WIOMSA ScienceNews: Upwelling and the influx of freshwater increase fisheries productivity


A study of primary productivity in Kenya’s territorial waters has demonstrated that upwelling is associated with high fisheries output.

Scientists from ten institutions in Kenya, South Africa, Tanzania, the United Kingdom and the United States of America collaborated in the Productivity in the East African Coastal Current under Climate Change (PEACC) project that produced the research findings. Funding for the project came from WIOMSA and the Intergovernmental Oceanographic Commission of UNESCO.

The study’s objective was to investigate the responses of biological productivity and fisheries to changes in atmospheric and oceanographic conditions in the upwelling region associated with the East African Coastal Current, with a focus on two case study sites: Tanzania’s Pemba Channel and Kenya’s North Kenya Bank.

Joseph Kamau, a senior research scientist at the Kenya Marine and Fisheries Research Institute (KMFRI), is the lead author of two papers that present the results of the study.  The first paper “Factors influencing spatial patterns in primary productivity in Kenyan territorial waters” presents an overview of the relationship between levels of primary productivity and the biomass of pelagic fish.  The second one “Employing multivariate analysis to determine the drivers of productivity on the North Kenya Bank and in Kenyan territorial waters”presents an analsyis of the oceanographic and biological, geological and chemical parameters and processes that influence productivity.

“Our goal was to gain an understanding of what is happening in our territorial waters and what is driving the productivity within these systems,” explains Kamau.

Oceanographic sampling was made possible by the commissioning of the Kenyan national research vessel Mtafiti. The vessel is equipped with  a vast array of sensors and mooring equipment used for sampling seawater and researchers working on board were able to collect a range of oceanographic data across multiple parameters that were applied in the study.

The regions of Kenya’s territorial waters associated with high productivity, were also associated with high fish densities; the fish density signal was highest on the North Kenya Bank and in the south around the Vanga–Shimoni area. The study showed that upwelling (the movement of dense, cold and nutrient-rich water to the surface of the ocean where it stimulates the growth and reproduction of phytoplankton) and the influx of fresh water loaded with sediments and nutrients, account for much of the productivity at the sites associated with high productivity. In the case of the North Kenya Bank, these processes are enhanced by localized disturbance caused by the collision of the East African Coastal Current with the Bank.

“The processes are interlinked,” explains Kamau. “Whereas much of the productivity is driven by upwelling, there was also a signature productivity driven by particulate organic carbon from the margins (of the marine waters), like the mangrove ecosystems, as well as riverine flows that were contributing to particulate organic carbon influx into the open waters.”

The Tana River, which discharges 7 million tons of sediment into marine waters every year, is a major source of riverine inputs.

Different oceanographic parameters influence primary productivity in the study area as reported in the second paper.  The process of remineralization – the breakdown or transformation of organic matter derived from a biological form into its simplest inorganic form – also has some influence in the productivity of the area.

Although both studies utilized complex oceanographic principles and techniques to generate results, their results have real application for Kenya, says Kamau:

“I cannot overemphasize the importance of these studies,” he says. “The blue economy is a priority for the Government of Kenya – the President has taken it upon himself to highlight the importance of blue economy because this is a resource that has not been harnessed by Kenya. The concept of blue economy is expansive, but I think the nation has taken it up and given it a lot of importance.”

The Kenyan fishing industry is increasingly embracing offshore fishing grounds and the North Kenya Bank is emerging as the next fishing frontier. Both studies have provided insight into the processes driving the productivity in Kenya’s territorial waters and, in turn, its fisheries.

“It is very important that if you are going to harness a resource, you need to understand that resource. Management is informed by information and data collection that can drive policies on how to harness such a resource,” he says.

According to Kamau, the research conducted under the umbrella of the PEACC project stimulated interest in oceanographic studies. These have continued under SOLSTICE-WIO, a four-year project funded by the Global Challenges Research Fund which addresses sustainable development challenges facing developing countries. The Nairobi Convention, through the SAPPHIRE project, has also complemented the research initiated by WIOMSA.

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