Whale killers: Prevalence and ecological implications of killer whale predation on humpback whale calves off Western Australia

Reports of killer whales (Orcinus orca) preying on large whales have been relatively rare, and the ecological significance of these attacks is controversial. Here we report on numerous observations of killer whales preying on neonate humpback whales (Megaptera novaeangliae) off Western Australia (WA) based on reports we compiled and our own observations. Attacking killer whales included at least 19 individuals from three stable social groupings in a highly connected local population; 22 separate attacks with known outcomes resulted in at least 14 (64%) kills of humpback calves. We satellite‐tagged an adult female killer whale and followed her group on the water for 20.3 h over six separate days. During that time, they attacked eight humpback calves, and from the seven known outcomes, at least three calves (43%) were killed. Overall, our observations suggest that humpback calves are a predictable, plentiful, and readily taken prey source for killer whales and scavenging sharks off WA for at least 5 mo/yr. Humpback “escorts” vigorously assisted mothers in protecting their calves from attacking killer whales (and a white shark, Carcharodon carcharias). This expands the purported role of escorts in humpback whale social interactions, although it is not clear how this behavior is adaptive for the escorts.     

Migratory movements of individual humpback whales photographed off the eastern coast of Australia

Humpback whales (Megaptera novaeangliae) migrate long distances each year on a return journey from low‐latitude breeding grounds to high‐latitude feeding grounds. Migration is influenced by subtle and complex social behaviors and the assumption that whales transit directly through the migratory corridor off the east coast of Australia requires further investigation. From 2003 to 2005, we followed the movements of 99 individual whales within one migratory cycle from three locations, off Byron Bay during the whales' northern migration and in Hervey Bay and at Ballina during the southern migration. The median sighting interval of whales between Byron Bay and Hervey Bay (n = 26) was 52 d (IQR = 42.5–75.5); between Byron Bay and Ballina (n = 21) was 59 d (IQR = 47.0–70.0); and between Hervey Bay and Ballina (n = 33) was 9 d (8.0–14.0). The overall pattern observed from these resightings suggests that Group E1 humpback whales spend approximately two months in the northern quarter of their range during the austral winter months. Intraseason resightings of whales at Ballina (n = 13, median sighting interval = 7 d) also suggest that some individuals, particularly adult males, may circle back north during their general southward journey along this part of the coast, perhaps in an attempt to increase mating opportunities.     

Resightings of humpback whales in Hawaiian waters over spans of 10–32 years: Site fidelity,sex ratios,calving rates,female demographics,and the dynamics of social and behavioral roles of individuals

From a database of approximately 5,000 Hawaiian humpback whales identified photographically between 1976 and 2010, we extracted 71 males and 39 females having resighting spans of 10 or more years, from first to most recent sighting. Findings included: (1) the male‐biased sex ratio was like that found in breeding grounds worldwide; (2) the mean span for males of 20.7 yr (maximum = 32 yr) did not differ significantly from the mean of 19.8 yr (maximum = 29 yr) for females, but males were seen in significantly more years during their spans than were females; (3) the mean number of females seen with and without calf across 11 three‐year intervals from 1977 to 2009 did not differ significantly; (4) the calving rate for the 39 females was 0.48 and seven females produced two to eight calves over spans of 22–26 yr; (5) females attracted significantly more escorts in years without calf than in years with calf; (6) individuals showed great diversity in the social units they occupied over their sighting spans, but with the most frequently observed unit for both sexes being the trio of mother, calf, and escort. Males were also observed frequently in competitive groups centered about a female without calf.     

Behavioral responses of humpback whales (Megaptera novaeangliae) to whale-watching vessels on the southeastern coast of Australia

This study assessed the short-term responses of humpback whales to whale-watching vessels during their southward migration along the south coast of New South Wales (NSW), Australia. The behavior of pods was recorded from commercial whale-watching vessels during tours and compared to pods observed in the absence of vessels from the shore in the same area. While some individuals showed obvious signs of horizontal avoidance, others approached vessels, initiating interactions. Calf pods were more sensitive to the presence of vessels than non-calf pods. Dive times and the overall percentage of time whales spent submerged were higher in the presence of vessels, but respiration intervals did not differ. Some surface behaviors occurred less often in the presence of vessels. Whales' responses differed according to whether vessels were operating in accordance with regulations or not. Whales were more likely to avoid a vessel moving within the permitted 100 m approach limit than vessels outside the limit. Whales showed some behavioral changes when vessels operated in accordance with whale-watching regulations, compared with whales in the absence of vessels. Pods that showed no obvious horizontal responses to vessels changed their diving and surface activity when compared with pods in the absence of vessels. Because the long-term impacts of effects of vessels are unknown, management of the humpback whale-watching industry should adopt a conservative approach. Improved knowledge of long-term impacts of multiple exposures to vessels is required to inform management of the effects of whale-watching.     

Estimating Cetacean Carrying Capacity Based on Spacing Behaviour

Conservation of large ocean wildlife requires an understanding of how they use space. In Western Australia, the humpback whale (Megaptera novaeangliae) population is growing at a minimum rate of 10% per year. An important consideration for conservation based management in space-limited environments, such as coastal resting areas, is the potential expansion in area use by humpback whales if the carrying capacity of existing areas is exceeded. Here we determined the theoretical carrying capacity of a known humpback resting area based on the spacing behaviour of pods, where a resting area is defined as a sheltered embayment along the coast. Two separate approaches were taken to estimate this distance. The first used the median nearest neighbour distance between pods in relatively dense areas, giving a spacing distance of 2.16 km (±0.94). The second estimated the spacing distance as the radius at which 50% of the population included no other pods, and was calculated as 1.93 km (range: 1.62–2.50 km). Using these values, the maximum number of pods able to fit into the resting area was 698 and 872 pods, respectively. Given an average observed pod size of 1.7 whales, this equates to a carrying capacity estimate of between 1187 and 1482 whales at any given point in time. This study demonstrates that whale pods do maintain a distance from each other, which may determine the number of animals that can occupy aggregation areas where space is limited. This requirement for space has implications when considering boundaries for protected areas or competition for space with the fishing and resources sectors.     

Migratory movements and surfacing rates of humpback whales (Megaptera novaeangliae) satellite tagged at Socorro Island,Mexico

Humpback whales wintering in the Revillagigedo Archipelago, Mexico, have been considered a different subpopulation from those found off mainland Mexico and Baja California. The primary feeding grounds for Revillagigedo humpbacks remain unknown. In February 2003, we deployed 11 Argos satellite‐monitored radio tags to track movements and surfacings of humpback whales (five adults without calves, five mothers with calves, one calf) off Socorro Island in the Revillagigedo Archipelago. Tracking ranged from 222 to 10,481 km over 4.9–149.1 d. Eight whales left Socorro Island: five visited other Mexican wintering destinations, seven moved north of these areas. Migration routes were primarily offshore (average 444 km). Two whales were tracked to feeding grounds: one to British Columbia (46 d migration), and one to Alaska (49 d migration). Mean travel speeds were 1.2 km/h in wintering areas, 4.0 km/h during migration, and 2.2 km/h in feeding areas. Overall surfacing rates ranged from 21 to 88 surfacings/h. Surfacing rates differed between the calf and all other whales, and between feeding areas and migratory/wintering areas for the calf and an adult without a calf. The calf also showed diel variation in surfacing rates. The offshore habits of tagged whales may explain scarce resightings of Revillagigedo humpbacks outside the Revillagigedo Archipelago.     

Distribution and migratory destinations of humpback whales off the Pacific coast of Central America during the boreal winters of 1996–2003

Here, we examine the distribution, habitat use, and migratory destinations of North Pacific humpback whales wintering off Central America. Coastal boat surveys were conducted off Costa Rica and Panama between 1996 and 2003. In 1999, a broader survey was conducted along most of Central America. Over 23,000 km were surveyed, with the greatest effort off southern Costa Rica. We made 191 sightings of 320 individual humpback whales. Whales were seen between 14°N and 8°N, making this the most southerly of the North Pacific wintering areas. Encounters included singles, adult pairs, singers, and mother/calf pairs. Mother/calf pairs accounted for 27% of all groups sighted, which is one of the highest sighting rates reported among North Pacific wintering areas. Sixty percent of sightings occurred in depths <50 m. Average sea surface temperature was 28.6°C (±1.0 SD). Ninety percent of the 77 unique whales photo‐identified were also seen in the California–Oregon–Washington feeding aggregation. The 1999 survey showed that humpback whales were widely distributed along the Central American coast at relatively low densities. The extensive distribution of animals, the higher proportion of calves, and the almost exclusive migration to a single feeding area contrast with observations in other regions.     

Population size and migratory connectivity of humpback whales wintering in Las Perlas Archipelago,Panama

From 2003 to 2009, we surveyed Las Perlas Archipelago off the Pacific coast of Panama 53 times between the months of August and October to estimate abundance of humpback whales and to test for a migratory connection with populations from the southern hemisphere. We identified 295 individuals using photo‐identification of dorsal fins, including 58 calves, and the population estimate for a single season was 100–300 solitary adults plus 25–50 mothers with calves; the estimated population of animals across all seasons using a mark and recapture model was over 1,000. Eight of the 139 fluke identifications were matched to whales in photograph catalogues from the Antarctic Peninsula and a ninth was matched to a whale sighted in Chilean waters; four of these nine individuals have also been sighted in Colombia. We conclude that Panama (Las Perlas Archipelago in particular) is an important calving area for humpback whales in the Southern Hemisphere. These data should provide a foundation for monitoring of population change and to increase awareness in Panama about the need to manage vessel traffic and tourism related to the whales at Las Perlas.     

Effect of Fruiting Traits on the Field Resistance of Cocoa (Theobroma cacao L.) Clones to Phytophthora megakarya

The effects of some traits of field resistance (precocity and duration of the fruiting cycle, age of diseased fruit and vertical pod distribution on the tree) to Phytophthora megakarya of four known cocoa clones were studied in an on‐station clonal plot planted in 1982 in the south‐west of Cameroon. Weekly observations of fruit set and development, black pod and rainfall were carried out during three growing seasons (1999, 2000 and 2001). The study confirmed the previous field and laboratory assessments of resistance of these clones based on the mean percentages of rotten pods obtained annually. The present study has permitted the identification of fruit aged 2–3 months as the highly susceptible stage of development in the most susceptible clone. In addition, precocity and pod cycle duration varied significantly among the clones. The earlier the pod cycle began, the more susceptible was the clone: the most resistant clone started flowering 1 month after the most susceptible clone and therefore escaped the peak of disease severity. Rainfall intensity greatly modified the incidence of the disease in 2001, with high yield losses occurring in all four clones (70–93%), but their ranking remained stable over the 3 years. The spatial distribution of pods on the trees showed that pods on the trunk were more likely to become diseased than those on the branches, but its effect as a clone resistance component is variable among the four clones; the resistant clone producing more pods on the trunk and the susceptible clone more in the canopy.     

From flower to seed: identifying phenological markers and reliable growth functions to model reproductive development in the common bean (Phaseolus vulgaris L.)

The lack of dependable morphological indicators for the onset and end of seed growth has hindered modeling work in the common bean (Phaseolus vulgaris L.). We have addressed this problem through the use of mathematical growth functions to analyse and identify critical developmental stages, which can be linked to existing developmental indices. We performed this study under greenhouse conditions with an Andean and a Mesoamerican genotype of contrasting pod and seed phenotypes, and three selected recombinant inbred lines. Pods from tagged flowers were harvested at regular time intervals for various measurements. Differences in flower production and seed and pod growth trajectories among genotypes were detected via comparisons of parameters of fitted growth functions. Regardless of the genotype, the end of pod elongation marked the beginning of seed growth, which lasted until pods displayed a sharp decline in color, or pod hue angle. These results suggest that the end of pod elongation and the onset of color change are reliable indicators of important developmental transitions in the seed, even for widely differing pod phenotypes. We also provide a set of equations that can be used to model different aspects of reproductive growth and development in the common bean.     

Cultural transmission within maternal lineages: vocal clans in resident killer whales in southern Alaska

Cultural lineages are based on learned social traditions that are stable for several generations. When cultural lineages also reflect common ancestry and/or are shared by individuals that live together they are called clans. The existence of clans among killer whales has been previously proposed but has not been confirmed. Here, we show that clans exist among resident type killer whales, Orcinus orca, in southern Alaska. Resident killer whales live in stable matrilines from which emigration of either sex has not been observed. Matrilines that associate regularly (≥50% observation time) are called pods. Pods are believed to consist of closely related matrilines and share a unique repertoire of discrete call types. Pods that share parts of their repertoire form what Ford (1991, Canadian Journal of Zoology,69, 1454-1483) called an acoustic clan. Here, we identified discrete call types of seven pods from southern Alaska, using a method based on human discrimination of distinct aural and visual (spectrogram) differences. Mitochondrial DNA of members of each pod was also analysed. The repertoires of the seven pods were compared and two acoustically distinct groups of pods were identified. Each group was monomorphic for a different mitochondrial D-loop haplotype. Nevertheless, pods from different clans associated frequently. It thus appears that the acoustic similarities within groups, which we presume to be cultural, reflect common ancestry, and that these groups therefore meet the above definition of clans. We also argue that a combination of cultural drift and selection are the main mechanisms for the maintenance of clans. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Humpback whale songs during winter in subarctic waters

The songs of the male humpback whales (Megaptera novaeangliae) have traditionally been associated with mating at tropical and subtropical mating grounds during winter. However, songs also occur out of mating season, both on feeding grounds in spring, late summer and fall. This study provides the first report of humpback whale singing behaviour in the subarctic waters of Northeast Iceland (Skjálfandi Bay) using long-term bottom-moored acoustic recorders during September 2008–February 2009 and from April to September 2009. Singing started in late November and peaked in February, within the breeding season. No songs were detected from spring to fall, despite visual detections of humpback whales. Non-song sound signals from humpback whales were detected during all recording months. Songs were partly composed of fundamental units common with other known mating grounds, and partly of song units likely unique to the study area. The variety of song unit types in the songs increased at the end of the winter recordings, indicating a gradual change in the songs throughout the winter season; as has been shown on traditional mating grounds. The relative proportion of songs compared with non-song signals was higher during dark hours than daylight hours. The short light periods of the winter, and where food is available, likely influence the daily occurrence of humpback whales’ songs in the subarctic.     

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.     

Responses of Kamchatkan fish‐eating killer whales to playbacks of conspecific calls

Killer whales produce repertoires of stereotyped call types that are primarily transmitted vertically through social learning, leading to dialects between sympatric pods. The potential function of these call repertoires remains untested. In this study, we compared the reaction of Kamchatkan fish‐eating killer whales to the playbacks of calls from the same and different pods. After the playback of recordings from a different pod, in three cases whales changed the direction of their movement toward the boat, and in three cases no changes in direction were observed. After the playback of recordings from the same pod (either from the same or a different unit within the pod), in seven cases whales changed the direction of their movement toward the boat, and in only one case no change in direction was observed. Whales remained silent after all six playbacks of recordings from a different pod, even when they changed direction toward the boat. After the playback of recordings from the same pod, however, in all eight cases whales started calling in response. Our playback study shows that killer whales may react to playbacks of conspecific sounds and that reactions are dependent on the type of playback stimuli.     

Potential vessel collisions with Southern Hemisphere humpback whales wintering off Pacific Panama

Vessel collision is a threat to many whale species, and the risk has increased with expanding maritime traffic. This compromises international conservation efforts and requires urgent attention from the world's maritime industry. Humpback whales (Megaptera novaeangliae) are at the top of the death toll, and although Central America is a wintering area for populations from both the Northern and Southern Hemispheres, existing efforts to reduce ship‐whale collisions are meager. Herein, we evaluated the potential collisions between vessels and humpback whales wintering off Pacific Panama by following the movements of 15 whales tagged with satellite transmitters and comparing these data with tracks plotted using AIS real‐time latitude‐longitude points from nearly 1,000 commercial vessels. Movements of whales (adults and calves) in the Gulf of Panama coincide with major commercial maritime routes. AIS vessel data analyzed for individual whale satellite tracks showed that 53% (8 whales) of whales had 98 encounters within 200 m with 81 different vessels in just 11 d. We suggest implementing a 65 nmi Traffic Separation Scheme and a 10 kn maximum speed for vessel routing into the Gulf of Panama during the wintering season. In so doing, the area for potential whale‐vessel collisions could be reduced by 93%.     

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.     

An assessment of shore‐based counts of gray whales

Counts of migrating whales depend on accurate sightings data. In this study, teams of shore‐based observers independently tracked whale pods during the southbound migration of gray whales (Eschrichtius robustus) while a routine (“standard watch”) census was underway. A comparison of sighting records showed that time and location accuracy was limited to 45 s, 3° (magnetic) horizontally, and 0.0057° (0.2 reticles) vertically. Of 242 attempts to track whale groups, 72 failed, 120 were “good tracks,” and 83 qualified as “best tracks” because they had ≥8 sightings/pod, ≥16‐min observation time, and unequivocal matches to sightings in the standard watch during uncompromised visibility. Between paired tracking teams, 39 attempts to conduct concurrent tracks resulted in 21 “good tracks” with complete agreement in 71% of the cases. Of 133 comparisons between trackers and the standard watch, 43% of the pod‐size estimates were the same, but the standard watch overestimated 10% of the pods and underestimated 47%. Thus, according to results from tracking teams, pods recorded as size 1 by observers on the standard watch should be corrected by +0.6; pods of 2 by +0.5; pods of 3 by +0.8; and pods >3 (4–10) were overestimated and should be corrected by ?0.6.     

Fine‐scale spatial differences in humpback whale diet composition near Kodiak,Alaska

On the North Pacific feeding grounds, humpback whales (Megaptera novaeangliae) are recovering from commercial whaling at a rapid rate (6.8%). The potential effect that this recovery will have on trophic dynamics involving these predators is currently unknown. To better elucidate complex trophic dynamics, variability in diet composition of apex predators on their respective feeding grounds needs to be understood. Thus, we explored the diet composition of two defined subaggregations of humpback whales of the Kodiak Archipelago population (“North,” “South”) using stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of humpback whale skin and regional prey samples in Bayesian dietary mixing models. Humpback whales in the “North” region consumed proportionally more fish, dominated by capelin (Mallotus villosus), whereas, whales in the “South” region consumed predominantly krill. The difference in diet composition appears to reflect regional differences in prey availability. Thus, regional variability in diet composition by humpback whales may have disproportionate impacts on prey resources of sympatric predators depending on available prey biomass. As a result, we suggest fine‐scale studies of apex predator diets are needed to better model trophic dynamics with accuracy.     

Maturational changes in patterns of association in male and female humpback whales, Megaptera novaeangliae

The patterns of association of juvenile male and female humpback whales, Megaptera novaeangliae , in the southern Gulf of Maine were studied for evidence of maturational changes. Both males and females became less solitary with age. In males, time spent alone changed from a mean of 55.8% of observations at age one to 26.8% at age six. Females were alone in a mean of 49.9% of observations at age one, but in only 20.5% by age six. However, females that produced calves at five, six or seven were associated with no whales but the calf in 73.8% of observations. Males exhibited a clear age-related trend of increasing associations with adults, notably with adult females which constituted approximately 80% of the associates of males aged six years or more. Females showed a similar trend of increasing associations with adults of both sexes. Tests of association data for whales of known age with similar data for adults of the same sex showed that the association patterns of young males and females became statistically indistinguishable from those of adults by the ages of five and four, respectively. The data suggest that the observed changes in social behaviour are closely linked to the attainment of sexual maturity and preparation for adult roles. The different patterns of males and females after maturity may reflect differing reproductive and life-history strategies.     

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.