Locascio and Burton: A passive acoustic survey of fish sound production at Riley's Hump 
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Date (month/year) 
Figure 3 
Time series of the ratio of the number of calls of 3 grouper species, (A) black grouper ( Mycteroperca bonaci), (B) red 
grouper ( Epinephelus morio), and (C) red hind ( Epinephelus guttatus), recorded at Riley’s Hump, Tortugas South 
Ecological Reserve, Florida Keys, 2010-2012 to the number of files reviewed in a subsample of 10,000 randomly 
selected audio files. For each species, call volume increased during the winter-spring reproductive season. The 2012 
season had a greater call volume and appears more protracted than the 2011 season for red grouper and red hind; 
the higher numbers of calls in 2012 may represent the presence of more fish species at these sites in 2012 than in 
2011. Red grouper and red hind both demonstrated a preference for the deepwater site (RHDW) in 2012 and for sites 
RH2 and RH3 in 2011, respectively. Black grouper were recorded at all sites yet did not produce particularly high 
numbers of calls at a specific site, although, overall, most sound production by this species was recorded at site RH2 
during both years. 
resulted in relatively poor signal-to-noise ratios which 
prevented identification of a clear diel pattern in the 
power spectra results associated with groupers. Record- 
ings of red hind at the RHDW site were the only excep- 
tion to this and diel patterns in the power spectra as- 
sociated with this species were clearly discernible from 
background levels. 
Sound production by each grouper species occurred 
year-round, but levels were highest from January 
through May and typically peaked in March for each 
species during 2011 and 2012 (Fig. 3). Black grouper 
were recorded at all sites; the highest standardized 
number of calls was recorded at site 12A in 2011 and 
at site RH2 in 2012. A modestly higher number of 
black grouper calls were recorded in 2011. Red grouper 
were recorded at all sites; the highest number of calls 
by this species was recorded at site RH2 in 2011 and 
at site RHDW in 2012. Red hind were recorded only at 
sites RH1, RH2, and RH3 and at site RHDW; the high- 
est number of calls by this species was recorded at site 
RH3 in 2011 and at site RHDW in 2012. The seasonal 
pattern of calls by black grouper indicates a more even 
distribution over the winter-spring period than that of 
the seasonal pattern of sound production by red grou- 
per and red hind, which peaked more sharply in March 
and April of each year. Sound pressure levels recorded 
at site RHDW reached amplitudes that were 15 dB 
SPL (re: 1 pPa) greater than daytime background lev- 
els and were positively associated with the last quarter 
moon phase. All 3 grouper species were recorded at site 
RHDW, but sound production was dominated at this 
site by the red hind (Figs. 3 and 4). 
Red and black groupers and red hind were the dom- 
inant grouper species recorded at Riley’s Hump, but 
other low-frequency, pulsed and modulated tonal calls 
were occasionally discovered during review of audio 
files. Three instances of calls by yellowfin grouper were 
positively identified in recordings made at site 12A 
during November 2010 by comparison with document- 
ed characteristic sound production of yellowfin grouper 
(Scharer et ah, 2012). Several instances of a call type 
that resembled that of the Nassau grouper were also 
noted in recordings made during winter-early spring 
at site RHDW. Both the yellowfin grouper and Nassau 
grouper were observed in visual surveys conducted by 
divers at Riley’s Hump during this study. More detailed 
studies of sound production of Nassau grouper are in 
progress, and the results will be useful for quantifying 
the presence of this species in the recordings made at 
Riley’s Hump. 
Additional information on sound production by 
black grouper was documented in this study. Two 
