Full Description

"All weakfish"purring"sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 JlPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously."

"Furthermore, it is apparent that males of the Sciaenidae, especially the weakfish Cynoscion regalis, make species-specific calls during courtship of the females at locations where spawning occurs (Fish and Mowbray 1970, Connaughton and Taylor 1995, Connaughton and Taylor 1996)."

"Hydroacoustic monitoring of"drumming"or calling by male sciaenids, including weakfish, has been undertaken recently in the field and laboratory (Mok and Gilmore 1983, Johnson and Funicelli 1991, Saucier et al. 1992, Saucier and Baltz 1993, Connaughton and Taylor 1995). Weakfish drumming has been observed immediately prior to spawning in the laboratory (Connaughton and Taylor 1996). Only male weakfish make drumming sounds (Tower 1908, Fish and Mowbray 1970, Connaughton and Taylor 1996}, which we describe here as"purring"sounds."

"A spectrograph of a typical individual male weakfish"purring"sound shows that the peak intensity of pulses occurs in three"purrs"or sequences of pulses (Figure 1): the first is 1.68 sin length; after a 1.59-s delay, the second"purr"lasts 1.48 s; and then after a 1.55-s delay, there is a third burst that lasts 0.98 sec. The highest power spectral densities occurred between 300 Hz and 400 Hz during the recording."

"For a subset of these recordings with"purring"sounds (n = 7), in which we were able to clearly distinguish individual weakfish males, we measured the average pulse repetition rate as 15.4 pulses/s and the average dominant frequency was 360 Hz. Individual weakfish had a maximum sound pressure level of 127 dB (re 1 J..LPa), based on these field recordings. On all of the recordings in which"purring"was heard, there were portions in which individual weakfish could not be distinguished; we believe that such recordings are of aggregations of"purring"weakfish. There are no distinct"purrs"in a spectrograph of such a recording, because the spaces between each individual's"purrs"are filled with the"purrs"of the other individuals of the aggregation, so that there is an almost continuous sound at the dominant frequency (x = 350 Hz, n = 26) of an individual"purr"(Figure 2). For all individual and aggregation recordings, the overall sound pressure levels ranged from 110 to 147 dB (re 1 11Pa) and averaged 134 dB."

"Nonetheless, sciaenid-type eggs appeared to be most abundant at stations where weakfish"purring"and silver perch"clucking"were recorded in May 1996."

"The"purring"sounds were associated with weakfish spawning behavior, because sciaenid-type eggs were collected in plankton samples made at many of those sites, including the recordings characterized above."

"During some nights at some locations, we recorded"purring"sounds but did not collect developing eggs, which contributed to the imperfect correlation between sound pressure level and egg density."

"Connaughton and Taylor (1996) reported that the"purring"or drumming sound made by male weakfish under laboratory conditions began before spawning, ceased during the actual spawning activity, then began again immediately after spawning. In our samples, the detection of weakfish"purring"and the absence of eggs may indicate that male weakfish were present and signaling their readiness to spawn, but that spawning had not yet occurred (perhaps because females were not yet present or ready to spawn at that time)."

"The sounds were as loud as 127 dB (re 1 f.!Pa) for individual weakfish, 136 dB for individual silver perch, and 147 dB for groups of these two fishes. It was apparent that some of the recordings contained the"purring"sounds of many individual male weakfish along with"clucking"sounds of many individual silver perch calling simultaneously."

Observation Environment Quotes

"In May 1997, we sampled weakfish spawning populations with hydrophone surveys and plankton nets at twelve stations off the North Carolina coast, USA: on the eastern side of Pamlico Sound near Ocracoke Inlet (Teaches Hole stations 1, 2, 3, and 4; Wallace Channel; Lehigh Dredge; and Royal Shoal) and near Hatteras Inlet (Hatteras Hole and Hatteras North); and on the western side of the sound near Rose Bay (Rose Bay 1 and 2) and Fishermans Bay."

"At all hydrophone sampling locations, precise geographical positions (latitude and longitude) were determined using either a Trimble Pathfinder Basic Plus Global Positioning System (GPS) satellite receiver or a Trimble NT200 GPS chartplotter receiver with a ProBeacon MSK receiver operating in real-time differential mode (± 10 m Circular Error Probable accuracy; see Pietraszewski et al. 1993)."

Behaviour Description Quotes

"Furthermore, it is apparent that males of the Sciaenidae, especially the weakfish Cynoscion regalis, make species-specific calls during courtship of the females at locations where spawning occurs (Fish and Mowbray 1970, Connaughton and Taylor 1995, Connaughton and Taylor 1996)."

"Hydroacoustic monitoring of 'drumming' or calling by male sciaenids, including weakfish, has been undertaken recently in the field and laboratory (Mok and Gilmore 1983, Johnson and Funicelli 1991, Saucier et al. 1992, Saucier and Baltz 1993, Connaughton and Taylor 1995). Weakfish drumming has been observed immediately prior to spawning in the laboratory (Connaughton and Taylor 1996). Only male weakfish make drumming sounds (Tower 1908, Fish and Mowbray 1970, Connaughton and Taylor 1996},, which we describe here as 'purring' sounds. "

"The 'purring' sounds were associated with weakfish spawning behavior, because sciaenid-type eggs were collected in plankton samples made at many of those sites, including the recordings characterized above."

Sound Name Quotes

"All weakfish 'purring' sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 JlPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. "

"Hydroacoustic monitoring of 'drumming' or calling by male sciaenids, including weakfish, has been undertaken recently in the field and laboratory (Mok and Gilmore 1983, Johnson and Funicelli 1991, Saucier et al. 1992, Saucier and Baltz 1993, Connaughton and Taylor 1995). Weakfish drumming has been observed immediately prior to spawning in the laboratory (Connaughton and Taylor 1996). Only male weakfish make drumming sounds (Tower 1908, Fish and Mowbray 1970, Connaughton and Taylor 1996},, which we describe here as 'purring' sounds. "

"A spectrograph of a typical individual male weakfish 'purring' sound shows that the peak intensity of pulses occurs in three 'purrs' or sequences of pulses (Figure 1): the first is 1.68 sin length; after a 1.59-s delay, the second 'purr' lasts 1.48 s; and then after a 1.55-s delay, there is a third burst that lasts 0.98 sec. The highest power spectral densities occurred between 300 Hz and 400 Hz during the recording."

"For a subset of these recordings with 'purring' sounds (n = 7), in which we were able to clearly distinguish individual weakfish males, we measured the average pulse repetition rate as 15.4 pulses/s and the average dominant frequency was 360 Hz. Individual weakfish had a maximum sound pressure level of 127 dB (re 1 J..LPa), based on these field recordings. On all of the recordings in which 'purring' was heard, there were portions in which individual weakfish could not be distinguished; we believe that such recordings are of aggregations of 'purring' weakfish. There are no distinct 'purrs' in a spectrograph of such a recording, because the spaces between each individual's 'purrs' are filled with the 'purrs' of the other individuals of the aggregation, so that there is an almost continuous sound at the dominant frequency (x = 350 Hz, n = 26) of an individual 'purr' (Figure 2)."

"A spectrograph ofan aggregation silver perch and weakfish recorded on 18May 1997 at the Lehigh Dredge at 19:38EasternStandardTime."

Full Description

"We were able to compare the spectrographs of weakfish"purring"sounds with the spectrographs of silver perch Bairdiella chrysoura courtship calls."

"The soniferous silver perch Bairdiella chrysoura (Sciaenidae) were recorded"clucking"on the inlet recordings, but were also recorded away from the inlets at 2 sites (5 recordings out of 12 made after sunset in Rose Bay and Fishermans Bay)."

"The peak intensity of silver perch sounds occurred in pulses or"clucks"; twelve distinct"clucks"can be seen in the spectrograph of an individual male silver perch recorded in Fisherman's Bay on the western side of Pamlico Sound (Figure 3). For a subset (n = 13) of all inlet recordings with fishes, in which individual male silver perch were clearly distinguished from background sounds, the average"cluck"or pulse repetition rate was 6.5 pulses/s, with each of the"clucks"having an average peak frequency of 1080 Hz. The maximum overall sound pressure level of these recordings was 136 dB (re 1 11Pa). Silver perch were also heard"clucking"in groups; a typical spectrograph of a group of silver perch had an average dominant frequency of 1025 Hz (Figure 4). The average sound pressure levels were 135 dB for groups of silver perch calling without weakfish present, with one standard deviation in sound pressure above the mean sound pressure corresponds to a sound pressure level of 138 dB, and one standard deviation below the mean sound pressure is 130 dB."

"Nonetheless, sciaenid-type eggs appeared to be most abundant at stations where weakfish"purring"and silver perch"clucking"were recorded in May 1996."

"The sounds were as loud as 127 dB (re 1 f.!Pa) for individual weakfish, 136 dB for individual silver perch, and 147 dB for groups of these two fishes. It was apparent that some of the recordings contained the"purring"sounds of many individual male weakfish along with"clucking"sounds of many individual silver perch calling simultaneously."

Observation Environment Quotes

"In May 1997, we sampled weakfish spawning populations with hydrophone surveys and plankton nets at twelve stations off the North Carolina coast, USA: on the eastern side of Pamlico Sound near Ocracoke Inlet (Teaches Hole stations 1, 2, 3, and 4; Wallace Channel; Lehigh Dredge; and Royal Shoal) and near Hatteras Inlet (Hatteras Hole and Hatteras North); and on the western side of the sound near Rose Bay (Rose Bay 1 and 2) and Fishermans Bay."

"At all hydrophone sampling locations, precise geographical positions (latitude and longitude) were determined using either a Trimble Pathfinder Basic Plus Global Positioning System (GPS) satellite receiver or a Trimble NT200 GPS chartplotter receiver with a ProBeacon MSK receiver operating in real-time differential mode (± 10 m Circular Error Probable accuracy; see Pietraszewski et al. 1993)."

Behaviour Description Quotes

"We were able to compare the spectrographs of weakfish 'purring' sounds with the spectrographs of silver perch Bairdiella chrysoura courtship calls."

Sound Name Quotes

"The peak intensity of silver perch sounds occurred in pulses or 'clucks'; twelve distinct 'clucks' can be seen in the spectrograph of an individual male silver perch recorded in Fisherman's Bay on the western side of Pamlico Sound (Figure 3). "

"A spectrograph of an aggregation silver perch, recorded in Teaches Hole on 19 May 1997 at 20:31 Eastern Standard Time."