Cecilia S. Krahforst

The Lombard effect in fishes: How boat noise impacts oyster toadfish vocalization amplitudes in natural experiments

The Lombard effect (an involuntary increase in vocal levels in noisy environments) has been shown for humans, birds, and mammals. Here, we use experimental playbacks of vessel noise and other natural sounds in the normal soundscape of the oyster toadfish Opsanus tau to test if the Lombard effect occurred. Experiments were conducted at a noisy site adjacent to a port with high vessel traffic and in a quiet embayment. We played back vessel noise (inboard and outboard motor noise), predator sounds (bottlenose dolphins) and snapping shrimp sounds for 600 s and recorded the vocalizations made by toadfish in experimental dens during 600 s periods before, during, and after the playback period. Average call power of vocalizations increased by 6.8 dB during and 8.7 dB re 1 μPa2 after playbacks of noise relative to pre-period levels, demonstrating the Lombard effect in toadfish. Fish at the noisy site had higher average call power relative to the quiet site. There was no change in the fundamental frequency of calls...

Does Vessel Noise Change the Calling Rate and Intensity of Soniferous Fishes

Fishes of the family Sciaenidae (drums and croakers) are well-known for their abilities to produce sounds using both sonic muscles and the swim bladder (Luczkovich et al. 2008a, b; Rountree et al. 2006; Sprague and Luczkovich 2004). Calls of sciaenid fishes like Micropogonias undulatus (Atlantic croaker) can be heard with hydrophones throughout the day, producing sounds when disturbed, during aggression, and during spawning (male advertisement calls). In this study, we examined if the noise associated with coastal vessels (ferry boats and tugboats) that operated daily during the early morning through early evening had any effect on the seasonal and daily calling rate of Micropogonias undulatus.

Does Vessel Noise Affect Oyster Toadfish Calling Rates

The question we addressed in this study is whether oyster toadfish respond to vessel disturbances by calling less when vessels with lower frequency spectra are present in a sound recording and afterward. Long-term data recorders were deployed at the Neuse (high vessel-noise site) and Pamlico (low vessel-noise site) Rivers. There were many fewer toadfish detections at the high vessel-noise site than the low-noise station. Calling rates were lower in the high-boat traffic area, suggesting that toadfish cannot call over loud vessel noise, reducing the overall calling rate, and may have to call more often when vessels are not present.

Passive acoustics monitoring as part of integrated ocean observing systems

Passive acoustic monitoring can be a useful tool to include on Ocean Observing Systems. As an example, we describe the monitoring the acoustic environment in the coastal waters of North Carolina (USA) using an instrumented platform. The ECU Itpod (instrumented tripod) has been deployed in several locations in Pamlico Sound and river estuaries since 2006 to study fishes in the Family Sciaenidae (drums and croakers). We will present data recorded with hydrophones deployed on the Itpod with remote data loggers, acoustic Doppler current profilers, turbidity meters and water quality instruments. We have used passive acoustic recordings to study the correlations of fish sounds and environmental parameters (temperature, salinity, turbidity, dissolved oxygen, wave action, river discharge, tropical storms). The long-term data suggest that spring temperature increases are associated with increased activity of acoustically mediated courtship and spawning behavior of sciaenid fishes; these sounds decline in the fall ...

Influence of Turbidity on the Incidence of Sound Production in Atlantic Croaker (Micropogonias undulatus) in Pamlico Sound, North Carolina

Increased sound production by fishes, which is used for communication during mating, in territorial defense, and possibly in echolocation, has been associated with decreased light and increased temperature and salinity (Luczkovich et al. 2008; Mok and Gilmore 1983). There has not been an attempt to associate changes in sound production with other environmental factors such as turbidity. Sediment deposition and resuspension commonly occur in estuaries due to changes in current velocity and direction, water runoff, and wave height. These factors can lead to shearing on the bed surface and thus an overall increase in water column turbidity (Whitehouse et al. 2000). It has been hypothesized that increased water column turbidity will lead to increased sound production in fishes because visual cues will be impaired. The goal of this research is to associate the incidence of sound production by Micropogonias undulatus (Atlantic croaker) to variations in estuarine temperature, salinity, dissolved oxygen, and particularly turbidity.

HEARING AND LATERAL LINE | Acoustic Behavior

Fishes hear and produce a variety of sounds that allow them to interpret their environment as well as communicate with their conspecifics. Some sounds are incidental sounds made while swimming and feeding. Other sounds are signals associated with feeding, predator avoidance, territory defense, reproduction, and echolocation. Of these sounds, one of the most pervasive is when males make advertisement sounds to communicate their readiness to spawn, as found especially in the families Sciaenidae, Gadidae, and Batrachoididae. Sounds may provide information to the listener on the behaviors, sex, or size of the fish, allowing scientists to use sound to better understand the fish behavior.

Are passive acoustics an appropriate method to accurately represent a soniferous Atlantic croaker (Micropogonias undulatus) population

It was observed that the fundamental frequency of Atlantic croaker sounds is inversely correlated with the length of the fish. We used fundamental frequency as a method to estimate the average length of the croaker population at any given time. Croaker were collected using an otter trawl and simultaneously counted and measured acoustically with a 200‐kHz split‐beam echosounder at two sites within the Pamlico Sound estuary, NC from June to November 2008. Passive acoustic recorders [long‐term acoustic recording system (LARS) recordings 10‐s wave files < 10 kHz at 15‐min intervals] were deployed near each trawling site to obtain in‐situ recordings of croaker over the same period. Based on captive fish recordings, a linear regression analysis related total length to fundamental frequency, where TL = 305.323 mm−(0.270 Hz−1)f0(r2 = 0.84). This equation was then used to estimate croaker lengths from LARS recordings. Lengths of fish collected in the trawls, compared with the estimate from the passive LARS recordi...

Noise propagation from vessel channels into nearby fish nesting sites in very shallow water

Noise exposure has been shown to have negative impacts on fish. This study introduces the F-weighting function for assessing the effects of audible sounds on fish. Sound levels with the F-weighting function emphasize the frequencies that the fish can detect and suppresses frequencies the fish cannot detect. A hydrophone was placed at locations of shelters or “dens” colonized by oyster toadfish Opsanus tau in very shallow water (1 – 2 m depth). Sounds produced by three representative passing vessels – an inboard boat, an outboard boat, and a tugboat pushing a barge – in nearby channels were recorded. Each vessel produced sounds at the den location at levels audible to the fish. The vessel sounds were not loud enough to produce temporary threshold shifts or permanent hearing losses in the fish, but they were loud enough to produce behavioral effects, masking of conspecific and predator sounds, the Lombard effect, and possibly an increase of stress hormones. Also, for comparison with the noisy site, sounds w...

The impact of vessel noise on oyster toadfish (Opsanus tau) communication

Male oyster toadfish (Opsanus tau) produce boatwhistle sounds to attract females to shelters in shallow water estuaries. Calls are produced in a natural soundscape that include snapping shrimp (Alpheidae sp.) and bottlenose dolphin (Tursiops truncatus, toadfish predators) sounds. The purpose of this study is to determine if soundscape alterations from vessels and predators cause acoustic disturbance in toadfish courtship calling behavior. Six sound types were played to toadfish in shelters positioned at 1 m from an underwater speaker: snapping shrimp sounds (Shrimp, control), low-frequency (LFDolphin) and high-frequency (HFDolphin) bottlenose dolphin biosonar, inboard (Inboard) and outboard motorboat (Outboard) noises, and a combination of vessel and predator sounds (Both). Toadfish calling rates were quantified in 600 s intervals before, during, and after noise exposure and an ANOVA was used to compare mean rates. Playback type and site (noisy vs quiet) significantly influenced toadfish calling rates (F ...

Passive acoustic monitoring of fish in shallow water estuaries

Passive acoustic monitoring is a useful tool for studying soniferous fishes in shallow water estuaries. We have used a variety of techniques for monitoring the acoustic environment in the coastal waters of North Carolina (USA) to study fishes in the Family Sciaenidae (drums and croakers), which produce sounds with frequencies below 1000 Hz. We will present data recorded with hydrophones deployed from a small boat, a hydrophone array towed behind a boat, and remote data loggers. We have used passive acoustic recordings to study the distributions (large- and small-scale) and seasonality of acoustically active courtship and spawning behavior, acoustic interactions between predators and prey, the effects of noise from tugs and small boats on fish sound production, and relationships between fish sound production and environmental parameters such as temperature and salinity. One limitation on shallow-water acoustic monitoring is the sound propagation cutoff frequency, which depends on the water depth. All frequ...