Wavelet analysis.

<p>Wavelet scalogram of the snap rate data generated using a Morlet wavelet. The black boxes delineate the 1-week duration time series examples shown in Figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143691#pone.0143691.g007" target="_blank">7</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143691#pone.0143691.g009" target="_blank">9</a>. Unlike short-time Fourier techniques, the wavelet transform method makes use of variable length analysis windows and can often provide better temporal resolution than fixed-window-length spectral methods. The figure highlights the persistence, and varying strength, of the diurnal periodicity in snap count throughout the monitoring period. The snap rate time series intermittently exhibits additional variance at longer periods (2–4 days), which may be related to variations in water temperature (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143691#pone.0143691.g004" target="_blank">Fig 4</a>) or water quality.