Journal articles

2021

Cioffi WR, Quick NJ, Foley HJ, Waples DM, Swaim ZT, Shearer JM, Webster DL, Friedlaender AS, Southall BL, Baird RW, Nowacek DP, Read AJ. 2021. Adult male Cuvier’s beaked whales (Ziphius cavirostris) engage in prolonged bouts of synchronous diving. Marine Mammal Science. 1-16. [link][github]

Studies of the social behavior of Cuvier's beaked whales (Ziphius cavirostris) are challenging because of their deep-water habitat usually far from shore and the limited time they spend at the surface. The sociality of these deepest diving mammals is of interest, however, especially for our understanding of how social systems evolve in extreme habitats. High levels of scarring suggest that males compete agonistically for access to females and so we predicted that associations among adult males would be unstable due to competitive exclusion. We tested this prediction by evaluating the diving behavior of animals within social groups off Cape Hatteras, North Carolina, considering diving synchrony a proxy for group membership. Using data from satellite-linked depth-recording tags, we found that adult male–male pairs showed extended periods of synchrony in diving behavior, while all pairs that included an adult male with an individual of another age and/or sex dove synchronously for less than a day. We assessed three hypotheses to explain these surprising results: sexual segregation; extended bouts of male–male competition; and the presence of male alliances. Finally, we considered testable predictions to distinguish among these explanations.


Foley HJ, Pacifici K, Baird RW, Webster DL, Swaim ZT, Read AJ. 2021. Residency and movement patterns of Cuvier's beaked whales Ziphius cavirostris off Cape Hatteras, North Carolina, USA. Marine Ecology Progress Series. 660:203-216. [link]

Cuvier's beaked whales (Ziphius cavirostris) are wide-ranging, deep-diving cetaceans that are particularly sensitive to anthropogenic noise. Current stock assessments assume a single population in the western North Atlantic Ocean, but knowledge of the residency patterns and distribution of the species is currently lacking in the region. Here we describe the spatial ecology of 20 Cuvier's beaked whales equipped with satellite-linked tags off Cape Hatteras, North Carolina, U.S.A. from 2014 to 2017. We applied a hierarchical switching state-space model to filter location estimates and define behavioral states of area-restricted search (ARS) and transit. We used kernel density estimation to identify high use areas, and net squared displacement analyses to assess residency. The vast majority (96%) of locations were classified as ARS behavior, suggesting tagged whales allocated much of their time to foraging. Maximum net displacement had a sample median of 50 km, and 81% of individual Cuvier's beaked whales were classified as demonstrating a resident, or 'home range', movement pattern. Overall, our research indicates a localized population of Cuvier's beaked whales occupying the area off Cape Hatteras. The tagged animals demonstrated a small, defined core use area and exhibited little displacement from the region. These patterns of movement and spatial use can inform future conservation and management of this species, which is vulnerable to anthropogenic disturbances caused by several sources, including mid-frequency active sonar (MFAS) and seismic exploration.


Hewitt J, Schick RS, Gelfand AE. 2021. Continuous-Time Discrete-State Modeling for Deep Whale Dives. Journal of Agricultural, Biological and Environmental Statistics. [link]

Understanding unexposed/baseline behavior of marine mammals is required to assess the effects of increasing levels of anthropogenic noise exposure in the marine environment. However, quantifying variation in the baseline behavior of whales is challenging due to the fact that they spend much of their time at depth, and therefore, their diving behavior is not directly observable. Data collection employs tags as measurement devices to record vertical movement. We focus here on satellite tags, which have the advantage of collection over a time window of weeks. The type of data we analyze here suffers the disadvantage of being in the form of depths attached to an arbitrarily created set of depth bins and being sparse in time. We provide a multi-stage generative model for deep dives using a continuous-time discrete-space Markov chain. Then, we build a likelihood, incorporating dive-specific random effects, in order to fit this model to a set of satellite tag records, each consisting of a temporally misaligned collection of deep dives with sparse binned depths for each dive. Through simulation, we demonstrate the ability to recover true model parameters. With real satellite tag records, we validate the model out of sample and also provide inference regarding stage behavior, inter-tag record behavior, dive duration, and maximum dive depth.


2020

Quick NJ, Cioffi WR, Shearer JM, Fahlman A, Read AJ. Extreme diving in mammals: first estimates of behavioural aerobic dive limits in Cuvier's beaked whales. Journal of Experimental Biology. 2020 Sep 15;223(18). [link] [github ] [video ]

We analysed 3680 dives from 23 satellite-linked tags deployed on Cuvier's beaked whales to assess the relationship between long duration dives and inter-deep dive intervals and to estimate aerobic dive limit (ADL). The median duration of presumed foraging dives was 59min and 5% of dives exceeded 77.7min. We found no relationship between the longest 5% of dive durations and the following inter-deep dive interval nor any relationship with the ventilation period immediately prior to or following a long dive. We suggest that Cuvier's beaked whales have low metabolic rates, high oxygen storage capacities and a high acid-buffering capacity to deal with the by-products of both aerobic and anaerobic metabolism, which enables them to extend dive durations and exploit their bathypelagic foraging habitats.


2019

Quick NJ, Cioffi WR, Shearer J, Read AJ. Mind the gap—optimizing satellite tag settings for time series analysis of foraging dives in Cuvier’s beaked whales (Ziphius cavirostris). Animal Biotelemetry. 2019 Dec;7(1):1-4. [link (open access)]

Background

Studies of deep-diving beaked whales using Argos satellite-linked location-depth tags frequently return data with large gaps in the diving record. We document the steps taken to eliminate these data gaps and collect weeks of continuous time series data for a behavioral response study that took place in 2017. We used baseline data collected from 2014 to 2016 to analyze message diagnostics, and assess our current programming schedule using a multiple criteria decision making matrix (MCDM), as a robust way to develop a new sampling regime.

Results

The MCDM approach suggested animal behavior and the quantity of data collected were the main causes of gaps in our baseline tag records. We implemented a new sampling regime to sample only long-duration, presumed foraging dives, simultaneously increasing temporal coverage of each individual message and reducing the number of messages by 50%. The reduction of gaps increased the data available for continuous time series analysis from an average of just over 2 days and 13.5 sequential presumed foraging dives in our baseline tags to just over 19 days and 118 sequential presumed foraging dives in tags deployed during the 2017 behavioral response study.

Conclusions

We demonstrate that a critical approach, based on analysis of baseline data and question-driven weighted criteria, enabled the reduction and even elimination of gaps in the diving records of these tags. This approach enabled us to develop specific settings for our tags to ensure that our data collection was optimized for statistical analysis of the specific hypotheses we were testing.


Schick RS, Bowers M, DeRuiter S, Friedlaender A, Joseph J, Margolina T, Nowacek DP, Southal BL. Accounting for Positional Uncertainty When Modeling Received Levels for Tagged Cetaceans Exposed to Sonar. Aquatic Mammals. 2019 Dec 1;45(6). [link]

Exposure to anthropogenic sound can have a range of negative behavioral and physical effects on marine species and is of increasing ecological and regulatory concern. In particular, the response of marine mammals, and notably the family of cryptic deep-diving beaked whales, to military sonar is a timely and complex issue. To make inference on aspects of response by individual whales to noise of any type, it is critical to either measure or systematically estimate what received levels (RLs) the animal actually experienced. Various tools and techniques exist to monitor RLs and associated responses, each with advantages and disadvantages. Most behavioral response studies to date have used relatively short-term (hours to a few days), high-resolution acoustic tags that provide direct RL measurements. Because of their short duration, these tags do not allow for assessments of longer-duration baseline behavior before and following a disturbance that may tell us more about the nature of response within a broader context for tagged individuals. In contrast, longer-duration (weeks to months), satellite-transmitting tags lack high-resolution kinematic data and the ability to directly measure RL. Herein, we address these issues and efforts to derive robust statistical RL characterizations using animal movement and fine-scale, site-specific sound propagation modeling for longer-duration tags in the context of a behavioral response study off Cape Hatteras, North Carolina. In the autumn of 2017, we tagged nine Cuvier’s beaked whales and three short-finned pilot whales and conducted controlled exposure experiments using simulated and operational military mid-frequency active sonar. We used sound propagation modeling methods and modeled positions of individual animals to estimate RLs in four dimensions and to statistically describe uncertainty within volumes of water space where animals were predicted to occur during exposure periods. By properly accounting for positional error in this study, it is clear that previous studies using single median RL estimates drastically underestimate the full range of plausible values; ranges in estimated RLs here often exceeded 40 dB. We also demonstrate how ancillary data from visual focal follows of tagged individuals can significantly narrow estimated RL ranges. Further, we compared measured RLs on a calibrated acoustic tag to modeled RLs at the same position to evaluate our volumetric modeling results. While satellite tags record data over longer time frames, their substantial geospatial error coupled with the unique deep-diving behavior of beaked whales means that estimates of RL can vary broadly and, consequently, that single point estimates from less robust approaches may be substantially in error. Accounting for this uncertainty using robust statistical modeling is critical to fairly characterize variance and effectively assess exposure-response relationships.


Shearer JM, Quick NJ, Cioffi WR, Baird RW, Webster DL, Foley HJ, Swaim ZT, Waples DM, Bell JT, Read AJ. Diving behaviour of Cuvier's beaked whales (Ziphius cavirostris) off Cape Hatteras, North Carolina. Royal Society open science. 2019 Feb 6;6(2):181728. [link (open access)]

Cuvier's beaked whales exhibit exceptionally long and deep foraging dives. The species is little studied due to their deep-water, offshore distribution and limited time spent at the surface. We used LIMPET satellite tags to study the diving behaviour of Cuvier's beaked whales off Cape Hatteras, North Carolina from 2014 to 2016. We deployed 11 tags, recording 3242 h of behaviour data, encompassing 5926 dives. Dive types were highly bimodal; deep dives (greater than 800 m, n = 1408) had a median depth of 1456 m and median duration of 58.9 min; shallow dives (50–800 m, n = 4518) were to median depths of 280 m with a median duration of 18.7 min. Most surface intervals were very short (median 2.2 min), but all animals occasionally performed extended surface intervals. We found no diel differences in dive depth or the percentage of time spent deep diving, but whales spent significantly more time near the surface at night. Other populations of this species exhibit similar dive patterns, but with regional differences in depth, duration and inter-dive intervals. Satellite-linked tags allow for the collection of long periods of dive records, including the occurrence of anomalous behaviours, bringing new insights into the lives of these deep divers.


Annual reports

2020 - Southall et al. 2021 [Supplementary Figures ]

2019 - Southall et al. 2020

2018 - Southall et al. 2019

2017 - Southall et al. 2018