BROWN 

 SHRIMP 



RED DRUM 





/'.WHITE 

 ' 'SHRIMP 



DEC 



TIME OF YEAR 



Figure 2. Approximate period of movement (in and out combined) through the canals between 

 the marsh and Calcasieu Lake, and eventually the Gulf of Mexico, by the young-of-the-year of 

 eight important species. A value of 100 on the index equals the period of maximum movement 

 for that species. During the entire Sabine Fisheries Study, members of 117 fish and 12 

 crustacean species were caught 



50%, it will reduce turnover rate from the semi-impounded marsh by 50%. Thus, if a biologist 

 took samples from both areas, the catch per unit of effort (the index of standing crop) should be 

 about the same; productivity would appear to be about equal, whereas the unimpounded area 

 would actually be twice as productive because shrimp using it were cycling in and out twice as fast. 



In the early 1980's we began a study, funded by the U.S. Soil Conservation Service, to determine 

 quantitatively the effect of a fixed-crest weir on fishery annual production. A levee was constructed 

 around 70 ha of natural marsh, and an interior levee divided this area into two areas of 35 ha each 

 (Figure 3). Each area contained about 25% emergent marsh and 75% open water. The natural 

 inlet from Grand Bayou was closed off and identical plywood-lined chutes, opening on a common 

 vestibule from Grand Bayou, were constructed into each area (Figure 4). 



A solid weir with a fixed crest set 30 cm (instead of the usual 15) below average marsh ground 

 level was installed in one chute; the other chute was left unweired. Identical trap systems were 

 installed in each chute. Incoming larvae and juveniles could enter each area by passing through 

 the 6-mm mesh openings in the traps, or through the 7.6-cm-wide vertical slit at the pondward end 

 of the trap system. All outgoing organisms too large to pass through the 6-mm mesh were shunted 

 into the traps. 



199 



