MARSH MANAGEMENT AND FISHERIES ON THE STATE 



WILDLIFE REFUGE-OVERVIEW AND BEGINNING 



STUDY OF THE EFFECT OF WEIRS 



Mark Konikoff and H. Dickson Hoese 



Department of Biology 



University of Southwestern Louisiana 



Lafayette, LA 70504 



ABSTRACT 



The State Wildlife Refuge is a brackish marsh, with oligohaline, tidal, and heterotrophic water, 

 a mostly undisturbed system on the western shore of Vermilion Bay about 15 m by water from the 

 Gulf of Mexico. The main management practices are burning most of the refuge each year and 

 construction of low water weirs on most small water bodies off Fearman Lake and Bayou. These 

 have been recently expanded and refurbished. Burning may limit the abundance of intertidal 

 mollusks, such as Geukensia demissa, but the effects on fisheries are unknown. The overall effects 

 of weirs on estuarine animals are not known, but there is evidence that they limit movement. They 

 may also serve to create and maintain different aquatic habitats. Studies begun in September 1987 

 using gill nets, trawls, and a quantitative sampler in comparable weired and unweired ponds and 

 a common area in Fearman Lake have discovered some differences, but it is too early to tell if 

 these are due to weirs, locations, or other factors. 



The oligohaline fauna consists of the infaunal Rangia cuneata and Macoma mitchelli, demersal 

 juveniles of Callinectes sapidus, Penaeus setiferus and estuarine fishes, and adults of some freshwater 

 species such as Ictalurus furcatus, Lepisosteus spp. and Dorosoma cepedianum. While scattered 

 studies and observations made since the late 1950's, mostly in adjacent Vermilion Bay, suggest the 

 lowering of salinities, especially during the flood years of 1973-75, there is also some evidence of 

 saltwater intrusion. The important commercial and sport fishery species produced on the refuge 

 are Lepisosteus spatula, Brevoortia patronus, Ictalurus furcatus, Sciaenops ocellatus, Paralichthys 

 lethostigma, Callinectes sapidus, and Penaeus setiferus. Perhaps long term study of such a low 

 diversity habitat will make for better understanding of natural and artificial effects of water levels. 



INTRODUCTION 



The State Wildlife Refuge, comprising 27,000 acres, is located in a low-salinity (brackish) marsh 

 on the western shore of Vermilion Bay (Figure 1). Although the refuge is one of the most natural 

 and least modified marshes in Louisiana, nearly all water bodies have low water weirs used as a 

 management practice to retain water in the marsh for navigation, vegetation, waterfowl, and to 

 slow erosion on the Vermilion Bay shoreline. Toms Bayou and a small connecting pond system 

 leading from the refuge to the Audubon Refuge to the west is the only major system not weired. 



Although weirs have been long used in Louisiana brackish waters (Chabreck and Hoffpauir 

 1962), a recent study suggests that there is a significant reduction in exported fisheries production 

 compared to a similar unweired area, due either directly or indirectly to the weir (Herke et al. 

 1987). While we will not discuss these arguments here (see Chabreck and Hoffpauir 1962 for a 



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