Noise exposure of commercial divers in the Norwegian Sector of the North Sea.

It is well known that exposure to high noise levels can adversely affect human hearing. Legislation exists in Europe to control or restrict the level of noise to which employees may be exposed during the course of their work. While the noise levels to which a worker may be exposed is well defined in air, human sensitivity to noise is different in high-pressure and mixed-gas conditions. Relatively little research exists to define human hearing in these circumstances, and few measurements exist of the levels of noise to which divers working in these conditions are exposed. A study using specially designed equipment has been undertaken in Norwegian waters to sample the noise levels present during typical saturation dives undertaken by commercial divers working in the Norwegian oil and gas industry. The divers were working in heliox at depths of 30 msw and 120 msw. It found noise levels were generally dominated by self-noise: flow noise while breathing and communications. The noise levels, both when corrected for the difference in hearing sensitivity under pressure in mixed gas and uncorrected, would exceed legislated limits for noise exposure in a working day without the use of noisy tools.

The hearing abilities of the silver carp (Hypopthalmichthys molitrix) and bighead carp (Aristichthys nobilis).

Concern regarding the spread of silver carp (Hypopthalmichthys molitrix) and bighead carp (Aristichthys nobilis) through the Illinois River has prompted the development of a Bio-acoustic Fish Fence (BAFF) to act as an acoustic fish deterrent. The application of this technology has resulted in a need to understand the auditory physiology of the target species, in order to maximise the effect of the barrier in preventing the migration of the non-indigenous carp species into Lake Michigan, whilst minimising the effect on indigenous fish populations. Therefore, the hearing thresholds of 12 H. molitrix and 12 A. nobilis were defined using the Auditory Brainstem Response (ABR) technique, in a pressure-dominated sound field generated by submerged transducers of the type used in the construction of the BAFF system. The results clearly show that these fish are most sensitive to sounds in a frequency bandwidth of between 750 Hz and 1500 Hz, with higher thresholds below 300 Hz and above 2000 Hz.

The inner ear morphology and hearing abilities of the Paddlefish (Polyodon spathula) and the Lake Sturgeon (Acipenser fulvescens).

Concern regarding the spread of silver carp (Hypopthalmichthys molitrix) and bighead carp (Aristichthysc nobilis) through the Illinois River has prompted the development of an Acoustic Fish Deterrent (AFD) system. The application of this technology has resulted in a need to understand the auditory physiology of fish other than the target species, in order to minimise the effect of the AFD barrier on the ecology of indigenous fish populations. To this end, both the structures involved in sound reception and the hearing abilities of the paddlefish (Polyodon spathula) and the lake sturgeon (Acipenser fulvescens) are studied here using a combination of morphological and physiological approaches, revealing that both fish are responsive to sounds ranging in frequency from 100 to 500 Hz. The lowest hearing thresholds from both species were acquired from frequencies in a bandwidth of between 200 and 300 Hz, with higher thresholds at 100 and 500 Hz. The rationale for studying hearing in P. spathula and A. fulvescens in particular, is the value placed on them by both the commercial caviar producing industry and by the recreational fisheries sector. The hearing abilities of twelve P. spathula and twelve A. fulvescens were tested in sound fields dominated by either sound pressure or particle motion, with the results showing that acipenseriform fish are responsive to the motion of water particles in a sound field, rather than the sound pressure component. In this study, we measure the intensity of the sound field required to evoke threshold responses using a pressure sensitive hydrophone, as pressure dominated sound fields are the most audible acoustic condition for specialists like H. molitrix and A. nobilis (the target species). The results of the auditory examination clearly show that P. spathula and A. fulvescens are not sensitive to sound pressure, and will therefore have a significantly higher deterrent threshold than H. molitrix and A. nobilis in a pressure dominated sound field.