Temporal and demographic variation in partial migration of the North Atlantic right whale

Do beluga whales truly migrate? Testing a key trait of the classical migration syndrome

BACKGROUND

Migration enables organisms to access resources in separate regions that have predictable but asynchronous spatiotemporal variability in habitat quality. The classical migration syndrome is defined by key traits including directionally persistent long-distance movements during which maintenance activities are suppressed. But recently, seasonal round-trip movements have frequently been considered to constitute migration irrespective of the traits required to meet this movement type, conflating common outcomes with common traits required for a mechanistic understanding of long-distance movements. We aimed to test whether a cetacean ceases foraging during so-called migratory movements, conforming to a trait that defines classical migration.

METHODS

We used location and dive data collected by satellite tags deployed on beluga whales (Delphinapterus leucas) from the Eastern Beaufort Sea population, which undertake long-distance directed movements between summer and winter areas. To identify phases of directionally persistent travel, behavioural states (area-restricted search, ARS; or Transit) were decoded using a hidden-Markov model, based on step length and turning angle. Established dive profiles were then used as a proxy for foraging, to test the hypothesis that belugas cease foraging during these long-distance transiting movements, i.e., they suppress maintenance activities.

RESULTS

Belugas principally made directed horizontal movements when moving between summer and winter residency areas, remaining in a Transit state for an average of 75.4% (range = 58.5-87.2%) of the time. All individuals, however, exhibited persistent foraging during Transit movements (75.8% of hours decoded as the Transit state had ≥ 1 foraging dive). These data indicate that belugas actively search for and/or respond to resources during these long-distance movements that are typically called a migration.

CONCLUSIONS

The long-distance movements of belugas do not conform to the traits defining the classical migration syndrome, but instead have characteristics of both migratory and nomadic behaviour, which may prove adaptive in the face of unpredictable environmental change. Such patterns are likely present in other cetaceans that have been labeled as migratory. Examination of not only horizontal movement state, but also the vertical behaviour of aquatic animals during directed movements is essential for identifying whether a species exhibits traits of the classical migration syndrome or another long-distance movement strategy, enabling improved ecological inference.

Genetic identifications challenge our assumptions of physical development and mother–calf associations and separation times: a case study of the North Atlantic right whale (Eubalaena glacialis)

While photo-identification is an effective tool to monitor individuals in wild populations, it has limitations. Specifically, it cannot be applied to very young animals before their identifying features have stabilized or to dead, decomposed animals. These shortfalls leave gaps in our understanding of survival, parentage, age structure, physical development, and behavioral variability. Here we report on 13 case studies of North Atlantic right whale, Eubalaena glacialis, calves that required genetics to track their life history data. These case studies revealed unexpected variations in mother–calf associations and separation times, as well as calf physical development. Prior to this study, calves were assumed to have died if their mothers were always alone on the feeding ground in the calf’s birth year. Using genetics and photo-identification, four such calves were discovered to be alive; two of the four possibly weaned earlier than expected at 7.5–8.0 months. To put these early separations in context, photo-identification data were queried and revealed that mothers and calves are seen apart from each other on the feeding grounds in 10–40% of all spring/summer sightings; previously, there were no published data on how often pairs are seen apart in the calf’s birth year. Two dead whales initially logged as calves of the year were discovered to be juveniles, thus allowing skewed survival estimates for calves of the year to be corrected. Genetically sampling animals early in their lives before they disperse or separate from their mothers provides an important means of individual identification at a time when photo-identification is not reliable.

Estimating abundance, temporary emigration, and the pattern of density dependence in a cyclic snowshoe hare (Lepus americanus) population in Yukon, Canada

Estimates of demographic parameters based on capture–mark–recapture (CMR) methods may be biased when some individuals in the population are temporarily unavailable for capture (temporary emigration). We estimated snowshoe hare abundance, apparent survival, and probability of temporary emigration in a population of snowshoe hares (Lepus americanus Erxleben, 1777) in the Yukon (Canada) using Pollock’s robust design CMR model, and population density using spatially explicit CMR models. Survival rates strongly varied among cyclic phases, seasons, and across five population cycles. We found strong evidence that temporary emigration was Markovian (i.e., nonrandom), suggesting that it varied among individuals that were temporary emigrant in the previous sampling period and those that were present in the sampled area. The probability of temporary emigration for individuals that were in the study area during the previous sampling occasion (γ″) varied among cycles. Probability that individuals that were temporarily absent from the sampled area would remain temporary emigrants (γ′) showed strongly seasonal pattern, low in winter and high during summers. Snowshoe hare population density ranged from 0.017 (0.015–0.05) hares/ha to 4.43 (3.90–5.00) hares/ha and showed large-scale cyclical fluctuations. Autocorrelation functions and autoregressive analyses revealed that our study population exhibited statistically significant cyclic fluctuations, with a periodicity of 9–10 years.

Residency, demographics, and movement patterns of North Atlantic right whales Eubalaena glacialis in an offshore wind energy development area in southern New England, USA

Offshore wind energy development is growing quickly around the world. In southern New England, USA, one of the largest commercial offshore wind energy farms in the USA will be established in the waters off Massachusetts and Rhode Island, an area used by the Critically Endangered North Atlantic right whale Eubalaena glacialis. Prior to 2011, little was known about the use of this area by right whales. We examined aerial survey data collected between 2011-2015 and 2017-2019 to quantify right whale distribution, residency, demography, and movements in the region. Right whale occurrence increased during the study period. Since 2017, whales have been sighted in the area nearly every month, with peak sighting rates between late winter and spring. Model outputs suggest that 23% of the species’ population is present from December through May, and the mean residence time has tripled to an average of 13 d during these months. Age and sex ratios of the individuals present in the area are similar to those of the species as a whole, with adult males the most common demographic group. Movement models showed that southern New England is an important destination for right whales, including conceptive and reproductive females, and qualitative observations included animals feeding and socializing. Implementing mitigation procedures in coordination with these findings will be crucial in lessening the potential impacts on right whales from construction noise, increased vessel traffic, and habitat disruption in this region.

Foraging habitat of North Atlantic right whales has declined in the Gulf of St. Lawrence, Canada, and may be insufficient for successful reproduction

Climate-induced changes in calanoid copepod (Calanus spp.) availability in traditional feeding areas might explain why a large proportion of the North Atlantic right whale Eubalaena glacialis population has fed in the Gulf of St. Lawrence (Canada) in recent years. However, little is known about the distribution of copepods in the gulf, and whether their abundance is sufficient to energetically sustain right whales. We used a mechanistic modelling approach to predict areas within the gulf that have foraging potential for adult female right whales, based on the annual energetic needs of resting, pregnant and lactating females, and their theoretical prey density requirements. We identified suitable foraging areas for right whales by coupling a foraging bioenergetics model with a 12 yr data set (2006-2017) describing the abundance and 3-dimensional distribution of late-stage Calanus spp. in the gulf. Prey densities in the southern gulf (from Shediac Valley to the Magdalen Islands) supported all 3 reproductive states in most (≥6) years. However, foraging habitat became progressively sparse in the southern gulf over time, with noticeably less suitable habitat available after 2014. Few other potentially suitable foraging areas were identified elsewhere in the gulf. Overall, the availability of foraging habitat in the gulf varied considerably between years, and was higher for resting females than for pregnant and lactating females. Our findings are consistent with the recent low calving rates, and indicate that prey biomass in the Gulf of St. Lawrence may be insufficient in most years to support successful reproduction of North Atlantic right whales.

REVIEW: Assessing North Atlantic right whale health: threats, and development of tools critical for conservation of the species

Whaling has decimated North Atlantic right whales Eubalaena glacialis (NARW) since the 11th century and southern right whales E. australis (SRW) since the 19th century. Today, NARWs are Critically Endangered and decreasing, whereas SRWs are recovering. We review NARW health assessment literature, NARW Consortium databases, and efforts and limitations to monitor individual and species health, survival, and fecundity. Photographs are used to track individual movement and external signs of health such as evidence of vessel and entanglement trauma. Post-mortem examinations establish cause of death and determine organ pathology. Photogrammetry is used to assess growth rates and body condition. Samples of blow, skin, blubber, baleen and feces quantify hormones that provide information on stress, reproduction, and nutrition, identify microbiome changes, and assess evidence of infection. We also discuss models of the population consequences of multiple stressors, including the connection between human activities (e.g. entanglement) and health. Lethal and sublethal vessel and entanglement trauma have been identified as major threats to the species. There is a clear and immediate need for expanding trauma reduction measures. Beyond these major concerns, further study is needed to evaluate the impact of other stressors, such as pathogens, microbiome changes, and algal and industrial toxins, on NARW reproductive success and health. Current and new health assessment tools should be developed and used to monitor the effectiveness of management measures and will help determine whether they are sufficient for a substantive species recovery.

Satellite derived offshore migratory movements of southern right whales (Eubalaena australis) from Australian and New Zealand wintering grounds

Southern right whales (Eubalaena australis) migrate between Austral-winter calving and socialising grounds to offshore mid- to high latitude Austral-summer feeding grounds. In Australasia, winter calving grounds used by southern right whales extend from Western Australia across southern Australia to the New Zealand sub-Antarctic Islands. During the Austral-summer these whales are thought to migrate away from coastal waters to feed, but the location of these feeding grounds is only inferred from historical whaling data. We present new information on the satellite derived offshore migratory movements of six southern right whales from Australasian wintering grounds. Two whales were tagged at the Auckland Islands, New Zealand, and the remaining four at Australian wintering grounds, one at Pirates Bay, Tasmania, and three at Head of Bight, South Australia. The six whales were tracked for an average of 78.5 days (range: 29 to 150) with average individual distance of 38 km per day (range: 20 to 61 km). The length of individually derived tracks ranged from 645–6,381 km. Three likely foraging grounds were identified: south-west Western Australia, the Subtropical Front, and Antarctic waters, with the Subtropical Front appearing to be a feeding ground for both New Zealand and Australian southern right whales. In contrast, the individual tagged in Tasmania, from a sub-population that is not showing evidence of post-whaling recovery, displayed a distinct movement pattern to much higher latitude waters, potentially reflecting a different foraging strategy. Variable population growth rates between wintering grounds in Australasia could reflect fidelity to different quality feeding grounds. Unlike some species of baleen whale populations that show movement along migratory corridors, the new satellite tracking data presented here indicate variability in the migratory pathways taken by southern right whales from Australia and New Zealand, as well as differences in potential Austral summer foraging grounds.

Phenological changes in North Atlantic right whale habitat use in Massachusetts Bay

The North Atlantic right whale (Eubalaena glacialis) is one of the world's most highly endangered baleen whales, with approximately 400-450 individuals remaining. Massachusetts Bay (MB) and Cape Cod Bay (CCB) together comprise one of seven areas in the Gulf of Maine where right whales seasonally congregate. Here, we report on acoustically detected presence of right whales in MB over a nearly 6 year period, July 2007-April 2013, a time of both rapid ocean warming throughout the Gulf of Maine and apparent changes in right whale migratory dynamics. We applied an automated detection algorithm to assess hourly presence of right whale "up-calls" in recordings from a 19-channel acoustic array covering approximately 4,000 km² in MB. Over the survey, up-calls were detected in 95% of 8 day periods. In each year, as expected, we observed a "peak season" of elevated up-call detections in late winter and early spring corresponding to the season when right whales congregate to feed in CCB. However, we also saw an increase in right whale occurrence during time periods thought to be part of the "off-season." With the exception of 2009-2010, when acoustic presence was unusually low, the mean percent of hours in which up-calls were detected increased every year, both during the peak season (from 38% in 2008 to 70% in 2012), and during the summer-fall season (from 2% in 2007 to 13% in 2012). Over the entire study, the peak season start date varied between 17 January and 26 February. Changes in right whale phenology in MB likely reflect broadscale changes in habitat use in other areas within the species range. This study demonstrates the value of continuous long-term survey datasets to detect and quantify shifts in cetacean habitat use as environmental conditions change and the long-term continued survival of right whales remains uncertain.