Abundance Of Whales Research Articles

Dietary habits of polar bears in Foxe Basin, Canada: possible evidence of a trophic regime shift mediated by a new top predator.

Polar bear (Ursus maritimus) subpopulations in several areas with seasonal sea ice regimes have shown declines in body condition, reproductive rates, or abundance as a result of declining sea ice habitat. In the Foxe Basin region of Nunavut, Canada, the size of the polar bear subpopulation has remained largely stable over the past 20 years, despite concurrent declines in sea ice habitat. We used fatty acid analysis to examine polar bear feeding habits in Foxe Basin and thus potentially identify ecological factors contributing to population stability. Adipose tissue samples were collected from 103 polar bears harvested during 2010–2012. Polar bear diet composition varied spatially within the region with ringed seal (Pusa hispida) comprising the primary prey in northern and southern Foxe Basin, whereas polar bears in Hudson Strait consumed equal proportions of ringed seal and harp seal (Pagophilus groenlandicus). Walrus (Odobenus rosmarus) consumption was highest in northern Foxe Basin, a trend driven by the ability of adult male bears to capture large‐bodied prey. Importantly, bowhead whale (Balaena mysticetus) contributed to polar bear diets in all areas and all age and sex classes. Bowhead carcasses resulting from killer whale (Orcinus orca) predation and subsistence harvest potentially provide an important supplementary food source for polar bears during the ice‐free period. Our results suggest that the increasing abundance of killer whales and bowhead whales in the region could be indirectly contributing to improved polar bear foraging success despite declining sea ice habitat. However, this indirect interaction between top predators may be temporary if continued sea ice declines eventually severely limit on‐ice feeding opportunities for polar bears.

Abundance and Distribution of Sperm Whales in the Canary Islands: Can Sperm Whales in the Archipelago Sustain the Current Level of Ship-Strike Mortalities?

Sperm whales are present in the Canary Islands year-round, suggesting that the archipelago is an important area for this species in the North Atlantic. However, the area experiences one of the highest reported rates of sperm whale ship-strike in the world. Here we investigate if the number of sperm whales found in the archipelago can sustain the current rate of ship-strike mortality. The results of this study may also have implications for offshore areas where concentrations of sperm whales may coincide with high densities of ship traffic, but where ship-strikes may be undocumented. The absolute abundance of sperm whales in an area of 52933 km2, covering the territorial waters of the Canary Islands, was estimated from 2668 km of acoustic line-transect survey using Distance sampling analysis. Data on sperm whale diving and acoustic behaviour, obtained from bio-logging, were used to calculate g(0) = 0.92, this is less than one because of occasional extended periods when whales do not echolocate. This resulted in an absolute abundance estimate of 224 sperm whales (95% log-normal CI 120–418) within the survey area. The recruitment capability of this number of whales, some 2.5 whales per year, is likely to be exceeded by the current ship-strike mortality rate. Furthermore, we found areas of higher whale density within the archipelago, many coincident with those previously described, suggesting that these are important habitats for females and immature animals inhabiting the archipelago. Some of these areas are crossed by active shipping lanes increasing the risk of ship-strikes. Given the philopatry in female sperm whales, replacement of impacted whales might be limited. Therefore, the application of mitigation measures to reduce the ship-strike mortality rate seems essential for the conservation of sperm whales in the Canary Islands.

Horvitz–Thompson whale abundance estimation adjusting for uncertain recapture, temporal availability variation, and intermittent effort

A Horvitz–Thompson‐type estimator is introduced to estimate total abundance of the Bering–Chukchi–Beaufort Seas population of bowhead whales using combined visual and acoustic location data. The estimator divides sightings counts by three correction factors that are themselves estimated from various portions of the data. The first correction models how detection probabilities depend on covariates like offshore distance and visibility. The second correction adjusts for availability using the acoustic location data to estimate a time‐varying smooth function of the probability that animals pass within visual range of the observation stations. The third correction accounts for whales passing during periods when one or both sighting stations were temporarily closed down. We derive an asymptotically unbiased estimator of abundance incorporating all these components and a corresponding variance estimate. Correcting the count of 4011 observed whales yields a 2011 abundance estimate of 16,820 with a 95% confidence interval of (15,176, 18,643) and an estimated annual rate of population increase of 3.7% (2.9%, 4.6%). These results are indicative of very low conservation risk for this population under the current low levels of aboriginal hunting permitted by the International Whaling Commission. Although few other capture–recapture surveys will confront exactly the same set of challenges addressed here, many studies face one or more issues that could be resolved by adapting portions of our approach or relevant underlying concepts thereof. Moreover, the generic estimator we derive represents an improved way to handle random correction factors rather than assuming fixed values. Copyright © 2016 John Wiley & Sons, Ltd.

Baleen whale abundance and distribution in relation to environmental variables and prey density in the Eastern Bering Sea

The Bering Sea is one of the most productive marine ecosystems in the world and an important habitat for various marine mammal species. Once abundant in this region, most baleen whale species were severely depleted by commercial whaling in the 19th and early 20th centuries. Since their protection in mid-20th century, baleen whale populations have been recovering and reoccupying their historical habitats. These species can consume large amounts of their prey and thus can modify the local structure of ecosystems. Characterizing the extent to which environmental conditions and prey density influence baleen whale abundance in the Eastern Bering Sea is essential to improve our understanding of ecosystem dynamics and to predict how these species might respond to ecosystem variability associated with climate changes. In this study, physiographic, oceanographic, and biological datasets from 2008 to 2010 were combined to model the habitat characteristics of fin whales, humpback whales, and minke whales in the EBS in early summer (June and July) using generalized additive models (GAMs). The explained deviances of the best-supported models were 54.9%, 20.6%, and 68.3% for minke, fin and humpback whales, respectively. Minke and fin whales had similar distribution patterns in the EBS but their abundance was predicted by different explanatory variables. Euphausiid and pollock biomasses, and depth were important predictors of minke whale numbers, while distance to shore, euphausiid biomass, distance to the 200m isobath, and chlorophyll-a concentration better explained fin whale abundance. Humpback whales showed a preference for shallow, coastal waters north of the Alaska Peninsula. For this species, sea surface temperature, depth, chlorophyll-a concentration and euphausid biomass were important predictors of abundance. This study is the first to provide a habitat baseline for baleen whales in the EBS based on a quantitative assessment of the relationship between whale abundance, environmental variables, and density of euphausiids and age-1 pollock in early summer. Because this study was conducted during a cold temperature regime in the Bering Sea, additional research is needed to assess how whales respond to environmental variables and prey biomass in years with warm conditions.

Assessing the design and power of capture-recapture studies to estimate demographic parameters for the Endangered Oceania humpback whale population

Capture−recapture studies offer a powerful tool to assess abundance, survival and population rate of change (λ). A previous capture−recapture study, based on DNA profiles, esti- mated that the IUCN-listed Endangered Oceania population of humpback whales had a super- population size of 4329 whales (95% confidence limits, CL: 3345, 5315) and λ = 1.03 (95% CL: 0.90−1.18) for the period 1999−2005. This low estimate of λ contrasts with the high estimated λ for the neighbouring east Australia population (1.11; 95% CL: 1.105−1.113). A future assessment of Oceania humpbacks through capture−recapture methodology has been proposed to meet 3 objec- tives: (1) estimate population size with a coefficient of variation of < 20%, and detect if λ is signif- icantly different from (2) 1.00 or (3) λ of east Australia. The proposed survey design involves using DNA profiles to identify whales on principal breeding grounds within Oceania in proportion to the abundance of whales on these grounds over the 10 to 12 wk wintering period, to minimise capture heterogeneity between individuals and to maximise capture probabilities. Simulations of the idealised survey design incorporating data from the previous surveys (1999−2005) with 3 new survey years were conducted under a range of scenarios for the 'true' demographic status of the population. Simulations of the entire Oceania region showed that the proposed design will give sufficient power to meet objectives (1) under all scenarios, (2) if the true λ≥ 1.05 and (3) if the true λ≤ 1.05. Region-specific simulations suggested there was scope to test for differences in recovery between principal breeding sites within Oceania.

Residency and abundance of sperm whales (Physeter macrocephalus) in the Bleik Canyon, Norway

Sperm whales (Physeter macrocephalus) are widely distributed in the Norwegian Sea and feeding aggregations occur. One of these aggregations is in the Bleik Canyon, close to shore in Norway, where the present study was performed. The study used a whale safari company as a platform from which to conduct a photo-identification study of male sperm whales. Data for this study was comprised of a total of 3856 images from 22 seasons (1987–2010) of whale-watching tours. In total, 411 individuals were identified. This study supports the results from previous photo-identification studies in the Bleik Canyon and confirms the presence of both transient and resident male sperm whales in the Bleik Canyon. These results suggest that the sperm whale group(s) found there are a loose feeding aggregation and not a closed population. Total residence time varied between one day and 14 years, although most individuals were only seen in one or two years. The number of sighted whales fluctuated between years, from eight to 77 individuals. No trend in the number of sighted whales was found. The estimated size of the feeding aggregation in the Bleik Canyon also fluctuated between years, from 11 to 116 individuals, with no trend evident.

Spatial and temporal occurrence of fin whales (Balaenoptera physalus) and euphausiids (Nyctiphanes simplex) in the Ballenas Channel, Gulf of California, Mexico

Fin whales (Balaenoptera physalus) are observed year-round in the Ballenas Channel and Bahía de los Ángeles region, Gulf of California, where their main food item is the euphausiid Nyctiphanes simplex. This investigation was designed under the hypothesis that the spatial and temporal occurrence of whales and euphausiids coincides. The aim was to establish the geographic, seasonal, and interannual changes in the abundance of the fin whale and its main prey in the region during 2003 and 2004. Four field trips were carried out per year. Surveys to search for whales and carry out horizontal surface tows were conducted from small boats. Fin whales and euphausiids were mainly observed off the coast of Baja California and in the southern Ballenas Channel. Their abundance varied significantly from one season to another in both years. The highest relative abundance of whales occurred in July (warm season), followed by June (cold–warm transition period) and March–April (cold season), and the lowest in October (late warm season). Euphausiid abundance was significantly higher in June (cold–warm transition period), followed by July (warm season). There was no direct correlation between weekly abundances of both species, probably because whale peak abundance occurred four weeks later than euphausiid peak abundance. Fin whale relative abundance was significantly higher in 2004 than in 2003 (2.22 and 0.46 whales h–1, respectively), but euphausiid abundance remained almost the same (geometric means 255 and 174 ind/1000 m3). Even though there was no weekly correlation between both species, their geographic distribution did overlap.

Oceanographic connectivity between right whale critical habitats in Canada and its influence on whale abundance indices during 1987–2009

The Roseway and Grand Manan basins on the Canadian Atlantic coast are neighboring late-summer critical feeding habitats for endangered North Atlantic right whales. Although in late summer these habitats regularly contain thick aggregations of right whale food – the copepod Calanus spp. – right whales periodically abandon one or both habitats in the same year. The causes of abandonments, their relationship to food supply, and the locations of whales during abandonment periods are unclear. The goals of this study were to explain variation in right whale abundance indices from a habitat perspective, and to determine whether or not oceanographic variation in the habitats influences occupancy. Four indices of whale abundance and habitat occupancy, including sightings per unit effort (SPUE), photographic sightings of known individuals, population size and habitat transition probabilities, were analyzed in relation to unique datasets of Calanus concentration and water mass characteristics in each basin over the period 1987 through 2009. Calanus concentration, water mass sources and various hydrographic properties each varied coherently between basins. Calanus concentration showed an increasing trend over time in each habitat, although a short-lived reduction in Calanus may have caused right whales to abandon Roseway Basin during the mid-1990s. Food supply explained variation in right whale sightings and population size in Roseway Basin, but not in Grand Manan Basin, suggesting that the Grand Manan Basin has important habitat characteristics in addition to food supply. Changes in the distribution of whale abundance indices during years when oceanographic conditions were associated with reduced food supply in the Scotia-Fundy region suggest that other suitable feeding habitats may not have existed during such years and resulted in negative effects on whale health and reproduction.

A hidden getaway for bowhead whales in the Greenland Sea

The critically endangered Spitsbergen stock of bowhead whale (Balaena mysticetus) seems to be increasing. However, research effort has also been increasing confounding a firm conclusion. A systematic aerial survey for walrus (Odobaenus rosmarus), applying distance sampling methodology in part of the Northeast Water Polynya (NEW), revealed a ‘bycatch’ of several observations of bowhead whales, which resulted in an estimated abundance of 102 (95 % CI 32–329) individuals. This is the largest abundance of bowhead whales reported from the Greenland Sea since the days of whaling in the sixteenth to seventeenth centuries. The NEW was inaccessible to vessels during the whaling period because of heavy pack ice, and it is only recently that researchers have visited this area; thus only a few sightings of bowhead whales within the NEW exist prior to the survey in 2009. The NEW may nevertheless be one of the most important summering grounds for the Spitsbergen stock, and the whales may benefit from advection of calanoid copepods from the productive deep basins along the coast of Svalbard east of the NEW. This discovery provides renewed hope for the Spitsbergen stock of bowhead whales that until now has shown only inconclusive signs of recovery despite more than 100 years of protection from whaling.

Distribution, abundance, and feeding ecology of baleen whales in Icelandic waters: have recent environmental changes had an effect?

The location of Iceland at the junction of submarine ridges in the North-East Atlantic where warm and cold water masses meet south of the Arctic Circle contributes to high productivity of the waters around the island. During the last two decades, substantial increases in sea temperature and salinity have been reported. Concurrently, pronounced changes have occurred in the distribution of several fish species and euphausiids. The distribution and abundance of cetaceans in the Central and Eastern North Atlantic have been monitored regularly since 1987. Significant changes in the distribution and abundance of several cetacean species have occurred in this time period. The abundance of Central North Atlantic humpback and fin whales has increased from 1,800 to 11,600 and 15,200 to 20,600, respectively, in the period 1987-2007. In contrast, the abundance of minke whales on the Icelandic continental shelf decreased from around 44,000 in 2001 to 20,000 in 2007 and 10,000 in 2009. The increase in fin whale abundance was accompanied by expansion of distribution into the deep waters of the Irminger Sea. The distribution of the endangered blue whale has shifted northwards in this period. The habitat selection of fin whales was analyzed with respect to physical variables (temperature, depth, salinity) using a generalized additive model, and the results suggest that abundance was influenced by an interaction between the physical variables depth and distance to the 2000m isobaths, but also by sea surface temperature and sea surface height, However, environmental data generally act as proxies of other variables, to which the whales respond directly. Overall, these changes in cetacean distribution and abundance may be a functional feeding response of the cetacean species to physical and biological changes in the marine environment, including decreased abundance of euphausiids, a northward shift in summer distribution of capelin and a crash in the abundance of sand eel.

First time series of estimated humpback whale (Megaptera novaeangliae) abundance in Prince William Sound

In Prince William Sound (PWS), changes in abundance of humpback whales (Megaptera novaeangliae), one of PWS’s primary marine predator species, have until now been largely unknown. Using a historical dataset (1978–2009), we constructed the first time series of estimated humpback whale abundance in western PWS that is also one of the longest time series used in analyses of humpback whale mark-recapture data. Photographs from this dataset were used to “mark” and re-sight individual animals using the unique pigmentation pattern on the ventral flukes of each whale in a mark-recapture analysis. Specifically, the POPAN implementation of the Jolly-Seber mark-recapture model in program MARK was used. Estimates of probabilities of capture and survival, recruitment parameters, and total abundance over the study were obtained, leading to a time series of abundance estimates. Our results show an increase from 39 (SE = 26) to 194 (SE = 17) whales ( $$\approx $$ 500 %) over the time series. The average annual rate of increase (ROI) was 4.53 % (95 % CI 3.28–5.79 %) which is only slightly lower than the 5–7 % ROI estimated for the North Pacific. Trends in the number of whales encountered per unit effort were not consistent with abundance estimates from mark-recapture, showing that sightability changes annually.

Health of the Salish Sea as measured using transboundary ecosystem indicators

The Salish Sea ecosystem is a transboundary area of ecological, social, and economic significance shared by Canada and the United States. Accordingly, the United States Environmental Protection Agency and Environment Canada have committed to cross-border collaboration on Salish Sea issues. The transboundary ecosystem indicators project was established to support knowledge sharing and to identify common priorities for action. Mixed trends were observed among ecosystem indicators, reflecting the complexity of the system. Improvements were demonstrated among indicators of air quality, freshwater quality, and toxics in the food web. Declining trends were observed among indicators of marine water quality, marine species at risk, Chinook Salmon, and summer stream flow. Variable or neutral trends were observed among indicators of southern resident Killer Whale abundance, access to Shellfish beaches, and access to swimming beaches. While the indicators represent separate ecosystem components, including air, water, species condition, and human wellbeing, these indicators are interrelated through biophysical cycles. Methods and results of tracking transboundary ecosystem indicators are presented to facilitate the identification of primary drivers and pressures of observed trends, and responses that have had positive results on a site specific basis.

From clicks to counts: Applying line-transect methods to passive acoustic monitoring of sperm whales in the Gulf of Alaska

A visual and acoustic line-transect survey of marine mammals was conducted in the central Gulf of Alaska (GoA) during the summer of 2013. The survey area was divided into four sub-strata to reflect four distinct habitats; “inshore,” “slope,” “offshore,” and “seamount.” Passive acoustic monitoring was conducted using a towed-hydrophone array system. One of the main objectives of the acoustic survey was to obtain an acoustic-based density estimate for sperm whales. A total of 241 acoustic encounters of sperm whales during 6,304 km of effort were obtained compared to 19 visual encounters during 4,155 km of effort. Line-transect analytical methods were used to estimate the abundance of sperm whales. To estimate the detection function, target motion analysis was used to obtain perpendicular distances to individual sperm whales. An acoustic-based density and abundance estimate was obtained for each stratum (N = 78; CV = 0.36 offshore; N = 16; CV = 0.55 seamount; N = 121; and CV = 0.18 slope) and for the entire survey area (N = 215; D = 0.0013; and CV = 0.18). These results will be compared to visual-based estimates. The advantages and disadvantages of acoustic-based density estimates as well as application of these methods to other species (e.g., beaked whales) and areas will be discussed.

Abundance and movements of sperm whales in the western Mediterranean basin

ABSTRACT Sperm whales in the Mediterranean are classified as ‘Endangered’ by the IUCN. They are apparently isolated from adjacent Atlantic populations, and subject to anthropogenic pressures including interactions with illegal driftnet fisheries, ship strikes, ingestion of debris and underwater noise. Photo‐identification data opportunistically collected from the western Mediterranean basin show that individual sperm whales regularly move in excess of 500 km across the western basin, suggesting that this area is occupied by a single population. The best abundance estimate for this region is approximately 400 animals, with confidence intervals between 200 and 1000. Given the mortality levels reported in the literature, this figure suggests that the conservation status of sperm whales in this region is very serious. Immediate priority should be placed both on conducting systematic surveys for abundance estimation and on measures to reduce the mortality associated with driftnet fishing. Copyright © 2014 John Wiley &amp; Sons, Ltd.

GeneGIS: Geoanalytical Tools and Arc Marine Customization for Individual‐Based Genetic Records

AbstractTo improve understanding of population structure, ecosystem relationships and predictive models of human impact in cetaceans and other marine megafauna, we developed geneGIS, a suite of GIS tools and a customized Arc Marine data model to facilitate visual exploration and spatial analyses of individual‐based records from DNA profiles and photo‐identification records. We used the open source programming language Python 2.7 and ArcGIS 10.1 software to create a user‐friendly, menu‐driven toolbar linked to a Python Toolbox containing customized geoprocessing scripts. For ease of sharing and installation, we compiled the geneGIS program into an ArcGIS Python Add‐In, freely available for download from the website http://genegis.org. We used the Lord‐Castillo et al. (2009) Arc Marine data model customization as the starting point for our work and retained nine key base Arc Marine classes. We demonstrate the utility of geneGIS using an integrated database of more than 18,000 records of humpback whales (Megaptera novaeangliae) in the North Pacific collected during the Structure of Populations, Levels of Abundance and Status of Humpback Whales in the North Pacific (SPLASH) program. These records represent more than 8,000 naturally marked individuals and 2,700 associated DNA profiles, including 10 biparentally inherited microsatellite loci, maternally inherited mitochondrial DNA, and genetic sex.

A simulation study of acoustic-assisted tracking of whales for mark-recapture surveys.

Collecting enough data to obtain reasonable abundance estimates of whales is often difficult, particularly when studying rare species. Passive acoustics can be used to detect whale sounds and are increasingly used to estimate whale abundance. Much of the existing effort centres on the use of acoustics to estimate abundance directly, e.g. analysing detections in a distance sampling framework. Here, we focus on acoustics as a tool incorporated within mark-recapture surveys. In this context, acoustic tools are used to detect and track whales, which are then photographed or biopsied to provide data for mark-recapture analyses. The purpose of incorporating acoustics is to increase the encounter rate beyond using visual searching only. While this general approach is not new, its utility is rarely quantified. This paper predicts the “acoustically-assisted” encounter rate using a discrete-time individual-based simulation of whales and survey vessel. We validate the simulation framework using existing data from studies of sperm whales. We then use the framework to predict potential encounter rates in a study of Antarctic blue whales. We also investigate the effects of a number of the key parameters on encounter rate. Mean encounter rates from the simulation of sperm whales matched well with empirical data. Variance of encounter rate, however, was underestimated. The simulation of Antarctic blue whales found that passive acoustics should provide a 1.7–3.0 fold increase in encounter rate over visual-only methods. Encounter rate was most sensitive to acoustic detection range, followed by vocalisation rate. During survey planning and design, some indication of the relationship between expected sample size and effort is paramount; this simulation framework can be used to predict encounter rates and establish this relationship. For a case in point, the simulation framework indicates unequivocally that real-time acoustic tracking should be considered for quantifying the abundance of Antarctic blue whales via mark-recapture methods.

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

AbstractEstimates 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.

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

AbstractFrom 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.

Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis).

For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action.

Counting whales in a challenging, changing environment

Estimating abundance of Antarctic minke whales is central to the International Whaling Commission's conservation and management work and understanding impacts of climate change on polar marine ecosystems. Detecting abundance trends is problematic, in part because minke whales are frequently sighted within Antarctic sea ice where navigational safety concerns prevent ships from surveying. Using icebreaker-supported helicopters, we conducted aerial surveys across a gradient of ice conditions to estimate minke whale density in the Weddell Sea. The surveys revealed substantial numbers of whales inside the sea ice. The Antarctic summer sea ice is undergoing rapid regional change in annual extent, distribution, and length of ice-covered season. These trends, along with substantial interannual variability in ice conditions, affect the proportion of whales available to be counted by traditional shipboard surveys. The strong association between whales and the dynamic, changing sea ice requires reexamination of the power to detect trends in whale abundance or predict ecosystem responses to climate change.