The cichlid fishes of Lake Victoria in East Africa, the 2nd largest freshwater lake in the world, are famous for their diversity. They are a textbook example of adaptive radiation, that almost every student of evolution will have heard about. What they will also learn about, however, is that the cichlids are en route to extinction and depletion, because of the Nile Perch, a predatory fish introduced to the Lake in the 1960s for food and sport. In combination with eutrophication and pollution, cichlid populations and diversity declined considerably in the following decades.
Now, however, the populations may be recovering, according to scientists studying the lake. Part of the explanation lies in the heavy fishing pressure on the Nile Perch, and on improvements to the quality of water running into the lake, but the adaptive potential of the cichlid to changing conditions may have some role to play. Much of the research has been conducted by Ole Seehausen of Eawag Aquatic Research in Switzerland. His research had previously found that the increased turbidity of the lake impaired the ability of female fishes to discriminate the colors of their prospective mates, reducing the effectiveness of sexual selection and allowing more hybridization between previously reproductively-isolated species. As a result, the cichlid species in the lake today are of a very different composition and genetic makeup than those found before human modification of the lake environment.
Showing posts with label eutrophication. Show all posts
Showing posts with label eutrophication. Show all posts
Saturday, July 10, 2010
Friday, September 07, 2007
Counteracting [phosphorus-induced] phytoplankton blooms with filter-feeding fish
Yang, S.L., 1982. Fish culture and reservoir management in the Republic of Singapore. In: Soewardi, K.Mahar, C. (eds.), Proceedings of the Seminar on Production and Exploitation of Open waters (with special emphasis on reservoirs), Bogor, 15-17 June, 1982. SEAMEO-BIOTROP, Bogor (Indonesia), 1987. Biotrop Special Publication (Indonesia) (ISSN 0125-975X), No. 27. Pp. 89-101.
Abstract - The primary function of impounding reservoirs in the Republic of Singapore is the collection and storage of rain water for the nation's water supply. The quality of reservoir water is a prime concern and the Public Utilities Board of the Republic has a responsibility to ensure that any activity in these reservoirs does not lead to deterioration of water supply. The objective of fish culture and reservoir management, apart from protection, is therefore to improve the quality of the raw water in these reservoirs.
A Biology Unit was established toward the end of 1970 to undertake these biological activities. The project on fish culture in reservoirs was initiated in 1972 at Seletar Reservoir. The feasibility of rearing the bighead carp (Aristichthys nobilis) in floating net-cages without supplemental feed was studied and the growth rates of the carp at different stocking rates were compared.
The stocking rate of 300 carp per net-cage of 6 m (length) x 4 m (width) x 5 m (depth) was found to have an optimum yield of about 680 kilograms at Seletar Reservoir. At this stocking rate, the carp attained an average weight of 2.0-3.0 kilograms during a grouping period of 12 months. A pilot project of 48 net-cages introduced at Seletar Reservoir in 1973 resulted in a harvest of 20.000 kilograms of carp in 1974. The project was then expanded at Seletar Reservoir and extended to other reservoirs. By the end of 1981, a total of 342 net-cages were operated in 4 reservoirs with a total harvest of 88.000 kilograms of carp.
The bighead carp which feeds solely on planktonic organisms in the reservoirs acts as a natural biological filter and thus helps to remove the excessive nutrients in the reservoirs. The carps, after growing big, are sold. Proceeds from the sales help to defray the cost of operating the Biology Unit.
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I thought this was a pretty neat exercise. We used to gaze out to cages in Kranji Reservoir and hear about it and later tell students, so its nice to see this abstract; the NUS Science Library is digging this up and there might be a couple more papers that I hope to get. Now that I'm using it in class, I'd like to cite a paper, since its possible, rather then my memory!
It was not the only measure exercised to reduce eutrophication in our reservoirs, of course. Besides relocation of farms near rivers, the government even discouraged phosphorus-rich residential soap water runoff into drains as that eventually led to the catchment water. So I remember them removing backyard tap heads in the 1970's! The backyards of residential area were where pre-washing machine clothes were laundered, and the spent soap water was poured into drains. By removing the tap heads in backyards, families redesigned their backyard areas. From then on, waste soap water was directed into the sewage system instead.
Nowadays you can find biodegradable, phosphorus-free soap powder for sale.
Links
Abstract - The primary function of impounding reservoirs in the Republic of Singapore is the collection and storage of rain water for the nation's water supply. The quality of reservoir water is a prime concern and the Public Utilities Board of the Republic has a responsibility to ensure that any activity in these reservoirs does not lead to deterioration of water supply. The objective of fish culture and reservoir management, apart from protection, is therefore to improve the quality of the raw water in these reservoirs.
A Biology Unit was established toward the end of 1970 to undertake these biological activities. The project on fish culture in reservoirs was initiated in 1972 at Seletar Reservoir. The feasibility of rearing the bighead carp (Aristichthys nobilis) in floating net-cages without supplemental feed was studied and the growth rates of the carp at different stocking rates were compared.
The stocking rate of 300 carp per net-cage of 6 m (length) x 4 m (width) x 5 m (depth) was found to have an optimum yield of about 680 kilograms at Seletar Reservoir. At this stocking rate, the carp attained an average weight of 2.0-3.0 kilograms during a grouping period of 12 months. A pilot project of 48 net-cages introduced at Seletar Reservoir in 1973 resulted in a harvest of 20.000 kilograms of carp in 1974. The project was then expanded at Seletar Reservoir and extended to other reservoirs. By the end of 1981, a total of 342 net-cages were operated in 4 reservoirs with a total harvest of 88.000 kilograms of carp.
The bighead carp which feeds solely on planktonic organisms in the reservoirs acts as a natural biological filter and thus helps to remove the excessive nutrients in the reservoirs. The carps, after growing big, are sold. Proceeds from the sales help to defray the cost of operating the Biology Unit.
----
I thought this was a pretty neat exercise. We used to gaze out to cages in Kranji Reservoir and hear about it and later tell students, so its nice to see this abstract; the NUS Science Library is digging this up and there might be a couple more papers that I hope to get. Now that I'm using it in class, I'd like to cite a paper, since its possible, rather then my memory!
It was not the only measure exercised to reduce eutrophication in our reservoirs, of course. Besides relocation of farms near rivers, the government even discouraged phosphorus-rich residential soap water runoff into drains as that eventually led to the catchment water. So I remember them removing backyard tap heads in the 1970's! The backyards of residential area were where pre-washing machine clothes were laundered, and the spent soap water was poured into drains. By removing the tap heads in backyards, families redesigned their backyard areas. From then on, waste soap water was directed into the sewage system instead.
Nowadays you can find biodegradable, phosphorus-free soap powder for sale.
Links
- "Historical perspective of the phosphate detergent conflict," by Chris Knud-Hansen.
Working Paper 94-54, February 1994. - "Shoreline Stewardship for Landowners." NSLandsCo.com. Has a nice illustration.
- "Province's dish-soap step too timid, critics charge," by Mary Agnes Welch. Winnnipeg Free Press, 05 Sep 2007.
- FAO: Cultured Aquatic Species Information Programme: Aristichthys nobilis
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