Locascio and Mann: Diel and seasonal timing of sound production by Pogonias cromis 
329 
Table 1 
Correlation coefficients (r) and P-values calculated for total acoustic energy (TAE) and maximum sound pressure level (Max 
SPL), and chorus duration and maximum sound pressure level produced by black drum ( Pogonias cromis) from each site and 
season. PG=Punta Gorda, FL; CC=Cape Coral, FL. Mean daily background sound pressure levels and chorus thresholds are 
expressed as dB SPL (re: IpPa) of the 100-200 Hz band. df=degrees of freedom, SD = standard deviation. 
Background Chorus TAE Chorus duration 
dB SPL threshold Max SPL Max SPL 
Site 
Dates 
df 
mean 
SD 
dB SPL 
r 
P 
r 
P 
PG 
3/22/04-5/3/04 
25 
85.0 
4.1 
93.2 
0.97 
<0.01 
0.76 
<0.01 
PG 
12/12/04-5/4/05 
82 
85.7 
4.3 
94.3 
0.98 
<0.01 
0.79 
<0.01 
CC1 
2/12/05-4/6/05 
42 
91.6 
3.2 
98.0 
0.99 
<0.01 
0.93 
<0.01 
CC2 
2/12/05-5/6/05 
102 
90.7 
3.8 
98.3 
0.99 
<0.01 
0.75 
<0.01 
CC2 
12/3/05-6/7/06 
42 
90.0 
3.5 
97.0 
0.99 
<0.01 
0.85 
<0.01 
CC3 
2/12/05-4/6/05 
39 
93.1 
3.5 
100.1 
0.95 
<0.01 
0.59 
<0.01 
The threshold was used to mark chorus start and end 
times from which nightly parameters of chorus dura- 
tion, total acoustic energy (TAE), and maximum SPL 
were calculated. TAE (dB re: 1 pPa 2 -s) was calculated 
by converting SPL to pPa and then integrating the 
acoustic energy (squared acoustic pressure) over the 
time period that the SPL exceeded the threshold (i.e., 
by summing the area under the curve). This method 
is equivalent to the calculation of sound exposure level 
described by the American National Standards Institute 
(ANSI, SI. 1-1994). 
Correlations between TAE and maximum SPL and 
between chorus duration and maximum SPL were calcu- 
lated with time series data from each site and for each 
season. The purpose was to evaluate maximum SPL 
as a quantitative representation of nightly black drum 
sound production. Linear regressions were calculated 
between chorus start time and time of sunset. Correla- 
tions between chorus start and end times, between cho- 
rus start time and time of maximum SPL, and between 
chorus start time and maximum SPL were calculated 
for each time series. Data were tested for normality 
on the basis of standardized kurtosis and skewness. 
If data were non-normal, a Spearman nonparametric 
correlation was calculated instead of a Pearson corre- 
lation. The ascending and descending slopes of nightly 
chorus events were calculated from the chorus start to 
the time when the sound level first reached 6 dB below 
maximum SPL and from the time the sound level de- 
creased from 6 dB below maximum SPL to the chorus 
end. Ascending and descending slopes were compared 
by using the Wilcoxon signed rank nonparametric test. 
Correlations between sites for data of chorus start time, 
chorus end time, chorus duration, and time of maximum 
SPL were calculated from data recorded concurrently at 
all sites during 14 February-6 April 2005. Alpha values 
were adjusted by using sequential Bonferroni tests to 
correct for experiment-wise error (Sokol and Rolf, 1995). 
Cross correlations between nightly maximum SPL and 
surface and bottom water temperature were calculated 
for the 2005-06 CC2 time series. Fourier analysis was 
used to examine for patterns of lunar periodicity in 
black drum sound production in the Punta Gorda time 
series recorded during December 2004-May 2005 and 
the CC2 time series recorded during October 2005- 
June 2006. 
Results 
Total acoustic energy (TAE) and maximum sound pres- 
sure level (SPL), and chorus duration and maximum 
SPL, were positively and significantly correlated for all 
sites and seasons (Table 1). The high association between 
TAE and maximum SPL (r=0.95 to 0.99) qualified maxi- 
mum SPL to quantitatively represent black drum sound 
production on a nightly basis. The gulf toadfish ( Opsa - 
nus beta ) was the only other soniferous fish recorded. 
The call of this species has a fundamental frequency 
of approximately 280Hz (Thorson and Fine, 2002) and 
therefore did not contribute to the SPL calculated in 
the 100-200 Hz frequency band used for analysis of 
black drum acoustic data. Invertebrate sounds (so called 
“snapping-shrimp”) were not recorded at the study sites. 
Black drum sound production was strongly periodic. 
Calls were occasionally recorded during the mid-morn- 
ing through early afternoon but increased sharply from 
late afternoon to early evening, and chorus duration 
lasted up to 12 hours during peak season (Fig. 2). 
Regressions of chorus start time and time of sunset 
resulted in higher r 2 values for the shorter time se- 
ries, which began during the mid to late season in 
February 2005 (CC1, CC2, CC3) and March 2004 (PG) 
(r 2 = 0.39 to 0.54), than for the two longer time series 
which covered the majority of the season, CC2 2005-06 
(r 2 =0.04) and PG 2004-05 (r 2 =0.02). Data used for 
all correlations were normally distributed, except for 
chorus start time data from CC3. Chorus start and 
end times were negatively and in most cases signifi- 
cantly correlated and indicated that later start times 
