104 
Fishery Bulletin 1 14(1) 
among offshore atolls (Paz and Sedberry, 2008). In con- 
trast, red grouper (E. morio) do not form large aggrega- 
tions but instead appear to use more discretely formed 
spawning sites, where individual male territories are 
indicated by shallow pits excavated in the sediment 
(Coleman and Koenig, 2010; Nelson et al., 2011). 
At many traditional aggregation sites, a variety of 
species may co-occur and form seasonal reproductively 
active communities; hence these sites are of value for 
conservation and research purposes (Heyman et ah, 
2001). The establishment of marine reserves at such 
locations provides an effective approach for the man- 
agement of stocks in multispecies fisheries (Huntsman 
et al., 1999; Ault et al., 2008a). 
In addition to the more traditional methods, pas- 
sive acoustics represents a relatively new and unde- 
rused approach to survey fish populations at spawn- 
ing sites. Sound production is common among many 
fishes and is associated most often with courtship 
and spawning behaviors (Mok and Gilmore, 1983). 
Because sounds are species-specific, once the source 
has become positively identified, the information can 
be referenced to all future recordings to identify the 
presence of a given species at a monitoring site. Time 
series from the acoustic monitoring of fish sound pro- 
duction, therefore, can be used as a proxy to docu- 
ment the timing and location of reproductive behav- 
ior (Locascio and Mann, 2008). Recording technolo- 
gies now allow multiyear deployments during which 
short periods of data (e.g., tens of seconds) may be 
recorded every few minutes. The trend in recording 
technologies becoming more sophisticated and less 
costly to acquire and deploy will continue and result 
in the collection of larger, synoptic acoustic data sets 
at more locations. 
Groupers are among the most economically impor- 
tant fishes currently being studied with passive acous- 
tics, and accomplishments from such monitoring are 
still few but increasing. Thus far, the sounds of Atlan- 
tic goliath grouper (E. itajara ), red hind, red grouper, 
yellowfin grouper (M. venenosa), Nassau grouper, and 
black grouper have been positively identified and cor- 
related with known spawning seasons (Mann et al., 
2009; Mann et al., 2010; Nelson et al., 2011; Scharer 
et al., 2012, 2013). Other grouper species are also like- 
ly to produce sound, and these sounds await discovery. 
Only one study has attempted to quantify population 
size of a grouper species (red hind) with the use of 
passive acoustics in combination with visual surveys 
made by divers (Rowell et al., 2012). 
Riley’s Hump was a historically productive com- 
mercial fishing ground, particularly for mutton snap- 
per ( Lutjanus analis) (Burton et al., 2005). Anecdotal 
input from fishermen and the recommendations of a 
25-member working group of commercial and recre- 
ational fishermen, divers, conservationists, scientists, 
concerned citizens, and representatives from govern- 
ment agencies led to the creation of the Tortugas 
South Ecological Reserve (TSER), a research-only 
marine reserve, in 2001 to protect the overexploited 
population of mutton snapper. Mutton snapper use Ri- 
ley’s Hump as a spawning aggregation site in the late 
spring and early summer months (NOAA 1 ; Domeier, 
2004; Burton et al., 2005). Since the inception of the 
TSER and the protection of the aggregation of mutton 
snapper at Riley’s Hump, increased numbers of mut- 
ton snapper have been seen in visual surveys at Ri- 
ley’s Hump, at downstream locations along the Florida 
Keys reef tract (Ault et al., 2013), and in recreational 
headboat fishery landings (Brennan 2 ). Many grouper 
species also inhabit Riley’s Hump, but their use of the 
site for reproductive purposes has not been document- 
ed. The primary purpose of this study was to conduct 
an acoustic survey of Riley’s Hump to document grou- 
per sound production, which is generally used as a 
proxy for reproductive behavior. 
Materials and methods 
Riley’s Hump, a geologic feature of approximately 10 
km 2 , marks the western extent of the south Florida 
reef tract and lies entirely within the TSER (Fig. 1, 
A and B). The limestone composition at Riley’s Hump 
is typical of the sedimentary geology of the Gulf of 
Mexico, and its surface ranges from sandy bare areas 
to rugose hard bottom and low-relief outcroppings. 
Depths range from approximately 30 m on the hump 
to approximately 60 m immediately adjacent to it (Mal- 
linson et al., 2003). Relief is highest along the edges, 
especially from the northeast to southern edges in a 
clockwise direction. The steepest vertical drop-off is lo- 
cated along the south-southwestern edge, which also 
has been observed to have the highest fish densities 
(Burton et al., 2005). The benthic community is com- 
posed of hard and soft corals, gorgonians, and a variety 
of sponges (Weaver et al., 2006). 
Acoustic digital spectrum recorders (Loggerhead 
Instruments 3 , Sarasota, FL) were deployed at 7 loca- 
tions on Riley’s Hump during multiple periods from 
2010 through 2012 (Table 1; Fig. 1). These locations 
included 3 previously established study sites (12, 12A, 
and 15), where visual surveys of fishes were conducted 
during prior years, along with 4 new sites established 
for this study, including 3 sites on Riley’s Hump (RH1, 
RH2, and RH3) and a deepwater site off the south- 
western edge of Riley’s Hump (RHDW) at a depth of 
approximately 60 m. Digital spectrum recorders were 
programmed to record 10 s of sound every 10 min at a 
1 NOAA. 2000. Draft supplemental environmental impact 
statement/draft supplemental management plan for the Tor- 
tugas Ecological Reserve, 250 p. Mar. Sanctuaries Div., Off. 
Ocean Coast. Resour. Manage., Natl. Ocean Serv., NOAA, Sil- 
ver Spring, MD. [Available at website.] 
2 Brennan, K. J. 2013. Personal commun. Beaufort Labo- 
ratory, Southeast Fisheries Science Center, National Marine 
Fisheries Service, NOAA, Beaufort, NC 28516-9722. 
3 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
