This African dust acts as an unexpected driver of marine dynamics. It carries radioactive elements and also serves as agricultural fertilizer. Researchers have confirmed that it attracts tuna and helps shape their northward migration. A study involving the Scientific Research Council and partners tracked tropical tuna moving from the equator toward the Canary Islands between January and August. The movement aligns with Sahara dust deposition patterns across the Atlantic, underscoring the Sahara dust’s influence on the marine ecosystem.
These findings carry meaningful implications for fishing and economics. The annual tuna catch in this region is substantial, and the species remains the most important commercial tuna in the Atlantic. Skipjack tuna, commonly found canned, accounts for a large share of landings. The study notes that skipjack represents about 48 percent of total tuna catches, and tropical tuna comprises roughly 56 percent of the ocean’s tropical tuna harvest, according to data from the International Commission for Atlantic Tuna. This insight comes from Sergio Rodríguez, a CSIC researcher in the Institute of Natural Products and Agrobiology who is also the study’s lead author.
Examples of tuna illustrate their importance in the fishing sector. The study highlights the migratory efforts of skipjack as a key example of how environmental factors shape fishing opportunities.
The key to tuna migration
Each year, tuna move northward from the equatorial Atlantic to subtropical waters, reaching areas off Mauritania and the Canary Islands among others. During this journey, tuna groups gather where prey is abundant, feeding on small fish and cephalopods, which in turn sustains sizable tuna concentrations.
Nutrient input in feeding zones matters greatly. Phytoplankton support fuels herbivores, which then energize higher levels of the food web and eventually nourish carnivores including tuna.
The researchers from CSIC, the University of Las Palmas de Gran Canaria, the University of La Laguna, and the French Institute for Research and Development focused on the movement patterns driven by Saharan dust. The Sahara dust travels from North Africa to the Atlantic via the Saharan air layer. Waters beneath this dusty plume often show enhanced nutrient levels due to atmospheric deposition.
Chasing the dust
Because the atmosphere circulates, the Saharan dust layer shifts northward through the year. Tuna drift below this dust stream as it moves. Consequently, main tuna fishing areas shift with the dust layer: equatorial waters in winter, open waters near Liberia and Guinea in spring, and waters off Mauritania in summer. The Canary Islands see peak fishing from June through September, with July and August yielding the strongest catches when the Saharan layer influences the archipelago. The study notes this Atlantic-Saharan tuna migration pattern.
Nutrient input from the Sahara
Marine ecosystems require nutrients to support phytoplankton growth. This research highlights how atmospheric inputs contribute essential nutrients to surface waters. In open oceans, often referred to as blue deserts due to low nutrients, atmospheric deposition becomes the largest nutrient source. Dust from the Sahara contains iron and phosphorus that phytoplankton need to fix nitrogen and build amino acids, along with silicon and calcium that support shell and skeleton formation. Trace metals such as manganese, zinc, cobalt, and nickel are also present, contributing to metabolic processes.
In the Atlantic, the highest tuna concentrations are found off the northwest African coast. Nutrient delivery occurs through a combination of deep-sea nutrient elevations rich in silicon and nitrogen, and Saharan dust deposition that supplies iron, phosphorus, and other essential elements. About 89 percent of Atlantic tuna are harvested in the zone between the equator and the Canary Islands, where Sahara dust makes the strongest contribution.
Dust and broader implications
The accumulation of nutrients from desert dust can benefit other fishing interests as well, including other tropical tuna species of commercial value. The study also suggests a potential parallel migration between Gabon and Angola-Namibia related to desert dust contributions from Namibia and the Kalahari. The team notes that this region may experience uplift effects similar to those observed in the Atlantic-Saharan route, though with a smaller tuna stock.
The research team is multidisciplinary, bringing together experts in tropical tuna, marine biology, meteorology, atmospheric physics, and Saharan dust geochemistry from IPNA-CSIC, EEZA-CSIC, the University of Las Palmas de Gran Canaria, the University of La Laguna, and the French Institute for Research and Development.
Reference work: DOI: https://doi.org/10.1016/j.atmosenv.2023.120022
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Note: This article contains observations about marine ecosystems and migratory patterns tied to dust transport and nutrient deposition in the Atlantic. No contact details are included here. This summary cites the CSIC study and its partners for attribution.