Gray whale localized acoustic detections in Granite Canyon 2014-2015

Scripps Institution of Oceanography, University of California San Diego

Eastern North Pacific gray whales make one of the longest annual
migrations of any mammal, traveling from their summer feeding areas in
the Bering and Chukchi Seas to their wintering areas in the lagoons of Baja
California, Mexico. Although a significant body of knowledge on gray whale
biology and behavior exists, little is known about their vocal behavior while
migrating. In this study, we used a sparse hydrophone array deployed
offshore of central California to investigate how gray whales behave and
use sound while migrating. We detected, localized, and tracked whales for
one full migration season, a first for gray whales. We verified and localized
10,644 gray whale M3 calls and grouped them into 280 tracks. Results
confirm that gray whales are acoustically active while migrating and their
swimming and acoustic behavior changes
on daily and seasonal time scales. The seasonal timing of the calls verifies
the gray whale migration timing determined using other methods such as
counts conducted by visual observers. The total number of calls and the
percentage of calls that were part of a track changed significantly over both
seasonal and daily time scales. An average calling rate of 5.7
calls/whale/day was observed, which is significantly greater than
previously reported migration calling rates. We measured a mean speed of
1.6 m/s and quantified heading, direction, and water depth where tracks
were located. Mean speed and water depth remained constant between
night and day, but these quantities had greater variation at night. Gray
whales produce M3 calls with a root mean square source level of 156.9 dB
re 1 µPa at 1 m. Quantities describing call characteristics were variable and
dependent on site-specific propagation characteristics.

N/A

[2017-10-27] The data sheets in the zipped shapefile download file are
updated.

[2017-09-26] The number of localizations has increased by about 400 based
on a more correct method of counting calls.

Four moored hydrophone arrays were used to detect.
Hydrophone, Latitude, Longitude, Depth, Channel
NE 36.43778, -121.94417 52, 1
NW 36.43512, -121.96082 95, 2
SE 36.42679, -121.93743 43, 3
SW 36.41872, -121.94925 79, 4


The original data sheets provided by the provider are included in the
downloadable zip file. To get it, choose "Dataset on Dataset Page" and "As
shapefile" as desired options through the download processes on the
OBIS-SEAMAP Dataset Page.

The sheet labeled M3 contains attributes of each of the M3 calls that were
localized.
JulianTime: Matlab's datenum. Days since January 0, 0000
Latitude: Localized latitude of call
Longitude: Localized longitude of call
Tracked: 0 if not part of a track, 1 if call was part of track
WaterDepth: Depth in meters
RangeXX: Range to each of the hydrophones (NE,NW,SE,SW)
Duration_XX: Duration of call in seconds at each hydrophone
RL_rms_XX: Root Mean Square received level at each hydrophone (µPa)
RL_p2p_XX: Peak-to-Peak received level at each hydrophone (µPa)
SL_rms_XX: Root Mean Square source level at each hydrophone (dB re 1
µPa)
SL_sel_XX: Sound Exposure Level source level at each hydrophone (dB re 1
µPa^2*s)
SL_p2p_XX: Peak-to-Peak source level at each hydrophone (dB re 1 µPa)
PeakFreq_XX: Peak frequency at each hydrophone (Hz)
BW_3dB_XX: 3 dB Bandwidth around peak frequency at each hydrophone
(Hz)
MeanFreq_XX: Mean frequency at each hydrophone (Hz)
SigmaBW_XX: +/- sigma bandwidth at each hydrophone (Hz)

The sheet labeled M1 contains attributes of each of the M1 calls manually
detected on a single hydrophone (NE)
JulianTime: Matlab's datenum. Days since January 0, 0000
IPI: mean inter-pulse interval between pulses within a call
IPI_SD2: variance of inter-pulse intervals between pulses within a call
NumPulses: Total number of pulses within a call
PeakFreq_NE: Peak frequency at NE hydrophone (Hz)
BW3dB_NE: 3 dB Bandwidth around peak frequency at NE hydrophone (Hz)
MeanFreq_NE: Mean frequency at NE hydrophone (Hz)
SigmaBW_NE: +/- sigma bandwidth at NE hydrophone (Hz)

The sheet labeled M3 contains noise levels for every minute of recording
JulianTime: Matlab's datenum. Days since January 0, 0000
NoiseLevel_XX: Root median square noise level for the one minute period
starting at JulianTime (µPa) on the recordings from each hydrophone

Overview

This section explains attributes included in the original dataset. OBIS-SEAMAP restricts the attributes available to the public to date/time, lat/lon and species names/counts only. Should you need other attributes described here, you are encouraged to contact the data provider.

Attributes described below represent those in the original dataset provided by the provider.
All attributes are included in the downloadable file (CSV or ESRI File Geodatabase) for "Complete Set of Dataset".

Attributes in dataset

Attribute (table column)	Description
oid	Unique ID number (generated by OBIS-SEAMAP)
juliantime	Julian time, Matlab
obs_datetime	Date and time of the detection
latitude	Latitude in decimal degrees
longitude	Longitude in decimal degrees
species	Species name recorded
sp_tsn	Taxonomic Serial Number added by OBIS-SEAMAP
obs_count	Group size (blank; presence only)
pruned_ne	1 if call was verified as a gray whale M3 on NE hydrophone, 0 otherwise
tracked	1 if call was part of a track of verified gray whale calls, 0 otherwise
inarray_4hyds	1 if a call was localized within the array and could be verified as a gray whale M3 call when looking at spectrograms from all four hydrophones, 0 otherwise
delaynwne	Time difference of arrival (TDOA) in seconds between NW and NE hydrophones
delaysene	Time difference of arrival (TDOA) in seconds between SE and NE hydrophones
delayswne	Time difference of arrival (TDOA) in seconds between SW and NE hydrophones
samplestart	Detection start time in samples since the start of the deployment
sampleend	Detection end time in samples since the start of the deployment
samplemean	Mean of samplestart and sampleend
lsq	Least-squared difference between the theoretical and measured TDOAs summed over the three TDOA measurements
geom	Geometry field added by OBIS-SEAMAP