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A member of the fish Family Cynoglossidae found in the catch from the multi-net.
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3rd Cruice Diary: Plankton and environmental monitoring

During this leg of the cruise Bjørn Krafft (Institute of Marine Research, IMR, Norway) and Ivance Monteiro (National Institute for Fisheries Development- INDP, Republic of Cape Verde) collect data that are analyzed for marine nutrients, chlorophyll, pheopigments, phytoplankton and zooplankton. They also analyze data used to calibrate instruments operated from the ship to gather information on physical and biological oceanographic properties (Conductivity, Temperature and Depth (CTD), saturated oxygen, chlorophyll and fluorescence).

The survey area is a coastal upwelling system with a continental shelf that extends 150 km offshore at the most, sustaining large populations of pelagic fish and consequently very important fisheries. It is a dynamic system with seasonal fluctuations and the production rate and species composition of both phyto- and zooplankton is influenced by a number of physical factors such as bottom bathymetry, ocean currents, wind strength and direction and temperature. In this upwelling system the deep water; low on oxygen but rich on nutrients, mix at a high rate with the nutrient poor, warm oxygen rich surface water and increase the production of marine life.
However, some areas within this region have very strong stratified deep layers with oxygen depleted water, and very little mixing occurs. Here the dissolved oxygen has reached a point where it becomes detrimental to aquatic organisms living in the system, so called “dead zones”. As a consequence of the global climate change, increased warming of the surface water may strengthen the stratification of these water layers, reducing the mixing effect between the deep and surface layers.

In other parts of the world such dead zones have been observed moving into relatively shallow water, where the richest marine ecosystems are, with adverse consequences for ocean life. Our study focuses on the distribution, biomass and species composition of the plankton communities and investigates effects on these communities from the physical properties that they depend on. This will enhance our understanding of the linkage between the physical and biological environment for this area and contribute to predict future changes.

The data collected during our survey will be compared with historical data and will constitute the basis for a long time monitoring of this system. Our results will be implemented with the output from the other parts of this ecosystem survey, and will together with these constitute an important knowledge tool for the management system to set quotas for a sustainable fishery.

The two scientists represent two different countries with different scientific background, and find it very interesting and instructive to compare and exchange knowledge. Ivance, will return back to her home country in a few days, when we reach Dakar in Senegal and looks forward to see her family again, while Bjørn continues this adventurous journey until this leg of the cruise ends in Nouadhibou, Mauritania.