Fig 1.
Deployment locations of acoustic recording packages.
The study area is off central California as denoted by the red box in the inset map. Acoustic recording packages are indicated with black triangles and labeled according to their relative positions. The location of the NOAA Southwest Fisheries Science Center surveys are indicated with a black star. Colors indicate land elevation and seafloor depth with respect to sea level. Black contour lines show seafloor depth in 50 m increments. Bathymetry data from the NOAA National Centers for Environmental Information’s Southern California Coastal Relief Model with 1 arc-second resolution.
Table 1.
Deployment locations of acoustic recording packages.
Fig 2.
Gray whale M3 and M1 recorded vocalizations.
An example (A) M3 call and (B) M1 call recorded on the NE hydrophone. Spectrograms are on top with frequency on the y-axis, time on the x-axis, and color indicating pressure magnitude squared (or equivalently pressure magnitude) in dB. A 40 dB dynamic range was used and all magnitudes were normalized to the greatest dB magnitude of the spectrogram. Note the different axes limits for the two call types. Time series plots are on the bottom with normalized amplitude on the y-axis and time on the x-axis. The M3 spectrogram has an FFT length of 512 with 99% overlap and a Hamming window and is bandpass filtered from 20 to 200 Hz. The M1 spectrogram has an FFT length of 256 with 99% overlap and a Hamming window and is bandpass filtered from 20 to 1,000 Hz.
Fig 3.
Examples of gray whale tracks from acoustic localization.
Gray whale positions determined by localizing their vocalizations on the hydrophone array. Plots (A) and (B) show southbound whales (21 January 2015 and 10 February 2015, respectively) and plots (C) and (D) show northbound whales (13 March 2015 and 9 April 2015, respectively). Dots indicate position of the calling animal and their color matches the minutes since the start of the track with earlier in time in blue and later in red. The four black triangles mark the positions of the four bottom-mounted hydrophones and the black star marks the position of the NOAA visual and infrared camera research site. Contour lines show water depth in 20 m increments. The axes limits are 36.4° to 36.45° for latitude and -121.98° to -121.92° for longitude.
Table 2.
Characteristics of received gray whale M3 calls.
Table 3.
Characteristics of received gray whale M1 calls.
Table 4.
Source level of gray whale M3 calls.
Fig 4.
Estimated source level of gray whale M3 calls.
These histograms show the source level of gray whale M3 calls. RMS is shown in blue (dB re 1 μPa at 1 m), SEL is shown in orange (dB re 1 μPa2 s at 1 m), and peak-to-peak is shown in yellow (dB re 1 μPa at 1 m).
Fig 5.
Probability of localization in 93.5 dB re 1 μPa root median square noise.
This map shows the probability of localization of a call produced at locations close to the hydrophone array in 93.5 dB re 1 μPa root median square background noise. In the 50th percentile noise conditions, the probability of localization within the area of the array was approximately 100%. Probability of localization increases as noise levels decrease. The four black triangles mark the positions of the four bottom-mounted hydrophones. The dashed box indicates the area inside the hydrophone array. The axes limits are 36.4° to 36.45° for latitude and -121.98° to -121.92° for longitude.
Fig 6.
Seasonal cycle: Normalized calls and percentage of calls that were part of a track.
The normalized number of localized calls per day is shown in (A), the percentage of those calls that were part of a track is shown in (B), and the percentage of the day with no effort due to probability of localization less than 50% is shown in (C). The first localized gray whale call within the area bounded by the array was detected on 7 December 2014 and the last was detected on 18 April 2015. All of the calls counted were manually verified on all four hydrophones to be gray whale M3 calls.
Fig 7.
Seasonal cycle: Swimming behavior.
Three track metrics used to assess swimming behavior of vocalizing gray whales. (A) displays average speed, (B) displays average heading, and (C) displays direction index.
Fig 8.
Seasonal cycle: Seafloor depth.
The mean seafloor depth at the position of tracks over the migration season. (A) shows depth as a function of time and (B) categorizes tracks as southbound or northbound based on their heading and shows the same data in boxplot format.
Fig 9.
Diel cycle: Total calls and percentage of calls that were part of a track.
The total number of localized calls (orange) compared with the percentage of those calls that were part of a track (blue). The calls are binned in daytime or nighttime according to the time they occurred with respect to the local sunrise and sunset. (A) shows the data for the full migration, (B) shows the data for calls before 15 February, and (C) shows the data for calls on or after 15 February. All of the calls included were manually verified to be gray whale M3 calls.
Fig 10.
The total number of gray whale tracks binned into different start times. Since the time of sunrise and sunset changes substantially throughout the migration, these plots use scaled start time of each track where 0 indicates sunrise, 1 indicates sunset, and 2 indicates the following sunrise with gray hatching indicating night. (A) shows the entire migration, (B) shows all tracks with a southbound heading, and (C) shows all tracks with a northbound heading.
Fig 11.
Diel cycle: Swimming behavior, entire migration.
Three track metrics used to assess swimming behavior of vocalizing gray whales. (A) displays speed, (B) displays heading, and (C) displays direction index. All track metrics are shown as a function of scaled start time of the tracks where 0 indicates sunrise, 1 indicates sunset, and 2 indicates the following sunrise with gray hatching indicating night.
Fig 12.
Diel cycle: Swimming behavior, split by heading.
The speed (A and C) and direction index (B and D) split based on track heading. All track metrics are shown as a function of scaled start time of the tracks where 0 indicates sunrise, 1 indicates sunset, and 2 indicates the following sunrise with gray hatching indicating night.
Fig 13.
The mean seafloor depth of tracks as a function of scaled start time where 0 indicates sunrise, 1 indicates sunset, and 2 indicates the following sunrise with gray hatching indicating night.