FAO.org

After one month of surveying the waters around the Cabo Verde Islands, the research vessel Dr Fridtjof Nansen returned to port in Las Palmas, Spain.

In total, more than 400 fish and invertebrate species were documented during the survey carried out from 19 November to 15 December within the framework of the EAF-Nansen Programme. Almost 8000 individuals were measured and weighed to obtain information on the abundance and distribution of demersal and pelagic resources around the Cabo Verde Islands. Sixteen scientists from Cabo Verde took part in the survey, contributing knowledge on marine resources and ecosystem as well as supporting fish sampling, plankton research and oceanography. Participants also received on-the job-training and learned about the use of various equipment, sampling procedures and species identification from the scientists from the Norwegian Institute of Marine Research (IMR) in Bergen, Norway, and a taxonomy expert from the Spanish Institute of Oceanography (IEO), respectively.

Comparing current findings with those from the two previous Nansen surveys in Cabo Verde, in 1981 and in 2011, the 2021 survey demonstrated a considerable decline in both pelagic and demersal species over time. Species like Decapterus macarellus (mackerel scad), D. punctatus (round scad) and D. rhonchus(false scad) accounted for the main pelagic species documented during the 2011 Nansen survey in Cabo Verde, whereas during the recent survey only a few individuals of Decapterus punctatus and none of the other two species were caught. While these findings need to be carefully evaluated, the current results raise some concerns as regards the status of these stocks.

Interesting oceanographic features were also recorded, such as strong currents and high exchange of water masses in some areas, probably affecting the transport of eggs and larvae of the various fish species around the Cabo Verde Islands. Further studies are needed to identify key spawning areas and to analyze how spatial and temporal closures of these areas could enhance fisheries sustainability. Data and information on species occurrence and their life cycle, coupled with information on environmental variables within which they are found, provide useful information on environmental preferences or so-called “essential habitats.”

“Different species have different environmental preferences. Understanding these can for example help understand the potential effects of climate change on their distribution and abundance,” explains Kathrine Michalsen, survey-coordinator at IMR and the cruise leader of the Cabo Verde survey.

During the expedition a few rare species were also found. One of them is the mollusc Diadora tereza discovered for the first time during the Nansen survey in 2011 by a local expert. Another interesting finding during the survey was catching a species of sandperch (Parapercis atlantica), a rare endemic fish caught for the first time 138 years ago by the French vessel Talisman in São Vicente – Santo Antão Channel. Since then, it was caught again, 128 years later, during the 2011 survey in Cabo Verde by the research vessel Dr Fridtjof Nansen and during the 2021survey, a decade later.

Attention was also given to the occurrence of marine debris and microplastics in the survey area. Only a few microplastics particles were observed in surface waters, probably because of the strong winds and high waves that resulted in the particles becoming unavailable to the sampling gear. The expedition team found marine debris, including lost fishing gears in trawl catches as deep as 150 m.  
All data and samples collected from this survey will be further analyzed, in close collaboration with scientists from the Institute of Sea (IMar) in Cabo Verde. The survey report and scientific publications will soon be made available to inform improved fisheries and ocean management.