PERCENTAGE OF 1st PROTOZOEAE 

 IN TOTAL 



OJ -^ tn m -a 



o o o o o 





FiQDRE 5. — The relation between moon phase and relative 

 spawning intensity (as measured by the relative abun- 

 dance of first protozoeae) in the Tortugas Shelf area, 

 August 1962 to October 1964. 



Using a chi-square test, we found that the prob- 

 ability of such a distribution arising by chance 

 is slight (<0.02) ; we conclude, therefore, that 

 spawning occiu's mainly during the last half of 

 the lunar month. That most spawning occurs in 

 the last half of the lunar month agrees with the 

 observations of Korringa (1957), who stated that 

 in animals showing lunar periodicity in spawning, 

 the spawning is often concentrated around the 

 last lunar quarter. He suggested that this con- 

 centration is a result of a photoperiodic effect, 

 the final stages of maturation of the gonads being 

 triggered by the greater exposure to light during 

 the full-moon period. This photoperiodic effect 

 on maturation may also hold for Penaeus, but the 

 advantages of lunar periodicity are obscure 

 because copulation occurs in advance of spawning 

 (Hudinaga, 1942, for P. jajwnicus) , and all eggs 

 are fertilized at extrusion. Alternating periods 

 of high and low larval density may be advantageous 

 in that they prevent a concentrating of major 

 predators, thus reducing mortality caused by 

 prolonged predation. 



Table 6. — Data for the analysis of the efect of moon phase on 

 rate of spawning of P. duorarum; all data are in terms 

 of estimated numbers of larvae under 10 m.' surface 

 area at 10 stations on the Tortugas Shelf, August 1962 to 

 October 1964 



Year and 

 cruise 

 number 



Date 



First 

 proto- 

 zoeae 



Total 

 larvae 



Percentage 

 of first 



protozoeae 

 in total 

 catch 



Time of 



spawning 



(moon age 



minus 



5 days) 



1961 Number 



6201 Aug. 14-16 _ 1,669.7 



6202 Aug. 28-30 3,201.8 



6203 Sept. 11-12 _. 2,465.1 



6204 Sept. 25-28 5,508.0 



6205 Oct. 9-10 5,560.3 



!96S 



6303 Mar. 11-12 171.2 



6304 Mar. 26-27.- 63.7 



6305 Apr. 8-10.. 322.4 



6306 May 5-7 1,119.1 



6307 May 20-23 1,757.5 



6308 June 4-5.... 93.3 



6309 June 18-22 1,145.1 



6310 July 1-2 3,346.6 



6311 July 30-Aug. 1... 1,105.2 



6313 Aug. 13-14 1,633.3 



6314 Aug. 27-28 3,943.0 



6315 Sept. 10-11. 2,976.5 



6316 Oct. 1-2 3,463.5 



6317 Oct. 15-16 2,126.2 



6318 Nov. 5-6 1,737.2 



6401 Feb. 17-18 126.9 



6402 Mar. 3-J 202.9 



6403 Mar. 17-18 3,348.6 



6404 Apr, 1-2 6,831.7 



6405 Apr. 14-15 6,662.2 



6406 Apr. 28-30 1,087.9 



6407 May 12-14 1,219.6 



6408 Mav 26-28 1,291.2 



6409 June 9-11 4,210.7 



6410 June 23-25 9,665.8 



6411 July 7-9 4,885.2 



6412 July 21-23 2,5506 



6413 Aug. 4-5 3,447.4 



6414 Aug. 18-21 498.9 



6415 Sept. 1-2 206.4 



Number 

 3,412.3 

 4, 605. 4 



7, 335. 4 



8, 086. 7 



9, 028. 6 



343.7 

 144.2 

 474.8 



1, 822. 2 



2, 792. 

 371.2 



2,411.6 

 5, 608. 9 

 4, 975. 4 



3, 501. 6 

 11,386.5 



7,171.8 

 9, 787. 2 

 2, 688. 2 

 3, 602. 2 



170.8 



349.8 



6, 672. 6 



21, 589. 3 



8, 936. 7 



1, 943. 7 



1, 947. 5 



2, 716. 6 

 7, 725. 1 



23, 766. 5 

 10, 544. 6 

 6, 082. 8 

 6, 602. 7 

 1, 393. 3 

 400.9 



Percent 

 48.9 

 57.1 

 33.6 

 68.1 

 61.6 



49.8 

 44.2 

 67.9 

 61.4 

 62.9 

 25.1 

 57.5 

 59.7 

 22.2 

 46.6 

 34.6 

 41.5 

 36.4 

 79.1 

 48.2 



74.2 

 58.0 

 60.2 

 31.6 

 63.3 

 65.9 

 62.2 

 47.5 

 54.5 

 40.7 

 46.3 

 41.9 

 52.2 

 35.8 

 51.5 



Daps 

 10-12 

 24-25 



8-9 

 22-24 



7-8 



11-12 

 26-27 

 10-12 

 10-12 

 23-25 



8-9 

 22-23 



6-7 



6-8 

 20-21 



4-5 

 18-19 

 10-11 

 24-25 

 15-16 



0-1 

 15-16 

 27-29 

 14-15 

 27-28 

 12-13 

 26-27 

 11-12 

 25-26 



9-10 

 23-24 



8-9 

 19-20 



5-9 

 17-18 



MORTALITY AND MIGRATION 



The two factors of larval mortality and migra- 

 tion toward the inshore nursery grounds are 

 inseparable and will be dealt with concurrently. 

 Sampling stations which lie on the migration 

 route will always receive immigrant larvae, and, 

 as a result, survival rates calculated from the 

 catch of larvae at such stations will be higher than 

 the true value; conversely, calculations of survival 

 based upon the catch taken at stations from which 

 larvae consistently emigrate will underestimate 

 the true survival rates. 



Totals are given in table 7 of the estimates of 

 numbers of each larval stage under 10 m.^ surface 

 area for 37 cruises in the sampling area from 

 August 1962 to July 1964. These estimates provide 

 a measure of the relative abundance of each larval 

 stage for 2 calendar years. 



Calculation of survival rates on a temporal 

 basis requires knowledge of the duration of the 

 various larval stages. The following figures for the 



PINK SHRIMP ON FLORIDA TORTUGAS SHELF 



173 



