4 $ 7.5 fm. 



12 ^ I5fm. 



25(;40fn). 



20 



10- 



BROWN AND WHITE SHRIMP 



UtI 



; ■-BROWN 

 H I jjiji-WHITE 



ilUolJ 



I I I I I I T T^ 



10-1 



SEA CATFISH 



Figure 13. — Catch per unit effort (pounds/hour) by seasons 

 for two — brown and white — commercial shrimp and 

 three finfish — sea catfish, shoal flounder, and rock sea- 

 bass — occurring in three depth zones off the Texas 

 coast, in 1963. (Winter is Jan.-Mar.; spring, Apr.-June; 

 summer July-Sept.; and fall, Oct.-Dec.) 



ABUNDANCE AND DISTRIBUTION OF PINK 



SHRIMP LARVAE ON THE TORTUGAS 



SHELF OF FLORIDA 



This report covers the final phase of the 

 studies on pink shrimp larvae on the Tortugas 

 shelf. We have now analyzed all data and are 

 preparing a detailed description of the results. 



During the past year, we made six cruises 

 to the Tortugas shelf and obtained 1 54 plankton 

 samples. We stopped sampling in October 

 1964 and began examining a backlog of sam- 

 ples. The resulting data were then prepared 

 for automatic data processing and analyzed. 



In 1963, the production of first protozoeal 

 stages of pink shrimp within a sampling 

 area of 1,000 sq. nautical miles was esti- 

 mated at 5 trillion individuals. Seasonal "'aria- 

 tion in larval production was considerable 

 however. The sampling area yielded an esti- 

 mate of 2.1 trillion first protozoea from 

 January to July 1963 and a threefold increase 

 to about 6.5 trillion over the same period in 

 1964. For a variety of reasons, however, 

 we believe these estimates may be low. 



Analysis of larval and temperature data 

 suggested a relation between spawning in- 

 tensity and bottom temperatures. The greatest 

 amount of spawning over the past 6 yr. has 

 occurred when temperatures exceeded 27° C. 

 (80.6° F.); usually less than 10 percent of 

 each year's spawning occurred when tem- 

 peratures were below 24° C. (75.2° F.). 



Spawning intensity appeared to be related 

 to moon phases. Most spawning was around 

 the full-moon period and least at new moon. 

 It appears possible to estimate from catch 

 curves the apparent mortalities of the larvae 

 as they proceed through successive larval 

 stages. Mortality for various stages varied 

 in a consistent fashion between stations; some 

 stations were consistently losing younger 

 stages, whereas other sampling stations 

 (possibly located along the migration routes) 

 were consistently receiving older stages. Thus, 

 because spawning occurred at all stations, 

 the apparent survival rates of the larvae 

 varied according to station, and the survival 

 rates could be used to indicate migration 

 patterns. Survival throughout larval life ap- 

 pears to be nearly constant, averaging 80.4 

 percent per day; therefore, we estimate that 

 only 0.14 percent of the first protozoea pro- 

 duced survive to postlarval stages that enter 

 the nursery grounds at an average age of 

 35 days. 



A single survey cruise (42 stations) under- 

 taken in October 1964 showed concentration 

 of larvae along the margin of the Gulf Stream 

 south of the Florida Keys. It is possible that 

 migration between the Tortugas spawning 

 grounds and the Florida mainland nursery 

 grounds may take place via Rebecca Channel 

 and the Gulf Stream. If so, the larvae would 

 arrive at a point within 20 to 30 miles of the 

 nursery grounds only 6 days after leaving 

 the spawning area. 



The release and subsequent recovery of sea- 

 bed drifters have provided further evidence 

 that currents in the Tortugas-Florida Bay area 

 are weak--about 1 mile per day--and that 

 the movement is primarily toward the south- 

 west. This current might prevent movement 

 of larvae in a direct line between the spawning 

 grounds and the Everglades nursery areas, 

 thus adding weight to the possibility that the 

 Gulf Stream is the main mode of transporta- 

 tion. 



G. P. Idyll and J. L. Munro, Project Leaders 



Institute of Marine Science, 



University of Miami 

 (Contract No. 14-17-0002-98) 



ABUNDANCE OF JUVENILE PINK SHRIMP 



ON THE EVERGLADES NATIONAL PARK 



NURSERY GROUNDS 



The primary aims of this project are to 

 describe the relative abundance of pink shrimp 



19 



