Locascio and Mann: Diel and seasonal tinning of sound production by Pogomas cromis 
333 
Month 
Figure 5 
Monthly means and standard deviations (SD) of sound pressure level (SPL) data for black drum 
(Pogonias cromis) from all sites and years (top two graphs) along with gonadosomatic index (GSI) 
data reprinted from Fitzhugh et ah, 1993 (bottom graph). Patterns of black drum sound produc- 
tion are in general agreement with patterns in the GSI data collected from coastal waters of 
Louisiana. The peak in GSI data occurs slightly later in the season than peaks in sound produc- 
tion recorded in southwest Florida because of the influence of latitude and water temperature on 
spawning and sound production. CC = Cape Coral, FL, and PG = Punta Gorda, FL 
and Taylor, 1989; Peters and McMichael, 1990; Nieland 
and Wilson, 1993; and Fitzhugh et al., 1993). Results 
of these studies are in general agreement and have 
shown that the spawning season occurs from late fall 
through early spring and that peak spawning occurs 
during February and March, given some variability 
with latitude. Seasonal patterns of black drum sound 
production recorded in this study are consistent with the 
timing of the spawning season defined in the literature 
and show that passive acoustics can be as effective as 
traditional methods for documenting the seasonal repro- 
ductive period of black drum. Figure 5 features data of 
gonadosomatic indices of black drum, reprinted from 
a study by Fitzhugh et al., (1993) which illustrate the 
relationship between reproductive condition and sound 
production during the spawning season. 
Although the time series of black drum sound pro- 
duction at all sites and for all years conformed to the 
same general seasonal pattern, clear similarities and 
differences existed among them. Sound production at 
PG varied between the 2004 and 2005 seasons by only 
one day for the date of the last chorus and four days 
for the date of the last recorded black drum call. The 
dates of the last recorded chorus and call were identical 
among CC sites during 2005 and differed from the CC2 
2006 time series by only two and five days, respectively. 
Sound production consistently lasted two to three weeks 
longer at the PG site than at the CC sites. We do not 
have data to explain the similarities between years at 
the same sites or the differences that existed between 
the PG and CC sites, but the simplest explanation could 
be that water temperatures were responsible for these 
patterns. The PG and CC sites are only 40 km apart 
and therefore the influence of latitude alone may not 
be responsible for differences in water temperature. It 
is possible that local effects such as exposure to sun, 
wind, and influence of adjacent water bodies may have 
contributed to the temperature differences responsible 
for the later end to seasonal calling in PG. 
Differences were also evident in the lower and more 
variable maximum SPLs recorded at PG and CC3 and 
these may be associated with the distribution of call- 
ing fish relative to hydrophone locations. Because black 
drum source levels do not appear to be highly vari- 
able among individuals (Locascio, 2010) the patterns of 
maximum SPL at these sites may not be due to lower 
intensity calls, but rather to calls from fish at greater 
or more variable distances from the hydrophone. Both 
sites were located within smaller, narrower areas of the 
canal systems compared to the locations of CC1 and 
