Full Description

"The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm LT in the laboratory. It consists of individual pulses with average durations of 19.7 ms and 17.8 ms for the two males respectively, interpulse intervals of 496 ms and 718 ms, and dominant frequencies of 280 Hz and 316 Hz. Pulses are emitted in bouts of one to three min duration. Disturbance calls consist of a burst of pulses produced at short intervals, and the pulse duration, interpulse interval and dominant frequency of the pulses average 19.8 ms, 17.1 ms, and 363 Hz, respectively. Dominant frequency and interpulse interval decrease and pulse duration increases with fish size. Sound characteristics change markedly in young of the year individuals (lower than 25 cm LT) after which they appear to stabilize."

"The artisanal fishermen have two ways of detecting whitemouth croaker schools during the spawning season: (1) by tasting bottom water for the presence of salinity (Norbis 1995) (whitemouth croaker spawning occurs in salinities between 2 and 30‰; Macchi et al. 2003; Puig and Mesones 2005), and (2) by listening to the spawning sounds produced by the fish through the hull of their boats."

"Whitemouth croakers emit disturbance calls when held in-hand as in other sciaenids i.e., weakfish C. regalis (Connaughton et al. 2000)."

"The advertisement call consisted of a series of individual pulses that occur in bouts of 1 to 3 min with pauses of 5–20 min between bouts (Fig. 1a). Sound pulses consisted of 2–3 cycles of acoustic energy; most energy occurred in the second cycle, and the third cycle was greatly attenuated (Fig. 1). Advertisement calls were produced in the morning and again in the evening."

"Advertisement calls produced by male 28 LT had an average pulse duration of 19.7 ms, an interpulse interval of 496 ms and dominant frequency of 280 Hz; calls by male 30.5 LT had average values of 17.8 ms, 718 ms, and 316 Hz, respectively (see Table 1 for standard deviations and ranges). Pulse duration and dominant frequency were relatively similar for the same individual whereas interpulse interval exhibited large differences (Fig. 3)."

"Advertisement calls recorded in the Rio de la Plata estuary fishing ground were similar to those from captive individuals (see Fig. 1)."

"The dominant frequency of the pulses recorded in the field (Fig. 1b) varied from 160 Hz to 400 Hz suggesting choruses of different sized males. Whitemouth croaker was the only fish caught in trawls after our sound recordings."

"Disturbance calls were produced when the fish were exposed to the three different stimuli. This call was not heard when fish swam freely, alone or in groups, in the experimental tanks or in the field. We analyzed 230 calls, with a total of 6900 pulses. The number of pulses per burst varied from 3 to 40, and each specimen emitted 1–5 bursts. No significant difference (p>0.05) in pulse duration (F2, 36=1.63), pulse interval (F2, 33= 3.01) and dominant frequency (F2, 22=0.52) occurred for the different stimuli. Trains of pulses characteristically increased in amplitude for the first ca 7 pulses; in longer trains the amplitude stabilized. Pulses consisted of about 4 cycles, and most energy occurred in the second and third cycle, with the fourth cycle often greatly attenuated (Fig. 2b). Disturbance calls consisted of a train of pulses with smaller interpulse intervals than for advertisement calls (Figs. 2 and 3). The coefficient of variation for the 28 LT male was 0.19, and for the male of 30.5 LT was 0.17, the combined coefficient for all 102 fish was 0.34, indicating that the interval is more stereotyped in the disturbance call than in the advertisement call. In the laboratory, the 28 LT and 30.5 LT males emitted a dominant frequency of 305–309 Hz and 340–360 Hz, respectively. Surprisingly, the dominant frequency of their disturbance calls averaged respectively 25 and 38 Hz higher than for the advertisement calls in these two males. The duration, interval and dominant frequency of pulses averaged 19.8 ms, 17.1, ms, and 363 Hz, respectively for fish recorded on board in the field (Table 1). The relationship between LT and pulse duration, pulse interval and dominant frequency indicated two phases that were fit separately with linear regressions (Table 2, Fig. 4). For individuals below the break point (BP) all correlations were significant (P<0.05) (Table 2). Interpulse interval decreased with fish size to about 25 cm (r=_0.501; P<0.05), after which it remained constant in larger fishes (r=0.031; P>0.05). Pulse duration more than doubled from less than 10 to greater than 20 ms as LT increased from ca 10 to 20 cm. For this relationship the BP of segmented linear regression occurred at 20 cm LT (for fish <20 cm, r=0.458; P<0.05). In fish >20 cm duration varied between 10 and 30 ms but did not change with fish size (r=_0.077; P>0.05). Dominant frequency decreased from over 800 to less than 250 Hz (r=_0.768; P<0.05) before the BP at 19.1 cm LT and again remained constant in larger individuals (r=_0.045; P>0.05). Dominant frequency was inversely related to pulse duration: it decreased rapidly to the BP in maturing fish (r=_0.540; P<0.05) and then continued to decrease at a slower rate in larger individuals (r= _0.635; P<0.05) (Table 2, Fig. 5)."

"We suspect that the interpulse intervals would be shorter in field recordings from animals in large mating aggregations than from our two individuals in captivity."

Observation Environment Quotes

"The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm LT in the laboratory."

Behaviour Description Quotes

"The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm LT in the laboratory. It consists of individual pulses with average durations of 19.7 ms and 17.8 ms for the two males respectively, interpulse intervals of 496 ms and 718 ms, and dominant frequencies of 280 Hz and 316 Hz. Pulses are emitted in bouts of one to three min duration. Disturbance calls consist of a burst of pulses produced at short intervals, and the pulse duration, interpulse interval and dominant frequency of the pulses average 19.8 ms, 17.1 ms, and 363 Hz, respectively. Dominant frequency and interpulse interval decrease and pulse duration increases with fish size. Sound characteristics change markedly in young of the year individuals (lower than 25 cm LT) after which they appear to stabilize."

"Whitemouth croakers emit disturbance calls when held in-hand as in other sciaenids i.e., weakfish C. regalis (Connaughton et al. 2000). We exposed each individual captured to three stimuli that evoked disturbance calls: (1) a shadow over the surface of the tank, (2) a dip net moving through the water, and (3) grabbing them by the tail or otherwise handling them. We obtained recordings from 107 individuals and then measured total length (LT, cm) and determined sex (abdominal stripping in males and genital pore characteristics in females) and gonad maturity following Vizziano (2002)."

Sound Name Quotes

"The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm LT in the laboratory. It consists of individual pulses with average durations of 19.7 ms and 17.8 ms for the two males respectively, interpulse intervals of 496 ms and 718 ms, and dominant frequencies of 280 Hz and 316 Hz. Pulses are emitted in bouts of one to three min duration. Disturbance calls consist of a burst of pulses produced at short intervals, and the pulse duration, interpulse interval and dominant frequency of the pulses average 19.8 ms, 17.1 ms, and 363 Hz, respectively. Dominant frequency and interpulse interval decrease and pulse duration increases with fish size. Sound characteristics change markedly in young of the year individuals (lower than 25 cm LT) after which they appear to stabilize."