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Mating Call of the Plainfin Midshipman as an Indicator of Stress due to Anthropogenic Noise and Other Environmental Factors

Roger Bland, Newell Garfield, Matt Sanchez, Jemma Lorenat, Daniel Cuneo, and Ratna Lama

The calling of the Plainfin Midshipman (Porichthys notatus) in San Francisco Bay was recorded over the course of two summer mating seasons. A loud, continuous humming was observed during summer months, mainly during the night-time. This has been identified by others as the mating call of the male Midshipman.

The frequency and intensity of this call was measured for every 15-minute time interval. Three results of interest were obtained.

  • The humming is generally nocturnal, with well-defined times for starting (about 8:00 PM) and stopping (about 6:00 AM). This is in general agreement with a hypothesis that the fish call at times when there is relatively little competition from shipping noise. However, certain details of the calling seem to be more compatible with a correlation with darkness. In particular, the pattern was broken by considerable calling during the late morning in July of 2010, when unusual cloudy weather may have provided a "low-light-level" signal to the calling Midshipmen.
  • The frequency of humming is tightly correlated with the water temperature, with a linear relation over the full range of variation observed.
  • On October 12, 2009, an unseasonal heavy rainstorm coincided with a sudden resurgence of calling from the Midshipman, just as they appeared to be leaving for the winter, suggesting that a chemical trigger for mating behavior washed in with the runoff.

More work remains to draw conclusions about humming and ship noise; in particular, an effective computer algorithm for identifying the sound pattern from ships remains to be developed.

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