Figure 7. — Fiberglass tank for holding green crabs. 



was supplied from the laboratory salt-water 

 system and the tank was placed out-of-doors 

 in an area free from shadows. Naylor (1958) 

 found that the normal precision and level of 

 the rhythmic activity declined after the crabs 

 had been held for 3 to 4 days. For my study 

 the crabs were placed in the tank two days 

 before the eclipse and took refuge in the shelter 

 immediately. Activity was recorded by count- 

 ing the crabs that left this cover. A control 

 was established by making observations period- 

 ically during the day before the eclipse and at 

 15-minute intervals from 1600 to 2200 hours, 

 well past sunset. 



On July 19 no crabs left the sheltered area 

 until 2035. From that time until the last ob- 

 servation at 2205 the activity generally in- 

 creased; as many as 11 males and 10 females 

 left the covered area ; the average number of 

 active males was 5.7 and the average number 

 of females 5.2. On the day of the eclipse, July 

 20, no activity was observed until 2050, more 

 than 3 hours after totality; the greatest num- 

 ber of males in the unsheltered area at any 

 time was 13, and the highest number of fe- 

 males 5; between 2050 and 2200 the average 

 number of active males was 9.2 and females, 

 3.6. 



Because the crabs were not active during the 

 eclipse, other experiments were conducted the 



following day to determine light conditions 

 which would elicit a response. When the tank 

 was in daylight (27,000 luxes) and then cov- 

 ered by a heavy tarpaulin that reduced the 

 light to less than 10 luxes, 2 minutes elapsed 

 before any activity was noted. Under condi- 

 tions of subdued artificial light of 500 luxes, 

 which was then reduced to less than 10 luxes, 

 the response was more rapid; 3 crabs were 

 active within 30 seconds and as many as 10 

 came out of the shelter within 2 minutes. As in 

 the observations made on the date of the eclipse, 

 the males were the first to respond. The light 

 intensity in the half hour before totality was 

 considerably greater than that of the artificial 

 light; apparently the duration of subdued light 

 during the eclipse was too short or the in- 

 tensity too high to elicit a response from the 

 crabs. 



BEHAVIOR OF HERRING 



Generally, the behavior of Atlantic herring 

 (Clupea harengus harengus) is well document- 

 ed, but specific responses are extremely vari- 

 able. Blaxter and Parrish (1965), studying 

 vertical movement, concluded that it was not 

 possible to show any relationship between the 

 preferred depth, or the extent of upward move- 

 ment, and such factors as gradients of salinity, 

 temperature, or food. The herring used in the 

 eclipse study had been held in large tanks for 

 several weeks. Though their behavior could not 

 be considered comparable to that of herring in 

 their natural environment, the fish were ac- 

 climated to confined conditions which were nec- 

 essary for the observations made during the 

 eclipse. 



About 75 two-year-old herring were placed 

 in a small-meshed holding pen during early 

 morning of July 19. Observations were made 

 at 15-minute intervals from 1600 to 2200 hours 

 on July 19 and 20. The pen (dimensions, 3 by 3 

 by 2 m.) was visually separated into quadrants 

 A, B, C, and D (fig. 8) . Each quadrant was 

 divided into two sections by an imaginary 

 plane midway between the surface and the 

 bottom of the pen. The presence or absence of 

 fish in these quadrants and the depth divisions 

 were recorded, along with remarks on schooling 

 and directional movement. On both days, thei-e 



MARINE ORGANISMS DURING SOLAR ECLIPSE 



265 



