Planktonic stages of five known genera of 

 penaeids-- Penaeus , Sicyonia , Trachypeneus , 

 Solenocera , and Parapenaeus --were taken in 

 plankton hauls. The data have been analyzed, 

 however, only for the commercial shrimps 

 of the genus Penaeus . 



Seasonal Trends in Abundance 



Seasonal trends in the abundance of Penaeus 

 spp. larvae (postlarvae excluded) in 1962-64 

 were similar in Lomsiana and Texas (fig. 1). 

 Differences did exist between depths, however. 

 Catches in 7 to 13 m. (4-7 fathoms) of water 

 were restricted to April-October; the yearly 

 trend was more unimodal here than at deeper 

 depths, where a definite bimodal trend was 

 evident. Catches of larvae at 27 m. (15 

 fathoms) or deeper, in general, increased 

 in the spring from the winter low, decreased 

 in the summer, and were maxinnum in the fall. 

 The only exceptions were in Texas in 1963 

 and 1964, where catches at 27 to 64 m. (15 to 

 35 fathoms) in the spring approximated those 

 made in the fall. 



Overwintering of Postlarval Brown Shrimp 



Because of the bathymetric distribution of 

 adult white and brown shrimp, we believe that 

 larval abundance trends in 7 to 13 m. (4-7 

 fathoms) of water (fig. 1) reflect spawning 

 of white shrimp, and those in deeper water 

 the spawning of brown shrimp. Such an as- 

 sumption creates a problem, however, for 

 the movement of most postlarvalbrown shrimp 

 into the GalvestonBay nursery area in January- 

 April is well documented. The period of 



125 7-13 METER STATrONS 



^A\ 





1-27-64 METER STATIONS 





73- 110 METER STATIONS 



/; ' 



■,.;=f-,-^^-,.^..;^:;3:;^jb^..y-,40° W^ i I , , W r-f4-^Wi-r 



JMMJSNJMMJSNJMMJSN 

 1962 1963 1964 



Figure 1.— Abundance of Penaeus larvae by depth zones 

 in Louisiana and Texas waters, 1962-64. 



time between the high catches of larvae 

 offshore in the fall and the large catches 

 of immigrating postlarvae through Galveston 

 Pass is unaccounted for unless the develop- 

 ment of larvae is retarded offshore, or larvae 

 overwinter offshore, or both. 



To investigate the possibility of postlarvae 

 overwintering offshore, we made cruises off 

 Galveston between September and April to 

 waters between the surf zone and to a depth 

 of 12 m. (6-7 fathoms). Samples were taken 

 on bottom with a specially constructed sled 

 and in the water column with Clarke-Bumpus 

 and half-meter nets. Postlarval brown shrimp 

 increased in numbers from October to March 

 in a narrow zone of water along the coast 

 before they entered the estuary (table 3). 



Table 3 Catches of postlarval brown shrimp per 1 ,000 m. ^ (35.000 cubic 



feet) of water filtered, by month and depth zone, September 1966 to 

 April 1967 



Personnel of the Shrimp Dynamics Pro- 

 gram, who sampled immigrating postlarvae 

 in Galveston Pass, made their greatest catches 

 in February and March. These large catches 

 coincided with ours along the coast, and the 

 decrease in catch in April was apparent in 

 both locations. 



Monthly length-frequency distributions of 

 the postlarval shrimp taken in our tows show 

 a general increase in size from September 

 to December but no increase thereafter (fig. 2). 

 The significance of this finding is important 

 only when considered with existing water tem- 

 peratures and the documented effects of tem- 

 perature on shrimp growth. In the study area, 

 bottom water temperatures averaged about 

 28.0° C. (82.4° F.) in September but de- 

 creased to 15.5° C. (59.9° F.) in December. 

 During December-March, they ranged be- 

 tween 11.8° C. (53.2° F.) and 15.5° C. (59.9° 

 F.)--temperatures which have been shown by 

 z'ein-Eldin and Aldrich^ to arrest postlarval 

 shrimp growth. The apparent increase in num- 

 bers of postlarvae along the beach in the 

 winter months and their retarded growth 



^Zein-EIdin, Zoula P., and David V. Aldrich. 1965. 

 Growth and survival of postlarval Penaeus aziecus under 

 controlled conditions of temperature and salinity. Biol. 

 Bull. (Woods Hole) 129(1): 199-216. 



