Although the present report concerns the electrof ishing survey, 

 other sampling techniques such as trawling, seining, and trapping in 

 both the river and lateral lakes were used during the same period, and 

 information on the relative abundance of certain species in commercial 

 catches was obtained from commercial fishermen. Hence, it was possible 

 to judge whether a low number of a certain species in the electrof ishing 

 catch was due to low populations in the river or to biases in the sam- 

 pling technique. 



Physical-Chemical Measurements 



In 1974, before sampling fish populations, several physical-chemical 

 measurements were made at each station. Dissolved oxygen (DO) concentra- 

 tions at a depth of 3 ft and at the bottom in the deepest part of the 

 station were measured by the Winkler method or with YSI Model 57 dis- 

 solved oxygen meter. Surface water and air temperatures were measured 

 with a mercury thermometer. Wind direction and velocity and cloud 

 cover were noted. Transparency was measured with a Secchi disk. 



The same measurements were made during some of the electrof ishing 

 surveys prior to 1974. In addition, turbidity of the river was measured 

 with a Jackson turbidimeter during earlier surveys. 



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