Abstract

Anthropogenic sound not only can affect hearing and behavior in marine mammals, but may potentially impact health, as in the cases of other mammals. The effect of intense sound on the health and immune status of marine mammals has not been studied. To this end, we have initiated investigations of the effects of intense underwater sound such as simulated explosions, seismic impulses and sonar pings on autonomic nervous system activation and immune function in marine mammals.

The current study was carried out in conjunction with a U.S. Navy Marine Mammal Program effort to determine acoustic safety criteria for marine mammals. These investigations determine underwater hearing thresholds before and after exposure to single underwater impulsive sounds (up to 200 kPa) produced from a seismic watergun and/or before and after exposure to tones (simulated sonar pings) (up to 201 dB re 1µPa) in a white whale, Delphinapterus leucas and a bottlenose dolphin, Tursiops truncatus. Sound pressures from the watergun were sufficient to cause temporary elevations in hearing thresholds in the white whale, but not the bottlenose dolphin.

Blood samples were obtained before and after sound exposures to measure responses of the nervous and immune systems. Measurements included catecholamines (norepinephrine, epinephrine and dopamine), hormones (cortisol and aldosterone), lymphoid cell subsets, serum chemistry constituents, hematologic parameters and complete blood cell counts.

Mean norepinephrine, epinephrine and dopamine levels were significantly higher after high-level sound exposures compared to low-level sound exposures or controls (P-values = 0.003, 0.006, 0.020) for the white whale. Mean norepinephrine levels increased by 337.75 pg/ml (95 percent confidence interval (CI) for the mean difference (23.58, 651.92)); mean epinephrine levels increased by 30.92 pg/ml (95 percent CI for the mean difference (3.60, 58.24)); mean dopamine levels increased by 37.42 pg/ml (95 percent CI for the mean difference (5.31, 69.52)). Furthermore, all three catecholamine levels increased with increasing sound levels (P-values=0.021, 0.012, 0.021). Mean cell volume (MCV) and alkaline phosphatase decreased over the experimental period (P-value = 0.004, 0.000), while Gamma glutamyl transferase increased over the experimental period (P-value = 0.000).

Significant neural-immune measurements were different in the bottlenose dolphin than the white whale after exposure to impulsive sounds. Aldosterone levels were significantly higher in the sound exposure group (P-value=0.000), whereas the absolute number of monocytes was significantly lower (P-value=0.015) compared to the control group. No significant differences were observed in the dolphin's neural-immune measurements after exposures to simulated sonar pings.

These studies are the first attempt to investigate anthropogenic noise as a "stressor" and potential impacts on the marine mammal immune system. The studies are intended to contribute to an understanding of the effects of sound on marine mammal health.

Acknowledgments

This work was supported by a grant from the Office of Naval Research # N00014-00-1-0041. The authors wish to thank Drs. Robert Gisiner and Linda Chrisey (ONR), Lily Tran (Loma Linda University), Dr. Jeff Stott (UC Davis), John Metos (ARUP laboratories), Dr. Sam Ridgway (US Navy Marine Mammal Program) and the veterinary, animal care and training staffs at SSC, San Diego.