Non-lethal entanglement of humpback whales (Megaptera novaeangliae) in fishing gear in northern Southeast Alaska

Aim Entanglement in fishing gear is recognized as a potentially significant source of serious injury and mortality for humpback whales (Megaptera novaeangliae) in some parts of their range. In recent years, the number of humpback whales reported to have been entangled in Alaska has increased. In 2003–04 we quantified the prevalence of non‐lethal entanglements of humpback whales in northern Southeast Alaska (SEAK) with the ultimate goal of informing management discussions of the entanglement issue for the Central North Pacific stock of humpback whales. Location The near‐shore waters of northern Southeast Alaska. Methods We photographed individual humpback whales’ caudal peduncles as they dived and then examined the photographs for scars indicative of a previous entanglement. Results The percentage of whales assessed to have been non‐lethally entangled at some time in their lives ranged from 52% (minimal estimate) to 71% (conditional estimate) to 78% (maximal estimate). Of these, the conditional estimate is recommended because it is based solely on unambiguous scars. Eight per cent of the whales in one portion of the study area (Glacier Bay/Icy Strait) acquired new entanglement scars between 2003 and 2004, although the sample size was small. Calves were less likely than older whales to have entanglement scars, and males may be at higher risk than females. Whales with more photographs and/or photographic coverage may be more likely to be assessed as having been entangled than whales with fewer photographs and/or coverage. Main conclusions Caudal peduncle scars reveal that the majority of humpback whales in northern SEAK have been entangled. Comparison with statistics on reported entanglements suggests that most whales apparently shed the gear on their own, unless humans are disentangling whales much more often than is reported. While cumulative estimates of the percentage of whales with entanglement scars (e.g. the conditional estimate) provide useful baseline information, future efforts should focus on monitoring the annual rate of entanglement scar acquisition as a more powerful measure of contemporary entanglement rates. Our findings indicate that entanglement of humpback whales in fishing gear in SEAK is a management issue warranting increased attention. A proactive approach is needed to address the problem and to identify and implement preventive measures.     

Incorporating tides into the acoustic ecology of humpback whales

North Pacific humpback whales (Megaptera novaeangliae) migrate annually to foraging grounds in Southeast Alaska that are characterized by semidiurnal tidal cycles. Tidal activity is an important driver of marine mammal behavior on foraging grounds, but is often omitted in studies of acoustic ecology. To better understand the role of sound in this vocal species we investigated the influence of tidal height and direction on humpback whale nonsong calling behavior in Frederick Sound and described new call types for this population. The likelihood of detecting a call from the low‐frequency‐harmonic, pulsed, or noisy‐complex call classes was independent of tidal activity. The likelihood of detecting a call from the tonal call class, and a feeding call in particular, was 2.1 times higher during flood tides than during ebb tides (95% CI 1.1–4.4). This likely reflects an indirect relationship between humpback whale foraging and tides.     

Morphological specializations of baleen whales associated with hydrodynamic performance and ecological niche

Feeding behavior, prey type, and habitat appear to be associated with the morphological design of body, fluke, and flippers in baleen whales. Morphometric data from whaling records and recent stranding events were compiled, and morphometric parameters describing the body length, and fluke and flipper dimensions for an "average" blue whale Balaenoptera musculus, humpback whale Megaptera novaeangliae, gray whale Eschrichtius robustus, and right whale Eubalaena glacialis were determined. Body mass, body volume, body surface area, and fluke and flipper surface areas were estimated. The resultant morphological configurations lent themselves to the following classifications based on hydrodynamic principles: fast cruiser, slow cruiser, fast maneuverer, and slow maneuverer. Blue whales have highly streamlined bodies with small, high aspect ratio flippers and flukes for fast efficient cruising in the open ocean. On the other hand, the rotund right whale has large, high aspect ratio flukes for efficient slow speed cruising that is optimal for their continuous filter feeding technique. Humpbacks have large, high aspect ratio flippers and a large, low aspect ratio tail for quick acceleration and high-speed maneuvering which would help them catch their elusive prey, while gray whales have large, low aspect ratio flippers and flukes for enhanced low-speed maneuvering in complex coastal water habitats.     

Distributional patterns of humpback whales (Megaptera novaeangliae) along the Newfoundland East Coast reflect their main prey,capelin (Mallotus villosus)

On the Newfoundland foraging ground, humpback whales (Megaptera novaeangliae) primarily consume capelin (Mallotus villosus), which experienced a population collapse in the early 1990s, associated with altered timing of spawning and spawning migration. We examined whether humpback whale movement and distribution match these prey changes. Combining tour company whale sighting reports and photographs, citizen science reports of capelin spawning and scientific monitoring, whales were found to move northward along the east coast and whale aggregation presence within bays was associated with spawning capelin presence, being later in northerly bays. Whale aggregations arrived 8–20 days later than spawning capelin in northern bays, however, suggesting inconsistent tendencies to track high abundance spawning capelin aggregations during migration. Repeated scientific surveys during July–August 2009, 2010, 2012, 2014–2017, within a biological hotspot associated with capelin spawning sites in Notre Dame Bay, revealed that whale presence was influenced by the date of capelin spawning rather than capelin abundance metrics (i.e., biomass, number of shoals, shoal density, shoal area). A photo-identification catalog compiled during July–August, 2003–2017, revealed a 22% return rate of whales to the hotspot. Overall, findings suggest that capelin spawning sites are important foraging areas for humpback whales in coastal Newfoundland under these altered prey conditions.     

POPULATION CHARACTERISTICS AND MIGRATION OF SUMMER AND LATE-SEASON HUMPBACK WHALES (MEGAPTERA NOVAEANGLIAE) IN SOUTHEASTERN ALASKA

A total of 326 humpback whales (Megaptera novaeangliae) were individually identified in southeastern Alaska during five summer seasons (July to September) and four late seasons (November to February) spanning the years 1979 to 1983. Peak numbers of whales were found late in August or early in September. Whales arrived 1–2 wk later in 1982 than in 1981. Whales sighted in both the summer and late seasons of 1981 and 1982 remained about 3.7 mo and one whale remained for at least 4.9 mo. Humpback whales from southeastern Alaska wintered in Hawaiian or Mexican waters, but generally did not travel to other feeding regions. The most rapid migratory transit between Hawaii and southeastern Alaska was 79 d. Based on mark-recapture analyses of the photographic data, we estimate a population of 270–372 whales in the southeastern Alaska feeding herd.     

Evidence for the functions of surface‐active behaviors in humpback whales (Megaptera novaeangliae)

As part of their social sound repertoire, migrating humpback whales (Megaptera novaeangliae) perform a large variety of surface‐active behaviors, such as breaching and repetitive slapping of the pectoral fins and tail flukes; however, little is known about what factors influence these behaviors and what their functions might be. We investigated the potential functions of surface‐active behaviors in humpback whale groups by examining the social and environmental contexts in which they occurred. Focal observations on 94 different groups of whales were collected in conjunction with continuous acoustic monitoring, and data on the social and environmental context of each group. We propose that breaching may play a role in communication between distant groups as the probability of observing this behavior decreased significantly when the nearest whale group was within 4,000 m compared to beyond 4,000 m. Involvement in group interactions, such as the splitting of a group or a group joining with other whales, was an important factor in predicting the occurrence of pectoral, fluke, and peduncle slapping, and we suggest that they play a role in close‐range or within‐group communication. This study highlights the potentially important and diverse roles of surface‐active behaviors in the communication of migrating humpback whales.     

NORTH PACIFIC HUMPBACK WHALE SONGS: A COMPARISON OF SOUTHEAST ALASKAN FEEDING GROUND SONGS WITH HAWAIIAN WINTERING GROUND SONGS

Humpback whales sing long, complex songs on their wintering grounds. On 25 August 1979 and 3 September 1981, we made recordings of humpback whale songs in southeastern Alaska, showing that humpback whales also sing on the summer feeding grounds. Both these Alaskan samples are songs in that they are repeating cyclical sound patterns and follow the known structure for humpback whale song. The Alaskan songs contain all the same material sung in the same order as that heard off Mexico and Hawaii in the surrounding wintering seasons. However, song, theme and some phrase durations are abbreviated in the Alaskan songs. The recording of these two songs represents the full sample of song recorded from 155 days over five years of attempting to record humpback whale song in Alaskan waters.     

Future recovery of baleen whales is imperiled by climate change

Historical harvesting pushed many whale species to the brink of extinction. Although most Southern Hemisphere populations are slowly recovering, the influence of future climate change on their recovery remains unknown. We investigate the impacts of two anthropogenic pressures—historical commercial whaling and future climate change—on populations of baleen whales (blue, fin, humpback, Antarctic minke, southern right) and their prey (krill and copepods) in the Southern Ocean. We use a climate–biological coupled “Model of Intermediate Complexity for Ecosystem Assessments” (MICE) that links krill and whale population dynamics with climate change drivers, including changes in ocean temperature, primary productivity and sea ice. Models predict negative future impacts of climate change on krill and all whale species, although the magnitude of impacts on whales differs among populations. Despite initial recovery from historical whaling, models predict concerning declines under climate change, even local extinctions by 2100, for Pacific populations of blue, fin and southern right whales, and Atlantic/Indian fin and humpback whales. Predicted declines were a consequence of reduced prey (copepods/krill) from warming and increasing interspecific competition between whale species. We model whale population recovery under an alternative scenario whereby whales adapt their migratory patterns to accommodate changing sea ice in the Antarctic and a shifting prey base. Plasticity in range size and migration was predicted to improve recovery for ice‐associated blue and minke whales. Our study highlights the need for ongoing protection to help depleted whale populations recover, as well as local management to ensure the krill prey base remains viable, but this may have limited success without immediate action to reduce emissions.     

Cetaceans of Southeast Alaska: distribution and seasonal occurrence

Aim To assess the distribution, group size, seasonal occurrence and annual trends of cetaceans. Location The study area included all major inland waters of Southeast Alaska. Methods Between 1991 and 2007, cetacean surveys were conducted by observers who kept a constant watch when the vessel was underway and recorded all cetaceans encountered. For each species, we examined distributional patterns, group size, seasonal occurrence and annual trends. Analysis of variance (anova F) was used to test for differences in group sizes between multiple means, and Student’s t‐test was used to detect differences between pairwise means. Cetacean seasonal occurrence and annual trends were investigated using a generalized linear model framework. Results Humpback whales (Megaptera novaeangliae) were seen throughout the region, with numbers lowest in spring and highest in the fall. Fin whale (Balaenoptera physalus) and minke whale (Balaenoptera acutorostrata) distributions were more restricted than that reported for humpback whales, and the low number of sightings precluded evaluating seasonal trends. Three killer whale (Orcinus orca) eco‐types were documented with distributions occurring throughout inland waters. Seasonal patterns were not detected or could not be evaluated for resident and offshore killer whales, respectively; however, the transient eco‐type was more abundant in the summer. Dall’s porpoise (Phocoenoides dalli) were distributed throughout the region, with more sightings in spring and summer than in fall. Harbour porpoise (Phocoena phocoena) distribution was clumped, with concentrations occurring in the Icy Strait/Glacier Bay and Wrangell areas and with no evidence of seasonality. Pacific white‐sided dolphins (Lagenorhynchus obliquidens) were observed only occasionally, with more sightings in the spring. For most species, group size varied on both an annual and seasonal basis. Main conclusions Seven cetacean species occupy the inland waters of Southeast Alaska, with distribution, group size, seasonal occurrence and annual trends varying by species. Future studies that compare spatial and temporal patterns with other features (e.g. oceanography, prey resources) may help in identifying the key factors that support the high density and biodiversity of cetaceans found in this region. An increased understanding of the region’s marine ecology is an essential step towards ensuring the long‐term conservation of cetaceans in Southeast Alaska.     

Determination of steroid hormones in whale blow: It is possible

The feasibility of using analysis of hormone content of whale blow samples to assess reproductive function is addressed. A suitable collection method and analytical technique using liquid chromatography-mass spectrometry (LC-MS) has been developed. Blow samples were collected opportunistically from free-ranging humpback whales ( Megaptera novaeangliae ) ( n = 35) and North Atlantic right whales ( Eubalaena glacialis ) ( n = 18) using a 13-m carbon fiber pole with a collection device. Samples were analyzed for the presence of testosterone and progesterone using a 55% isocratic gradient with LC-MS. Testosterone was detected in four humpback whale samples and eight northern right whale samples. Progesterone was detected in seven humpback whale samples and eight northern right whale samples. This is the first documented use of lung mucosa to determine the presence of reproductive hormones in any free-swimming cetacean and may provide a novel non-invasive technique to quantify the hormonal condition of free-swimming animals that spend brief periods of time at the water's surface.     

Immature euphausiids do not appear to be prey for humpback whales (Megaptera novaeangliae) during spring and summer in Southeast Alaska

Humpbacks whales (Megaptera novaeangliae) have shown a remarkable recovery in the North Pacific, raising concerns regarding their impact on marine communities. In Southeast Alaska, humpbacks feed heavily on euphausiids; however, it remains unclear whether they target immature individuals despite evidence that they do so elsewhere. I evaluate the hypothesis that humpbacks target immature euphausiids in late spring‐summer in Southeast Alaska. Plankton samples were collected at random sites (n = 44) and near whales (n = 53) between 8 June and 9 September 2008 in Frederick Sound and Stephens Passage. The proportion of samples containing immature euphausiids, and immature euphausiid abundance within those samples, were compared between the two sample types. Similar analyses were conducted for adult euphausiids (prey) and calanoid copepods (nonprey) for comparison. I found no statistical difference between the whale and random samples with respect to the occurrence or numerical density of immature euphausiids, which is consistent with the hypothesis that whales did not target them in 2008. Smaller size, insufficient numerical densities and lower energy density of immature euphausiids are suggested as possible reasons. These findings can assist in resolving regional humpback abundance and distribution patterns, and can contribute to an understanding of the trophic interactions characterizing the local ecosystem.     

Evidence of two subaggregations of humpback whales on the Kodiak,Alaska, feeding ground revealed from stable isotope analysis

Knowledge of humpback whale (Megaptera novaeangliae) foraging on feeding grounds is becoming increasingly important as the growing North Pacific population recovers from commercial whaling and consumes more prey, including economically important fishes. We explored spatial and temporal (interannual, within‐season) variability in summer foraging by humpback whales along the eastern side of the Kodiak Archipelago as described by stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of humpback whale skin (n = 118; 2004–2013). The trophic level (TL) of individual whales was calculated using basal food web δ¹⁵N values collected within the study area. We found evidence for the existence of two subaggregations of humpback whales (“North,” “South”) on the feeding ground that fed at different TLs throughout the study period. Linear mixed models suggest that within an average year, Kodiak humpback whales forage at a consistent TL during the feeding season. TL estimates support mixed consumption of fish and zooplankton species in the “North” (mean ± SE; 3.3 ± 0.1) and predominant foraging on zooplankton in the “South” (3.0 ± 0.1). This trend appears to reflect spatial differences in prey availability, and thus, our results suggest North Pacific humpback whales may segregate on feeding aggregations and target discrete prey species.     

Mother Knows Best: Occurrence and Associations of Resighted Humpback Whales Suggest Maternally Derived Fidelity to a Southern Hemisphere Coastal Feeding Ground

Site fidelity is common among migratory cetaceans, including humpback whales (Megaptera novaeangliae). In the Northern Hemisphere it has been found that fidelity to humpback whale feeding grounds is transferred maternally but this has never been shown for the species in the Southern Hemisphere. We examined this in a unique feeding area off west South Africa using resighting data of 68 individually identified humpback whales by means of photographic (tail flukes and dorsal fins) and/or molecular methods (microsatellite genotyping) over an 18 year span. We found short-term association patterns and recurrent visits typical of other feeding grounds. Males and females had different seasonality of attendance. Significant female-dominated presence corresponded to timing of an expected influx of females on their southward migration from the breeding ground: firstly non-nursing (possibly pregnant) females in mid-spring, and mothers and calves in mid-to late summer. The potential benefit of this mid-latitude feeding area for females is illustrated by a record of a cow with known age of at least 23 years that produced calves in three consecutive years, each of which survived to at least six months of age: the first record of successful post-partum ovulation for this species in the Southern Hemisphere. We recorded association of a weaned calf with its mother, and a recurring association between a non-lactating female and male over more than two years. Moreover, three animals first identified as calves returned to the same area in subsequent years, sometimes on the same day as their mothers. This, together with numerous Parent-Offspring relations detected genetically among and between resighted and non-resighted whales is strongly suggestive of maternally derived site fidelity at a small spatial scale by a small sub-population of humpback whales.     

Straight as an arrow: humpback whales swim constant course tracks during long-distance migration

Humpback whale seasonal migrations, spanning greater than 6500 km of open ocean, demonstrate remarkable navigational precision despite following spatially and temporally distinct migration routes. Satellite-monitored radio tag-derived humpback whale migration tracks in both the South Atlantic and South Pacific include constant course segments of greater than 200 km, each spanning several days of continuous movement. The whales studied here maintain these directed movements, often with better than 1° precision, despite the effects of variable sea-surface currents. Such remarkable directional precision is difficult to explain by established models of directional orientation, suggesting that alternative compass mechanisms should be explored.     

The blubber adipocyte index: A nondestructive biomarker of adiposity in humpback whales (Megaptera novaeangliae)

The ability to accurately evaluate the energetic health of wildlife is of critical importance, particularly under conditions of environmental change. Despite the relevance of this issue, currently there are no reliable, standardized, nonlethal measures to assess the energetic reserves of large, free‐roaming marine mammals such as baleen whales. This study investigated the potential of adipocyte area analysis and further, a standardized adipocyte index (AI ), to yield reliable information regarding humpback whale (Megaptera novaeangliae ) adiposity. Adipocyte area and AI , as ascertained by image analysis, showed a direct correlation with each other but only a weak correlation with the commonly used, but error prone, blubber lipid‐percent measure. The relative power of the three respective measures was further evaluated by comparing humpback whale cohorts at different stages of migration and fasting. Adipocyte area, AI , and blubber lipid‐percent were assessed by binary logistic regression revealing that adipocyte area had the greatest probability to predict the migration cohort with a high level of redundancy attributed to the AI given their strong linear relationship (r = −.784). When only AI and lipid‐percent were assessed, the performance of both predictor variables was significant but the power of AI far exceeded lipid‐percent. The sensitivity of adipocyte metrics and the rapid, nonlethal, and inexpensive nature of the methodology and AI calculation validate the inclusion of the AI in long‐term monitoring of humpback whale population health, and further raises its potential for broader wildlife applications.     

Horizontal niche partitioning of humpback and fin whales around the West Antarctic Peninsula: evidence from a concurrent whale and krill survey

A dedicated aerial cetacean survey was conducted concurrently to a standardised net trawl survey for krill in order to investigate distribution patterns of large whales and different krill species and to investigate relationships of these. Distance sampling data were used to produce density surface models for humpback (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) around the West Antarctic Peninsula (WAP). Abundance for both species was estimated over two strata in the Bransfield Strait and Drake Passage. Distinct distribution patterns suggest horizontal niche partitioning of the two whale species around the WAP, with fin whales aggregating at the shelf edge of the South Shetland Islands in the Drake Passage and humpback whales in the Bransfield Strait. Krill biomass estimated from the concurrent krill survey was used along with CTD data from the same expedition, bathymetric parameters and satellite data on chlorophyll-a and ice concentration to model krill distribution. Comparisons of the predicted distributions of both whale species with the predicted distributions of Euphausia superba, Euphausia crystallorophias and Thysanoessa macrura suggest a complex relationship rather than a straightforward correlation between krill and whales. However, results indicate that fin whales were feeding in an area dominated by T. macrura, while humpback whales were found in areas of higher E. superba biomass. Our results provide abundance estimates for humpback whales and, for the first time, fin whales in the WAP and contribute important information on feeding ecology and habitat use of these two species in the Southern Ocean.     

Trophic niche partitioning and diet composition of sympatric fin (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in the Gulf of Alaska revealed through stable isotope analysis

Fin and humpback whales are large consumers that are often sympatric, effectively sharing or partitioning their use of habitat and prey resources. Stable carbon and nitrogen isotopes in the skin of fin and humpback whales from two regions in the western Gulf of Alaska, Kodiak, and Shumagin Islands, were analyzed to test the hypothesis that these sympatric baleen whales exhibit trophic niche partitioning within these regions. Standard ellipse areas, estimated using Bayesian inference, suggested that niche partitioning between species is occurring in the Kodiak region but not in the Shumagin Islands. Isotopic mixing models based on stable isotopes from whales and local prey samples, were used to estimate possible diet solutions for whales in the Kodiak region. Comparison of isotopic niches and diet models support niche partitioning, with fin whales foraging primarily on zooplankton and humpback whales foraging on zooplankton and small forage fish. The results of this study show that niche partitioning between sympatric species can vary by region and may be the result of prey availability, prey preferences, or both.     

Intra‐season variations in distribution and abundance of humpback whales in the West Antarctic Peninsula using cruise vessels as opportunistic platforms

Fine‐scale knowledge of spatiotemporal dynamics in cetacean distribution and abundance throughout the Western Antarctic Peninsula (WAP) is sparse yet essential for effective ecosystem‐based management (EBM). Cruise vessels were used as platforms of opportunity to collect data on the distribution and abundance of humpback whales (Megaptera novaeangliae) during the austral summer of 2019/2020 in a region that is also important for the Antarctic krill (Euphausia superba) fishery, to assess potential spatiotemporal interactions for future use in EBM. Data were analyzed using traditional design‐based line transect methodology and spatial density surface hurdle models fitted using a set of physical environmental covariates to estimate the abundance and distribution of whales in the area, and to describe their temporal dynamics. Our results indicate a rapid increase in humpback whale abundance in the Bransfield and Gerlache Straits through December, reaching a stable abundance by mid‐January. The distribution of humpback whales appeared to change from a patchier distribution in the northern Gerlache Strait to a significantly concentrated presence in the central Gerlache and southern Bransfield Straits, followed by a subsequent dispersion throughout the area. Abundance estimates agreed well with previous literature, increasing from approximately 7000 individuals in 2000 to a peak of 19,107 in 2020. Based on these estimates, we project a total krill consumption of between 1.4 and 3.7 million tons based on traditional and contemporary literature on per capita krill consumption of whales, respectively. When taken in the context of krill fishery catch data in the study area, we conclude that there is minimal spatiotemporal overlap between humpback whales and fishery activity during our study period of November–January. However, there is potential for significant interaction between the two later in the feeding season, but cetacean survey efforts need to be extended into late season in order to fully characterize this potential overlap.     

Investigation of foraging habits and prey selection by humpback whales (Megaptera novaeangliae) using acoustic tags and concurrent fish surveys

Tags containing acoustic time-depth transmitters (ATDT) were attached to four humpback whales near Kodiak, Alaska. Tags allowed for whale dive depths to be recorded in real time. Acoustic and mid-water trawl surveys were conducted concurrent with tagging efforts within the study area to quantify available fish resources and describe potential prey selection by humpback whales. Recorded dives were grouped through visual assessment and t -tests. Dives that indicated likely foraging occurred at a mean maximum depth of 106.2 m with 62% of dives occurring between 92 m and 120 m. Acoustic backscatter from fish surveys was attributed to potential humpback prey based on known target strength values and 10 net tows. Capelin comprised 84% of the total potential prey abundance in the region followed by age 0 (12%) and juvenile pollock (2%), and eulachon (<1%). Although horizontally segregated in the region, both capelin and age 0 pollock were distributed at depths exceeding 92 m with maximum abundance between 107 m and 120 m. The four-tagged humpbacks were found to forage in areas with greatest capelin densities but bypassed areas of high age 0 pollock abundance. The location and diving behavior of tagged whales suggested that whales were favoring capelin over pollock as a prey source.