Freshwater Fishes of Iran, Introduction - Drainage Basins

Introduction - Drainage Basins - Lake Maharlu

Revised: 26 June 2007

Acknowledgements Purpose Materials and Methods History of Research Fisheries Geography Climate Habitats Environmental Change Drainage Basins Scientific Names Fish Structure Collecting Fishes Preserving Fishes Quotes

The Maharlu basin is the valley of Shiraz (29°36'N, 52°32'E) and encompasses about 4100 sq km. Lake Maharlu is at an altitude of about 1460 m, has an estimated average area of 220 sq km, a maximum depth variously cited as 0.5 and 3 m, a salinity of 124‰ or 304.95 gl^-1 and is fishless. The lake dried out completely in 1967 (Cornwallis, 1968a). The lake is fed by minor streams and springs around its margin. The stream flowing through Shiraz is dry for much of the year or composed mostly of polluted wastes. The basin also has a number of qanats. Stream temperatures vary between 8°C in January to 32°C in June while qanats can be warm, e.g. at Sarvestan (29°16'N, 53°13'E) in December a qanat was 25°C. Surber (1969) gives some spot data on pH, total alkalinity, calcium-magnesium hardness, chlorides and free CO₂ in this area.

The basin is separated by only a small rise from the Mand River of the Gulf basin, but is treated separately here because fish collections have been focused on this valley as Shiraz is the major city of southern Iran.

Major fresh to brackish springs and their associated marshes (Ab-e Paravan (2.5 sq km), Barm-e Shur (1.5 sq km) and Soltanabad (7 sq km)) are concentrated at the northern end of the lake (Cornwallis, 1968a). Larger springs have pools which are about 2 m deep and reed beds of Phragmites and Typha, some of which are cut. Livestock grazing occurs. Amphibious tanks were tested in Barm-e Shur, stirring up anoxic bottom mud and leading to a fish kill.

Numerous small springs around the lake are isolated from one another by the intervening hypersaline water. Lake levels fluctuate markedly and allow streams to meet on the exposed salt flat when the water level is low. At high levels, salty water invades the lower springs and eliminates their fishes, which only recolonise when the lake level falls again and connection is made with a stream from a spring which was above the last rise in lake level. One spring had a salinity of 34‰ at the source when the lake had risen to "invade" the spring. Aphanius persicus were concentrated close to the source but would attempt to evade capture by swimming into the salt lake where salinity was 180‰. Their excursions into water of this salinity was brief and fish paled visibly while darting in and out. Another spring was replete with tooth-carps at 144‰. Temperature on 8 June 1976 at one spring was 27°C at the surface and 32°C on the bottom, at about 1 m depth.

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