Browsing by Author "Ladich, Friedrich"
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- Development of vocalization, auditory sensitivity and acoustic communication in the Lusitanian toadfish Halobatrachus didactylusPublication . Vasconcelos, Raquel Ornelas; Ladich, FriedrichThe ontogenetic development of acoustic communication has so far only been investigated in one fish species. In order to determine whether detectability of conspecific sounds changes during growth in a species with limited hearing abilities (generalist), we investigated the development of auditory sensitivity and agonistic vocalizations in the Lusitanian toadfish Halobatrachus didactylus. Agonistic grunts were recorded, their sound pressure levels determined, and auditory sensitivities measured in five different size groups ranging from 3 to 32·cm standard length. Hearing thresholds were obtained using the auditory evoked potentials (AEP) recording technique. Dominant frequency, sound duration and number of pulses decreased, whereas pulse period and sound level increased with increasing fish size. The best hearing was below 300·Hz in all groups. Lower hearing sensitivity was found in the smallest juveniles at 100·Hz as well as at higher frequencies (800 and 1000·Hz). Comparisons between audiograms and sound spectra within the same-sized fish revealed that smaller juveniles would be barely able to detect agonistic grunts, while these vocalizations were clearly perceived by larger fish. In the latter, the main energy of sounds was found at the most sensitive frequencies. This study demonstrates that acoustic communication in the Lusitanian toadfish might be absent in early developmental stages and seems to start when juveniles are able to generate grunts of higher sound level and lower dominant frequency.
- Effects of ship noise on the detectability of communication signals in the Lusitanian toadfishPublication . Vasconcelos, Raquel Ornelas; Amorim, Maria Clara Pessoa; Ladich, FriedrichUnderwater noise pollution is an increasing environmental problem which might affect communication, behaviour, fitness and consequently species' survival. The most common anthropogenic noises in aquatic habitats derive from shipping. In the present study we investigated the implications of noise pollution from a ship on the sound detectability, namely of conspecific vocalizations in the Lusitanian toadfish, Halobatrachus didactylus. Ambient and ferry-boat noises were recorded in the Tagus River estuary (Portugal), as well as toadfish sounds, and their sound pressure levels determined. Hearing sensitivities were measured under quiet lab conditions and in the presence of these masking noises at levels encountered in the field, using the auditory evoked potentials (AEP) recording technique. The Lusitanian toadfish is a hearing generalist, with best hearing sensitivity at low frequencies between 50 and 200 Hz (below 100 dB re. 1 microPa). Under ambient noise conditions, hearing was only slightly masked at lower frequencies. In the presence of ship noise, auditory thresholds increased considerably, by up to 36 dB, at most frequencies tested. This is mainly because the main energies of ferry-boat noise were within the most sensitive hearing range of this species. Comparisons between masked audiograms and sound spectra of the toadfish's mating and agonistic vocalizations revealed that ship noise decreased the ability to detect conspecific acoustic signals. This study provides the first evidence that fishes' auditory sensitivity can be impaired by ship noise and that acoustic communication, which is essential during agonistic encounters and mate attraction, might be restricted in coastal environments altered by human activity.
- Effects of ship noise on the detectability of communication signals in the Lusitanian toadfishPublication . Vasconcelos, Raquel Ornelas; Amorim, Maria Clara Pessoa; Ladich, FriedrichUnderwater noise pollution is an increasing environmental problem which might affect communication, behaviour, fitness and consequently species’ survival. The most common anthropogenic noises in aquatic habitats derive from shipping. In the present study we investigated the implications of noise pollution from a ship on the sound detectability, namely of conspecific vocalizations in the Lusitanian toadfish, Halobatrachus didactylus. Ambient and ferry-boat noises were recorded in the Tagus River estuary (Portugal), as well as toadfish sounds, and their sound pressure levels determined. Hearing sensitivities were measured under quiet lab conditions and in the presence of these masking noises at levels encountered in the field, using the auditory evoked potentials (AEP) recording technique. The Lusitanian toadfish is a hearing generalist, with best hearing sensitivity at low frequencies between 50 and 200·Hz (below 100·dB re. 1· Pa). Under ambient noise conditions, hearing was only slightly masked at lower frequencies. In the presence of ship noise, auditory thresholds increased considerably, by up to 36·dB, at most frequencies tested. This is mainly because the main energies of ferry-boat noise were within the most sensitive hearing range of this species. Comparisons between masked audiograms and sound spectra of the toadfish’s mating and agonistic vocalizations revealed that ship noise decreased the ability to detect conspecific acoustic signals. This study provides the first evidence that fishes’ auditory sensitivity can be impaired by ship noise and that acoustic communication, which is essential during agonistic encounters and mate attraction, might be restricted in coastal environments altered by human activity.
- Representation of complex vocalizations in the Lusitanian toadfish auditory system: Evidence of fine temporal, frequency and amplitude discriminationPublication . Vasconcelos, Raquel Ornelas; Fonseca, Paulo Jorge; Amorim, Maria Clara Pessoa; Ladich, FriedrichMany fishes rely on their auditory skills to interpret crucial information about predators and prey, and to communicate intraspecifically. Few studies, however, have examined how complex natural sounds are perceived in fishes. We investigated the representation of conspecific mating and agonistic calls in the auditory system of the Lusitanian toadfish Halobatrachus didactylus, and analysed auditory responses to heterospecific signals from ecologically relevant species: a sympatric vocal fish (meagre Argyrosomus regius) and a potential predator (dolphin Tursiops truncatus). Using auditory evoked potential (AEP) recordings, we showed that both sexes can resolve fine features of conspecific calls. The toadfish auditory system was most sensitive to frequencies well represented in the conspecific vocalizations (namely the mating boatwhistle), and revealed a fine representation of duration and pulsed structure of agonistic and mating calls. Stimuli and corresponding AEP amplitudes were highly correlated, indicating an accurate encoding of amplitude modulation. Moreover, Lusitanian toadfish were able to detect T. truncatus foraging sounds and A. regius calls, although at higher amplitudes. We provide strong evidence that the auditory system of a vocal fish, lacking accessory hearing structures, is capable of resolving fine features of complex vocalizations that are probably important for intraspecific communication and other relevant stimuli from the auditory scene.