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Passive Acoustics: Program Summaries
US: Southeast: Donald Baltz
Spawning Site Selection by Coastal Fishes in the Northern Gulf of Mexico
Donald M. Baltz
Department of Oceanography and Coastal Sciences
Coastal Fisheries Institute, Louisiana State University
Baton Rouge, LA 70803-7503
Phone: 225-578-6512 Fax: 225-578-6513 Email: [email protected]
Overall Research Goal
To develop basic ecological information on the habitat requirements of spawning soniferous
fishes that can be used to study their breeding behavior and understand environmental factors
that influence their spawning success and the successful recruitment of early life history stages
into nursery habitat.
Introduction
Passive acoustics can contribute to our understanding of how fishes use their environment for
important life history functions. For the family Sciaenidae, which includes more than 30 species
of croakers, drums, seatrout, etc., in US coastal waters, males generally gather in the late
afternoon or early evening and drum to attract females in spawning condition to aggregation
sites. These sites are apparently selected by males because they are suitable for the fertilization,
survival, and dispersal of early life history stages (i.e., eggs and early embryos). Simple
hydrophones can be used to locate and identify spawning aggregations of species of interest and
also to learn about the daily and seasonal patterns of reproductive activity. Combined with other
scientific instruments, researchers can use hydorphones to describe the time and place of
spawning in terms of important environmental variables such as depth, substrate, salinity,
oxygen concentration, turbidity, light intensity, water temperature and current velocity. Careful
analysis of this suite of variables tells us what is important to the fish in selecting sites for
spawning.
Approach
We use a microhabitat approach to make multiple, randomly selected, independent observations
with hydorphones at times and places where spawning is suspected (Figure 1). We also record
environmental conditions and make short tape recordings for laboratory analyses. When
suspected spawning sites are located, we collect water samples to gather eggs for rearing to an
identifiable stage to verify spawning. Comparison of all randomly selected sites (All sites) with
those used for spawning helps us to identify the environmental conditions that are most
important to the fish (Figure 2). A suitability analysis offers valuable insights into the range
along environmental gradients (e.g., water temperature) that are most essential for successful
spawning.
Passive Acoustics: Program Summaries
US: Southeast: Donald Baltz
Figure 1
Figure 2
Future Studies
A variety of important Sciaenid fishes are found in the coastal waters of the northern Gulf of
Mexico and the spawning requirements of most of them have not been well studied. One reason
for this is that many of them spawn late in the evening in open waters that are often not safe for
small boats. Most notably, the red drum (Sciaenops ocellatus) spawns on Louisiana’s coastal
shelf amid a dynamic landscape that is experiencing natural and anthropogenic changes due to a
variety of factors, including water management, sea-level rise, canal dredging, industrial
development, land loss, shipping, and the effects of fishing. For this and other species, we need
to know what ecological conditions along complex environmental gradients in our coastal water
Passive Acoustics: Program Summaries
US: Southeast: Donald Baltz
are most suitable for spawning so that these essential habitats can be identified and protected.
My wish list is topped by a fixed or moveable listening array with overlapping directional
capabilities to generate position fixes, computer programs to process fix data, and real-time
transmission capabilities to allow relatively small boats to move to aggregation sites and random
sites for measurements of resource use and availability.
Past and Current Studies
Baltz, D. M. and J. A. Campos M. 1996. Hydrophone identification and characterization of
Cynoscion squamipinnis (Perciformes: Sciaenidae) spawning sites in the Gulf of Nicoya,
Costa Rica. Revista de Biologia Tropical 44(2):743-751.
Saucier, M. H., D. M. Baltz, and W. A. Roumillat. 1992. Hydrophone identification of
spawning sites of spotted seatrout (Cynoscion nebulosus) near Charleston, South
Carolina. Northeast Gulf Science 12(2):141-145.
Saucier, M. H. and D. M. Baltz. 1993. Spawning site selection by spotted seatrout (Cynoscion
nebulosus) and black drum (Pogonias cromis) in Louisiana. Environmental Biology of
Fishes 36:257-272.
Passive Acoustics: Program Summaries
US: Southeast: Myra Brouwer
Potential for coupling of underwater TV monitoring with passive acoustics
Charles A. Barans, David Schmidt, Myra C. Brouwer*
Sonic signatures of some fishes have been corroborated with visual observations, yet
many more are needed to assist in interpretations of sonic data from hydrophones placed
in complex habitats with many interacting species of vertebrates and invertebrates. The
underwater television (UWTV) is ideal for direct correlations between specific sounds
and their causes, if the water visibility is acceptable.
Underwater video devices can provide a wealth of information to scientists and fishery
managers including seasonal movements of fishes, the potential for development of
indices of abundance for some migrating and resident populations, and any seasonal
behaviors associated with the formation of pre-spawning aggregations along a migration
route. An UWTV system offshore allows the study of fishes on the bottom throughout
the year without the costly trips to a research site in inclement weather. The present
visual capability of UWTV should be integrated with acoustic information to enhance
fisheries biologists’ understanding of fish behavior and movements within the region.
Herein we describe recent results from a permanent installation of an UWTV at an
artificial reef offshore.
The Underwater Television System
The research site was established in
25-28 m of water about 72 Km off
central Georgia on May 11, 1999 with
the deployment of several large fish
attraction units (Artificial Reefs, Inc.
The video system consists of two
main parts. A pressure housing,
located on the sea floor and a video
capture engine,
located remotely.
Six monochrome
video cameras are housed with a microcontroller and a few basic sensors. File
transfer and system parameter updates
Passive Acoustics: Program Summaries
US: Southeast: Myra Brouwer
are made possible by an interface between the web server and the console application
controlling the video system using pcANYWHERE
Daily observations (~65) were conducted between 1200 and 2130 GMT (Greenwich
Mean Time). Still images were recorded and logged at 10 minute intervals for 10 sec.
Video clips were recorded on the hour from camera No. 5, since only camera No. 5 was
directed at reef structure with any reef fish activity. Images were downloaded from the
remote computer to the laboratory computer for fish counts and long-term data storage.
Observations using UWTV
seasonal dates of the first appearance
of various fish species are especially
important for identification of any
prespawning migration to the south
by adult grouper, one of our main
target species. Seasonal changes in
the makeup of the fish assemblage at
the UWTV site appear much greater
than previously believed. We are
documenting the annual cycle of
juvenile recruitment in spring and
summer
followed
by
intense
predation by transient species later
in the year.
Large schools of bait fish have been
present
in
most
seasons
accompanied
by
schools
of
predatory greater amberjacks. The
subjects of interest to us, snapper
and grouper species, however, have
yet to establish resident populations
at the site.
We have temporally documented
species presence and activity. The
Year-round resident species included Atlantic spadefish, gray triggerfish, black seabass,
and great barracuda. Other resident species may not have been observed due to
decreased visibility and/or increased cryptic behavior during winter.
Passive Acoustics: Program Summaries
US: Southeast: Myra Brouwer
bottom.
Although resident predators must
significantly reduce recruitment of many
species, large predation events appear to
have a formidable influence on mortality
and survival of small and juvenile reef
fishes.
Two important large-scale
predation events observed in 1999-2000
were the arrival of migrating loons and
the mid-winter appearance of large
populations of ctenophores near the
We observed the loons to visually select fish prey in and near the structural reef units
within a meter of the bottom. Also, the large numbers of ctenophores and/or jellyfish in
winter corresponded to the temporary residence of an ocean sunfish and a relatively large
population of adult Atlantic spadefish. Both species are known to feed on jellyfish.
The primary scientific objective of the UWTV system established off Georgia was to
document and quantify prespawning aggregations of gag grouper as they move south
along the continental shelf. If an associated sound recognition pattern were associated
with such fish aggregations and movements, multiple listening stations could be
established at key locations across the shelf and along the potential migration path at a
cost for monitoring much less than that using other methods. The visual findings of the
present UWTV study expand our understanding of the importance of large scale
stochastic predation events on relatively localized reef fish aggregations, especially of
juveniles and bait species. The sounds generated by the assemblage interactions would
have filled chapters of a catalog on reef fish sounds. Synergistic information would come
from the simultaneous combination of visual and sonic information. The addition of less
expensive, passive acoustic data gathering devices could compensate for the lack of
spatial coverage by more expensive UWTV systems. It could also provide more complete
coverage of the events taking place in the vicinity of the cameras, but beyond their field
of view. The scientific community anxiously awaits the development and application of
tools that will allow simultaneous visual and sonic investigations of fish associations and
behaviors.
Passive Acoustics: Program Summaries
US: Southeast: Mark Collins
Locating sciaenid spawning aggregations in anticipation of harbor modifications,
and reactions of spotted sea trout spawners to acoustic disturbance
Mark Collins, Bridget Callahan, Bill Post, and Amanda Avildsen
SC Marine Resources Research Institute, SCDNR, Charleston, SC, USA
The drum family, which includes spotted seatrout, red drum, and other
recreationally (= economically) important fishes, spawn in estuaries with males making
drumming sounds to attract mates to spawning aggregations. Populations of many of
these species have declined in abundance in recent years throughout much of the
southeast. Most southern states have responded by tightening harvest regulations.
Plans for major modifications and deepening of the Savannah Harbor (GA/SC, USA)
and shipping channel have caused fears that this will make the situation worse by
interfering with spawning success. It was not known if, or where, these important
fishes might spawn in the Savannah River estuary, so a study was conducted to
examine the possibility that dredging would cause major problems.
An acoustic survey was conducted during August- November 2000 and
February-November 2001 in the Savannah River estuary, with some coverage of the
shipping channel offshore. A directional hydrophone, analog receiver, and audio
recorder were used to detect and record signals, and specific locations of spawning sites
were determined through triangulation. Signal strength, prominent bottom
characteristics, light phase, tide stage, current velocity, depth, temperature, salinity, and
dissolved oxygen were recorded for each location. Emphasis was on the lower estuary
where salinities were >15 ppt, but occasional broader surveys were conducted to ensure
that no spawning activity was occurring farther upriver.
During June 2001, preliminary dredging operations began in one turning basin in
the lower harbor, which had been identified as the location of one of the primary
spawning aggregations of spotted seatrout. The reaction of the spawning aggregation
to dredging activity was monitored through the end of the spawning season.
Drumming males of red drum, spotted seatrout, black drum, and weakfish were
found. Sporadic drumming of all species occurred in various locations of the lower
estuary. However, six primary spawning sites were identified for spotted seatrout, one
for weakfish, and one for black drum. All sites were in salinities > 16 ppt, and all were
within 12.2 river km of the river mouth. Time of day of spawning varied somewhat
among species, but in general it appeared to be anchored around sunset with peak
activity from about 1 hr before through about 3 hr after. This was especially evident
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Passive Acoustics: Program Summaries
US: Southeast: Mark Collins
with spotted seatrout, which had the longest spawning season. As day length
shortened and sunset occurred progressively earlier at the end of the summer,
spawning activity began earlier.
Spotted seatrout spawning activity took place during May-September, peaking
in July-August. Water temperature apparently was a seasonal spawning cue, as activity
ceased abruptly and did not resume when there was a 2oC drop to 24oC over a 2-day
period (although spawning in lower temperatures has been previously reported). All
six sites located in 2000 were again used in 2001, but activity did not begin at all sites
simultaneously. The sites had several characteristics in common: they were in the main
river channel rather than side-creeks, they were in or adjacent to deep water (7-10 m),
and they were associated with structure of some type. Structure varied among sites, but
was generally a large channel marker or a rocky area such as a submerged jetty.
Drumming activity appeared strongest when a high or early ebb tide occurred during
the appropriate time of day.
Black drum spawned during late March to mid-June at river km 0 (the river
mouth) in water temperatures of 14-19oC. Weakfish spawning activity was
concentrated just upriver at river km 2 during June to early October at temperatures of
23.9-29.0oC. Weakfish appeared to be less site-specific than black drum or spotted
seatrout, with the aggregation sometimes moving about somewhat. Weakfish also
tended to aggregate around structure like spotted seatrout, although more weakly,
while black drum aggregated in the middle of the channel where no structure could be
detected.
No large red drum spawning aggregations were located. A number of times,
individuals or very small groups of drumming males were found. This was most
consistently at the mouth of the river and in the shipping channel outside the mouth.
All activity noted was during August-September.
The active dredge in the vicinity of a large spotted seatrout aggregation began
operations at the upriver end of the turning basin, the opposite end from the
aggregation, and moved slowly downriver. No changes in drumming intensity or
periodicity relative to the dredge were noted. However, the spawning season ended (as
confirmed by checking other known spawning sites) before the dredge actually reached
the fish; it was ~100 m away at that point. Large and small vessels transited the area
but did not disturb the fish. One acoustic disturbance that was dramatically apparent,
however, was a total cessation of drumming when bottlenose dolphin (which make a
pronounced acoustic signal) passed by. This behavior was also noticed on two
occasions with red drum.
Passive acoustic mapping of drum spawning sites in preparation for harbor
modifications was successful. It confirmed spawning of important species within the
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Passive Acoustics: Program Summaries
US: Southeast: Mark Collins
harbor area, and it defined the spawning temporally and spatially. There was
considerable temporal overlap in spawning activity among species, and in the lower 2
river km there appeared to be spatial overlap. However, on a finer scale (hundreds of
meters) there was little or no overlap. It is obvious, however, that the lower 2 river km
can be considered the most important sciaenid spawning area in the Savannah estuary,
as all four species aggregated in that stretch of river. Aggregations of red drum were
very small. Comparing this behavior to previous reports from the region is problematic
due to the limited number of systems that have been studied; the aggregation in
Charleston Harbor, SC was quite large, while the aggregation detected in St. Helena
Sound, SC was very small. Thus, it is not known whether red drum typically form large
aggregations in this region, or if in some systems they generally spawn in small groups.
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Passive Acoustics: Program Summaries
US: Southeast: Mark Collins
Despite the apparent importance of acoustic signals in spawning
aggregations for these species, noise from boats, dredges, etc. did not interfere
with drumming behavior, even when the source of the noise was close by.
Certainly, these fish must be acclimated to vessel passage due to the fact that the
Savannah River is a major port. It is unknown whether fish in a less populous
habitat would be so impervious to noise. The only response to an acoustic signal
was exhibited toward bottlenose dolphin, which prey on these fishes; the
cessation of drumming was apparently a predator avoidance behavior.
While spotted seatrout males do not respond to dredging noise, it is
unknown what effect a dredge would have as it worked in the midst of the
aggregation. Relatively large fishes (e.g., juvenile Atlantic sturgeon ) are
reported with some regularity having been sucked up by dredges elsewhere.
Further, because two (and possibly three) of these species appear to cue in on
structures, removal of these structures, as commonly occurs during deepening
and channelization operations, may have a negative impact. Future research
plans include statistical analyses of environmental variables as related to
drumming activity, and re-examination in 2002 of spotted seatrout spawning
behavior in the turning basin that was dredged in 2001.
Acknowledgments
Hayne von Kolnitz assisted extensively in both field and laboratory.
Bruce Stender verified identifications of larval fishes. Joseph Luczkovich (East
Carolina University), Mark Spraque (East Carolina University), Archibald
McCallum (University of Charleston), Grant Gilmore (Dynamac Corp.), and Bill
Roumillat provided invaluable assistance in verifying species identifications
from acoustic recordings of aggregations. South Carolina Department of Natural
Resources, Georgia Ports Authority, and Southern Liquid Natural Gas provided
funding.
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Passive Acoustics: Program Summaries
US: Southeast: Scott Holt
Scott A. Holt
University of Texas at Austin
Marine Science Institute
Fisheries and Mariculture Laboratory
750 Channel View Drive
Port Aransas, Texas 78373
(361)749-6715
[email protected]
Program Goals
The overall goal of our research program is to provide new knowledge about the
ecology and biology of coastal fishes, with emphasis on sciaenids, through field and
laboratory investigations. Our field investigations focus on the egg and larval stages
and investigations of spawning activity are an essential component of analysis of larval
supply issues. Passive acoustics is being employed as a primary tool in locating
spawning sites of soniferous sciaenids
Research Activities
Our current efforts are directed almost exclusively at red drum (Sciaenops
ocellatus). This species spawns primarily in coastal waters and within tidal inlets. We
are using two techniques to locate spawning sites and to investigate spawning
activities. One employs a fixed hydrophone on a pier extending into the Aransas Pass
tidal inlet. This hydrophone is connected to a desktop computer that records 20 seconds
of audio every 15 every minutes every evening from 1700 hrs to 0100 hrs in the morning
during August, September, and October. Previous research has shown that red drum
spawn during the fall season and only in the evening (Holt et al 1985). The time
window encompasses the daily spawning period. These investigations are designed to
document daily drumming activity at a single spawning site. Results from the previous
two years (2000 and 2001) show that drumming occurs essentially every night at the site
and peaks during a two hour period beginning about dusk.
The second technique is to use a towed hydrophone array to determine the
distribution of red drum spawning sites in nearshore coastal waters. We have found
that an array can be towed at about 3.0-4.0 kts and still produce good quality recording
of red drum calls. Based on the results of the fixed hydrophone results described above,
we can sample only during a 4-5 hour period each evening and thus can cover
approximately 20-25 km per day. Initial surveys along a portion of the central Texas
coast line have shown that spawning is relatively widespread along the 10 meter
contour. Additional surveys will be conducted to outline the total extent of the red
drum spawning area.
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Passive Acoustics: Program Summaries
US: Southeast: Scott Holt
Future Activities
Our primary focus will be to determine the extent of the red drum spawning
sites along the central and southern Texas coast. In addition to the towed array, we
intend to employ remote, fixed hydrophones to study site fidelity and daily activity.
Huge volumes of data are collected during these investigations and we will work with
other investigators to develop means for automated processing of both archived and
real-time data. Passive acoustic data also has the potential to reveal substantial insight
into the behavior of fish at spawning sites. Observations of red drum spawning in
captivity at the Fisheries and Mariculture Lab will aid in these interpretations. We
ultimately intend to extend our investigations to other sciaenids in the area, especially
spotted seatrout and Atlantic croaker.
Holt, G.J., S.A. Holt, and C.R. Arnold. 1985. Diel periodicity of spawning in sciaenids.
Marine Ecology Progress Series 27(1-2):1-7.
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Passive Acoustics: Program Summaries
US: Southeast: David Mann
Note: Figure 1 refers to information that is color-based on the diagram
David Mann
University of South Florida
College of Marine Science
140 7th Avenue South
St. Petersburg, FL 33701
727-553-1192
[email protected]
Program Summary
Sound is an ideal way for animals to communicate in the ocean. Sound attenuates little in the
ocean, is directional, and is very useful where there is no light. It is not surprising then that
many fishes have evolved the ability to produce sounds by drumming the swimbladder with
specialized muscles or bones. While many fishes are known to produce sound, most have not
been studied.
Identifying Sound Producing Fishes
One goal of my laboratory is to identify sounds produced by fishes and to document the
behaviors that accompany sound production. One species that we are intensively studying, the
Gulf toadfish (Opsanus beta), produces a call that sounds like a fog horn known as the
‘boatwhistle’. This call is used to attract females to nests that the male has prepared. The
toadfishes are a good example of how much basic information about sounds has yet to be
gathered. While there are 69 species of toadfishes, the sounds of only six species have been
recorded and analyzed.
Ecology of Sound Production
Since many fish sounds are associated with reproduction, they can be used to measure the time
and place of spawning. We are using passive acoustics to identify spawning periodicity for
several species in Sarasota Bay and Charlotte Harbor in southwestern Florida. One thrust of
these studies is the development of instrumentation for passive acoustic detection in the field.
For example, we have programmed an advanced digital signal processing datalogger to
automatically detect and record toadfish calls. Figure 1 shows the calls of the gulf toadfish
produced over a one night period (they appear as horizontal red bands on the graph). This type
of device will be useful for fisheries bioacoustics once measures of sound production have been
ground-truthed against data of interest to fisheries managers, such as when and where fish spawn
and the size of spawning aggregations.
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Passive Acoustics: Program Summaries
US: Southeast: David Mann
Underwater datalogger and housing used to record fish sounds. The assembled device is shown
on the left. The datlogger (in black) and batteries in green are shown on the right.
Figure 1. Spectrogram of a series of automatically-detected toadfish (Opsanus beta) calls plotted
one after another (the calls appear as the red lines moving across the image).
Effects of Noise on Fishes
One final area of research that we are undertaking is to study the impacts of noise on soundproducing fishes. Great emphasis has been recently placed on understanding the impacts of
anthropogenic noise from boats, geologic exploration (from air guns), and scientific research on
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Passive Acoustics: Program Summaries
US: Southeast: David Mann
cetaceans (whales and dolphins). Yet, very few studies have investigated the impact of noise on
fishes, especially sound-producing fishes. Figure 2 shows a recording of the sound from an
outboard boat in Charlotte Harbor, FL. This sound includes the same frequencies as fish sounds.
The range over which sound-producing fishes could attract mates could be severely limited by
increased levels of background noise.
Figure 2. Sounds produced by a small outboard boat recorded in Charlotte Harbor, FL. Most of
the sounds are between 100 and 2500 Hz, which are in the same range as most fish sounds.
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Passive Acoustics: Program Summaries
US: Southeast: Bill Roumillat
Applications of underwater acoustics data in fisheries management for spotted
seatrout, Cynoscion nebulosus, in estuaries of South Carolina
Bill Roumillat, Myra Brouwer
Marine Resources Research Institute, South Carolina Department of Natural Resources,
217 Ft.Johnson Rd., Charleston, SC 29412.
[email protected], [email protected]
The spotted seatrout, Cynoscion nebulosus, is an estuarine-dependent member of the
family Sciaenidae, commonly known as “drums” or “croakers.” Spotted seatrout are
year-round residents of estuaries along the South Atlantic coast and spawning takes place
inshore and in coastal areas. During summer months, male spotted seatrout produce
“drumming” sounds, presumably to attract females that are reproductively active. By
listening to these sounds using hydrophone equipment we determined the locations,
seasonality and periodicity of spawning aggregations in Charleston Harbor, South
Carolina.
Spotted seatrout are batch-spawning
fish. That is, they release gametes in
small batches over the course of the
spawning season. The latter extends
from April through September along the
South Atlantic and Gulf of Mexico
coasts. In this species, the total number
of eggs a female produces in a season
(annual fecundity) is dictated by the
number of eggs released during each
spawning event (batch fecundity) and
the number of such spawning events
during the course of the season
(spawning frequency). Estimating the
annual fecundity is necessary to
determine reproductive potential, and is
made even more useful for fisheries
management purposes if separated by
size or age class within a population.
Behavior patterns based on acoustic data enabled us to target females in imminent
spawning condition, then carry out egg counts to estimate batch fecundity and spawning
frequency for each of the three dominant age classes (ages 1–3) in our waters.
Ultimately, our annual fecundity estimates for each age class will facilitate management
of this species in South Carolina.
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Passive Acoustics: Program Summaries
US: Southeast: Bill Roumillat
Over a decade of sampling the Charleston Harbor estuarine system we have observed that
from mid to late afternoon female trout start leaving our sampling areas-- the shallow
water adjacent to the edge of the marsh-- and head for deeper water to spawn. Our
hydrophone surveys have indicated that spawning typically begins around 1800h and
ceases around 2200h. Females then return to feeding grounds near the marsh. Knowledge
of this reproductive behavior enabled us to target spotted seatrout in the mid-late
afternoon specifically to capture fish that were readying for a spawn. Females that were
back in the shallows after having spawned the previous evening were available for
capture during daytime sampling.
We used trammel nets deployed from
shallow water boats to capture trout at
pre-selected sites in Charleston Harbor.
Sites were chosen based on proximity to
known spawning locales. We obtained
batch fecundity estimates by directly
counting the number of eggs in a small
sample of ovarian tissue. By knowing
the weight of the sample and the weight
of the entire ovary, we obtained
estimates of the total number of eggs in
each ovary. To determine the frequency
of spawning, we looked at histological
preparations. The presence of specific
structures in ovarian tissue indicates that
the fish has spawned within the previous
24 hours. By obtaining the inverse of
the proportion of females that spawned
the previous evening, we could estimate
how often the fish were spawning.
Aging was accomplished by observing
sections of the fish’s earbones (otoliths)
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Passive Acoustics: Program Summaries
US: Southeast: Bill Roumillat
under the microscope. Otoliths are bony structures in the animal’s head that help the fish orient
properly in the water. They accumulate growth rings, much like a tree trunk does. By counting
the growth rings we could confidently discern the fish’s age.
The main impetus behind this study was to establish realistic annual fecundity estimates by age
class that could be used in predictive modeling of the spotted seatrout population in coastal
South Carolina. We were able to develop equations relating fecundity to length and age that can
be used to estimate the reproductive potential for each age class.
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