The frequency response of the vibrissae of harp seal, Pagophilus Groenlandicus, to sound in air and water.

The motion of isolated seal vibrissae due to low frequency sound in air has been measured using a microscope with a video camera and modeled using an FEM method with good agreement between the measurements and the model; the model has also been used to predict the motion of seal vibrissae in water. The shape of the seal vibrissae is that of a tapered right rectangular prism, unlike that of the previously studied rat vibrissae which are conical in shape. Moreover, unlike rat vibrissae which oscillate in the direction of the sound stimulus, two different modes of vibration of seal vibrissae were observed - one corresponding to the wider side being stimulated and one with the narrow side stimulated. The tuning of the seal vibrissae was much sharper than those of rat vibrissae, with quality factors about three times as large as those of rat vibrissae. As shown by the model, this increased sharpness is caused by the larger cross-sectional areas (by more than a factor of ten) of the seal vibrissae. This increased sharpness may be necessary for seal vibrissae so that they can have tuning in water, where the drag more heavily dampens the tuning than in air. The results suggest that vibrissae tuning may be important in the seal's ability to track the wake of its prey.

Toneburst-evoked auditory brainstem response in a leopard seal, Hydrurga leptonyx.

Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leopard seal. Three frequencies from 1 to 4 kHz were tested at sound levels from 68 to 122 dB peak equivalent sound pressure level (peSPL). Results illustrate brainstem activity within the 1-4 kHz range, with better hearing sensitivity at 4 kHz. As is seen in human ABR, only wave V is reliably identified at the lower stimulus intensities. Wave V is present down to levels of 82 dB peSPL in the right ear and 92 dB peSPL in the left ear at 4 kHz. Further investigations testing a wider frequency range on seals of various sex and age classes are required to conclusively report on the hearing range and sensitivity in this species.

Detoxification mechanism of heavy metals in marine mammals and seabirds: interaction of selenium with mercury, silver, copper, zinc, and cadmium in liver.

Subcellular distribution of mercury, selenium, silver, copper, zinc, and cadmium was determined in the liver of northern fur seals (Callorhinus ursinus), black-footed albatrosses (Diomedea nigripes), and Dall's porpoises (Phocoenoides dalli). Mercury, selenium, and silver were preferentially accumulated in nuclear, lysosomal, and mitochondrial fraction with an increase in their hepatic concentrations, whereas copper, zinc, and cadmium were accumulated mainly in cytosol with an increase in the hepatic concentrations for all three species. To gain insight into the existing state of the metals, they were extracted with four extractants--sodium dodecylsulfate (SDS); 2-mercaptoethanol; 2-mercaptoethanol + guanidinium thiocyanate; and copper sulfate (CuSO4)--at several concentrations from nuclear, lysosomal, and mitochondrial fraction in liver from a specimen of northern fur seal. Extraction efficiencies of the metals for 2-mercaptoethanol + guanidinium thiocyanate and CuSO4 were much higher than those for SDS and 2-mercaptoethanol. Also, for all individuals of the three species, metals were extracted by the three extractants--2% SDS; 0.25 mol/L 2-mercaptoethanol + 5 mol/L guanidinium thiocyanate; and 0.1 mol/L CuSO4--from nuclear, lysosomal, and mitochondrial fraction of liver. In the northern fur seals with higher concentration of mercury, the molar ratio of selenium to mercury approached unity in the nonextractable fraction of 0.25 mol/L 2-mercaptoethanol + 5 mol/L guanidinium thiocyanate, suggesting the possible formation of mercuric selenide (HgSe) with increasing hepatic concentration. Because the nonextractable content of mercury and its distribution were larger for black-footed albatross than those for the other two species, it was suggested that the black-footed albatross has a stronger ability to form a stable compound(s) of mercury in the liver. It is notable that the existing state of silver was similar to that of mercury as judged by their subcellular distribution and the extraction tests, suggesting that silver also interacted with selenium in the liver of marine animals used in this study.

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.

[Sound reception in marine mammals depending on sound parameters and conduction pathways]. / Zvukovaia retseptsiia morskikh mlekopitaiushchikh v zavisimosti ot parametrov i putei provedeniia zvuka.

The interaction of complex sounds with the body tissues of Black Sea dolphin (Tursiops truncatus) was studied by the method of instrumental conditioned reflexes with food reinforcement. The thresholds of detecting underwater acoustic signals of different frequencies for dolphin and northern fur seal (Callorhinus ursinus) were measured as a function of pulse duration under conditions of full and partial (head above water) submergence of animals into water. It was found that sound conduction through dolphin tissues was more effective than that in a northern fur seal in a wide frequency range. Presumably, the process of sound propagation in dolphin is accompanied by changes in the amplitude-frequency structure of broad-band sounds. The temporal summation in dolphin hearing was observed at all frequencies under conditions of full and partial submergence, whereas in northern fur seal it was nearly absent at a frequency of 5 kHz under the conditions of head lifting above water.

Thermoregulatory responses to altering hypothalamic temperature in the harbor seal.

The rostral brainstem of the harbor seal Phoca vitulina was cooled and heated 33-41 degrees C while oxygen consumption and rectal, hypothalamic, flipper and dorsal skin temperatures were measured. These experiments were made on restrained seals at ambient temperatures -15 to 30 degrees C. Cooling the preoptic and hypothalamic (POH) tissue increased oxygen consumption in a way that could be approximated by a linear regression line with slope and threshold temperature at which the metabolic rate was minimal. The slope of the regression line was a function of ambient temperature and rectal temperature. At each ambient temperature, the slope was significantly higher for lower rectal temperature. At all rectal temperatures, the slope was significantly higher for lower ambient temperature. The threshold hypothalamic temperatures did not very consistently or significantly with either rectal temperature or ambient temperature. These results on the harbor seal are explicable by suggesting that the thermal-sensitive and reference neurons in the POH which regulate body temperature are inhibited equally by extrahypothalamic cold transducing neural elements.

Brown adipose tissue-a factor in the survival of harp seal pups.

The respiratory characteristics of mitochondria isolated from the subcutaneous brown adipose tissue of newborn harp seals indicate that the tissue is thermogenically active. Temperature recordings in vivo revealed, in fact, that the tissue was maintained at a temperature close to that of the body core during immersion of the pups in ice-water. Beta-adrenergic blockade markedly increased the cooling rates at both locations in ice-water, while curarization, accompanied by artificial respiration did not. We conclude that nonshivering thermogenesis through activated brown adipose tissue plays a decisive role in the defence against cold in the newborn harp seal.