section involve groups of fish and, as will be seen, 

 temperature does exert a definite effect on herring 

 in groups. 



Experiment 6 (cf. experiment 1). Ninety her- 

 ring, selected at random, were tested in groups of 

 10 individuals at three temperatures: 6°, 12°, and 

 16° C. Three trials were made at each temperature. 

 The scores of 205, 129, and 121 at the three tem- 

 peratures, respectively, were significantly different 

 (F=6.19, P <0.05). 



Experiment 7. The purpose and methods of this 

 experiment were similar to those in experiment 6, 

 except that only two temperature levels were pro- 

 vided and these on alternate days. In the previous 

 experiment, trials at low temiDerature were made 

 first, followed by trials at the two higher 

 temperatures. 



Five trials were made ait. temperatures of 5 to 

 6° C. and five at 15 to 17° C. The fish were taken 

 from storage at 10 to 14° C. and held 6 hours at 

 the experimental temperature before each trial. 

 The mean scores were 201 at low temperature and 

 129 at high temperature (table 3). If the scores 

 are treated simply as two sets of five observations, 

 the difference in means is of marginal significance 

 (t=2.04, P = 0.075) ; if the scores are treated as 

 five sets of paired observations, however, t=10.1 

 and the differences are highly significant. Because 

 the low-temperature score for each trial was con- 

 sistently higher than the immediately following 

 high-temperature score, the analysis as paired ob- 

 servations seems reasonable, and the hypothesis 

 that lower temperature increases the attraction to 

 light is confirmed. 



Table 3. — Compariaon of scores ' for light attraction of 

 herring at low and high temperatures {ex-periment 7) 



Temp. Score Temp. Score 



Means .5.6 



201 



15.9 



129 



'Score = sum of numbers of herring counted in the illuminated half of 

 the tank at 30 1-minute intervals. Ten herring were used in each test; maxi- 

 mum possible score =300. 



EFFECTS OF TEMPERATURE, LIGHT INTENSITY, 

 AND LIGHT POSITION 



Experiment 8. The responses of groups of 10 

 herring were observed at two temperature levels 

 (8-10° and 15-17° C), at three levels of light 



intensity (fig. 1), and with the attracting light 

 either above or below the surface. Each combina- 

 tion of conditions was replicated once. The fish 

 were taken from storage at 13 to 16° C. and held 

 3 hours at the experimental temperature before 

 each trial. Table 4 shows the scores. The differ- 

 ences in response were highly significant between 

 high and low temperature (F = 69.2) and between 

 above- and below-surface lights (F = 48.7). There 

 was also a significant interaction between light 

 position and intensity, such that the bright light 

 above the surface had the poorest attraction and 

 the bright and medium lights below the surface 

 had the greatest. The difference in response due 

 to position of the light was significantly greater at 

 low temperature. In general, below-surface lights 

 were more effective at low temperature than at 

 hieh. 



ATTENUATION OF 



LIGHT 

 TIME 



ATTRACTION WITH 



Experiment 9. The degree to which light will 

 hold the herring in its vicinity is a significant 

 component of the total attraction to light. This 

 experiment was intended to determine whether 

 this holding effect would decrease with time, and, 

 if so, whether such decrease was affected by light 

 intensity or position. 



Table 4. — Comparison of scores ' for light attraction of 

 herring in relation to light location, light intensity, and 

 temperature {experiment 8) 



' Score = sum of numbers of heiTing counted in the illuminated halt of the 

 tank at 30 1-minute intervals. Ten herring were used in each test; maximum 

 possible score =300. 



The experiment comprised 24 trials. Each trial 

 consisted of three phases: the first, a 30-minute 

 series of counts on a group of 10 fish, the same as 

 the routine procedure used in other experiments; 

 the second, an 18-hour interval with the attracting 

 light left on; and the third, another 30-minute 

 series of coimts like the first. The 24 trials repre- 



FACrrORS INFLUENCING ATTRACmON OF ATLANiTIC HERRING rTO AR/TIPICIAL LIGHTS 



79 



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