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. 2014 Mar 26;9(3):e92633.
doi: 10.1371/journal.pone.0092633. eCollection 2014.

First long-term behavioral records from Cuvier's beaked whales (Ziphius cavirostris) reveal record-breaking dives

Gregory S Schorr  1 , Erin A Falcone  1 , David J Moretti  2 , Russel D Andrews  3
Affiliations

First long-term behavioral records from Cuvier's beaked whales (Ziphius cavirostris) reveal record-breaking dives

Gregory S Schorr et al. PLoS One. .

Abstract

Cuvier's beaked whales (Ziphius cavirostris) are known as extreme divers, though behavioral data from this difficult-to-study species have been limited. They are also the species most often stranded in association with Mid-Frequency Active (MFA) sonar use, a relationship that remains poorly understood. We used satellite-linked tags to record the diving behavior and locations of eight Ziphius off the Southern California coast for periods up to three months. The effort resulted in 3732 hr of dive data with associated regional movements--the first dataset of its kind for any beaked whale--and included dives to 2992 m depth and lasting 137.5 min, both new mammalian dive records. Deep dives had a group mean depth of 1401 m (s.d. = 137.8, n = 1142) and duration of 67.4 min (s.d. = 6.9). The group mean time between deep dives was 102.3 min (s.d. = 30.8, n = 783). While the previously described stereotypic pattern of deep and shallow dives was apparent, there was considerable inter- and intra-individual variability in most parameters. There was significant diel behavioral variation, including increased time near the surface and decreased shallow diving at night. However, maximum depth and the proportion of time spent on deep dives (presumed foraging), varied little from day to night. Surprisingly, tagged whales were present within an MFA sonar training range for 38% of days locations were received, and though comprehensive records of sonar use during tag deployments were not available, we discuss the effects frequent acoustic disturbance may have had on the observed behaviors. These data better characterize the true behavioral range of this species, and suggest caution should be exercised when drawing conclusions about behavior using short-term datasets.

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Conflict of interest statement

Competing Interests: DJM is employed by the United States Navy, though in a different division than the funders of this work. No part of the analysis or write up was influenced by the funders or sponsors of the research. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials.

Figures

Figure 1
Figure 1. Map of the study area displaying one daily position estimate of each tagged whale.
All eight whales were tagged within the Southern California Anti-submarine Warfare Range (outlined in solid white). Tagged whales were within the San Nicolas Basin for 51% of all days tags transmitted, and within the SOAR boundaries for 71% of the days when in the basin, suggesting site fidelity to the MFA sonar training range. Inset map shows the entire track-line of each tagged whale with the primary map region indicated by a dashed box. The SOCAL Range Complex, which encompasses all areas of authorized MFA sonar use , is lightly shaded and outlined in black in the inset map. Map created using Mysticetus Observation System, v1.8.0.124 (Entiat River Technologies, Preston, WA, USA).
Figure 2
Figure 2. Classification of dive type.
(A)Sample dive trace from Zc015 containing two reclassified dives. The four consecutive dives in the series beginning at 07∶49 were all unusually long for shallow dives, but unusually shallow for deep dives, and thus difficult to classify using depth and duration alone. The K-means cluster analysis for Zc015 (B) classified the two dives indicated by yellow circles in each panel as deep dives and the other two as shallow dives. All four of these dives in figure A were similar and presumably of the same class. Other deep dives in the adjacent period were up to 1000 m deeper than these two dives, and four deep dives in series would be exceedingly rare based on this dataset and prior studies. Thus, we believe all four of these dives were much more likely to be atypically long, shallow dives, and the two indicated with yellow circles were reclassified as such.
Figure 3
Figure 3. Variation in diving behavior.
(A) A 48-hr BL dive trace from Zc015, illustrating the pattern of “deep” and “shallow” dives. Darkened areas represent night. The gap in the dive record during the first night period reflects data that were not received via Argos. (B) Box plot of deep dive duration by day for the first 26 days of Zc015. The dashed line represents the overall median dive duration for Zc015 of 64.0 min. (C) Histogram plot of “deep” dive duration by individual, demonstrating the variability both within and among individuals. The solid black line connects the median value for each individual; the dashed lines connect the upper and lower 25th percentiles.
Figure 4
Figure 4. Box plot of surfacing bout duration by surfacing type, by individual.
First Surfacing bouts (FS), Intermediate Surfacing bouts (IS), Terminal surfacing bouts (TS), and Single Surfacing bouts between deep dives (SS). Only the five tags using the wet/dry sensor are included (Table 2). Zc019 had only one SS, and Zc017 did not conduct any consecutive deep dives. Boxes represent the median and inter-quartile range, with whiskers at 1.5 times the inter-quartile range. Severe outliers are indicated by plus symbols. Surfacing bouts were typically very short, however occasional severe outliers (representing unusually long surfacing bouts) occurred in all surfacing bout types.
Figure 5
Figure 5. Distance to deployment location from day of deployment, by individual.
Distance from deployment was calculated using the best location per day, as determined by the Douglas Argos Filter . All individuals were tagged on the SOAR MFA sonar training range, and most remained in close proximity to the area in which they were tagged. While Zc015 made an extra-regional excursion over 450 km away, she returned to within 5 km of her tagging location.
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