FRESH WATER HABITATS

Fish live in ponds, rivers, dams, lakes and oceans. Some habitats support more fish than others.

 Upper river

A few small fish are found in the upper reaches of a river. For example, where the Zambezi River rises in north -western Zambia, the small, slender kneria fish is found. Many river sources are in rocky high areas. The water is clear, fast flowing (due to steep gradient), oxygen-rich but nutrient-poor. Leaves from riverine trees form the basis of the food chain. Insects dominate the upper river and fish are few.

 Middle part of a river

In the middle of a river, there are more nutrients coming with riverlets. The river becomes wider. There is more light, more fish food but less oxygen. Fish are bigger in size and greater in number than upstream. Small-sized tilapia (about 15 cm long) live here. These areas can be important for fisheries.

 Lower part of a river

The lower section has more organic matter but still less oxygen. Both small and large plants are found. The fish are bigger (eg, catfish) and fish diversity is greater than upstream. Smaller fish such as squeakers live here too. The strong relationship between river size and fish size is not absolute.

 Floodplains

Floodplains are fish nurseries during the rainy season. They are rich in plant food. The matter brought in by floods and drowned vegetation and insects comprise the food. The major fishing areas of Zambia include the Barotse and Kafue floodplains. The Elephant Marshes of Malawi are important for spawning.

 Dams

When a new dam is built, vegetation matter is submerged. The vegetation rots and increases nutrients. And fish production increases. With time water becomes stratified. Light warm water sits on cold denser water. Between the waters, another thin layer of water (thermocline) develops which prohibits the mixing of water. Nutrients sink to the bottom where they cannot be used by minute plants.

But temperature changes or winds can break the division and cause the waters to mix. This is called an overturn. It brings nutrients to the surface where minute plants (phytoplankton), use them for growth. An overturn will kill fish if poisonous gases which accumulate between overturns are released from the bottom.

Natural lakes

The Great African lakes (Victoria,Tanganyika and Malawi/Nyasa) have the world's richest diversity of freshwater fish. They are old lakes and arefound in the East African rift valley. Lake Tanganyika has 230 fish species and over 150 of them are endemic (found nowhere else in the world). Lake Malawi/Nyasa has over 250 fish species and almost 90 percent of them are endemic. 

MARINE HABITATS

>From the Atlantic Ocean off the coast of Namibia, South Africa and Angola, over one million tonnes of salt water fish are landed every year. From the Indian ocean, Mozambique and Tanzania catch some 70,000 tonnes annually. 

OFFSHORE

The largest of marine habitats is the open sea and the richest fishing ground in the region is found in the nutrient-rich Benguela current where water flows almost vertically from the bottom bringing nutrients to the surface (on the coast of Angola, Namibia and part of South Africa). Nutrients result in good plant growth which in turn supports a food chain with high numbers of fish. The Agulhas and Mozambique currents off South Africa and Mozambique lack nutrients.  

NEARSHORE

Estuaries

Estuaries exist where freshwater and sea water meet. They are highly productive nursery areas for sea fish because of the nutrients from both the river and the sea. Fish in the estuaries feed on dead organic matter, suspended organic matter and on invertebrates such as worms.

Mangrove swamps

Mangrove swamps provide food and shelter for fish. They are found on the coasts of Angola, South Africa, Mozambique and Tanzania. Mangroves are plants that grow in salty water near the sea. Leaves shed from mangrove plants are eaten by crabs and also fertilize the water to promote growth of other plants and animals. From each hectare of mangrove about 100 kg of fish, 25 kg of prawns, 15 kg of crab meat, 200 kg of molluscs and 40 kg of sea cucumber can be harvested each year.

Seagrass meadows

Seagrass meadows are found on the sea bed to a depth not exceeding 40 metres. They can also be found on rocky shores. Seagrasses often grow together with algae. These plants provide grazing for fish, shellfish, turtles and dugongs.

Coral reefs

Coral reefs support many fish and nearly a third of all marine fish are found here. In terms of biological wealth, they are like the equatorial rain forests. Their productivity is so high because the algae that live with polyps can fix nitrogen and convert light energy into carbohydrate foods.

FISH CONSUMPTION

The world average fish consumption per person is about 12 kg a year. If all fish caught in southern Africa were equally distributed among the inhabitants each person would eat around 12.5kg a year. But the real average is much less as much fish are exported out of the region.

Even within the same country some people eat much more fish than others because of their location in relation to fish resources. In Angola, for instance, people living near the coast eat double the national average.

COULD WE BE EATING MORE FISH?

Yes, if it were not for:

Overfishing

Overfishing is a problem in southern Africa. In the 1960s and 1970s there was serious overfishing in the marine waters of South Africa and Namibia where pilchard and hake catches declined. Namibia, since independence in 1990, has been able to control fishing and increase fish stocks. However, there is overfishing by foreigners in the marine waters of Angola as control has been made difficult by war.