(Weinstein 1979, Shenker and Dean 1979, 



Bozeman and Dean 1980). These studies 



showed that young fish seek the creek 

 headwaters . 



A distinctly larger nekton biomass 

 has been found in waters associated with 

 marshes than in open waters of the same 

 salinity. These two zones are only 

 slightly different in depth. The shal- 

 low water marsh areas of the Barataria 

 basin have the three major requirements 

 outlined by Joseph (1973) for a nursery 

 area: (1) physiologically suitable 

 temperature, salinity, and other physio- 

 chemical parameters; (2) abundant suit- 

 able food with a minimum of competition 

 at critical trophic levels; and (3) a 

 degree of protection from predators. 



TERREBONNE HYDROLOGIC UNIT (V) 



Description of the Area 



The Terrebonne Hydrologic Unit 

 includes only a portion of the entire 

 Terrebonne basin, which is bounded by 

 Bayou Lafourche and the Barataria basin 

 on the north and east, and by the 

 Atchafalaya River Protection Levee and 

 the lower Atchafalaya River on the west 

 (Figure 53) . In addition to excluding a 

 large area that is hydrologically and 

 functionally a part of the basin, the 

 official boundary also excludes the 

 major and rapidly growing urban center 

 in the basin (Houma and surrounding 

 smaller towns). It also excludes much 

 of the natural levees that protrude 

 southward like fingers into the basin, 

 and on which most agricultural habitat 

 occurs. 



Nevertheless, as defined for this 

 study the Terrebonne Hydrologic Unit is 

 the second largest in the MDPR, and is 

 distinguished primarily by its high 

 proportion of wetland habitats (27% of 

 the total area). The areas of each 

 habitat in this hydrologic unit are 

 shown in Table 21, which also shows the 

 changes in area for each habitat between 

 1955 and 1978. 



The functional Terrebonne basin is 

 similar to the Barataria basin: these 



adjacent basins are about equivalent in 

 area, they are both interdistributary 

 wetland-dominated zones that receive 

 little riverine input, and both basins 

 are characterized by barrier islands at 

 their seaward extremities. In addition, 

 both basins have been especially noted 

 for their fishery production (Lindall et 

 al. 1979), but they are both experi- 

 encing severe problems of water quality 

 (eutrophication and salt water intru- 

 sion) and wetland loss (Craig and Day 

 1977). Field measurements of marsh 

 plant primary production performed in 

 the eastern part of the Terrebonne basin 

 were comparable to similar measurements 

 from the Barataria basin (Hopkinson et 

 al. 1978b). 



The description of the central and 

 eastern portion of the Terrebonne 

 Hydrologic Unit is therefore applicable 

 in many ways to the Barataria basin. On 

 the other hand, the western flank of the 

 Terrebonne basin is being heavily in- 

 fluenced by the Atchafalaya Delta devel- 

 opment, and the trend of wetland loss 

 and salinity intrusion has been dramati- 

 cally reversed here, as illustrated by 

 Figure 54 from Baumann and Adams (1982). 



High land is in short supply in the 

 Terrebonne Hydrologic Unit, as very 

 little land is more than 1 m (3 ft) 

 above sea level. The only naturally 

 occurring high land is on natural levees 

 (most of which is excluded in terms of 

 the official Terrebonne Hydrologic Unit 

 Boundary) . 



Major Problems 



The function of the Terrebonne 

 Hydrologic Unit has been dramatically 

 affected by the construction of artifi- 

 cial waterways, especially the east- 

 west-oriented Gulf Intracoastal waterway 

 (GIWW) and the north-south-oriented 

 Houma navigation canal. The latter 57.9 

 km (36 mi) channel was completed in 

 1962, and mean salinities have about 

 doubled at Bayou Terrebonne in Houma 

 since then (Gagliano et al. 1973). 

 Swamp forest habitat that formerly sur- 

 rounded the Pointe au Chien Ridge has 

 been killed by the increase in' salinity 

 caused by this channel and by canals 



129 



