Underwater Sound from the RTC Pier { Underwater Acoustics Research Group }

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The Mating Hum of the Plainfin Midshipman

A hydrophone in San Francisco Bay has recorded sound continuously since January 2009. Fourier-transform techniques have been used to isolate the monotone mating call from shipping noise and other ambient sound. The sound intensity is calculated for every 15-minute data file. Below we see the sound intensity over nearly a two-year span, and the diel distribution of this intensity for the two years.

Seasonal distribution. Blue=2009, red = 2010. Data points from January through May are noise, mainly due to ship traffic. There are two features of special interest. (1) Strong humming lasted much longer in 2009 than in 2010. (2) In October 2009 there is a sudden increase in humming power that corresponds to an intense unusual rainstorm on October 12, that produced 2 inches of rainfall in a few hours. We think that the resulting increase in Midshipman mating activity may have been triggered by chemical signals in the runoff. Click HERE for more plots of 15-min intensity.
Humming power, averaged over days. Click HERE for more plots of daily intensity.
Diel distribution in humming power, for the 2009 mating season (July to October). The humming jumps up in the 8:00-to-9:00 PM bin, and the last strong humming is from 5:00 to 6:00 AM. No wonder that people sleeping in houseboats were annoyed! Click HERE for more diel distributions.
Midshipman humming intensity, hour by hour and day by day, 2009. Click HERE for more 3-d displays.
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