds for local communities, given the value of the marine resources being extracted. The most prominent is a tuna deal with the European Union that allows in 56 industrial vessels.
Dyhia Belhabib, principal fisheries investigator at the NGO Ecotrust Canada, told Mongabay that the type of research Macedo led is essential to understanding the state of fish stocks. Belhabib said the findings of decline were not surprising but “it’s something that we will never say enough, we will never document enough.” She praised the researchers for doing fieldwork that centered local knowledge: “They actually went to the communities and spoke with the communities.”
Belhabib said she’d just returned from a work trip to coastal areas of mainland West Africa and noted the similarities to Cabo Verde, including small-scale fishers’ belief that industrial or semi-industrial vessels affect their own catch.
“I have spoken with the communities in Senegal and Sierra Leone and the same things are said over and over again,” she said. “’We catch less fish. We don’t want to see these big boats here again.’”
To develop fisheries management plans that center local interests will require good data, experts say. A study published earlier this year found that data based on local knowledge were on par with standard scientific methods for reconstructing catches. Macedo and her team conclude that local knowledge “should be regarded as a highly valuable cultural and ecological asset in fisheries management and conservation.”
Banner image: Small-scale fishers bring their boat to shore on the island of Maio in Cabo Verde, an archipelagic nation in the Eastern Atlantic Ocean. Most of the artisanal boats are 3-to-8 meters (10-to-26 feet) long. The Maio fishers generally use handlines. Image courtesy of Thais Peixoto Macedo.
Fishers’ memories on par with scientific data on historic catches: Study
Citations:
Macedo, T. P., Ziveri, P., Varela, B., & Colonese, A. C. (2025). Local knowledge and official landing data point to decades of fishery stock decline in West Africa. Marine Policy, 171, 106447. doi:10.1016/j.marpol.2024.106447
Failler, P. (2020). Fisheries of the canary current large marine ecosystem: From capture to trade with a consideration of migratory fisheries. Environmental Development, 36, 100573. doi:10.1016/j.envdev.2020.100573
Aquino, M. L. (2023). The limits of the European Union’s fisheries agreements as sustainable development instruments: The case of Cape Verde. Marine Policy, 148, 105455. doi:10.1016/j.marpol.2022.105455
Castello, L., Martins, E. G., Sorice, M. G., Smith, E., Almeida, M., Bastos, G. C., … Lopes, P. F. (2024). Local knowledge reconstructs historical resource use. Frontiers in Ecology and the Environment, 22(5). doi:10.1002/fee.2726
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