Learn more about sea creatures
Ocean Month talk
One of the sustainable development goals to look at is climate change, explained Unam lecturer, Margi Wilhelm.
Swakopmund hosted an Ocean Month talk at the Swakopmund Museum lecture hall on June 20. The main speaker was Margit Wilhelm, a lecturer at the University of Namibia (Unam) in the Department of Fisheries and Ocean Science.
“One of the sustainable development goals to look at is climate change. I examine climate change and fish growth in relation to that, and for that, I need to explain a little bit about the climate and the ocean.
“First, we have wind, particularly southwesterly wind, especially in Lüderitz, but all along the coast up to the Kunene. The wind comes from the southwest, but due to the movement of the wind and the Earth, called the Coriolis force, the surface water moves offshore, leaving a gap.
“As a result, nutrient-rich bottom water, rich in nitrogen, rises to the surface, a process called upwelling. When these nutrients come in contact with sunlight, plants can grow through photosynthesis, resulting in a plankton bloom. Plankton are the small plants in the ocean,” explained Wilhelm.
She further elaborated that when studying fish and their productivity, they analyze it in relation to climate, upwelling, and food sources.
The water is warm in some areas, such as the Angola-Benguela, which is one of the warm hotspots. Sea surface temperatures have been rising over time, making it one of the ocean warming hotspots in the world. Conversely, the Lüderitz upwelling cell has been decreasing, causing that area to cool. Fish accustomed to a certain temperature range are now experiencing conditions that are too warm on one side and too cold on the other, reducing their habitable range. The cooling area has been termed a refuge for fish that cannot tolerate warm waters.
“When it comes to growth rates, I need to explain what an otolith is. An otolith is a fish ear or ear bone. The term ‘otolith’ actually means ‘ear stone’. It’s a bone in the head, near the brain of the fish, similar to human ears but without external features,” said Wilhelm.
“We studied deep water hake otoliths, and when sliced, you can see rings, similar to tree rings. By measuring the increment widths, we can determine relative annual growth.
“We had otoliths from 1990, so if a fish was eight years old in 1990, we could trace back to 1982. Each fish has a growth increment width; when the fish is young, it grows quickly, and as it ages, growth slows,” she added.
“One of the sustainable development goals to look at is climate change. I examine climate change and fish growth in relation to that, and for that, I need to explain a little bit about the climate and the ocean.
“First, we have wind, particularly southwesterly wind, especially in Lüderitz, but all along the coast up to the Kunene. The wind comes from the southwest, but due to the movement of the wind and the Earth, called the Coriolis force, the surface water moves offshore, leaving a gap.
“As a result, nutrient-rich bottom water, rich in nitrogen, rises to the surface, a process called upwelling. When these nutrients come in contact with sunlight, plants can grow through photosynthesis, resulting in a plankton bloom. Plankton are the small plants in the ocean,” explained Wilhelm.
She further elaborated that when studying fish and their productivity, they analyze it in relation to climate, upwelling, and food sources.
The water is warm in some areas, such as the Angola-Benguela, which is one of the warm hotspots. Sea surface temperatures have been rising over time, making it one of the ocean warming hotspots in the world. Conversely, the Lüderitz upwelling cell has been decreasing, causing that area to cool. Fish accustomed to a certain temperature range are now experiencing conditions that are too warm on one side and too cold on the other, reducing their habitable range. The cooling area has been termed a refuge for fish that cannot tolerate warm waters.
“When it comes to growth rates, I need to explain what an otolith is. An otolith is a fish ear or ear bone. The term ‘otolith’ actually means ‘ear stone’. It’s a bone in the head, near the brain of the fish, similar to human ears but without external features,” said Wilhelm.
“We studied deep water hake otoliths, and when sliced, you can see rings, similar to tree rings. By measuring the increment widths, we can determine relative annual growth.
“We had otoliths from 1990, so if a fish was eight years old in 1990, we could trace back to 1982. Each fish has a growth increment width; when the fish is young, it grows quickly, and as it ages, growth slows,” she added.
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