Common Sole Larvae Survive High Levels of Pile-Driving Sound in Controlled Exposure Experiments

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited for juvenile and adult fish, and virtually non-existent for fish eggs and larvae. A device was developed in which fish larvae can be exposed to underwater sound. It consists of a rigid-walled cylindrical chamber driven by an electro-dynamical sound projector. Samples of up to 100 larvae can be exposed simultaneously to a homogeneously distributed sound pressure and particle velocity field. Recorded pile-driving sounds could be reproduced accurately in the frequency range between 50 and 1000 Hz, at zero to peak pressure levels up to 210 dB re 1µPa2 (zero to peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1µPa2s. The device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving sound. The highest cumulative sound exposure level applied was 206 dB re 1µPa2s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea pile-driving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. Although our findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur, they do indicate that previous assumptions and criteria may need to be revised

Controlled sonar exposure experiments on cetaceans in norwegian waters:Overview of the 3s-project

In mitigating the risk of sonar operations, the behavioral response of cetaceans is one of the major knowledge gaps that needs to be addressed. The 3SProject has conducted a number of controlled exposure experiments with a realistic sonar source in Norwegian waters from 2006 to 2013. In total, the following six target species have been studied: killer, long-finned pilot, sperm, humpback, minke, and northern bottlenose whales. A total of 38 controlled sonar exposures have been conducted on these species. Responses from controlled and repeated exposure runs have been recorded using acoustic and visual observations as well as with electronic tags on the target animal. So far, the first dose-response curves as well as an overview of the scored severity of responses have been revealed. In this paper, an overview is presented of the approach for the study, including the results so far as well as the current status of the ongoing analysis.</p

The ‘larvaebrator’ design.

<p>The larvaebrator is a device specifically designed to enable controlled exposure of fish larvae to sound in a laboratory setting.</p

Comparison of the original and measured signal shape.

<p>Comparison of the original signal shape (recorded in the field) and the observed signal shape (measured in the larvaebrator) for a pressure excitation (A, B) and a velocity excitation (C, D), in terms of sound pressure (A, C) and sound particle velocity (B, D). The original signal is scaled to match the peak of the measured signal. The sound levels are given in the header of each panel.</p

Mortality by larval stage and treatment at 5 and 7 days after the treatment.

<p>Estimated mean probability of death with 95% confidence limits (red symbols and bars) and observed mortality for each replicate within each treatment (black symbols). Each replicate consisted of 25 (±5) larvae. The labels of the sound exposure treatments refer to the distance from the pile, the associated sound levels are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033052#pone-0033052-t003" target="_blank">Table 3</a>.</p

Model estimates of the mean and 95% confidence limits for probability of death in each treatment and for the effect of exposure.

<p>The effect of exposure was defined as 100% • (p_e−p_c)/(1−p_c), in which p_e is the estimated mean probability of death in the exposure group and p_c is the estimated mean probability of death in the control group. The labels of the sound exposure treatments refer to the distance from the pile, the associated sound levels are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033052#pone-0033052-t003" target="_blank">Table 3</a>.</p

The larval stages of common sole (<i>Solea solea</i>) that were used in the experiments.

<p>The photos show a stage 1 larva of 5.3 mm (A), a stage 2 larva of 6.0 mm (B), a stage 3 larva of 6.5 mm (C) and a stage 4a larva of 7.1 mm (D).</p

Sound levels of the pressure excitation exposures applied in the final experiments.

<p>L_z−p  =  zero to peak sound pressure level, SEL_ss  =  single strike sound exposure level and SEL_cum  =  cumulative sound exposure level, see the text for further explanation. The last 2 columns present the corresponding distance from a ‘typical’ North Sea pile-driving installation and number of strikes.</p

Analysis of variance of the probability of death modelled as a function of treatment and random batch effect.

<p>Analysis of variance of the probability of death modelled as a function of treatment and random batch effect.</p