Survival rate, abundance, and residency of long-finned pilot whales in the Strait of Gibraltar

Long-finned pilot whales in the Strait of Gibraltar are distributed over the main shipping routes. This exposes them to risks of collisions and probable acoustic and physical disturbance. This species is also the target of whale-watching operations. The aim of this study was to estimate the annual population size, survival rate, and population growth rate of pilot whales occurring in the Strait and their inter-annual variation using photo-identification. A robust design was used to estimate all three parameters. A total of 10,784 individual pilot whale fins were photographed and analyzed. The population size estimation in summer ranged from a low of 147 individuals in 1999 to a high of 265 individuals in 2003. The annual population growth rate was estimated from mark recapture models to be 5.5%. The survival rate of adults was estimated at 0.982 (95% CI: 0.955–0.993). The same individuals have been observed between years. This suggests that this population is resident in the Strait, at least during summer. This study provides baseline knowledge prior to a predicted increase in shipping traffic throughout the main foraging area due to the opening in 2007 of a major shipping harbor along the Moroccan coast of the Strait.     

Do ship strikes threaten the recovery of endangered eastern North Pacific blue whales?

Blue whales were targeted in the North Pacific from 1905–1971 and are listed as endangered by the IUCN. Despite decades without whaling, abundance estimates for eastern North Pacific (ENP) blue whales (Balaenoptera musculus) suggest little evidence for a recent increase. One possible reason is fatal strikes by large ships, which have affected populations of other cetaceans and resulted in mitigation. We used a population dynamics model to assess the trends and status of ENP blue whales, and the effects of ship strikes. We estimate the population likely never dropped below 460 individuals, and is at 97% of carrying capacity (95% interval 62%–99%). These results suggest density dependence, not ship strikes, is the key reason for the observed lack of increase. We also estimate future strikes will likely have a minimal impact; for example, an 11‐fold increase in vessels would lead to a 50% chance the long‐term population would be considered depleted. Although we estimate ship strike mitigation would have minimal impacts on population trends and status, current levels of ship strikes are likely above legal limits set by the U.S. The recovery of ENP blue whales from whaling demonstrates the ability of blue whale populations to rebuild under careful management.     

Decline in abundance and apparent survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence

Estimates of abundance and survivorship provide quantifiable measures to monitor populations and to define and understand their conservation status. This study investigated changes in abundance and survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence in the context of anthropogenic pressures and changing environmental conditions. A long‐term data set, consisting of 35 years of photo‐identification surveys and comprising more than 5,000 identifications of 507 individuals, formed the basis of this mark–recapture study. Based on model selection using corrected Akaike Information Criterion, the most parsimonious Cormack–Jolly–Seber model included a linear temporal trend in noncalf apparent survival rates with a sharp decline in the last 5 years of the study and a median survival rate of 0.946 (95% confidence interval (CI) 0.910–0.967). To account for capture heterogeneity due to divergent patterns of site fidelity, agglomerative hierarchical cluster analysis was employed to categorize individuals based on their annual and survey site fidelity indices. However, the negative trend in survivorship remained and was corroborated by a significant decline in the estimated super‐population size from 335 (95% CI 321–348) individuals in 2004–2010 to 291 (95% CI 270–312) individuals in 2010–2016. Concurrently, a negative trend was estimated in recruitment to the population, supported by a sharp decrease in the number of observed calves. Ship strikes and changes in prey availability are potential drivers of the observed decline in fin whale abundance. The combination of clustering methods with mark–recapture represents a flexible way to investigate the effects of site fidelity on demographic variables and is broadly applicable to other individual‐based studies.     

Survival and abundance of short‐finned pilot whales in the archipelago of Madeira,NE Atlantic

Estimates of population parameters for the short‐finned pilot whale, Globicephala macrorhynchus, are scarce in literature, contributing to an International Union for Conservation of Nature (IUCN) status of Data Deficient. In this study, photo‐identification data collected over 7 yr from Madeira were used to estimate for the first time survivorship, capture probability, and abundance in this species using mark‐recapture methodology. The Cormack‐Jolly‐Seber model estimated that the adult island‐associated (i.e., resident and regular visitor) whales had a constant survival rate of 0.960 (95% CI: 0.853–0.990) and an annual capture probability varying between 0.372 (CI: 0.178–0.619) and 0.843 (CI: 0.619–0.947). A parameterization of the Jolly‐Seber model estimated that 140 island‐associated whales (CI: 131–151) used the area throughout the course of the study. Based on a closed population model, the most precise (lower CV) annual estimate of the total number of pilot whales using the southern and eastern waters of Madeira (~900 km²) in a 3 mo period covering summer/autumn was 334 animals (CI: 260–437). No trend was observed. Despite including biases, the approach used in this study provided plausible estimates of population parameters, which can contribute to the regional conservation strategies.     

Abundance and site fidelity of Indo‐Pacific Humpback dolphins in the Great Sandy Strait,Queensland, Australia

This study examined the population of Indo‐Pacific humpback dolphins, Sousa chinensis, inhabiting the Great Sandy Strait Marine Park, Queensland, Australia. A total of 106 dolphins were identified during 228 boat‐based surveys, completed between April 2004 and April 2007. Based on the distribution of resighted individuals and the pattern of associations, it was established that this population consists of two largely geographically distinct communities, referred to as the Northern Community (NC) and the Southern Community (SC). The only recorded interaction between the two groups was a single pod composed of one member of the NC and 11 dolphins from the SC. Abundance was estimated for the entire population and by geographical area using open population models. Estimates for the Great Sandy Strait indicate that about 150 dolphins (N_GSS= 148.4, SE = 8.3, 95% CI: 132.5–165.2) used this area during the study. The NC and SC total population sizes was estimated to be 76 (N_NGSS= 75.80, SE = 3.88, 95% CI = 71–86) and 75 (N_SGSS= 74.98, SE = 4.43, 95% CI: 66–83), respectively. Analysis of residence patterns indicates that a majority of the identified dolphins are long‐term residents.     

Vessel collision injuries on live humpback whales,Megaptera novaeangliae,in the southern Gulf of Maine

North Atlantic humpback whales (Megaptera novaeangliae) in the Gulf of Maine overlap with both recreational and commercial vessel activity. Vessel strikes are one source of anthropogenic impact that has the potential to inhibit the recovery of this protected species. There are currently no regulations or guidelines specifically devised to reduce the likelihood of collisions for vessels transiting in the vicinity of humpback whales, except for vessels actively engaged in whale watching. To understand interactions between vessels and humpback whales better, we analyzed injuries on 624 individuals photographed in the southern Gulf of Maine from 2004 to 2013. Multiple reviewers evaluated 210,733 photos for five categories of injury consistent with a vessel strike. In total, 14.7% (n = 92) of individuals photographed showed injuries consistent with one or more vessel strikes. These results likely underestimate vessel collision rates and impacts because multiple events, events resulting in mortality, and those that involved only blunt force trauma could not be detected. Nevertheless, our results indicate that vessel strikes are underreported and that healing is dependent on the severity and location of the injury. We recommend that a management strategy be developed for all classes of vessels transiting in the vicinity of whales.     

Humpback whale (Megaptera novaeangliae) and killer whale (Orcinus orca) feeding aggregations for foraging on herring (Clupea harengus) in Northern Norway

Aggregations of predators on food patches have been documented for both terrestrial and marine animals. Here, we documented for the first time, and investigated, non-predatory aggregations occurring between humpback whales (Megaptera novaeangliae) and killer whales (Orcinus orca) while feeding on wintering Norwegian spring spawning herring (Clupea harengus) in Andfjord, northern Norway. Observational data were collected during 109 opportunistic surveys through three seasons 2013–2016. Killer whales were observed feeding on 59 occasions, with one to three humpback whales involved in 47 of these feeding events (79.7%), and there was an increased probability of finding feeding humpback whales when feeding killer whales also were observed. With killer whales identified as the initiating species in 94.4% of the feeding aggregations for which the first species was known, and with humpback whales joining and feeding on the fish ball afterwards, we suggest that humpback whales may benefit more from these aggregations than the opposite.     

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.     

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.     

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.     

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.     

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

The 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 <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.     

The potential beginning of a postwhaling recovery in New Zealand humpback whales (Megaptera novaeangliae)

Between the 1940s and 1970s Southern Hemisphere populations of humpback whales (including eastern Australia and Oceania populations) were hunted to near extinction by extensive commercial whaling activities in Antarctica, with fewer whales taken in shore whaling operations in New Zealand, Australia (including Norfolk Island) and Tonga. Variable rates of recovery of these populations have been documented, ranging from recovery to prewhaling numbers in eastern Australian humpbacks to very little sign of recovery in many Oceania populations. Here we analyze recent sighting data collected over 12 yr, from annual surveys in Cook Strait, New Zealand. The data show an increase in sightings, at an estimated rate of 13% (95% CI of 4.9% and 21.7%) in 2015, of humpback whales migrating through Cook Strait. The wide confidence intervals preclude substantive conclusions about the rate of increase but suggest humpback whales are returning to this region in increasing numbers, indicating an influx of immigrants from neighboring areas, namely eastern Australia.     

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.     

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.     

Low levels of genetic differentiation characterize Australian humpback whale (Megaptera novaeangliae) populations

Humpback whales undertake long‐distance seasonal migrations between low latitude winter breeding grounds and high latitude summer feeding grounds. We report the first in‐depth population genetic study of the humpback whales that migrate to separate winter breeding grounds along the northwestern and northeastern coasts of Australia, but overlap on summer feeding grounds around Antarctica. Weak but significant differentiation between eastern and western Australia was detected across ten microsatellite loci (F_ST = 0.005, P = 0.001; D_EST = 0.031, P = 0.001, n = 364) and mitochondrial control region sequences (F_ST = 0.017 and Φ_ST = 0.069, P = 0.001, n = 364). Bayesian clustering analyses using microsatellite data could not resolve any population structure unless sampling location was provided as a prior. This study supports the emerging evidence that weak genetic differentiation is characteristic among neighboring Southern Hemisphere humpback whale breeding populations. This may be a consequence of relatively high gene flow facilitated by overlapping summer feeding areas in Antarctic waters.     

Entanglement‐scar acquisition rates and scar frequency for Bering‐Chukchi‐Beaufort Seas bowhead whales using aerial photography

The Bering‐Chukchi‐Beaufort Seas (BCBS) bowhead whale (Balaena mysticetus) has been considered at low‐risk for entanglement injuries and ship strikes because their range is mainly north of commercial fisheries; nevertheless, changes to their arctic habitat, including a longer open water period and declining sea ice, have resulted in increasing commercial activity and concern about fisheries interactions. We examined interyear matches (between 1985 and 2011) from a photo identification project and identified whales that had acquired entanglement injuries. We estimated the probability of a bowhead acquiring an entanglement injury using two statistical methods: interval censored survival analysis and a simple binomial model. Both methods give similar results, suggesting a 2.2% (95% CI: 1.1%–3.3%) annual probability of acquiring a scar. We also include an entanglement scar frequency analysis of aerial photographs from the 2011 spring and fall surveys near Point Barrow, Alaska, which suggest 12.4% of live bowheads show evidence of entanglement scarring. Entanglement rates for the BCBS bowhead stock are lower than many other large whale stocks, and abundance has increased over the past 35 yr; however, our findings indicate that fishing gear entanglement is a more serious concern for the BCBS bowhead whale population than previously thought.     

Using dive behavior and active acoustics to assess prey use and partitioning by fin and humpback whales near Kodiak Island,Alaska

Near the Kodiak Archipelago, fin (Balaenoptera physalus) and humpback (Megaptera novaeangliae) whales frequently overlap spatially and temporally. The Gulf Apex Predator‐prey study (GAP) investigated the prey use and potential prey partitioning between these sympatric species by combining concurrent analysis of vertical whale distribution with acoustic assessment of pelagic prey. Acoustic backscatter was classified as consistent with either fish or zooplankton. Whale dive depths were determined through suction cup tags. Tagged humpback whales (n = 10) were most often associated with distribution of fish, except when zooplankton density was very high. Associations between the dive depths of tagged fin whales (n = 4) and the vertical distribution of either prey type were less conclusive. However, prey assessment methods did not adequately describe the distribution of copepods, a potentially significant resource for fin whales. Mean dive parameters showed no significant difference between species when compared across all surveys. However, fin whales spent a greater proportion of dive time in the foraging phase than humpbacks, suggesting a possible difference in foraging efficiency between the two. These results suggest that humpback and fin whales may target different prey, with the greatest potential for diet overlap occurring when the density of zooplankton is very high.