Full Description

"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 were heard predominantly at inlet locations in May and June, whereas spotted seatrout (peak drumming in July) and red drum (peak drumming in September) were heard predominantly at lower-salinity river mouth locations in western Pamlico Sound."

"A male spotted seatrout captured by hook and line in Roanoke Sound on 8 August 1998 was recorded in air 3 h after capture. In the recording, the fish makes three long aggregated grunts (LAGs; Mok and Gilmore 1983; Sprague et al. 2000) within 1 s: the first lasts 0.19 s, the second lasts 0.13 s, and the third lasts 0.11 s (Figure 5A). The dominant frequencies are again less than 1,000 Hz (Figure 5 B). In an oscillogram of the field recording (Figure 5C), one LAG occurs between 2.9 and 3.2 s; this LAG is also clearly distinguishable in the spectrogram (Figure 5D), even with other spotted seatrout calling in the background."

"The pulse repetition rate changed with increasing temperature; this rate was low for weakfish (15.9 Hz) and silver perch (6.5 Hz) at temperatures less than 23C (21.5 Hz) but was high at temperatures above 23C (12.1 Hz). Spotted seatrout and red drum did not call at temperatures below 23C, but their pulse repetition rates were different from those of weakfish and silver perch (18.1 Hz for spotted seatrout LAGs; 5.1 Hz for red drum knocks)."

"For sounds of captive- versus field-recorded fish, the dominant frequency was 667 versus 691 Hz for silver perch, 293 versus 386 Hz for weakfish, 210 versus 269 Hz for spotted seatrout, and 152 versus 128 Hz for red drum (Figure 7A, B). The dominant frequencies of field recordings are similar to those of the captive recordings for each species (r = 0.98) and are inversely correlated with the mean size of the species (r=0.65) recorded in captivity."

"Spotted seatrout had the shortest period of drumming activity, which began after sunset (2100 hours), peaked at 2200 hours, and ended at 2300 hours."

"The sounds recorded on the nocturnal sonobuoy deployments were dependent upon the month; weakfish and silver perch had the greatest SNDI in the early part of the survey (May and June), but values declined as autumn approached (September). Spotted seatrout exhibited peak activity in the summer months (June– August) but were also recorded in the spring (May) and autumn (September). Red drum were only recorded in the late summer and autumn (August and September). There was a slight increase in the SNDI for weakfish in August 1998, suggesting the occurrence of a second spawning peak."

"With respect to bottom salinity, weakfish were more commonly heard in higher salinity (Figure 17; Table 2; mean = 15.4%, range = 7.8–28.3%) than were spotted seatrout (mean = 11.8%, range = 7.1–26.9%), but there was a good deal of overlap between these two congeners. However, peak SNDIs of the spotted seatrout occurred in lower salinities than did those of the weakfish. Silver perch tended to co-occur with weakfish in water of similar salinity (mean = 14.0%, range = 7.1–28.3%). Red drum generally produced sounds at higher salinities (mean = 14.4%) but called over a wide range of salinities (7.8–27.1%). In Pamlico Sound, which generally has low salinity because of its few restricted inlets, these fishes produced sounds at salinities lower than might be expected in other estuaries but at a wide salinity range. For bottom dissolved oxygen, a critical habitat variable that is of great concern to biologists because of the potential for hypoxia (<4 mg/L), there was quite a difference in the distribution of SNDI values among the species. Weakfish had a very well-defined lower limit (Table 2; mean = 7.6 mg/L, range = 2.65–10.4), and only a single sonobuoy recorded their calls at dissolved oxygen levels below 4 mg/L (Figure 18). Spotted seatrout, on the other hand, were recorded at dissolved oxygen levels as low as 0.05 mg/L (mean = 6.1 mg/L, range = 0.05–9.73 mg/L), suggesting that hypoxia did not limit their sound production. Indeed, some of the highest SNDI values occurred at hypoxic (<4 mg/L) sonobuoy stations. Some fairly high SNDI values were recorded for silver perch in hypoxic bottom waters, although most sonobuoy recordings were from normoxic waters (mean = 7.0 mg/L, range = 1.03–10.4 mg/L), as was true for red drum (mean = 6.7 mg/L, range = 4.5–9.5 mg/L)."

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

"Spotted seatrout inhabited Bay River sites where surface temperature exceeded 28C."

Observation Environment Quotes

"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. "

"Fish were caught by hook-and-line methods and placed in aerated seawater transport tanks. They were taken to the Pamlico Aquaculture Field Laboratory, Aurora, or to the East Carolina University Department of Biology, Greenville, and held in tanks for recording purposes."

Behaviour Description Quotes

"Air recordings of silver perch and spotted seatrout were made using an electret condenser microphone (Panasonic; Model WM-54B; frequency range = 20– 16,000 Hz +- 2 dB; sensitivity =164 dB re 1 V/uPa) and amplifier (gain adjustable from 0 to 40 dB in 20- dB increments, plus vernier adjustment) and recorded to the same DAT recorder."

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

" Sound production associated with spawning is likely to be an advertisement call produced by the males (Connaughton and Taylor 1996) in a manner similar to that used by Atlantic cod Gadus morhua to attract females to group spawning aggregations (Nordeide and Folstad 2000) or by oyster toadfish Opsanus tau to attract females to the territories of individual males (Fine and Thorson 2008, this issue)."

Sound Name Quotes

"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 were heard predominantly at inlet locations in May and June, whereas spotted seatrout (peak drumming in July) and red drum (peak drumming in September) were heard predominantly at lower-salinity river mouth locations in western Pamlico Sound."

"A male spotted seatrout captured by hook and line in Roanoke Sound on 8 August 1998 was recorded in air 3 h after capture. In the recording, the fish makes three long aggregated grunts (LAGs; Mok and Gilmore 1983; Sprague et al. 2000) within 1 s: the first lasts 0.19 s, the second lasts 0.13 s, and the third lasts 0.11 s (Figure 5A). The dominant frequencies are again less than 1,000 Hz (Figure 5 B). In an oscillogram of the field recording (Figure 5C), one LAG occurs between 2.9 and 3.2 s; this LAG is also clearly distinguishable in the spectrogram (Figure 5D), even with other spotted seatrout calling in the background."

"TABLE 1.—Pulse repetition rate (PRR) for the calls of four sciaenid species recorded on sonobuoys and with a mobile hydrophone in Pamlico Sound, North Carolina, 1997 and 1998 (N = number of calls analyzed)."

Full Description

"The ‘‘purr’’ of a male weakfish (340 mm SL) held in an 89-L cooler filled with seawater was recorded immediately after hook-and-line capture in Teaches Hole during June 1998). As can be seen on the oscillogram (Figure 4A), this purr consists of 15 bursts within a 0.5-s interval. Each burst has a broad frequency peak and a maximum PSD less than 1,000 Hz (Figure 4B). In the oscillogram of the field recording of a weakfish (Figure 4C; recorded at station 15 on 14 July 1997), one can see a series of 10 bursts in the 1-s recording, each of which shows the same pattern of pulsing as the captive fish recording in Figure 4A (i.e., a similar pulse repetition rate). However, the field recording is noisier, as reflected in the more variable nature of the oscillogram and the darker color of the spectrogram below 1,000 Hz. These noises are from other weakfish calling in the background during a spawning chorus. The overall similarity in dominant sound frequencies and pulsing patterns is visible in the spectrograms of the captive (Figure 4B) and field recordings (Figure 4D)."

"The pulse repetition rate changed with increasing temperature; this rate was low for weakfish (15.9 Hz) and silver perch (6.5 Hz) at temperatures less than 23C (21.5 Hz) but was high at temperatures above 23C (12.1 Hz). Spotted seatrout and red drum did not call at temperatures below 23C, but their pulse repetition rates were different from those of weakfish and silver perch (18.1 Hz for spotted seatrout LAGs; 5.1 Hz for red drum knocks)."

"For sounds of captive- versus field-recorded fish, the dominant frequency was 667 versus 691 Hz for silver perch, 293 versus 386 Hz for weakfish, 210 versus 269 Hz for spotted seatrout, and 152 versus 128 Hz for red drum (Figure 7A, B). The dominant frequencies of field recordings are similar to those of the captive recordings for each species (r = 0.98) and are inversely correlated with the mean size of the species (r=0.65) recorded in captivity."

"Weakfish followed a similar pattern: sounds began at sunset (when the DI exceeded that of silver perch) and the DI peaked at 2300 hours, but calling ceased at about 0200 hours."

"The sounds recorded on the nocturnal sonobuoy deployments were dependent upon the month; weakfish and silver perch had the greatest SNDI in the early part of the survey (May and June), but values declined as autumn approached (September). Spotted seatrout exhibited peak activity in the summer months (June– August) but were also recorded in the spring (May) and autumn (September). Red drum were only recorded in the late summer and autumn (August and September). There was a slight increase in the SNDI for weakfish in August 1998, suggesting the occurrence of a second spawning peak."

"With respect to bottom salinity, weakfish were more commonly heard in higher salinity (Figure 17; Table 2; mean = 15.4%, range = 7.8–28.3%) than were spotted seatrout (mean = 11.8%, range = 7.1–26.9%), but there was a good deal of overlap between these two congeners. However, peak SNDIs of the spotted seatrout occurred in lower salinities than did those of the weakfish. Silver perch tended to co-occur with weakfish in water of similar salinity (mean = 14.0%, range = 7.1–28.3%). Red drum generally produced sounds at higher salinities (mean = 14.4%) but called over a wide range of salinities (7.8–27.1%). In Pamlico Sound, which generally has low salinity because of its few restricted inlets, these fishes produced sounds at salinities lower than might be expected in other estuaries but at a wide salinity range. For bottom dissolved oxygen, a critical habitat variable that is of great concern to biologists because of the potential for hypoxia (<4 mg/L), there was quite a difference in the distribution of SNDI values among the species. Weakfish had a very well-defined lower limit (Table 2; mean = 7.6 mg/L, range = 2.65–10.4), and only a single sonobuoy recorded their calls at dissolved oxygen levels below 4 mg/L (Figure 18). Spotted seatrout, on the other hand, were recorded at dissolved oxygen levels as low as 0.05 mg/L (mean = 6.1 mg/L, range = 0.05–9.73 mg/L), suggesting that hypoxia did not limit their sound production. Indeed, some of the highest SNDI values occurred at hypoxic (<4 mg/L) sonobuoy stations. Some fairly high SNDI values were recorded for silver perch in hypoxic bottom waters, although most sonobuoy recordings were from normoxic waters (mean = 7.0 mg/L, range = 1.03–10.4 mg/L), as was true for red drum (mean = 6.7 mg/L, range = 4.5–9.5 mg/L)."

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

"Weakfish used the deep waters (>5 m) of Ocracoke Inlet."

Observation Environment Quotes

"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. "

"Fish were caught by hook-and-line methods and placed in aerated seawater transport tanks. They were taken to the Pamlico Aquaculture Field Laboratory, Aurora, or to the East Carolina University Department of Biology, Greenville, and held in tanks for recording purposes."

Behaviour Description Quotes

"Air recordings of silver perch and spotted seatrout were made using an electret condenser microphone (Panasonic; Model WM-54B; frequency range = 20– 16,000 Hz +- 2 dB; sensitivity =164 dB re 1 V/uPa) and amplifier (gain adjustable from 0 to 40 dB in 20- dB increments, plus vernier adjustment) and recorded to the same DAT recorder."

"As can be seen on the oscillogram (Figure 4A), this purr consists of 15 bursts within a 0.5-s interval. Each burst has a broad frequency peak and a maximum PSD less than 1,000 Hz (Figure 4B). In the oscillogram of the field recording of a weakfish (Figure 4C; recorded at station 15 on 14 July 1997), one can see a series of 10 bursts in the 1-s recording, each of which shows the same pattern of pulsing as the captive fish recording in Figure 4A (i.e., a similar pulse repetition rate). However, the field recording is noisier, as reflected in the more variable nature of the oscillogram and the darker color of the spectrogram below 1,000 Hz. These noises are from other weakfish calling in the background during a spawning chorus. The overall similarity in dominant sound frequencies and pulsing patterns is visible in the spectrograms of the captive (Figure 4B) and field recordings (Figure 4D)."

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

" Sound production associated with spawning is likely to be an advertisement call produced by the males (Connaughton and Taylor 1996) in a manner similar to that used by Atlantic cod Gadus morhua to attract females to group spawning aggregations (Nordeide and Folstad 2000) or by oyster toadfish Opsanus tau to attract females to the territories of individual males (Fine and Thorson 2008, this issue)."

Sound Name Quotes

"The ‘‘purr’’ of a male weakfish (340 mm SL) held in an 89-L cooler filled with seawater was recorded immediately after hook-and-line capture in Teaches Hole during June 1998). As can be seen on the oscillogram (Figure 4A), this purr consists of 15 bursts within a 0.5-s interval. Each burst has a broad frequency peak and a maximum PSD less than 1,000 Hz (Figure 4B). In the oscillogram of the field recording of a weakfish (Figure 4C; recorded at station 15 on 14 July 1997), one can see a series of 10 bursts in the 1-s recording, each of which shows the same pattern of pulsing as the captive fish recording in Figure 4A (i.e., a similar pulse repetition rate). However, the field recording is noisier, as reflected in the more variable nature of the oscillogram and the darker color of the spectrogram below 1,000 Hz. These noises are from other weakfish calling in the background during a spawning chorus. The overall similarity in dominant sound frequencies and pulsing patterns is visible in the spectrograms of the captive (Figure 4B) and field recordings (Figure 4D)."

"TABLE 1.—Pulse repetition rate (PRR) for the calls of four sciaenid species recorded on sonobuoys and with a mobile hydrophone in Pamlico Sound, North Carolina, 1997 and 1998 (N = number of calls analyzed)."

"Those authors found that drumming by male weakfish peaked in May and decreased in July."

Full Description

"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 were heard predominantly at inlet locations in May and June, whereas spotted seatrout (peak drumming in July) and red drum (peak drumming in September) were heard predominantly at lower-salinity river mouth locations in western Pamlico Sound."

"The pulse repetition rate changed with increasing temperature; this rate was low for weakfish (15.9 Hz) and silver perch (6.5 Hz) at temperatures less than 23C (21.5 Hz) but was high at temperatures above 23C (12.1 Hz). Spotted seatrout and red drum did not call at temperatures below 23C, but their pulse repetition rates were different from those of weakfish and silver perch (18.1 Hz for spotted seatrout LAGs; 5.1 Hz for red drum knocks)."

"For sounds of captive- versus field-recorded fish, the dominant frequency was 667 versus 691 Hz for silver perch, 293 versus 386 Hz for weakfish, 210 versus 269 Hz for spotted seatrout, and 152 versus 128 Hz for red drum (Figure 7A, B). The dominant frequencies of field recordings are similar to those of the captive recordings for each species (r = 0.98) and are inversely correlated with the mean size of the species (r=0.65) recorded in captivity."

"Red drum began drumming after sunset and the DI peaked at 2200 hours. Red drum sounds were detected during August and peaked in September, but none were apparent during May–July monitoring."

"The sounds recorded on the nocturnal sonobuoy deployments were dependent upon the month; weakfish and silver perch had the greatest SNDI in the early part of the survey (May and June), but values declined as autumn approached (September). Spotted seatrout exhibited peak activity in the summer months (June– August) but were also recorded in the spring (May) and autumn (September). Red drum were only recorded in the late summer and autumn (August and September). There was a slight increase in the SNDI for weakfish in August 1998, suggesting the occurrence of a second spawning peak."

"With respect to bottom salinity, weakfish were more commonly heard in higher salinity (Figure 17; Table 2; mean = 15.4%, range = 7.8–28.3%) than were spotted seatrout (mean = 11.8%, range = 7.1–26.9%), but there was a good deal of overlap between these two congeners. However, peak SNDIs of the spotted seatrout occurred in lower salinities than did those of the weakfish. Silver perch tended to co-occur with weakfish in water of similar salinity (mean = 14.0%, range = 7.1–28.3%). Red drum generally produced sounds at higher salinities (mean = 14.4%) but called over a wide range of salinities (7.8–27.1%). In Pamlico Sound, which generally has low salinity because of its few restricted inlets, these fishes produced sounds at salinities lower than might be expected in other estuaries but at a wide salinity range. For bottom dissolved oxygen, a critical habitat variable that is of great concern to biologists because of the potential for hypoxia (<4 mg/L), there was quite a difference in the distribution of SNDI values among the species. Weakfish had a very well-defined lower limit (Table 2; mean = 7.6 mg/L, range = 2.65–10.4), and only a single sonobuoy recorded their calls at dissolved oxygen levels below 4 mg/L (Figure 18). Spotted seatrout, on the other hand, were recorded at dissolved oxygen levels as low as 0.05 mg/L (mean = 6.1 mg/L, range = 0.05–9.73 mg/L), suggesting that hypoxia did not limit their sound production. Indeed, some of the highest SNDI values occurred at hypoxic (<4 mg/L) sonobuoy stations. Some fairly high SNDI values were recorded for silver perch in hypoxic bottom waters, although most sonobuoy recordings were from normoxic waters (mean = 7.0 mg/L, range = 1.03–10.4 mg/L), as was true for red drum (mean = 6.7 mg/L, range = 4.5–9.5 mg/L)."

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

"Red drum calling activity occurred primarily where surface salinity exceeded 22%."

"Guest and Lasswell (1978) demonstrated in laboratory studies that nocturnal sound production by spawning red drum was associated with males courting females."

Observation Environment Quotes

"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. "

"Fish were caught by hook-and-line methods and placed in aerated seawater transport tanks. They were taken to the Pamlico Aquaculture Field Laboratory, Aurora, or to the East Carolina University Department of Biology, Greenville, and held in tanks for recording purposes."

Behaviour Description Quotes

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

" Sound production associated with spawning is likely to be an advertisement call produced by the males (Connaughton and Taylor 1996) in a manner similar to that used by Atlantic cod Gadus morhua to attract females to group spawning aggregations (Nordeide and Folstad 2000) or by oyster toadfish Opsanus tau to attract females to the territories of individual males (Fine and Thorson 2008, this issue). "

"Guest and Lasswell (1978) demonstrated in laboratory studies that nocturnal sound production by spawning red drum was associated with males courting females."

Sound Name Quotes

"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 were heard predominantly at inlet locations in May and June, whereas spotted seatrout (peak drumming in July) and red drum (peak drumming in September) were heard predominantly at lower-salinity river mouth locations in western Pamlico Sound."

"The characteristic knock produced by a male red drum (within a 24-fish group; mean SL _ 660 mm; range _ 500–780 mm) was recorded in a tank at the Pamlico Aquaculture Field Laboratory (Figure 6A). The oscillogram and spectrogram show eight knocks, each lasting 0.13 s. The field recording shows four knocks in sequence (Figure 6C), and the dominant frequencies are less than 1,000 Hz (Figure 6D)."

"TABLE 1.—Pulse repetition rate (PRR) for the calls of four sciaenid species recorded on sonobuoys and with a mobile hydrophone in Pamlico Sound, North Carolina, 1997 and 1998 (N = number of calls analyzed)."

Full Description

"In the oscillogram (Figure 3A) and spectrogram (Figure 3B) of a silver perch (standard length [SL] = 150 mm; recorded in a transport container immediately after capture), one can see seven bursts of sound; these are the characteristic ‘‘clucks’’ (Luczkovich et al. 1999) or ‘‘knocks’’ (Mok and Gilmore 1983; Sprague et al. 2000) made by the silver perch. The echo in this recording, which is visible after each burst of sound, is due to the recording being made inside a container. The bursts occur all within 1 s, which is also characteristic of the silver perch. The sound intensity is dominated by frequencies less than 3,000 Hz; the dominant frequency is less than 1,000 Hz. Field recorded silver perch sounds were similar, as can be observed in the oscillogram (Figure 3C) and spectrogram (Figure 3D) of a recording made at station 11 on 14 July 1997. In this recording, an individual silver perch is knocking, producing six bursts within 1 s."

"The pulse repetition rate changed with increasing temperature; this rate was low for weakfish (15.9 Hz) and silver perch (6.5 Hz) at temperatures less than 23C (21.5 Hz) but was high at temperatures above 23C (12.1 Hz). Spotted seatrout and red drum did not call at temperatures below 23C, but their pulse repetition rates were different from those of weakfish and silver perch (18.1 Hz for spotted seatrout LAGs; 5.1 Hz for red drum knocks)."

"For sounds of captive- versus field-recorded fish, the dominant frequency was 667 versus 691 Hz for silver perch, 293 versus 386 Hz for weakfish, 210 versus 269 Hz for spotted seatrout, and 152 versus 128 Hz for red drum (Figure 7A, B). The dominant frequencies of field recordings are similar to those of the captive recordings for each species (r = 0.98) and are inversely correlated with the mean size of the species (r=0.65) recorded in captivity."

"Silver perch were detected most frequently during our study; their calls began just before sunset (2025–2029 hours; Eastern Daylight Time) and continued until just after sunrise (0553–0601 hours), but the DI peaked at 2300 hours."

"The sounds recorded on the nocturnal sonobuoy deployments were dependent upon the month; weakfish and silver perch had the greatest SNDI in the early part of the survey (May and June), but values declined as autumn approached (September). Spotted seatrout exhibited peak activity in the summer months (June– August) but were also recorded in the spring (May) and autumn (September). Red drum were only recorded in the late summer and autumn (August and September). There was a slight increase in the SNDI for weakfish in August 1998, suggesting the occurrence of a second spawning peak."

"With respect to bottom salinity, weakfish were more commonly heard in higher salinity (Figure 17; Table 2; mean = 15.4%, range = 7.8–28.3%) than were spotted seatrout (mean = 11.8%, range = 7.1–26.9%), but there was a good deal of overlap between these two congeners. However, peak SNDIs of the spotted seatrout occurred in lower salinities than did those of the weakfish. Silver perch tended to co-occur with weakfish in water of similar salinity (mean = 14.0%, range = 7.1–28.3%). Red drum generally produced sounds at higher salinities (mean = 14.4%) but called over a wide range of salinities (7.8–27.1%). In Pamlico Sound, which generally has low salinity because of its few restricted inlets, these fishes produced sounds at salinities lower than might be expected in other estuaries but at a wide salinity range. For bottom dissolved oxygen, a critical habitat variable that is of great concern to biologists because of the potential for hypoxia (<4 mg/L), there was quite a difference in the distribution of SNDI values among the species. Weakfish had a very well-defined lower limit (Table 2; mean = 7.6 mg/L, range = 2.65–10.4), and only a single sonobuoy recorded their calls at dissolved oxygen levels below 4 mg/L (Figure 18). Spotted seatrout, on the other hand, were recorded at dissolved oxygen levels as low as 0.05 mg/L (mean = 6.1 mg/L, range = 0.05–9.73 mg/L), suggesting that hypoxia did not limit their sound production. Indeed, some of the highest SNDI values occurred at hypoxic (<4 mg/L) sonobuoy stations. Some fairly high SNDI values were recorded for silver perch in hypoxic bottom waters, although most sonobuoy recordings were from normoxic waters (mean = 7.0 mg/L, range = 1.03–10.4 mg/L), as was true for red drum (mean = 6.7 mg/L, range = 4.5–9.5 mg/L)."

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

"Silver perch were recorded primarily in cool waters with bottom dissolved oxygen concentrations lower than 7.4 mg/L and temperatures less than 26C."

Observation Environment Quotes

"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. "

"Fish were caught by hook-and-line methods and placed in aerated seawater transport tanks. They were taken to the Pamlico Aquaculture Field Laboratory, Aurora, or to the East Carolina University Department of Biology, Greenville, and held in tanks for recording purposes."

Behaviour Description Quotes

"The passive acoustic survey reported here revealed a great deal about the sound production behavior, habitat use, and spawning activity of weakfish, spotted seatrout, red drum, and silver perch. Sound production has been associated with egg production and spawning in these four species (Mok and Gilmore 1983; Luczkovich et al. 1999; Lowerre-Barbieri et al., 2008 this issue); therefore, we assume that the recorded sounds were spawning-related calls used by males to attract females."

" Sound production associated with spawning is likely to be an advertisement call produced by the males (Connaughton and Taylor 1996) in a manner similar to that used by Atlantic cod Gadus morhua to attract females to group spawning aggregations (Nordeide and Folstad 2000) or by oyster toadfish Opsanus tau to attract females to the territories of individual males (Fine and Thorson 2008, this issue)."

Sound Name Quotes

"In the oscillogram (Figure 3A) and spectrogram (Figure 3B) of a silver perch (standard length [SL] = 150 mm; recorded in a transport container immediately after capture), one can see seven bursts of sound; these are the characteristic ‘‘clucks’’ (Luczkovich et al. 1999) or ‘‘knocks’’ (Mok and Gilmore 1983; Sprague et al. 2000) made by the silver perch. The echo in this recording, which is visible after each burst of sound, is due to the recording being made inside a container. The bursts occur all within 1 s, which is also characteristic of the silver perch. The sound intensity is dominated by frequencies less than 3,000 Hz; the dominant frequency is less than 1,000 Hz. Field recorded silver perch sounds were similar, as can be observed in the oscillogram (Figure 3C) and spectrogram (Figure 3D) of a recording made at station 11 on 14 July 1997. In this recording, an individual silver perch is knocking, producing six bursts within 1 s."

"TABLE 1.—Pulse repetition rate (PRR) for the calls of four sciaenid species recorded on sonobuoys and with a mobile hydrophone in Pamlico Sound, North Carolina, 1997 and 1998 (N = number of calls analyzed)."