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Figure 3. Diagram of the paired ponds. The middle levee divided the total area into two areas 

 of about 35 ha each. 



The traps fished continuously from 15 February 1983 through 13 February 1984 (Year 1), except 

 for about 30 minutes each morning when they were raised for emptying (at which time a screen 

 was inserted in place of the trap to prevent any outward movement of organisms). On 14 February 

 1984 the weir was switched to the other chute, and continuous trapping was resumed until 15 

 February 1985 (Year 2). 



The results of this quantitative study (Herke et al. 1987a, 1987b) confirmed what we had inferred 

 from the previous circumstantial evidence: members of 107 species were taken during the 2 years 

 from the unweired pond whereas members of only 83 species were taken from the weired pond, 

 and the catch of most species was substantially lower from whichever pond contained the weir in 

 its chute. The total catches of some of the economically important species are listed in Table 1 

 and shown graphically in Figure 5; the percentage of reduction in catch from the weired pond, 

 compared to that from the unweired pond, is given in Table 2. 



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