Underwater temporary threshold shift in pinnipeds: effects of noise level and duration

Behavioral psychophysical techniques were used to evaluate the residual effects of underwater noise on the hearing sensitivity of three pinnipeds: a California sea lion (Zalophus californianus), a harbor seal (Phoca vitulina), and a northern elephant seal (Mirounga angustirostris). Temporary threshold shift (TTS), defined as the difference between auditory thresholds obtained before and after noise exposure, was assessed. The subjects were exposed to octave-band noise centered at 2500 Hz at two sound pressure levels: 80 and 95 dB SL (re: auditory threshold at 2500 Hz). Noise exposure durations were 22, 25, and 50 min. Threshold shifts were assessed at 2500 and 3530 Hz. Mean threshold shifts ranged from 2.9-12.2 dB. Full recovery of auditory sensitivity occurred within 24 h of noise exposure. Control sequences, comprising sham noise exposures, did not result in significant mean threshold shifts for any subject. Threshold shift magnitudes increased with increasing noise sound exposure level (SEL) for two of the three subjects. The results underscore the importance of including sound exposure metrics (incorporating sound pressure level and exposure duration) in order to fully assess the effects of noise on marine mammal hearing.     

Auditory masking in three pinnipeds: aerial critical ratios and direct critical bandwidth measurements

This study expands the limited understanding of pinniped aerial auditory masking and includes measurements at some of the relatively low frequencies predominant in many pinniped vocalizations. Behavioral techniques were used to obtain aerial critical ratios (CRs) within a hemianechoic chamber for a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Simultaneous, octave-band noise maskers centered at seven test frequencies (0.2-8.0 kHz) were used to determine aerial CRs. Narrower and variable bandwidth masking noise was also used in order to obtain direct critical bandwidths (CBWs). The aerial CRs are very similar in magnitude and in frequency-specific differences (increasing gradually with test frequency) to underwater CRs for these subjects, demonstrating that pinniped cochlear processes are similar both in air and water. While, like most mammals, these pinniped subjects apparently lack specialization for enhanced detection of specific frequencies over masking noise, they consistently detect signals across a wide range of frequencies at relatively low signal-to-noise ratios. Direct CBWs are 3.2 to 14.2 times wider than estimated based on aerial CRs. The combined masking data are significant in terms of assessing aerial anthropogenic noise impacts, effective aerial communicative ranges, and amphibious aspects of pinniped cochlear mechanics.     

Why pinnipeds don't echolocate

Odontocete cetaceans have evolved a highly advanced system of active biosonar. It has been hypothesized that other groups of marine animals, such as the pinnipeds, possess analogous sound production, reception, and processing mechanisms that allow for underwater orientation using active echolocation. Despite sporadic investigation over the past 30 years, the accumulated evidence in favor of the pinniped echolocation hypothesis is unconvincing. We argue that an advanced echolocation system is unlikely to have evolved in pinnipeds primarily because of constraints imposed by the obligate amphibious functioning of the pinniped auditory system. As a result of these constraints, pinnipeds have not developed highly acute, aquatic, high frequency sound production or reception systems required for underwater echolocation. Instead, it appears that pinnipeds have evolved enhanced visual, tactile, and passive listening skills. The evolutionary refinement of alternative sensory systems allows pinnipeds to effectively forage, navigate, and avoid predators under water despite the lack of active biosonar capabilities.     

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the ground X1Sigma+ state. Copyright 1999 Academic Press.