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Figure 4 
Acoustic time-series data of black drum ( Pogonias cromis) sound production from all sites and years. 
Sound pressure level (SPL) was calculated as dB band level of 100 - 200 Hz (re: IpPa) from 10-second 
recordings made every 10 minutes. Increased nightly SPLs (evident as peaks in the data) during winter 
through early spring are consistent with the black drum spawning season and are similar between 
study areas and years. CC = Cape Coral, FL, and PG=Punta Gorda, FL 
i 
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and February at the CC sites and during February and 
March at the PG site (Figs. 4, and 5). 
The CC2 2005-06 time series began and ended some- 
what abruptly relative to chorus threshold levels. Data 
recorded at each of the CC sites during 2005 revealed 
a similar pattern at the end the season. In contrast, 
maximum SPL recorded during both years at the PG 
site increased and decreased more gradually at the 
start and end of each season and sound production 
continued for two to three weeks longer than at the 
CC sites. Maximum SPLs at PG were also generally 
lower and more variable than at the CC sites (Figs. 4 
and 5, Table 4). 
The greatest coefficient produced by the cross corre- 
lation of maximum SPL and bottom temperature was 
-0.81 at 0 days lag. The correlation coefficient produced 
by surface temperature and maximum SPL at 0 days 
lag was -0.14 and the greatest coefficient was -0.4 at 
22 days lag. Surface temperatures ranged from approxi- 
mately 17.5° to 26°C during the seasonal period of black 
drum sound production (4 December 2005-10 April 
2006) but fluctuated within a range of about 18° to 22°C 
during 4 December 2005-20 February 2006 (x=20.3, 
standard deviation [SD]=1.8, n- 78) and 22.5° to 26°C 
(x=23.9, SD=1.2, n = 48) during 21 February-10 April 
2006. Surface temperatures during these two periods 
were significantly different (£=—14. 8, PcO.Ol). Cross 
correlations between maximum SPL and surface tem- 
perature produced maximum correlation coefficients of 
-0.33 at two days lag for 4 December 2005-20 February 
2006 and -0.69 at one day lag for 21 February-10 April 
2006. Bottom temperatures ranged from approximately 
17° to 24°C over the entire time series and were less 
variable than surface temperatures. The seasonal peak 
in maximum SPL occurred when surface and bottom 
temperatures were both between 18° and 22°C during 
early January through late February. Time series data 
of maximum SPL and corresponding temperature data 
for CC2 are shown in Figure 6. 
Chorus start, end, and duration were positively cor- 
related between all sites, except PG and CC1 (Table 5). 
A stronger association existed among the Cape Coral 
sites for each of these variables and in particular for 
chorus start time (Fig. 7). The time of maximum SPL 
was weakly correlated between sites (either slightly 
positive or negative and insignificant). The FFT results 
of maximum SPL data did not indicate that black drum 
sound production occurred on a lunar cycle. 
Discussion 
The black drum spawning season has been defined 
within the Gulf of Mexico through histological exami- 
nation of oocyte development, gonadosomatic indices, 
and collection of eggs, larvae, and juveniles (Murphy 
