data indicated that postlarvae entered Whale 

 Harbor Channel year around. They usually 

 were most abundant during the spring, sum- 

 mer, and fall; the numbers were greatest in 

 the summer when water temperatures were 

 highest (fig. 6). Postlarvae were 5 to 14 mnn. 

 (0.2 - 0.5 inch) long. Sizes varied seasonally; 

 the snnallest postlarvae arrived in July and the 

 largest in April. 



Thomas J. Costello, Project Leader 

 Donald M. Allen 



SHRIMP DYNAMICS PROGRAM 



Work in this program continued toward the 

 goals of (1) predicting shrimp abundance, 

 (2) describing relations between the abundance 

 of shrimp at different stages in their life 

 history, (3) describing the effects of size at 

 harvest on weight and value of the harvest, and 

 (4) determining the levels of fishing that will 

 maximize long-term yields from the shrimp 

 fisheries. 



Our effort toward the first two goals con- 

 centrated on the refinement of our sampling 

 methods. An automatic plankton pump was 

 operated to sample continuously the postlarvae 

 entering Galveston Bay. We expanded the col- 

 lection of statistics and inforn-iation from inter- 



views from the white shrimp fishery and 

 worked toward a description of white shrimp 

 spawning times and locations off the upper 

 Texas coast. Our supplemental sampling of the 

 commercial landings was designed to dennon- 

 strate those portions of the standard landing 

 statistics that provide the best measures of 

 the abundance. Once established, past and future 

 landing data will be considerably more valuable 

 to us. 



Growth and nnortality rates necessary to 

 determine optimum size at harvest were cal- 

 culated primarily from the results of mark- 

 recapture experiments. We continued to im- 

 prove our nnethods for marking shrimp and 

 have made several modifications during the 

 year. It was apparent that we must plan care- 

 fully the location and timing of the releases of 

 marked shrimp if we are to obtain the specific 

 information we need. Knowledge of when and 

 where to release shrimp to obtain specific 

 information, gained previously through 

 numerous mark- recapture experiments, was 

 of considerable value to us as we planned the 

 studies that were completed this year. 



More intensive work with the commercial 

 landings statistics was begun to obtain inde- 

 pendent estimates of mortality rates, and in- 

 formation on the optimum level of fishing effort 

 on a long-term basis. We spent much effort 

 to interpret the landing statistics. In some 



3,000 



(n 2,000 



i 1,000 

 < 



>- 500 



ui 



O 



0. 



400 

 u. 

 o 



g 300 



< 



" 200 



100 







, TEMPERATURE 



t32 



26 



22 



88 



86 



84 



82 



80 



78 uj 

 (r 



Z) 

 Q: 



LU 



74 ^ 



LU 



(- 



72 

 70 

 68 

 66 

 64 



Figure 6. — Seasonal relation between planktonic postlarval shrimp ( Penaeus ) caught during new-moon periods and water 



temperature at Whale Harbor Channel, Fla., 1966-68. 



12 



