Mark W. Sprague

DELIMITING SPAWNING AREAS OF WEAKFISH CYNOSCION REGALIS (FAMILY SCIAENIDAE) IN PAMLICO SOUND, NORTH CAROLINA USING PASSIVE HYDROACOUSTIC SURVEYS

ABSTRACT Exact locations of spawning areas used by marine fishes are needed to design marine reserves and estimate spawning stocks. The location of spawning areas of soniferous fishes such as weakfish Cynoscion regalis can be determined by means of passive hydroacoustic surveys. We conducted nocturnal hydrophone surveys at 12 locations in Pamlico Sound in May of 1996 and 1997. Digital audio tapes were made of weakfish “purring” sounds, the tapes were analyzed spectrographically and compared with ichthyoplankton surveys taken at the same stations and times. All weakfish “purring” sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 (μPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. The maximum distance that an individual weakfish “purr” can be detected above the background sound, assuming a cylindrical spreading model, is approximately 50 m. There was a strong associ...

SOUNDS OF SEX AND DEATH IN THE SEA: BOTTLENOSE DOLPHIN WHISTLES SUPPRESS MATING CHORUSES OF SILVER PERCH

ABSTRACT Prey often exhibit avoidance behaviors when predators are present. We observed diminished loudness of mating choruses of male silver perch Bairdiella chrysoura in spawning areas when vocalizing bottlenose dolphins Tursiops truncatus, which hunt fish acoustically, were present. Experimental playback of bottlenose dolphin sounds revealed that male silver perch mating calls were reduced by an average of 9 dB. This “acoustical avoidance” behavior, demonstrated previously for interactions involving bats hunting insects and frogs, may also be a common phenomenon in acoustically mediated predator-prey interactions in the sea.

Identifying Sciaenid Critical Spawning Habitats by the Use of Passive Acoustics

Abstract Sounds produced by spawning fishes in Pamlico Sound, North Carolina, have been recorded both under captive conditions and in hydrophone and sonobuoy field surveys. These sounds, produced by males, are species specific, are associated with spawning, and are most likely used for advertisement to attract females. Sounds can be discriminated by use of spectral analysis (oscillograms and spectrograms) of recordings, and the peak frequencies produced by each species can be correlated with species and fish size. Sonobuoys were used for passive acoustic surveys, which were “sound truthed” from recordings of captive fishes to determine the timing and location of spawning sites for four species in the family Sciaenidae: Red drum Sciaenops ocellatus, spotted seatrout Cynoscion nebulosus, weakfish C. regalis, and silver perch Bairdiella chrysoura. During May-September 1998, sounds were first detected in the early evening, increased in loudness after sunset, and ended by sunrise. Weakfish and silver perch wer...

Do Striped Cusk-Eels Ophidion marginatum (Ophidiidae) Produce the “Chatter” Sound Attributed to Weakfish Cynoscion regalis (Sciaenidae)?

Abstract Weakfish Cynoscion regalis and striped cusk-eels Ophidion marginatum both produce sounds, but there has been confusion in the literature on a particular sound, the “chatter.” It has been stated that this sound is produced by weakfish using their pharyngeal teeth. Striped cusk-eels make a similar sound (but not identified in the literature as a chatter) using sonic muscles associated with the swim bladder and vertebral components. The striped cusk-eel identifications were based on captive fish sound recordings, whereas the weakfish identifications were based on recordings made in situ where weakfish were visually observed but other sound-producing organisms could have been present. Based on new signal analysis of striped cusk-eel sounds made in captivity, we identify that species as the source of the chatter sound in our field recordings. The dominant frequency of the sounds increased while the pulse period decreased over the temperature range 18.0–27.5 C. The acoustic characteristics presented here will aid researchers in their identification of these sounds.

Measurement of an individual silver perch Bairdiella chrysoura sound pressure level in a field recording

Simultaneous audio and video were recorded of a silver perch Bairdiella chrysoura producing its characteristic drumming sound in the field. The background noise contribution to the total sound pressure level is estimated using sounds that occurred between the pulses of the silver perch sound. This background contribution is subtracted from the total sound to give an estimate of the sound pressure level of the individual fish. A silver perch source level in the range 128-135 dB (re: 1 microPa) is obtained using an estimate of the distance between the fish and the hydrophone. The maximum distance at which an individual silver perch could be detected depends on the background sound level as well as the propagation losses. Under the conditions recorded in this study, the maximum detection distance would be 1-7 m from the hydrophone.

USING PASSIVE ACOUSTICS TO MONITOR ESTUARINE FISH POPULATIONS

Lobel, P.S. (2001b) Acoustic behaviour of cichlid fishes. J. Aquaculture Aquatic Sci. 9, 167-186. Lobel, P.S. & Kerr, L.M. (1999) Courtship sounds of the Pacific Damselfish, Abudefduf sordidus (Pomacentridae). Biol. Bull. 197, 242-244. Lobel P.S. & Mann, D.A. (1995) Spawning sounds of the damselfish, Dascyllus albisella (Pomacentridae), and relationship to male size. Bioacoustics 6, 187-198. Lobel, P.S. & Neudecker, S. (1985) Diurnal periodicity of spawning activity by the hamlet fish, Hypoplectrus guttavarius (Serranidae). In The Ecology of Coral Reefs, Vol. 3, Symposia Series for Undersea Research (M.L. Reaka, ed). NOAA; Rockville, MD, pp. 71-86. Myrberg, A.A., Ha, S.J., Walewski, S. & Branbury, J.C. (1972) Effectiveness of acoustic signals in attracting epipelagic sharks to an underwater source. Bull. Mar. Sci. 22, 926-944 Nordeide, J.T. & Kjellsby, E. (1999) Sound from spawning cod at their spawning grounds. ICES J. Mar. Sci. 56, 326-332. Sancho, G., Petersen, C.W. & Lobel, P.S. (2000) Predator-prey relations at a spawning aggregation site of coral reef fishes. Mar. Eco. Prog. Ser. 203, 275-288.

Using passive acoustics to monitor spawning of fishes in the drum family (Sciaenidae)

The goal of this study was to develop a passive acoustic survey protocol to identify spawning habitats of sciaenid fishes. Based on comparisons of recordings of captive‐fish and field recordings of species‐specific courtship sounds, spawning areas of red drum, weakfish, spotted sea trout, and silver perch (Family Sciaenidae) have been identified in Pamlico Sound, NC. Sciaenid sounds were recorded using either a portable hydrophone deployed from a boat or timer‐operated sonobuoys. Loudness of mating choruses of weakfish and silver perch was strongly correlated with the abundance of pelagic sciaenid‐type eggs, suggesting that these areas were used for spawning. Sonobuoy recordings showed that weakfish spawned only in the high‐salinity habitats near the inlets, spotted sea trout spawned predominantly in the low‐salinity areas near the river mouths, silver perch spawned in both high‐ and low‐salinity areas, and red drum spawned most commonly in low‐salinity areas, but only in September. The loudness of mating...

Modeling fish aggregation sounds in very shallow water to estimate numbers of calling fish in aggregations

Many fishes in the Family Sciaenidae produce courtship sounds associated with spawning. Some estuarine sciaenid species such as weakfish Cynoscion regalis, spotted seatrout C. nebulosus, and silver perch Bairdiella chrysoura occur in very shallow water (water depths 3–10 m) aggregations so large that individual calls are no longer audible above the combined sound of calling fish in the aggregation. We have measured sound levels in these aggregations that are 30 dB greater than the estimated received level of an individual fish at a distance of 1 m. To estimate the number of individual calling fish that would result in these sound levels, we have produced a model of virtual fish aggregations based on echosounder data. We used a finite difference time domain (FDTD) model to calculate the pulsed sounds from the individual fish in randomized aggregations at our virtual hydrophone location. We produced many randomized instances of fish aggregations to obtain statistical distributions of sound levels produced b...

Low frequency acoustic ground impedance measurement techniques

Abstract The low frequency (below 150 Hz) acoustic ground impedance was determined on a large uncultivated field using an impedance meter, the probe microphone method, a modified Biot-Stoll type calculation, and the phase gradient method. The impedance measured with the impedance meter has lower real and imaginary parts than the impedance determined from the probe microphone measurements. The modified Biot-Stoll type description of acoustic to seismic transfer based upon seismic and acoustic measurements gives an impedance which is consistent with probe microphone measurements. The impedance measured by the phase gradient method is largely consistent with the other measurements, but shows much more structure. This structure is believed to be caused by unwanted reflections during the measurement procedure rather than by actual structure in the ground impedance undetected by the other methods.

Speciation and sounds of fishes: Dividing up the bandwidth.

Fishes in the drum family (Sciaenidae) make sounds to communicate, but they do not make the same sounds. The species‐specific calls have different dominant frequencies, are produced in spawning aggregations at different times of the day and season, and there is spatial segregation among the spawning fish populations. We predicted that the pattern of bandwidth use by these species would show low overlap in space, time, and sound frequency. We monitored the seasonal pattern of sound production of Sciaenidae in Pamlico Sound (NC) using autonomous sound recorders that recorded 10 s of sound every 15 min during May–Nov. The observed bandwidth ranges and spawning season for species are weakfish 300–400 Hz in May–Aug, silver perch 800–1500 Hz May–Aug, spotted seatrout 200–400 Hz June–Sep, red drum 100–200 Hz in Sep–Oct. Overlapping calls in these species were rare temporally and spatially, as evidenced by long‐term passive acoustic monitoring. Two other species of fishes (oyster toadfish and striped cusk eels), ...