During the period January, 1943 to March, 1947, the louisiana 

 Department of liVild Life and Fisheries made daily salinity tests 

 at several stations in the west end of Mississippi Sound. Their 

 records show that average monthly salinities too low for oysters 

 occiurred with only one exception in the first half of each year. 

 Therefore, in showing the rates of Pearl River Basin discharge 

 into Mississippi Sound, the average rates for the period January 

 to June only are considered. In Table 7 and Fig. 5 these data 

 are compared with the records obtainable for average salinities 

 dxiring a part of this same period of time. Daily and monthly 

 figures have been averaged so that these charts present the trend 

 during the years rather than precise figures for any individual 

 date. 



These data demonstrate that in the years 1946, 1947 and 1949 

 when mass mortalities occurred in the west end of Mississippi Sound, 

 there were greatly increased rates of fresh water discharge from 

 the Pearl River Basin. The preliminary survey of the Mississippi 

 Sound area in the summer of 1948 and the second survey made in 

 December of that year showed oyster mortalities of le s than 10 per- 

 cent. On the basis of this, I had predicted that in the winter of 

 1948-49 there would be a return to normal growth on these reefs. 

 However, the extraordinarily high discharge from the Pearl River 

 in early 1949 prevented such a return to normalcy. 



The Impoivtiance of this watershed in controlling the hydrographic 

 factors In Mississippi Sound is indicated by the fact that during the 

 6 years for which we have data the salinity is directly correlated 

 with the flow from Pearl River. This relationship holds true even for 

 the year 1945, when the additional mass of water entered the area 

 from the Bonnet Carre Spillway. This presumably is due to the 

 averaging of figures for the six months period and obviously would 

 not hold true for the 56-day period when the spillway was flowing. 



On the basis of the records for the past ten years, it is 

 reasonable to expect that whenever the mean daily discharge rate 

 from the Pearl River Basin exceeds 20,000 second/feet for the 

 period January through June, there will be significant oyster mor- 

 talities in the west end of Mississippi Sound. This conclusion is 

 based also on the provision that the high discharge rate is spread 

 over an extended period rather than being confined to a flood of 

 short duration in the colder months. The validity of this hypothesis 

 is further shown by the records of 1948. In this year, the average 

 daily discharge rate in the period January through June was only 

 17,000 second/feet. Firom this it would have been possible to predict 

 a low oyster mortality in the sxiramer and fall of 1948. Conversely, 

 irtien surveys showed a low oyster mortality on the reefs in the west 

 end of Mississippi Sound in the latter half of 1948, it was possible 

 to assume a low average discharge rate from the Pearl River even 

 before the records had been examined. 



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