DOI: 10.5061/dryad.4tmpg4fg2
title: Daily and hourly sperm whale presence in the Gulf of Alaska and Bering Sea/Aleutian Islands

description: Sperm whales exhibit sexual dimorphism and sex-specific latitudinal
 segregation. Females and their young form social groups and are usually
 found in temperate and tropical latitudes, while males forage at higher
 latitudes. Historical whaling data and rare sightings of social groups in
 high latitude regions of the North Pacific, such as the Gulf of Alaska
 (GOA) and Bering Sea/Aleutian Islands (BSAI), suggest a more nuanced
 distribution than previously understood. Sperm whales are the most sighted
 and recorded cetacean in marine mammal surveys in these regions but
 capturing their demographic composition and habitat use has proven
 challenging. This study detects sperm whale presence using passive
 acoustic data from seven sites in the GOA and BSAI from 2010 to 2019.
 Differences in click characteristics between males and females (i.e.,
 inter-click and inter-pulse interval) was used as a proxy for animal
 size/sex to derive time series of animal detections. Generalized additive
 models with generalized estimation equations demonstrate how
 spatiotemporal patterns differ between the sexes. Social groups were
 present at all recording sites with the largest relative proportion at two
 seamount sites in the GOA and an island site in the BSAI. We found that
 the seasonal patterns of presence varied for the sexes and between the
 sites. Male presence was highest in the summer and lowest in the winter,
 conversely, social group peak presence was in the winter for the BSAI and
 in the spring for the GOA region, with the lowest presence in the summer
 months. This study demonstrates that social groups are not restricted to
 lower latitudes and capture their present-day habitat use in the North
 Pacific. It highlights that sperm whale distribution is more complex than
 accounted for in management protocol and underscores the need for improved
 understanding of sperm whale demographic composition to better understand
 the impacts of increasing anthropogenic threats, particularly climate
 change.
description: Passive acoustic recordings were collected at seven sites, two
 along the BSAI and five in the GOA, between June 2010 and September 2019
 (Figure 1; Table 1). Each site had from one to ten deployments which
 resulted in ~12 years of cumulative recordings between all sites.
 Individual site temporal coverage varied due to project goals, recorder
 battery life, data storage space, and duty cycle regimes as detailed
 below. The sites were in moderate water depths of 780 m to 1200 m (Table
 1). We used High-frequency Acoustic Recording Packages (HARPs; Wiggins
 & Hildebrand 2007) with a sampling rate of 200 kHz which can
 detect the high-frequency echolocation clicks of odontocetes, including
 but not limited to, sperm whales. Sperm whale
 echolocation clicks were detected using the multi-step approach described
 in Solsona-Berga <em>et al.</em> 2020 (appendix). These clicks
 have multiple pulses (Backus & Schevill 1966), 2-9 ms apart,
 depending upon the size of the animal (Norris & Harvey 1972). As a
 result, the detector had a lockout for clicks separated by less than 30 ms
 to avoid multiple detections of a single click. Band passing the data
 (5-95 kHz) minimized the effects of low-frequency noise from vessels,
 weather, or instrument self-noise on detections, but allowed for detection
 of the echolocation clicks of toothed whales. The Power Spectral Density
 (PSD) of detected signals was calculated with the
 <em>Pwelch</em> method (MATLAB, MathWorks Inc. 2016) using 4
 ms of the waveform and a 512-point Hann window with 50% overlap (Welch
 1967). Instrument specific full-system transfer functions were applied to
 account for the hydrophone sensor response, signal conditioning
 electronics, and analog-to-digital conversion. To provide a consistent
 detection threshold, only clicks exceeding peak-to-peak (pp) sound
 pressure level (RL) of at least 125 dBpp re 1 µPa were analyzed. This
 threshold was chosen to eliminate noise signals and the echolocation
 clicks of other odontocetes, while retaining sperm whale clicks.
 Sperm whale echolocation clicks can be confused with the
 impulsive signals from ship propeller cavitation. An automated classifier
 developed by Solsona-Berga <em>et al.</em> 2020 (appendix) was
 used to exclude periods of ship passages. The classifier identified
 potential ship passages from long-term spectral averages (LTSA), which are
 long duration spectrograms (Wiggins & Hildebrand 2007). Further
 averaging was calculated as Average Power Spectral Densities (APSD) per
 2-hour blocks over low (1-5 kHz), medium (5-10 kHz), and high (10-50 kHz)
 frequency bands with 100 Hz bins and 50% overlap. Using received sound
 levels, transient ship passage signals were separated from odontocete
 echolocation clicks and weather events. A trained analyst manually
 reviewed identified ship passages using the MATLAB-based custom software
 program <em>Triton</em> (Wiggins & Hildebrand 2007).
 Ship passage times were removed from further analysis and considered time
 periods with no effort. Instrument self-noise and the
 echolocation clicks of other odontocetes were also removed to reduce the
 number of false positive detections. A classifier using spectral click
 shape was implemented, taking advantage of a sperm whale click’s distinct
 low-frequency spectral shape to remove dissimilar clicks by delphinid and
 beaked whales, which typically have higher frequencies (Solsona-Berga
 <em>et al.</em> 2020). The remaining acoustic encounters
 containing putative sperm whale echolocation clicks were manually reviewed
 with <em>DetEdit</em>, a custom, MATLAB-based graphical user
 interface (GUI) software program used to view, evaluate, and edit
 automatic detections (Solsona-Berga <em>et al.</em> 2020).
   Histograms of ICI provide a visualization that can be
 used to indicate sperm whale size and sex (Solsona-Berga <em>et
 al.</em> 2022). A plot of concatenated histograms, referred to as
 ICIgrams, was annotated and categorized for each time period at each site.
 Examples of the ICIgram GUI can be found in Solsona-Berga <em>et
 al.</em> (2022). We used three ICI groups to correspond to three
 size classes (Fig. 2, bottom panels), as per Solsona-Berga <em>et
 al.</em> (2022). Detections with a modal ICI of 0.6 s or less were
 presumed to be females and their young, hereinafter referred to as Social
 Groups. Detections with a modal ICI of 0.8 s and greater were presumed to
 be adult males, hereinafter referred to as Adult Males. The detections
 with a modal ICI between the Social Groups and Adult Males (&lt; 0.6 s
 and &gt; 0.8 s) could contain large females or juvenile males,
 hereinafter referred to as Mid-Size. Sperm whale click
 detections were binned into 5-minute intervals. The mean daily presence
 per week was calculated by summing the number of 5-minute bins with
 detections for each size class and for each site. Since not all sperm
 whale clicks were categorized into a size class, a time series of
 unclassified clicks was also included for each site. The ratio of hourly
 as well as daily presence for each size class was calculated and displayed
 with Venn diagrams to show the overlap of the classes at each site.
 Finally, these data were grouped into one-hour bins for statistical
 modeling, as described in the next section. The one-hour bins were chosen
 as a compromise to maintain data granularity while ensuring at least 30
 minutes of recording effort in each one-hour bin for the two duty-cycled
 deployments. 
description: # Daily and Hourly Sperm Whale Presence in the Gulf of Alaska and Bering
 Sea/Aleutian Islands --- These .csv files contain compiled data from
 high-frequency acoustic recording package (HARP; Wiggins & Hildebrand,
 2007) deployments at 7 acoustic monitoring sites in the Gulf of Alaska and
 Bering Sea/Aleutian Islands. **AllSites_DayData. csv**: contains daily
 presence information from all seven deployments with the following
 variables: tbin - day (dd/mm/YYYY) Count_Click - number of sperm whale
 clicks detected Count_Bin - number of 5-min bins with sperm whale
 detections Effort_Bin - number of 5-min bins with recording effort
 Effort_Sec - number of seconds with recording effort Max_Effort_Bin -
 maximum number of 5-min bins Max_Effort_Sec - maximum number of seconds
 SocialGroup_Bin - number of 5-min bins categorized as Social Groups
 MidSize_Bin - number of 5-min bins categorized as Mid-Size AdultMale_Bin -
 number of 5-min bins categorized as Adult Male Site - which site does the
 data correspond to Region - which region does the data correspond to
 Julian - which julian day does the data correspond to PreAbs - binary
 presence(1)/absence(0) **AllSites_HourlyBinaryData.csv:** contains hourly
 presence information from all seven deployments with the following
 variables: tbin - hour (dd/mm/YYYY hh:mm:ss) Count_Click - number of sperm
 whale clicks detected Count_Bin - number of 5-min bins with sperm whale
 detections Effort_Bin - number of 5-min bins with recording effort
 Effort_Sec - number of seconds with recording effort Max_Effort_Bin -
 maximum number of 5-min bins Max_Effort_Sec - maximum number of seconds
 PreAbs - binary presence(1)/absence(0) for all sperm whales
 PreAbs_SocialGroups - binary presence(1)/absence(0) for Social Groups
 PreAbs_MidSize - binary presence(1)/absence(0) for Mid-Size
 PreAbs_AdultMales - binary presence(1)/absence(0) for Adult Males
 SocialGroup_Bin - number of 5-min bins categorized as Social Groups
 MidSize_Bin - number of 5-min bins categorized as Mid-Size Male_Bin -
 number of 5-min bins categorized as Adult Males Site - which site does the
 data correspond to Region - which region does the data correspond to
 Julian - which julian day does the data correspond to