Whale Migration Research Articles

First description of migratory behavior of humpback whales from an Antarctic feeding ground to a tropical calving ground

BackgroundDespite exhibiting one of the longest migrations in the world, half of the humpback whale migratory cycle has remained unexamined. Until now, no study has provided a continuous description of humpback whale migratory behavior from a feeding ground to a calving ground. We present new information on satellite-derived offshore migratory movements of 16 Breeding Stock G humpback whales from Antarctic feeding grounds to South American calving grounds. Satellite locations were used to demonstrate migratory corridors, while the impact of departure date on migration speed was assessed using a linear regression. A Bayesian hierarchical state–space animal movement model (HSSM) was utilized to investigate the presence of Area Restricted Search (ARS) en route.Results35,642 Argos locations from 16 tagged whales from 2012 to 2017 were collected. The 16 whales were tracked for a mean of 38.5 days of migration (range 10–151 days). The length of individually derived tracks ranged from 645 to 6381 km. Humpbacks were widely dispersed geographically during the initial and middle stages of their migration, but convened in two convergence regions near the southernmost point of Chile as well as Peru’s Illescas Peninsula. The state–space model showed almost no instances of ARS along the migratory route. The linear regression assessing whether departure date affected migration speed showed suggestive but inconclusive support for a positive trend between the two variables. Results suggestive of stratification by sex and reproductive status were found for departure date and route choice.ConclusionsThis multi-year study sets a baseline against which the effects of climate change on humpback whales can be studied across years and conditions and provides an excellent starting point for the investigation into humpback whale migration.

Modelling collective navigation via non-local communication.

Collective migration occurs throughout the animal kingdom, and demands both the interpretation of navigational cues and the perception of other individuals within the group. Navigational cues orient individuals towards a destination, while it has been demonstrated that communication between individuals enhances navigation through a reduction in orientation error. We develop a mathematical model of collective navigation that synthesizes navigational cues and perception of other individuals. Crucially, this approach incorporates uncertainty inherent to cue interpretation and perception in the decision making process, which can arise due to noisy environments. We demonstrate that collective navigation is more efficient than individual navigation, provided a threshold number of other individuals are perceptible. This benefit is even more pronounced in low navigation information environments. In navigation ‘blindspots’, where no information is available, navigation is enhanced through a relay that connects individuals in information-poor regions to individuals in information-rich regions. As an expository case study, we apply our framework to minke whale migration in the northeast Atlantic Ocean, and quantify the decrease in navigation ability due to anthropogenic noise pollution.

Bowhead and beluga whale acoustic detections in the western Beaufort Sea 2008-2018.

The Distributed Biological Observatory (DBO) was established to detect environmental changes in the Pacific Arctic by regular monitoring of biophysical responses in each of 8 DBO regions. Here we examine the occurrence of bowhead and beluga whale vocalizations in the western Beaufort Sea acquired by acoustic instruments deployed from September 2008-July 2014 and September 2016-October 2018 to examine inter-annual variability of these Arctic endemic species in DBO Region 6. Acoustic data were collected on an oceanographic mooring deployed in the Beaufort shelfbreak jet at ~71.4°N, 152.0°W. Spectrograms of acoustic data files were visually examined for the presence or absence of known signals of bowhead and beluga whales. Weekly averages of whale occurrence were compared with outputs of zooplankton, temperature and sea ice from the BIOMAS model to determine if any of these variables influenced whale occurrence. In addition, the dates of acoustic whale passage in the spring and fall were compared to annual sea ice melt-out and freeze-up dates to examine changes in phenology. Neither bowhead nor beluga whale migration times changed significantly in spring, but bowhead whales migrated significantly later in fall from 2008–2018. There were no clear relationships between bowhead whales and the environmental variables, suggesting that the DBO 6 region is a migratory corridor, but not a feeding hotspot, for this species. Surprisingly, beluga whale acoustic presence was related to zooplankton biomass near the mooring, but this is unlikely to be a direct relationship: there are likely interactions of environmental drivers that result in higher occurrence of both modeled zooplankton and belugas in the DBO 6 region. The environmental triggers that drive the migratory phenology of the two Arctic endemic cetacean species likely extend from Bering Sea transport of heat, nutrients and plankton through the Chukchi and into the Beaufort Sea.

Gear modifications reduced humpback whale entanglements in a commercial rock lobster fishery

AbstractEntanglement of whales in fishing gear occurs globally and where populations are recovering from past exploitation, entanglement frequency is likely to increase. The Western Australian population of humpback whales (Megaptera novaeangliae) is growing rapidly, yet from 1990 to 2010 the number of whales reported entangled in gear from the pot‐based western rock lobster fishery was relatively stable at around one per year. However, from 2010, reported entanglements increased, reaching a maximum of 17 in 2013. This increase occurred immediately after a shift to a year‐round quota‐based fishery that eliminated the annual 4½‐month closure that coincided with the whale migration. Gear modifications that eliminated surface rope, shortened rope lengths, and reduced float numbers were implemented in June 2014 to reduce whale entanglements. The effectiveness of these modifications was evaluated using a Bayesian model that incorporated changes in humpback whale population size, entanglement reporting probability, fishing effort, and whale migration timing. Our analyses indicate that gear modifications reduced entanglement in fishing gear from the rock lobster fishery by at least 25% (with 95% probability), with a median reduction of 64%. The model also showed that the greatest entanglement risk occurs on the northward migration and in water depths of 55–73 m.

Addressing dynamic uncertainty in the whale-watching industry under climate change and system shocks

Whale-watching is a global tourism industry whose annual revenue exceeds two billion dollars. Australia is a key player in this industry, especially on the east and west coast where humpback whales migrate each year between their breeding and feeding grounds. However, the global whale-watching industry faces uncertainty from changing whale migration patterns, with whales progressively ‘arriving’ at the traditional whale-watching areas earlier than in previous years/decades. If the whale-watching industry cannot evolve with these changing dynamics then the arrival of the whales might be missed resulting in a potential loss of revenue. This social-ecological issue has suddenly been exacerbated by the disruption to tourism caused by the global pandemic COVID-19. In this study, we use a systems modelling framework, which combines qualitative and quantitative processes, to evaluate the social-ecological system behaviour of the whale-watching industry. We apply this systems approach to the Gold Coast, one of Australia's premier tourist destinations and home to a vibrant whale-watching industry. The outcome of this systems assessment is that the efficacy of the whale-watching industry is affected through determinants of both supply (ability to respond to changes in whale behaviour) and demand (attractiveness of whale-watching). Furthermore, the recovery time of all tourism after COVID-19 will take years if not decades.

Migration and summer destinations of humpback whales (Megaptera novaeangliae) in the western South Atlantic Ocean

Southern Hemisphere humpback whales (Megaptera novaeangliae) migrate from wintering grounds in tropical latitudes to feeding areas in the Antarctic Ocean. In 2003 and 2005, satellite transmitters were deployed on humpback whales on their wintering grounds off the eastern coast of South America (Breeding Stock A). Seven whales were tracked for a period of 16 to 205 days travelling between 902 and 7,258km. The tracks of these whales provided partial or full information on the migratory schedule, migration routes and location of the feeding ground in the Southern Oceans. Whales departed from the coast of Brazil from late October to late December between 20˚ and 25˚S and gradually moved away from the South American coast as they moved towards high latitudes. They followed a somewhat direct, linear path, with an approximate geographic heading of 170˚. Satellite telemetry data indicated that the migratory corridors are restricted to a relatively narrow (~500–800km) strip in the South Atlantic Ocean. Migration speed to the feeding grounds averaged 80.2km/day and lasted from 40–58 days. Four individuals arrived at the feeding ground located to the north of the South Sandwich Islands, where they were tracked up to 102 days. Movements in this area were erratic at a mean travelling speed of 22.3km/day. Satellite telemetry data indicate that the main feeding grounds for the population wintering off eastern South America lie between 22˚W and 33˚W and in the southern South Atlantic Ocean south of the Antarctic Convergence but north of 60˚S. This is only partially consistent with the currently proposed stock boundaries for this population on the feeding grounds.

Bill Dawbin, Tasman Diplomacy, and the Great South Pacific Humpback Collapse of 1959–62

ABSTRACT The history of industrial whaling in Oceania, along with crucial moments in the diplomatic histories of Australia and New Zealand, sometimes turned on questions of whale behaviour. So did individual human lives. This article puts together the histories of whale communities and the history of cetacean science in order to unravel the meaning of some key moments in the environmental history of the South Pacific, including Oceanian attempts to increase their share of post-war whaling and the subsequent great humpback whale collapse of 1960–62. In the middle of these histories were the efforts of cetologist Bill Dawbin to understand humpback whale migrations in the late 1950s. Interwoven throughout was the crucial fact of humpback whales’ historical split into several different populations and their migratory choices, and the difficulties humans face in understanding these complex and mobile creatures.

Seasonal acoustic presence of blue, fin, and minke whales off the Juan Fernández Archipelago, Chile (2007–2016)

The southeast Pacific (SEP) contains the home ranges of several migratory large whale species, determined largely based on research in coastal waters. These whales’ pelagic seasonal residency is unknown. The Juan Fernandez Archipelago (JFA) is an offshore island in the SEP where passive acoustic monitoring (PAM) data collection is ongoing at the HA03 hydroacoustic station (sample rate of 250 Hz) maintained by the Preparatory Comprehensive Nuclear-Test-Ban Treaty Organization. Six years (2007–2009 and 2014–2016) of PAM data from HA03 were examined for the acoustic presence of Antarctic, Chilean (southeast Pacific 1, southeast Pacific 2), and southeast Indian Ocean blue whale song types; the fin whale 20-Hz song; and minke whale vocalizations. The weekly presence or absence of these six vocalization types was annotated manually by an expert analyst and then averaged across all years. For each vocalization type, the number of weeks per month with presence was averaged over all years. Consistently, we found austral wintertime presence of Antarctic blue, fin, and minke whales; and the year-round presence of Chilean blue whales. Southeast Indian Ocean blue whales were also detected, but very rarely. We discuss the possible seasonal movements of each species or acoustic group in the offshore SEP. This is the first year-round multispecies study of baleen whale in the offshore SEP and provides valuable information for understanding the migrations of endangered baleen whales in this region, highlighting the importance of offshore areas as hotspots for baleen whale biodiversity.

WHAT IDENTIFIES A WHALE BY ITS FLUKE? ON THE BENEFIT OF INTERPRETABLE MACHINE LEARNING FOR WHALE IDENTIFICATION

Abstract. Interpretable and explainable machine learning have proven to be promising approaches to verify the quality of a data-driven model in general as well as to obtain more information about the quality of certain observations in practise. In this paper, we use these approaches for an application in the marine sciences to support the monitoring of whales. Whale population monitoring is an important element of whale conservation, where the identification of whales plays an important role in this process, for example to trace the migration of whales over time and space. Classical approaches use photographs and a manual mapping with special focus on the shape of the whale flukes and their unique pigmentation. However, this is not feasible for comprehensive monitoring. Machine learning methods, especially deep neural networks, have shown that they can efficiently solve the automatic observation of a large number of whales. Despite their success for many different tasks such as identification, further potentials such as interpretability and their benefits have not yet been exploited. Our main contribution is an analysis of interpretation tools, especially occlusion sensitivity maps, and the question of how the gained insights can help a whale researcher. For our analysis, we use images of humpback whale flukes provided by the Kaggle Challenge ”Humpback Whale Identification”. By means of spectral cluster analysis of heatmaps, which indicate which parts of the image are important for a decision, we can show that the they can be grouped in a meaningful way. Moreover, it appears that characteristics automatically determined by a neural network correspond to those that are considered important by a whale expert.

Multi-Decadal Humpback Whale Migratory Route Fidelity Despite Oceanographic and Geomagnetic Change

Understanding how organisms respond to environmental change is one of the most pressing grand challenges of organismal biology. In the vast oceans that cover 71% of Earth’s surface, remote sensing technologies have created unprecedented opportunities to create new knowledge and deliver integrated understandings of marine organism-environment interactions via long-term monitoring. Using historic whaling records and >15 years of satellite-derived data, we show that movement parameters associated with long-distance humpback whale migrations, including utilization of a south-southeast directed migratory corridor, migration path straightness, direction, timing and velocity, have not significantly changed during a period of dynamic oceanographic and geomagnetic conditions. These findings reveal an apparent paradox: humpback whale migrations do not change in a changing ocean. Geophysical analyses of the same humpback whale movements demonstrate that these whales maintained prolonged migratory fidelity to a limited suite of spatiotemporal trajectories through gravitational coordinates, raising the possibility that migratory decisions are relatively insensitive to changing oceanographic and geomagnetic conditions. Our findings highlight the importance of filling the knowledge-gaps that currently limit our ability to understand and anticipate organismal responses to rapidly changing Earth system conditions.

Timing is everything: Drivers of interannual variability in blue whale migration

Blue whales need to time their migration from their breeding grounds to their feeding grounds to avoid missing peak prey abundances, but the cues they use for this are unknown. We examine migration timing (inferred from the local onset and cessation of blue whale calls recorded on seafloor-mounted hydrophones), environmental conditions (e.g., sea surface temperature anomalies and chlorophyll a), and prey (spring krill biomass from annual net tow surveys) during a 10 year period (2008–2017) in waters of the Southern California Region where blue whales feed in the summer. Colder sea surface temperature anomalies the previous season were correlated with greater krill biomass the following year, and earlier arrival by blue whales. Our results demonstrate a plastic response of blue whales to interannual variability and the importance of krill as a driving force behind migration timing. A decadal-scale increase in temperature due to climate change has led to blue whales extending their overall time in Southern California. By the end of our 10-year study, whales were arriving at the feeding grounds more than one month earlier, while their departure date did not change. Conservation strategies will need to account for increased anthropogenic threats resulting from longer times at the feeding grounds.

Adult female-calf acoustic communication signals in migrating east Australian humpback whales

ABSTRACT Humpback whale (Megaptera novaeangliae) calf survival during migration is dependent upon them maintaining contact with their mothers, and acoustics likely plays a significant role in this. Here, we analysed calls (n = 255) produced by migrating humpback whale adult female-calf pairs (n = 15) off the east coast of Australia. First, we identified nine common call types that were then quantitatively separated into two distinct clusters. One cluster contained calls that were considerably longer in duration, lower in frequency, and narrower in bandwidth than those in the second cluster. These are proposed to have been produced by the adult females and calves, respectively. We then compared acoustic features within presumed age class. Minimum, peak, and maximum frequencies were significantly different across both adult females and calves (Kruskal-Wallis, p < 0.05), suggesting that their calls encode socially relevant information regarding physical signaller attributes (i.e. age and body size). This study established a baseline adult female-calf call repertoire produced during the migration of east Australian humpback whales. Potential vocal masking from anthropogenic noise is of particular concern for communications between adult females and their calves, as it may put calves at risk of becoming separated from their mothers.

The North-South migration of humpback whales: Photo-identification match of an individual from the Pacific coast of eastern Hokkaido and breeding areas in Okinawa

The North-South migration of humpback whales: Photo-identification match of an individual from the Pacific coast of eastern Hokkaido and breeding areas in Okinawa

Humpback whales extend their stay in a breeding ground in the Tropical Eastern Pacific

AbstractDuring the austral winter, G-stock humpback whales, Megaptera novaeangliae, migrate to the Tropical Eastern Pacific to breed. To analyse if the whale migration times have changed over time, we analysed 31 years (1988–2018) of arrival and departure times to Gorgona National Park, Colombia, an important breeding site. During this period, whales have significantly changed their arrival time, coming now earlier, but their departure time has not changed significantly. Hence, humpback whales now stay 1 month longer than 31 years ago. Humpbacks arrived in Gorgona at the earliest during the beginning of May and stayed at the most until late December. The change observed in the arrival time to breeding grounds could be related to ice sheet mass changes in autumn in Antarctica and increase in population size over the past decades but we were unable to determine which factor is more important in explaining the observed trend. Management decisions in Colombia need to account for a longer stay, specifically restricting anthropogenic activities from 1May to 31December. We urge other researchers to review their data, in case this shift is evident in other regions and management plans need to be updated.

Stable isotope records of sei whale baleens from Chilean Patagonia as archives for feeding and migration behavior.

Carbon (δ13C) and nitrogen (δ15N) stable isotope variations in baleen plates of sei whales (Balaenoptera borealis) stranded after a mass mortality event in Chilean Patagonia were investigated to assess potential dietary and migratory patterns. Carbon and nitrogen isotope ratios of seven baleens from six individuals were analyzed. The δ13C values ranged from − 19.1 to − 15.9‰ and the δ15N values from 8.7 to 15.4‰. Variations of up to 2.9‰ for δ13C and 5.3‰ for δ15N were observed within one baleen. Carbon and nitrogen isotope records of each baleen were significantly correlated and showed recurring oscillations confirmed by wavelet analyses. Oscillations slightly differed in periodicity indicating variable baleen growth rates between 10.0 and 16.5 cm/year. Food sources of the whales are discussed in terms of available isotope data for potential prey taxa and potential migratory behavior on the basis of latitudinal isotope gradients of particulate organic matter. Cyclicity could be explained by regular migrations of the sei whales from subtropical calving areas to high‐latitude foraging grounds. δ15N records of baleens differed between individuals eventually pointing to diverse feeding and migratory preferences among sei whale individuals.

The use of passive acoustic monitoring as a census tool of gray whale (Eschrichtius robustus) migration

Passive acoustic monitoring adds to knowledge of whale presence and distribution over space and time. The gray whale (Eschrictius robustus) undertakes an annual migration between remote feeding and breeding locales, with its highly sonorous nature suggesting employment of low-frequency calls to be inherent to travel behaviours, perhaps aiding navigation and social cohesion. We consider whether these calling behaviours can be used to better understand the process of migration, where call presence and relative abundance might represent a means to track the progress of migrating whales. Passive acoustic recordings made on the west coast of Vancouver Island, a mid-way point of gray whale migration, were first analysed for abundance over time to examine the progression of migration. Then the acoustic record was compared to shore-based recordings undertaken from Point Vincente, California to better assess their use as a census tool. The timing in peaks of calling, particularly of far-ranging moan-like calls, and shore counts showed a high degree of congruence when considered with a lag time of 8 days to account for travel time between the two survey locations. This suggests that passive acoustic monitoring could complement the long running and shore-based counts in recording annual population movement, and add to our understanding of gray whales on poorly known segments of their migration route or at times when visual observations are not possible.

Behavioural responses of migrating humpback whales to swim-with-whale activities in the Ningaloo Marine Park, Western Australia

Swim-with-whale tourism is a lucrative and rapidly growing industry worldwide. Whale-watching can cause negative effects on the behaviour of targeted animals. Although this is believed to be particularly true for close-up interactions, such as swim-with operations, few empirical studies have investigated this. In 2016, the Western Australian State Government commenced a swim-with humpback whale (Megaptera novaeangliae) trial in the Ningaloo Marine Park, where 11 commercial licences were granted. The swim-with trial was conducted during both the northern and southern whale migration (August to November), during which we assessed potential short-term behavioural effects on humpback whales to swim-with activities. From both an independent research vessel (n = 300 h) and on-board commercial swim-with vessels (n = 357 h), we collected group-follow data (n = 224) on whale behaviour before, during and after swim-with activities. Behavioural effects on whales were investigated, including movement patterns (deviation and directness index, heading, swim speed), surfacing patterns (dive duration and respiration rate) and occurrence of agonistic behaviours. Results showed that the most common type of vessel approach to place swimmers in the water was in the path of whales (89.8% of interactions). During in-path approaches, vessels travelled significantly faster (P = .002) compared to when approaching from the side (side/line abreast approaches). When vessels approached in the whales' path, whales exhibited horizontal and vertical avoidance strategies by adopting a less predictable path (deviating from 32° to 46°), increasing turning angles away from the vessel (heading from 73° to >90°), increasing swim speeds (from 1.68 to 1.89 ms−1), and decreasing the duration of their dives (from 224 to 194 s). Whales displayed a higher frequency of agonistic behaviours when a swim-with vessel was <100 m distance from them compared to >100 m away (P = .011). Young-of-year calves were present during 19.6% (18 of 92) of group-follows that included swim attempts. To reduce potential impacts on whales and increase swimmer safety, we recommend to avoid in-path vessel approaches, not place swimmers in the water with groups of whales that perform agonistic behaviours, and avoid swimming with young-of-year calves.

The effects of vessel noise on the communication network of humpback whales.

Humpback whales rely on acoustic communication to mediate social interactions. The distance to which these social signals propagate from the signaller defines its communication space, and therefore communication network (number of potential receivers). As humpback whales migrate along populated coastlines, they are likely to encounter noise from vessel traffic which will mask their social signals. Since no empirical data exist on baleen whale hearing, the consequences of this are usually assumed, being the modelled reduction in their communication space. Here, the communication space and network of migrating humpback whales was compared in increasing wind-dominated and vessel-dominated noise. Behavioural data on their social interactions were then used to inform these models. In typical wind noise, a signaller's communication space was estimated to extend to 4 km, which agreed with the maximum separation distance between groups that socially interacted. An increase in vessel noise reduced the modelled communication area, along with a significant reduction in group social interactions, probably due to a reduction in their communication network. However, signal masking did not fully explain this change in social behaviour, implying there was also an additional effect of the physical presence of the vessel on signaller and receiver behaviour. Though these observed changes in communication space and social behaviour were likely to be short term and localized, an increase in vessel activity due to tourism and coastal population growth may cause more sustained changes along the humpback whale migration paths.

A citizen science approach to long‐term monitoring of humpback whales (Megaptera novaeangliae) off Sydney, Australia

AbstractThe Cape Solander Whale Migration Study is a citizen science project that annually counts northward migrating humpback whales (Megaptera novaeangliae) off Cape Solander, Sydney, Australia. Dedicated observers have compiled a 20‐year data set (1997–2017) of shore‐based observations from Cape Solander's high vantage point. Using this long‐term data set collected by citizen scientists, we sought to estimate the humpback whale population trend as it continues to recover postexploitation. We estimated an exponential growth rate of 0.099 (95% CI = 0.079–0.119) using a generalized linear model, based on observer effort (number of observation days) and number of whales observed, equating to 10% per annum growth in sightings since 1997. We found that favorable weather conditions for spotting whales off Cape Solander consisted of winds &lt;30 km/hr from a southerly through a north westerly direction. Incidental observations of other cetacean species included the endangered blue whale (Balaenoptera musculus) and data deficient species such as killer whales (Orcinus orca) and false killer whales (Pseudorca crassidens). Citizen science‐based studies can provide a cost‐effective approach to monitoring wildlife over the time necessary to detect change in a population. Information obtained from citizen science projects like this may help inform policy makers responsible for State and Federal protection of cetaceans in Australian waters and beyond.

Timing is everything: Drivers of interannual variability in blue whale migration

The growth and survival of large-bodied marine predators depend on temporal synchrony with resource availability. Baleen whales migrating long distances must therefore respond to interannual variability to avoid a predator-prey mismatch. Highly migratory and acoustically active, blue whales are a model species for investigating the drivers and timing of migration. Using passive acoustic recordings collected from 2007 to 2017, we examined the relationship among migration timing (inferred from blue whale “D” and “B” calls), environmental indices, and measured krill abundance. Arrival to Southern California feeding grounds was correlated with sea surface temperatures (SST) on Costa Rica breeding grounds (r = 0.81, <0.01). Colder SSTs in both regions resulted in early arrival and correlated with greater krill abundance in Southern California (r2 = 0.47, p = 0.03). The correlation between krill abundance and the transition from D to B calls (r2 = 0.55, <0.01) suggested that in high-krill-abundance years, whales switched earlier from social to reproductive-related behavior on their feeding grounds. This phenotypic plasticity may allow blue whales to accommodate environmental variability while balancing important biological needs. However, D call onset dates increased significantly over the 11-year study (r = 0.68, p = 0.03), shifting arrival two months earlier. Longer time on the feeding grounds may increase ship-strike and entanglement risk for this endangered species.