!» 7 



Figure 8.--Modified marsh net with retrieving line and bridle, for sampling 



juvenile shrimp. 



SEASONAL CHANGES IN RELATIVE 



ABUNDANCE OF POSTLARVAE OF 



PINK SHRIMP ENTERING THE 



EVERGLADES ESTUARY 



During the fiscal year, sampling for post- 

 larval pink shrimp, Penaeus duorarum , con- 

 tinued in Little Shark River and Buttonwood 

 Canal, Everglades National Park, Fla. Paired 

 surface and bottom hauls, each of 10-minute 

 duration, were made at about 45- to 60- 

 minute intervals during night flood tides. When 

 shrimp were abundant, samples were taken on 

 each of the four major moon phases. During 

 the winter, when abundance was lower, samples 

 weretaken only in new- and full-moon periods. 

 A total of 35 trips to each collecting site 

 produced 105 paired bottom and surface 

 samples at Buttonwood Canal and 117 at Little 

 Shark River. 



Abundance of postlarvae was highest in July 

 when the production of shrimp per 1 m.'' of 

 water strained was 28.9 in Buttonwood Canal 



and 7.7 in Little Shark River. Catches were 

 highest during new- and first-quarter-moon 

 phases, and the bottom net consistently pro- 

 duced higher catches than the surface net. 

 Maximum catch per 1 m.^ for each sampling 

 trip to Buttonwood Canal and Little Shark 

 River is shown in figure 9. Experiments are 

 being made to determine if the apparent 

 concentration of postlarvae near the bottom is 

 real or is caused by the movement of the 

 vessel (which may cause the postlarvae to 

 sound). 



After we discovered that shrimp reacted to 

 salinity gradients in aquaria, sampling pro- 

 cedures were modified slightly to include 

 collection of salinity samples before the start 

 of the night's fishing and at the midtime of 

 each tow. These samples permit the measure- 

 ment of salinity change in the time period 

 represented by each tow. 



The relation between carapace length and 

 total length of shrimp less than 4mm. (0.2 inch) 

 carapace length is being examined as well as 



12 



