Migrations Juvenile pink shrimp make extensive movements in migrating 



fronn estuaries to offshore waters. Experiments during the past year reveal 

 that adult pink shrimp have rather limited movements after reaching water 

 depths of 7 to 13 fathoms. Of 2, 091 pink shrimp marked with biological dyes 

 and released near the center of the Tortugas grounds in September 1961, 443 

 (22%) were recovered by commercial fishing vessels during a period of 85 

 days. Movement of the marked animals was generally west and northwest. 

 The greatest movement recorded for any marked shrimp of this group was 

 about 27 statute miles. 



In March 1962, 2,496 pink shrimp were captured, marked with bio- 

 logical dyes, and released at randonn on the Sanibel grounds west of Naples, 

 Fla. By May 21, 1962, 453 (18%) had been recaptured by commercial shrimp 

 trawlers. The greatest movement recorded for any of this group was 82 nau- 

 tical miles. Two of the marked shrimp released on the Sanibel grounds were 

 recovered near the northwest border of the Tortugas grounds after 115 days 

 at liberty. 



One marked shrimp released in lower Pine Island Sound in December 

 I960 was recovered in 9 fathoms on the Sanibel grounds in November 1961. 



Growth Some useful pink shrimp growth data w^ere obtained from the Tor- 



tugas experiment begun in September 1961. Shrimp (2,091) were individually 

 measured prior to marking and release. These had a narrow size range of 

 83.0 to 93. 5 nam. total length. Growth was calculated for 97 males and 82 

 females which had been at liberty from 29 to 36 days. Average grov^h for 

 males having an initial mean total length of 89. 3 mm. was 15. 6 mm. per 

 month. Average growth for females having an initial mean total length of 

 90. 5 mm. was 18. mm. per month. Regression analysis of growth for the 

 entire group of recoveries shows similar growth over the entire period dur- 

 ing which recoveries were made. 



This experiment depicts the surprisingly rapid rate at which these 

 prerecruits grow as they enter the trawling grounds and are subjected to 

 fishing. 



Mortality Offshore mark-recapture experiments on the Tortugas and 



Sanibel grounds have demonstrated the feasibility of using this method in es- 

 tinnating the natural and fishing mortality rates of shrinap. 



Survey of Species of Penaeus Shrimp in South Florida During the year, 



additional samples of shrimp were collected and examined to determine the 

 distribution and seasonal occurrence of three species of the genus Penaeus 

 occurring in south Florida waters. Since P. duorarum, P. brasiliensis, and 

 P. aztecus are extremely difficult to separate unless mature, such informa- 

 tion is necessary to evaluate the research on the more abundant P. duorarum. 

 Monthly samples collected in Biscayne Bay, Fla. , during I960 and 1961 showed 

 the following species composition: 



36 



