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Fishery Bulletin 109(3) 
70 1 1 1 1 1 I 1 j i i 1 I L_ 
1 000 1200 1400 1600 1800 2000 2200 0000 0200 0400 0600 0800 1000 
Time of day 
Figure 2 
Diel periodicity of black drum (Pogonias cromis ) sound production (expressed as sound 
pressure level) represented by an overlay plot of consecutive 24-hour periods recorded 
from 15 February-16 March 2005 at Cape Coral site 2. The white portion of the diel bar at 
the top of the figure represents daylight hours, the black represents night hours, and the 
gray represents time of sunset and sunrise over the dates when these data were recorded. 
Table 2 
Regression coefficients (r 2 ) and P-values calculated for chorus start time vs. time of sunset, and correlation coefficients (r) and 
P-values calculated for chorus start time and chorus end time, chorus start time and time of maximum SPL (Max SPL), and 
chorus start time and maximum SPL produced by black drum (Pogonias cromis). Asterisks denote a Spearman correlation was 
calculated instead of a Pearson correlation. PG=Punta Gorda, FL; CC=Cape Coral, FL. df=degrees of freedom. 
Site 
Dates 
df 
Chorus start time 
time of sunset 
Chorus start time 
chorus end time 
Chorus start time 
time of max SPL 
Chorus start time 
max SPL 
r 2 
P 
r 
P 
r 
P 
r 
P 
PG 
3/22/04-5/3/04 
25 
0.41 
<0.01 
-0.65 
0.01 
0.28 
0.12 
-0.67 
<0.01 
PG 
12/12/04-5/4/05 
82 
0.02 
0.33 
-0.56 
<0.01 
0.19 
0.10 
-0.74 
<0.01 
CC1 
2/12/05-4/6/05 
42 
0.54 
<0.01 
-0.34 
0.03 
0.41 
0.06 
-0.78 
<0.01 
CC2 
2/12/05-5/6/05 
102 
0.43 
<0.01 
-0.28 
0.07 
0.38 
0.01 
-0.78 
<0.01 
CC2 
12/3/05-6/7/06 
42 
0.04 
0.06 
-0.61 
<0.01 
0.02 
0.81 
-0.85 
<0.01 
CC3 
2/12/05-4/6/05 
39 
0.39 
<0.01 
*-0.27 
0.10 
*0.31 
0.06 
*-0.56 
<0.01 
generally meant earlier end times, and conversely, that 
earlier start times were associated with later end times 
(Fig. 3, Table 2). Correlations of chorus start time and 
maximum SPL were strongly negative and significant 
for comparisons of all time series and indicated that 
earlier chorus start times were associated with higher 
maximum SPL; however, chorus start time and time of 
maximum SPL were only weakly and slightly positively 
correlated (Table 2). Monthly mean chorus start and 
end times were more variable than the monthly mean 
