As the biodiversity of fish species is reduced for several different reasons ranging from toxic runoff to overfishing, researchers find that biomass compensation may impair the health of populations that depend on these fish for their daily nutritional intake.
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The global decline in fish biodiversity
It is estimated that about 2 billion people around the world depend on wild-caught or harvested species such as fish, insects, fruits, and other non-agriculturally produced food products for their nutritional needs. Of these, fish are considered to be the most common and important wild foods as they are often high in protein, zinc, iron, calcium, and omega-3 fatty acids.
Over the past several decades, several different factors have caused significant changes to arise in the biodiversity of wild fish. Some of these factors include overfishing, pollution, climate change, and habitat degradation. Despite these changes in fish biodiversity, there remains a consistent supply of fish to fisheries, as small and fast-growing species often compensate for declines in more vulnerable types of fish.
How can a decline in fish biodiversity affect human nutrition?
While these fish species are more tolerant to these biodiversity changes, they often differ significantly in their nutrient content, which can affect the health of individuals who live in areas that primarily rely on fish for their nutrient intake. In a recent Science Advances study, researchers from Columbia University in New York, NY aimed to understand how this decline in wild fish biodiversity can impact the nutrition status of those consuming these fish.
In their work, the researchers studied people living in the rural area of Loreto, which is a department of the Peruvian Amazon. For this population of approximately 800,000 people, the people of Loreto rely heavily on wild fish species to provide much of their daily nutrients.
Unfortunately, both the increase in local hydropower development, soil erosion, and persistent overfishing have significantly reduced the biodiversity of their freshwater fish population. In fact, it is estimated that Loreto inhabitants will consume fish at least once a day, which amounts to a total of approximately 52 kilograms of fish each year. Despite this reduction in fish diversity, the number of fish available to fisherman in Loreto has remained sustainable for the local population.
To understand how declining fish biodiversity can affect the nutritional status of locals, the Columbia University researchers first examined how many people of Loreto were meeting their annual reference nutrient intake (RNI) for the seven essential animal-derived nutrients. These nutrients include protein, iron, zinc, calcium, and the three omega-3 fatty acids of linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).
When biomass compensation did not occur, the researchers predicted that an average of 1.76% of all nutrients would be a loss to the local population. Notably, when the current fish supply was replaced by smaller and lower-trophic fish, nutrient supplies changed significantly, particularly protein and calcium supplies. While this may be true, the replacement of large-bodied and migrating species with smaller, sedentary, and low-trophic species could actually improve nutrient intake, as the smaller species were found to provide a greater amount of the three omega-3 fatty acids as compared to the larger fish.
Future impacts of reduced fish biodiversity
Overall, the findings of the current study were not purely hypothetical, as many of the stimulated biodiversity changes have been reported in many Amazonian and other tropical inland fish communities. Therefore, although the ability to predict the future of fish biodiversity in the Amazon is not easy, ongoing projects that continue to threaten fish diversity will likely continue to alter the nutritional intake of local populations.
Like any other complex system, you could see a tradeoff. Some things are going up, while other things are going down. But that only lasts up to a point.”
Sebastian Heilpern
While some potential advantages and disadvantages of biomass compensation were identified, the researchers anticipate that the extinction or loss of 40 of the fish species could significantly reduce the nutritional intake of the remaining species that are available for consumption.
- Heilpern, S. A., DeFries, R., Fiorella, K., et al. (2021). Declining diversity of wild-caught species puts dietary nutrient supplies at risk. Sciences Advances 7(22). doi:10.1126/sciadv.abf9967.
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