Table 1. Vascular plants of Little Pecan Lake and adjacent marsh (1986). 



Giant cutgrass Zizaniopsis miliaceae 



Bullwhip Scirpus californicus 



Water hyacinth Eichomia crassipes 



Banana waterlily Nymphaea mexicana 



American lotus Nelumbo lutea 



White waterlily Nymphaea odorata 



Wiregrass Spartina patens 



Rattlebox Daubentonia texana 



Roseau cane Phragmites australis 



Bulltongue Sagittaria lancifolia 



Fall panicum Panicum dichotomiflorum 



Pennywort Hydrocotyle sp. 



Jointgrass Paspalum vaginatum 



Walter's millet Echinochloa walteri 



Sprangletop Leptochloa fascicularis 



Flatsedges Cyperus sp. 



et al. 1987a; Rogers et al. 1987). Water exchange at each site was restricted to a 183-cm-wide and 

 162-cm-deep wooden chute. 



Management at Little Pecan Lake 



When juvenile white or brown shrimp were found in moderate abundance or were thought to 

 be present within several miles of the flap-gated water control structure, all stop-logs were removed 

 and the flap-gate was raised to provide ingress opportunities. After 45 to 60 days the flap-gate was 

 closed to protect lakeshore vegetation and freshwater fishes from salinities in excess of 5 ppt, or 

 to hold shrimp for harvesting after they had grown to suitable size (16-40/lb). See Table 2 for the 

 operational schedule of the water control structure (1984-86). 



Management of the Grand Bayou Sites 



From February 1983 to February 1984, unhindered water exchange was allowed through one 

 of the two wooden chutes. In the other chute, a low-level fixed-crest weir (31 cm below marsh 

 level) was installed. A deflecting screen and fish trap system (6.2-mm mesh) were installed in 

 both chutes. All organisms leaving both semi-impoundments were trapped, collected, and sorted 

 by species and weighed. 



From February 1984 to February 1985, the experiment was repeated except that the low-level 

 fixed-crest weir was switched to the other chute. Annual white shrimp production for these systems 

 was estimated as the total catch of white shrimp during each season. 



RESULTS AND DISCUSSION 



During 1984 and 1986, an estimated 907 kg of white shrimp were harvested from Little Pecan 

 Lake. Oxygen depletion in early October 1986 killed a large number of shrimp and fish. Shrimp 



173 



