Lake Naivasha Gives Up Its Tilapia
Thursday, March 17, 2005
The Nation (Nairobi)
March 17, 2005
Posted to the web March 16, 2005
Fish harvests in Lake Naivasha, particularly of the popular tilapia, have in the last few years declined from 40 metric tonnes annually to no more than a trickle today.
Less than 10 years ago, members of Lake Naivasha Fishermen Co-operative Society were managing 120 boats and landing about 40 metric tonnes of fish but today they can hardly afford a tilapia meal for their families.
Because of this decline of fish stocks in the lake, the Fisheries Department has cut down the number of boats to only 40, consequently putting a lot of fishermen out of business. Mr David Kilo, then the society's secretary, says during those good times they were landing at least 12 metric tonnes of blackbass in a year but the scenario had changed completely by the year 2000 when a ban was imposed ostensibly to check over-fishing.
Although the ban has since been lifted, fishermen complain that tilapia and blackbass species have declined so much that fishermen are now relying on the newly introduced common carp that is not popular with consumers. But even for this, a boat can hardly land a crate in a day.
The fishermen claim stocks failed to increase even when the ban was imposed because the water fowls that prey on fish had increased considerably since the 1998 El Nino deluge.
Mr Kilo said there were more than 1,500 cormorants and other birds that prey on fish in the fresh water lake. Among them are fish eagles and pelicans that harvest huge numbers of fish per day.
The fishermen say they have noticed a change in the colour of water during the last few years and that some of the common carp they caught had distended belies that contained a whitish fluid.
Mr Kilo who is also the chairman of the Lake Naivasha Anti-poaching Lobby Group has since abandoned fishing and switched to boat excursion business for survival.
Some scientists attending a 1999 conference on Sustainable Management of Tropical Waters in Naivasha said there was a likelihood of pesticides applied on plants and soil surface finding their way into ground and surface water.
Samuel Mbuthia Gitahi of Moi University said an earlier study to determine the extent of contamination and accumulation of various pesticides in the lake had shown very disturbing results.
"Water, sediment, the red swamp crayfish and the largemouth bass were collected from five sampling stations around the lake. All the organochlorine residues under investigation were detected in both blackbass and crayfish," Gitahi said.
This was an indication that farm pesticides such as dieldrin, aldrin, lindane and endosulfan were in use in the lake's water catchment. The samples were taken at the North Swamp, Lagoon Rema Island Stage and the Malewa River that feeds the lake.
"These findings suggested low continuing or occasional usage of pesticides particularly DDT, lindane and endosulfan. However none of them was found in sediment or water samples," Mr Gitahi said. The report said it was deduced that the residues existed in the system at low concentrations and manifested in living tissue mostly because of the chemicals affinity to fat.
Two scientists from the United Kingdom, Phil Hickley and David M. Harper who had also carried out a research in the lake said that the fish community at the time was under pressure from over-fishing, decreasing water levels and inadequate species diversity. They suggested the introduction of further species to both enhance ecological diversity and increase commercial catches.
George Nyang'au Morara who represented the Kenya Marine and Fisheries Institute at the conference said that up to 73 per cent of the area with either lake or river frontage had been exploited for agricultural farming, cattle ranching and other activities that require huge volumes of water.
Prof Paul Ndalut in his paper, argued that the increasing human settlements in the lake water catchment area was having a negative impact on its biodiversity. Because of increased soil erosion Prof Ndalut suggested the introduction of trees with potential economic value within the catchments area.
The Naivasha Riparian Association, which was one of the organisations that sponsored the conference, has been involved in the protection of the lake's delicate ecosystem. Some years ago the association donated boat engines to facilitate patrols in the lake with a view to stopping fish poaching.