African desert dust influences migrations and fisheries of the Atlantic skipjack-tuna

Atmospheric deposition of desert dust and other aerosols influence on the open ocean ecosystem and climate. These aerosols provide iron, phosphorus and bio-essential trace elements, which affect the composition and growth of phytoplankton, generating new organic matter that is distributed across the food web. Although this process has an impact on upper trophic levels and fisheries, direct evidence is lacking. Skipjack tropical tuna (Katsuwonus pelamis) is the most important commercial tuna in the Atlantic, main stocks occur in the tropical and subtropical North-East Atlantic. We found that the migrations and fisheries of skipjack are connected to Saharan dust variability. From boreal winter to summer, skipjack performs an Atlantic-Saharan migration, from equatorial (0-5 degrees N) to subtropical waters of the North-East Atlantic (regularly reaching open waters off Mauritania similar to 20 degrees N and the Canary Islands similar to 28 degrees N), tracking the seasonal shift of dust deposition in the North-East Atlantic. The observed long-term associations of skipjack catch with the seasonal cycles, anomalies and meridional variability of dust over the North-East Atlantic, shows that along the year skipjack catches mainly occur in waters affected by massive dust deposition linked (i) to dust wet deposition in tropical waters and (ii) to dust dry deposition in the Saharan desert-dust outflow. Atmospheric deposition of dust in the open ocean and in upwelling waters contributes to support zooplankton-rich areas, which are optimal for feeding small fish, molluscs and cephalopods, and suitable for feeding large predators, as skipjacks, where they are caught in abundance. The most important fishing area of Atlantic skipjack tuna is located off North West Africa in the waters affected by massive dust deposition that underly the dusty airstream from the North Africa desert. The role of dust as fertilizing and supporter of phytoplankton and zooplankton rich areas also has implications for other species of fishing interest, including other tropical tuna (e.g. bigeye and yellowfin), which are often exploited simultaneously with skipjack by the same fisheries. As far as we know this is the first study showing the connexions between atmospheric inputs of desert dust to ocean and the migrations and fisheries of marine species. These results have important implications on our understanding on the influence of atmospheric dust on marine ecosystems and on the management of fisheries.

Automated summary

Atmospheric deposition of desert dust and other aerosols has a significant impact on the open ocean ecosystem and climate by providing essential elements for phytoplankton growth and affecting the composition of the food web. However, direct evidence of its effects on upper trophic levels and fisheries is still limited.