Exposure to boat noise in the field yields minimal stress response in wild reef fish

Aquatic anthropogenic noise is on the rise, with growing concern about its impact on species that are sensitive to low-frequency sounds (e.g. most fish and invertebrates). We investigated whether the reef fish Halichoeres bivittatus living in both noisy and quiet areas had differing levels of baseline stress (measured as whole-body cortisol) and whether they would exhibit a physiological stress response when exposed to boat noise playbacks. While the playback experiments significantly increased cortisol levels in fish from our experiment compared to baseline levels, there were minimal pairwise differences across treatments and no difference in baseline stress for fish living in noisy vs. quiet areas. These results may be explained by low overall auditory sensitivity, habituation to a fairly noisy environment (due to biological sounds), or that boat noise simply may not represent an immediate threat to survival in this species. These findings contrast recent studies that have shown elevated stress responses in fishes when exposed to boat noise and highlights that inter-specific differences must be considered when evaluating potential impacts of anthropogenic noise on marine life

The sound of communication in underwater acoustic sensor networks: (Position paper)

Underwater environments have never been much of a constraint to the rich animal life they support at all depths of our seas and oceans. Indeed, nature has taken advantage of this environment to develop a rich variety of efficient communication strategies through evolutionary change and adaptation. The wealth of knowledge to be discovered will continue to dazzle and fascinate the world. For underwater sensor network communication, acoustic signalling is the preferred choice for designers because sound propagation is the most efficient when compared to other forms, like thermal, light, and electromagnetic. It is within this acoustic environment that researchers have to innovate and develop new ideas and methodologies so as to advance the state-of-the-art. In this paper, several fundamental issues and connections are discussed that arise in the study of underwater wireless sensor networks. A variety of ideas and solutions for further research is proposed and fundamental issues in topology control, directional underwater transducers, and monitoring and surveillance are disc

Exposure to boat noise in the field yields minimal stress response in wild reef fish

Aquatic anthropogenic noise is on the rise, with growing concern about its impact on species that are sensitive to low-frequency sounds (e.g. most fish and invertebrates). We investigated whether the reef fish Halichoeres bivittatus living in both noisy and quiet areas had differing levels of baseline stress (measured as whole-body cortisol) and whether they would exhibit a physiological stress response when exposed to boat noise playbacks. While the playback experiments significantly increased cortisol levels in fish from our experiment compared to baseline levels, there were minimal pairwise differences across treatments and no difference in baseline stress for fish living in noisy vs. quiet areas. These results may be explained by low overall auditory sensitivity, habituation to a fairly noisy environment (due to biological sounds), or that boat noise simply may not represent an immediate threat to survival in this species. These findings contrast recent studies that have shown elevated stress responses in fishes when exposed to boat noise and highlights that inter-specific differences must be considered when evaluating potential impacts of anthropogenic noise on marine life

Soundscapes from a Tropical Eastern Pacific reef and a Caribbean Sea reef

Underwater soundscapes vary due to the abiotic and biological components of the habitat. We quantitatively characterized the acoustic environments of two coral reef habitats, one in the Tropical Eastern Pacific (Panama) and one in the Caribbean (Florida Keys), over 2-day recording durations in July 2011. We examined the frequency distribution, temporal variability, and biological patterns of sound production and found clear differences. The Pacific reef exhibited clear biological patterns and high temporal variability, such as the onset of snapping shrimp noise at night, as well as a 400-Hz daytime band likely produced by damselfish. In contrast, the Caribbean reef had high sound levels in the lowest frequencies, but lacked clear temporal patterns. We suggest that acoustic measures are an important element to include in reef monitoring programs, as the acoustic environment plays an important role in the ecology of reef organisms at multiple life-history stages

Rumbling in the benthos: acoustic ecology of the California mantis shrimp Hemisquilla californiensis

Although much research has focused on acoustic mapping and exploration of the benthic environment, little is known about the acoustic ecology of benthic organisms, particularly benthic crustaceans. Through the use of a coupled audio–video system, a hydrophone array, and an autonomous recording unit, we tested several hypotheses about the field acoustics of a benthic marine crustacean, Hemisquilla califor­niensis. Living in muddy burrows in southern California, these large mantis shrimp produce low frequency ‘rumbles’ through muscle vibrations. First, we tested whether acoustic signals are similar in the field and in the laboratory, and discovered that field-produced rumbles are more acoustically and temporally variable than laboratory rumbles, and are typically produced in rhythmic series called ‘rumble groups.’ Second, we verified if the sounds were indeed coming from mantis shrimp burrows and explored whether rumble groups were produced by multiple individuals. Our results suggest that during certain time periods, multiple mantis shrimp in the vicinity of the hydro­phone produce sounds. Third, we examined the relationship between behavioral and acoustic activity, and found that H. californiensis is most active during ­crepuscular periods. While these crustaceans make a substantial contribution to the benthic soundscape, omnipresent and acoustically overlapping boat noise may threaten their acoustic ecology

Categorizing Active Marine Acoustic Sources Based on Their Potential to Affect Marine Animals

Marine acoustic sources are widely used for geophysical imaging, oceanographic sensing, and communicating with and tracking objects or robotic vehicles in the water column. Under the U.S. Marine Mammal Protection Act and similar regulations in several other countries, the impact of controlled acoustic sources is assessed based on whether the sound levels received by marine mammals meet the criteria for harassment that causes certain behavioral responses. This study describes quantitative factors beyond received sound levels that could be used to assess how marine species are affected by many commonly deployed marine acoustic sources, including airguns, high-resolution geophysical sources (e.g., multibeam echosounders, sidescan sonars, subbottom profilers, boomers, and sparkers), oceanographic instrumentation (e.g., acoustic doppler current profilers, split-beam fisheries sonars), and communication/tracking sources (e.g., acoustic releases and locators, navigational transponders). Using physical criteria about the sources, such as source level, transmission frequency, directionality, beamwidth, and pulse repetition rate, we divide marine acoustic sources into four tiers that could inform regulatory evaluation. Tier 1 refers to high-energy airgun surveys with a total volume larger than 1500 in3 (24.5 L) or arrays with more than 12 airguns, while Tier 2 covers the remaining low/intermediate energy airgun surveys. Tier 4 includes most high-resolution geophysical, oceanographic, and communication/tracking sources, which are considered unlikely to result in incidental take of marine mammals and therefore termed de minimis. Tier 3 covers most non-airgun seismic sources, which either have characteristics that do not meet the de minimis category (e.g., some sparkers) or could not be fully evaluated here (e.g., bubble guns, some boomers). We also consider the simultaneous use of multiple acoustic sources, discuss marine mammal field observations that are consistent with the de minimis designation for some acoustic sources, and suggest how to evaluate acoustic sources that are not explicitly considered here

Categorizing Active Marine Acoustic Sources Based on Their Potential to Affect Marine Animals

Marine acoustic sources are widely used for geophysical imaging, oceanographic sensing, and communicating with and tracking objects or robotic vehicles in the water column. Under the U.S. Marine Mammal Protection Act and similar regulations in several other countries, the impact of controlled acoustic sources is assessed based on whether the sound levels received by marine mammals meet the criteria for harassment that causes certain behavioral responses. This study describes quantitative factors beyond received sound levels that could be used to assess how marine species are affected by many commonly deployed marine acoustic sources, including airguns, high-resolution geophysical sources (e.g., multibeam echosounders, sidescan sonars, subbottom profilers, boomers, and sparkers), oceanographic instrumentation (e.g., acoustic doppler current profilers, split-beam fisheries sonars), and communication/tracking sources (e.g., acoustic releases and locators, navigational transponders). Using physical criteria about the sources, such as source level, transmission frequency, directionality, beamwidth, and pulse repetition rate, we divide marine acoustic sources into four tiers that could inform regulatory evaluation. Tier 1 refers to high-energy airgun surveys with a total volume larger than 1500 in3 (24.5 L) or arrays with more than 12 airguns, while Tier 2 covers the remaining low/intermediate energy airgun surveys. Tier 4 includes most high-resolution geophysical, oceanographic, and communication/tracking sources, which are considered unlikely to result in incidental take of marine mammals and therefore termed de minimis. Tier 3 covers most non-airgun seismic sources, which either have characteristics that do not meet the de minimis category (e.g., some sparkers) or could not be fully evaluated here (e.g., bubble guns, some boomers). We also consider the simultaneous use of multiple acoustic sources, discuss marine mammal field observations that are consistent with the de minimis designation for some acoustic sources, and suggest how to evaluate acoustic sources that are not explicitly considered here

Does motor noise from recreational boats alter parental care behaviour of a nesting freshwater fish?

Recreational boating activity has the potential to generate noise pollution that may influence wild fish. Such noise may be particularly relevant to fish engaged in parental care (PC), where alterations in behaviour could influence individual fitness and productivity of fish populations. Here, the PC behaviour of the freshwater largemouth bass (Micropterus salmoides) was examined to determine whether disturbance from boat noise altered paternal behaviour. Changes in nest-tending and brood-guarding behaviour were measured following exposure to noise treatments of 1-min duration using underwater playbacks of recorded boat noises. One experiment compared the behaviour of bass tending eggs before, during, and after exposure to high-speed or idling combustion motors, or an electronic bow-mounted trolling motor. No significant differences in the time on nest, number of pectoral fin beats, and number of turns between the pre-treatment, treatment, and post-treatment periods for all three motor types were observed. A second experiment assessed the impacts of noise (high-speed combustion motor only) on the behaviour of nesting bass across the development stages of offspring (i.e. egg, egg-sac fry, and swim-up fry). During the egg-sac fry stage, nest-guarding males turned significantly less on the nest during the noise treatment compared with the long-term post-treatment period, indicating a stage-specific impact of boat noise on parental behaviour. The effect was transient, however, and limited to the period that the noise was present. Given that PC and recreational boating activity tend to co-occur in nearshore areas, prolonged or frequent repeated exposure of nesting fish to boat noise during the egg-sac fry stage could have adverse consequences for fitness and reproductive output. Efforts to restrict recreational boating activity in the vicinity of fish engaged in PC (e.g. through the use of set-backs) would be a risk-averse approach to mitigating the effects of noise pollution on fish