for laboratory or other field experiments con- 

 cerned with rhythmic behavior patterns. 

 Cloudsley-Thompson (1961) cautioned that 

 rhythmical activities of an animal are not 

 necessarily all of one type and stated that 

 rhythms solely dependent on the environment 

 are rare and probably represent rhythms which 

 are independent but out of phase with the en- 

 vii-onment. In regard to field observations dur- 

 ing solar eclipses, he concluded that the results 

 agree with those of laboratory experiments, in 

 that certain animals exhibit some periodic 

 activities that appear to be dependent on the 

 environment and others that are more mark- 

 edly independent. 



SUMMARY 



1. A total eclipse of the sun occurred in 

 Maine on July 20. 1963. Totality lasted 59 

 seconds. 



2. Biological and physical observations were 

 made on the day before the eclipse and the day 

 of the eclipse and were continued through sun- 

 set each day to provide a comparison with 

 regular light-dark cycles. 



3. Surface and subsurface illuminance de- 

 clined markedly at totality, approximating 

 conditions at sunset. 



4. Barometric pre.ssure declined steadily for 

 the 2 days prior to the eclipse, reached a low 

 point 29.45 mm. at totality, and then increa.sed. 



5. Zooplankton volumes from surface waters 

 decreased during the eclipse and at sunset at 

 both of the .sampling areas. 



6. Of the dominant copepods, Pseudocalanus 

 minutus and Acarfia longiremis exhibited the 

 most pronounced rei5pon.se to the eclipse and 

 moved toward the surface. The reactions of 

 other species were either weak or ill-defined. 



7. Female Acarfia longiremis were more ac- 

 tive than males during the eclipse, and moved 

 toward the surface at totality. 



8. No change was ob.served in the behavior 

 of green crabs during the eclipse. Apparently, 

 the duration of the eclipse was too short or the 

 light intensity too high, or both, to elicit a re- 

 sponse. 



9. At totality, Atlantic herring held in a pen 

 responded in a manner comparable to that 

 observed at sunset. The response was not 



270 



strong, but some fi.sh began .schooling and 

 moved into the surface waters. 



10. Echo tracings documented a movement 

 toward the surface after sunset, but tracings 

 during the eclipse showed none of this activity. 

 Though large catches of jellyfish were taken, 

 the traces could have been made by fi.shes which 

 escaped the net. 



11. Comparisons of my observations with 

 tho-se made during other eclipses emphasize the 

 importance of designing experiments carefully 

 to assess properly the behavioral respon.ses in 

 relation to environmental changes. 



ACKNOWLEDGMENTS 



Scientists and technicians from the Bureau 

 of Commercial Fisheries Biological Laboratory, 

 Boothbay Harbor, Maine, a.ssisted in the col- 

 lection and preparation of the data; and 

 S. R. Studenet.sky, Atlant-NIRO, Kaliningrad, 

 U.S.S.R., arranged for the translation of 

 Petipa's paper. 



LITERATURE CITED 



Allee, W. C, a. E. Emerson, O. Park, T. Park, and 

 K. P. Schmidt. 



1949. Principles of animal ecology. W. B. .Saun- 

 ders Co., Philadelphia and London, 8,37 pp. 



ASCHOFF, JURGEN. 



1960. Exogenous and endogenous components in 

 circadian rhythms. Cold Spring Harbor Symp. 

 Quant. Biol. 25: 11-28. 

 Backus, Richard H., Robert C. Ciark, and Asa S. 



WiNR. 



19fi5. Behavior of certain marine organisms dur- 

 ing the solar eclipse of July 20, 1963. Nature 

 205; 989-991. 

 BiGELOw, Henry B. 



1926. Plankton of the offshore waters of the Gulf 

 of Maine. Bull. Bur. Fish. XI., Part II: 500 pp. 

 Blaxter, J. H. S., and B. B. Parrish. 



1965. The importance of light in shoaling, avoid- 

 ance of nets and vertical migration by herring. 

 J. Cons. 30(1) : 40-57. 

 Blaxter, J. H. S., and F. G. T. Holliday. 



1963. The behavior and physiology of herring and 

 other Clupeids. In F. S. Russell (editor). Ad- 

 vances in marine biology 1, pp. 261-393. Aca- 

 demic Press, London and New York. 

 Breder, C. M., Jr. 



1951. Studies on the structure of the fish school. 

 Bull. Amer. Mus. Natur. Hist. 98, Art. 1: 1-27. 



1959. Studies on social groupings in fishes. Bull. 

 Amer. Mus. Natur. Hist. 117, Art. 6: .393 482. 



U.S. FISH AND WILDLIFE SERVICE 



