This african haze It is a surprise drawer because although it is news that it contains radioactive elements, it also turns out to be agricultural fertilizer. It has now been confirmed to attract tuna and condition their migration. A study conducted with the participation of the Scientific Research High Council (CSIC), tropical tuna (Katsuwonus pelamis) are caught in abundance, moving north from January to August, from the equator to the Canary Islands, By following the dust deposition patterns of the Sahara in the Atlantic. The work published in atmospheric environment, It highlights the importance of Sahara dust in the marine ecosystem.
“These results major fishing and economic effectsWith an annual catch of about 253,000 tons per year, mounted tuna is the most important commercial tuna in the Atlantic.
It is an important species in fishing activities. Skipjack tuna is usually available canned. Their catch represents 48% of the total tuna catch According to data used in this study provided by the International Commission for Atlantic Tuna Conservation, this is 56% of tropical tuna caught in the ocean,” says Sergio Rodríguez, a CSIC researcher at the Institute of Natural Products and Agrobiology and the study’s first author.
The key to tuna migration
Heron tuna migrate north from winter to summer each year from the equatorial waters of the Atlantic to the subtropics and reach Mauritania and the Canary Islands, among other regions. During this migration, tuna fish It tends to gather in areas where it finds prey. which to feed (mainly small fish and cephalopods) and in turn, tuna is plentiful.
These areas require significant nutrient input. The feeding of marine herbivores with this phytoplankton, which enables the growth of phytoplankton (grass or seagrass) and the feeding of marine carnivores through the food web with these herbivores.
The study, published by researchers from CSIC, the University of Las Palmas de Gran Canaria, the University of La Laguna and the French Institute for Research and Development, focuses on the movement patterns of Saharan dust.
Desert dust from the Sahara is exported from North Africa to the Atlantic by an air current called the Saharan air layer. The Atlantic waters below this dusty airflow are generally Enriched with dust from the Saharadue to atmospheric deposition.
chasing the dust
“Due to the general circulation of the atmosphere, the dusty layer of Saharan air moves northward from month to month (winter to summer) and tuna drifting under this dust stream” indicates Rodriguez.
Because of this displacement, the main tuna fishing areas are near the equator in winter, in open waters off Liberia and Guinea in spring, and in open waters off Mauritania in summer. In these regions, the tuna fishing season usually begins with the seasonal shift of the Saharan air layer over them, starting in April in Senegal and June in the Canary Islands.
In the case of the Canary Islands, the skipper hunting season is usually from June to September, and maximum fishing takes place in July and August, a period when the Saharan air layer affects the archipelago. “Researchers have found this migration from the equator to the Canary Islands, Atlantic-Saharan migration of captain tuna”, explains the researcher.
Nutrient powder of the Sahara
Marine ecosystems need nutrients for phytoplankton growth. They can reach surface waters in various ways. This new study highlights the importance of the atmospheric contributions of these particular nutrients.
“To the open waters oceans are often called ‘blue deserts’ because they tend to be often poor in nutrients and therefore phytoplankton; in these areas atmospheric deposition represents the largest input of nutrients and in this sense we emphasize the contribution of dust from the Sahara. It contains iron (4%) and phosphorus (‰0.8), which are necessary for phytoplankton to fix nitrogen and use it to form amino acids,” says Rodríguez.
“It also contains silicon (18%) and calcium (4%), which are essential for phytoplankton to form the skeleton and shell, and also contains metals such as manganese, zinc, cobalt and nickel, which are essential for metabolic functions,” he adds.
In the Atlantic, the greatest concentration of Atlantic tuna is found off the northwest coast of Africa. two related contributions of nutrients: deep sea elevations (rich in silicon and nitrogen) and Saharan dust deposition (providing a cocktail of iron, phosphorus and essential trace elements). 89% of Atlantic tuna are caught between the equator and the Canary Islands, the region with the highest contribution of Sahara dust.
This large accumulation of nutrients with field dust it can also benefit other fishing interests, including other tropical tuna of commercial interest. This new study also suggests that there may be a similar migration between Gabon and Angola-Namibia to the Atlantic-Saharan migration, but that, although containing a smaller tuna stock, may be linked to contributions from desert dust from Namibia and the Kalahari to current uplift. benguela
The research team that conducted this study is multidisciplinary and includes experts in tropical tuna, marine biology, meteorology, atmospheric physics, and the geochemistry of Saharan dust from IPNA-CSIC, EEZA-CSIC, University of Las Palmas de Gran Canaria. 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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