Polar Biol (2011) 34:1513–1522 DOI 10.1007/s00300-011-1010-5 O R I G I N A L P A P E R Cetacean surveys in the Southern Ocean using icebreaker-supported helicopters Meike Scheidat · Ari Friedlaender · Karl-Hermann Kock · Linn Lehnert · Olaf Boebel · Jason Roberts · Rob Williams Received: 4 August 2010 / Revised: 29 March 2011 / Accepted: 31 March 2011 / Published online: 17 April 2011 © The Author(s) 2011. This article is published with open access at Springerlink.com Abstract Cetaceans in the Southern Ocean are potentially impacted by anthropogenic activities, such as direct hunting or through indirect eVects of a reduced sea ice due to cli- mate change. Knowledge on the distribution of cetacean species in this area is important for conservation, but the remoteness of the study area and the presence of sea ice make it diYcult to conduct shipboard surveys to obtain this information. In this study, aerial surveys were conducted from ship-based helicopters. In the 2006/07 (ANT XXIII/8) and 2008/09 (ANT XXV/2) polar summers, the icebreaker RV ‘Polarstern’ conducted research cruises in the Weddell Sea, which oVered the opportunity to use the helicopters to conduct dedicated cetacean surveys. Combining the results from both cruises, over 26,000 km were covered on survey eVort, 13 diVerent cetacean species were identiWed, and a total of 221 cetacean sightings consisting of a total of 650 animals were made. Using digital photography, it was pos- sible to identify four diVerent beaked whale species and to conduct individual photo-identiWcation of humpback and southern right whales. Helicopter surveys allow the collec- tion of additional information on sightings, (e.g. group size, species), as well as the coverage of areas with high ice cov- erage. The Xexibility and manoeuvrability of helicopters make them a powerful scientiWc tool to investigate ceta- ceans in the Southern Ocean, especially in combination with an icebreaker. Keywords Cetacean · Distribution · Sea ice · Southern Ocean · Surveys · Whales Introduction The Southern Ocean provides critical habitat for a large number of whale populations, several of which have been previously reduced extensively in size during twentieth century whaling activities. Many of the cetaceans in the Southern Ocean still face anthropogenic impacts, such as direct hunting (Clapham et al. 2003) or through indirect eVects of reduced sea ice due to climate change (Moore and Huntington 2008). Knowledge on the distribution of cetacean species in this area is especially important for conservation, but survey conditions in the Southern Ocean are far from ideal. In addition to its remoteness, large areas are covered with sea ice that makes it logistically and economically challenging, or even impossible, to conduct large-scale shipboard surveys. M. Scheidat (&) Department of Ecosystems, IMARES (Institute for Marine Resources and Ecosystem Studies), 1790 AB Den Burg, The Netherlands e-mail: meike.scheidat@wur.nl A. Friedlaender · J. Roberts Duke University Marine Laboratory, 135 Pivers Island Road, Beaufort, NC, USA K.-H. Kock Institut für SeeWscherei, Johann Heinrich von Thünen-Institut, Palmaille 9, 22767 Hamburg, Germany L. Lehnert Forschungs- und Technologiezentrum Westküste, Hafentörn 1, 25761 Büsum, Germany O. Boebel Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany R. Williams Marine Mammal Research Unit, University of British Columbia, Room 247, AERL, 2202 Main Mall, Vancouver, BC V6T 1Z4, Canada 123 1514 Polar Biol (2011) 34:1513–1522 This challenge has gained a greater sense of urgency in light of recent abundance estimates for Antarctic minke whales (Balaenoptera bonaerensis) (Branch and Butter- worth 2001). There is some suggestion from the most recent set of circumpolar surveys conducted under the aus- pices of the International Whaling Commission (IWC) that this population has undergone a dramatic decline (Branch and Butterworth 2001), but there is considerable disagree- ment within the IWC’s ScientiWc Committee whether the lower population size estimates are due to decreased abun- dance, changing survey methodology, or a shift in animal distribution due to changing sea ice conditions. Resolving this controversy, whilst of great importance for the IWC’s management decisions, is challenging, because the ships used to conduct systematic surveys are unable to penetrate the sea ice. For many other cetacean species, it has been diYcult to conduct comprehensive assessments due to lack of information on cetacean distribution both inside the mar- ginal ice zone and north of 60°S (Branch and Butterworth 2001). Alternatively, aerial surveys using ship-based heli- copters could allow information to be obtained on cetacean distribution relative to ice conditions that in turn could be used to estimate cetacean density across a range of habitats from open-water to ice-covered regions. In the 2006/2007 and 2008/2009 polar summers, the icebreaker RV Polarstern conducted two research cruises in the Weddell Sea. The ANT XXIII/8 cruise (26 November 2006–29 January 2007) and the ANT XXV/2 cruise (5 December 2008–5 January 2009) oVered an opportunity to use the helicopters on board to conduct dedicated cetacean surveys, which were a secondary research objective to be met in combination with the sur- veys’ obligation to resupply Neumayer station. The Xights spanned open water, the marginal ice zone, as well as deep pack ice. Helicopter surveys have been used in Antarctic waters to survey pinnipeds in the fast ice and pack ice zones (Southwell 2005), but very few sur- veys have included cetaceans as target species (Plötz et al. 1991; van Franeker et al. 1997). The goals of this paper are to: (1) introduce helicopter surveys as a viable means for conducting quantitative line-transect surveys of cetaceans in Antarctic waters; (2) illustrate the kind of data that can be obtained from such platforms; and (3) conduct a preliminary, exploratory analysis to identify factors that may inXuence distribution of diVerent cetacean species with respect to sea ice. This latter analysis, whilst preliminary, is necessary to guide future data collection and analysis, particularly in the Weddell Sea where heavy ice conditions generally pre- clude vessels from being able to penetrate beyond the marginal ice edge zone. For this region, reliable informa- tion on how diVerent cetacean species utilize this habitat is especially scarce. Methods Helicopter surveys and whale sightings Surveys were conducted by means of a helicopter BO-105 from RV Polarstern. The surveys could not follow a sys- tematic sampling design (see below), but Weld protocols for recording eVort and sightings data followed standard line- transect distance-sampling methods (Buckland et al. 2001). Flying time during each survey was generally around 2 h, with a range from 20 min to 3.5 h. Generally, surveys could not be designed in advance, because the ship’s position and ice conditions were unavailable ahead of time, and because the cetacean surveys were not the main objective of the cruise. Therefore, track-lines were normally planned a few hours prior to departure to cover a rectangular shape (Figs. 1, 2). The orientation and placement of these rectan- gles were arbitrary with respect to whale distribution (i.e. the ability to Xy or not Xy was a function of competing demands on the pilots’ time, rather than being planned in response to seeing whales). Surveys were adapted in an ad hoc manner to changing weather and ice conditions and the course of RV Polarstern through the ice. For safety reasons, these surveys usually employed a rectangular survey design that minimized the distance of the helicopter to the survey vessel at any given time. For the areas of Elephant Island and Larsen A and B ice shelves, surveys were conducted along pre-designed transects that involved equally spaced, parallel lines with a random start point, following speciWc depth gradients (Fig. 2). Surveys were conducted at an approximate altitude of 183 m (600 ft) at a speed of 80 km/h. One observer was positioned in the back left seat of the helicopter and observed the area to that side of the helicopter. A second observer sat in the front left seat of the helicopter and observed the area ahead, focusing on the transect line. Dur- ing the ANTXXV-2 survey, a third observer generally joined the team, sitting in the back seat on the right side. During the Xights, the program VOR (designed by Lex Hiby and Phil Lovell and described in (Hammond et al. 1995) was used to enter all relevant survey data and to store the helicopter’s GPS position every 4 s. Information on sea state (Beaufort Sea state scale), cloud cover (in octaves), glare (strength and area aVected), ice coverage (in percent) and overall sighting conditions (good, moderate, poor) was recorded at the beginning of each sur- vey and whenever conditions changed. Ice coverage was averaged for a search area 1 km in front of the helicopter, assessed by the front observer. The following data was collected for each cetacean sighting: location, species, group size, group composition, behaviour, cue, swimming direction and reaction to the helicopter. Group composition described the presence of 123 Polar Biol (2011) 34:1513–1522 1515 calves or adults. Behaviour was categorised into directional swimming, non-directional swimming (“milling”), feeding and resting (including logging at the surface or slow swim- ming). The initial cue of a sighting included body under water, body at the surface, splash, footprint and blow. It was also noted if the helicopter was thought to cause a visi- ble behavioural reaction in the animals. For the back observers, when a sighting was perpendicular to the track- line, the vertical angle in relation to the trackline was mea- sured using an inclinometer. The front observer covered the area directly around the trackline (not visible to the back observers). The front observer would take the vertical angle to the sighting as well as the horizontal angle in relation to the trackline. All measurements were reported to the near- est degree. As the helicopter was at a consistent height, the measurements could be converted easily to perpendicular distances post-survey (Buckland et al. 2001). The survey was conducted entirely in ‘closing mode’, which means that if a sighting could not be identiWed to the species level at the Wrst sighting, the helicopter left the trackline temporar- ily once the sighting was perpendicular to the trackline. The helicopter ‘closed’ on the sighting, approaching to identify species and group size. Photographs were taken to conWrm species identity at a later time and the helicopter returned to the trackline to resume the survey. A digital tape recorder was used to provide an audio backup throughout each sur- vey for later reference. Ice covariate data and analysis methods Two ice-related predictor variables were considered to explore the distribution and abundance of cetaceans with respect to sea ice conditions: ice concentration observed along the trackline by the helicopter (“ice_conc”) and dis- tance (in m) to the marginal ice edge (“UBIceDist”) observed by satellite remote sensing (deWned by the smooth line inscribing the 15% ice concentration margin (Ainley et al. 2007)). We used observer-derived data for the ice concentration predictor, rather than remotely sensed data, because it is the operational measure: that is, the one that actually determines whether a ship could penetrate into the region, and thus conduct a full-scale visual survey for ceta- ceans. To estimate the position of the marginal ice edge, we obtained daily, 6.25-km resolution ice concentration images collected by the advanced microwave scanning radiometer for EOS (AMSR-E) satellite sensor from the University of Bremen (Spreen et al. 2008). We calculated the position of the ice edge for each daily satellite image with ArcGIS 9.3.1 Spatial Analyst functions (ESRI 2009) Fig. 1 Overview with vessel track and helicopter surveys for ANTXXIII/8 (2006/2007) and ANTXXV/2 (2008/2009) 70° 70° 60° 60° 50° 50° 40° 40° 30° 30° 105° 60° 45° 15° 15° 45° 45° ANTXXIII-8 2006/07 ANTXXV-2 2008/09 123 1516 Polar Biol (2011) 34:1513–1522 by selecting the largest polygon of contiguous pixels hav- ing ¸15% ice concentration (i.e. the polygon encompassing the land-fast ice), extracting the outermost edge, and smoothing it using the Spatial Analyst “Boundary Clean” operator with the default parameters. We used the Marine Geospatial Ecology Tools software (Roberts et al. 2010) to match whale sightings to satellite images and calculate the distance to the closest ice edge for each sighting. In order to explore the relationships between baleen whale presence and sea ice conditions, we ran a classiWca- tion and regression tree (CART) analysis. This method has been used previously to not only determine the suitability of predictor variables for more rigorous multivariate analy- sis (e.g. Friedlaender et al. 2006) but also can be useful for determining thresholds for where the presence or absence of cetaceans occurs with respect to a continuous measure of Fig. 2 Results of the combined helicopter surveys during the ANTXXIII/8 (2006/2007) and ANTXXV/2 (2008/2009) cruises: a Western Weddell Sea, b Eastern Weddell Sea and transit from South Africa 123 Polar Biol (2011) 34:1513–1522 1517 a predictor variable (e.g. Hazen et al. 2009). Tree-based models use recursive partitioning methods to help resolve relationships of response variables to predictor variables by partitioning them into increasingly homogeneous sub- groups (Breiman et al. 1984). CARTs are non-parametric in nature and therefore assume no a priori relationships between response and predictor variables, allowing for a variety of data to be used without requiring equal sample sizes amongst response variables (Guisan and Zimmer- mann 2000; Redfern et al. 2006). For our CART, we chose to explore the relationships between baleen whale sightings with proximity to the mar- ginal ice edge and the total concentration of sea ice where sightings were made. We also included a third predictor variable, proximity to shore (“UBLandDist”), deWned as the distance (in m) from the sighting to the closest land pixel in the AMSR-E ice concentration images. We chose to use individual sightings of each whale species as a bino- mial response variable. CARTs were run with optimal recursive partitioning and cross-validation methods similar (Hazen et al. 2009) to ensure that the most signiWcant clas- siWcations were included in the Wnal model. Likewise, receiver operator characteristic (ROC) curves were Wtted to the sightings data, and the area under the curve (AUC) was calculated as a means to measure the likelihood of false positives in the CART (sensitivity versus speciWcity). In this measure, an AUC value of 1.0 would indicate no chance of false positives, whilst a 0 value would represent only false positives. Results During cruise ANT XXIII/8, ‘Polarstern’ entered the pack ice at 58°S and passed through approximately 2,200 km of ice in the eastern Weddell Sea to reach Neumayer Station (70°39’S, 08°15’W) on the Antarctic shelf ice. From Neumayer Station, the vessel continued in a north-westerly direction until the vessel left the pack ice southwest of Ele- phant Island (see Fig. 1). From 1 December 2006 to 26 Jan- uary 2007, a total of 58 aerial survey Xights covering 13,057 km were conducted (Fig. 1). During cruise ANT XXV/2, the helicopter survey started on 6 December 2008 and ended on 3 January 2009. The cruise track of the outward voyage followed an almost straight line from 57° S to Neumayer Station (see Fig. 2). The return voyage took place further to the East returning to Cape Town again in the morning of 5 January 2009. Sur- veys were slightly longer during this cruise covering 13,359 km in a total of 47 Xights (Fig. 1). During both surveys combined, a total of 221 cetacean sightings consisting of a total of 650 animals were made. In total, 13 diVerent cetacean species were identiWed in both surveys combined. An overview of all sightings is given in Table 1. Whale sightings in relation to ice conditions The CART was used to relate the number of sightings of the three most commonly observed baleen whale species (minke, humpback and Wn) to two ice-related, environmental response variables, ice concentration and distance to the ice edge, and to one other variable, distance to shore (Fig. 2). The other baleen whale species that were not included were observed fewer than 3 times (i.e. not frequently enough to include in a statistical model). We included 171 cetacean sightings, and the best-Wt model determined by optimal recursive partitioning had an R-squared = 0.681 with 5 splits. The Wrst fundamental split in the tree occurred at a distance of »143 km from the ice edge (Fig. 3). The majority of ceta- ceans (75 of 76) found farther than this threshold distance were humpback and Wn whales. Of the remaining 95 sight- ings made within this distance to the ice edge, 92 were minke whales. Of these 95 sightings, 84 were made in ice cover >5%, all of which were minke whales. In the ROC analysis Table 1 Overview of cetacean sightings and number of animals as recorded during two helicopter surveys conducted during ANTXXIII/8 (2006/2007) and ANTXXV/2 (2008/2009) Species (scientiWc name) # Sighting # Animals Calves Fin whale (Balaenoptera physalus) 26 75 6 Sei whale (Balaenoptera borealis) 2 5 2 Antarctic minke whale (Balaenoptera bonaerensis) 94 183 0 Humpback whale (Megaptera novaeangliae) 53 134 2 Southern right whale (Eubalaena australis) 1 2 1 Sperm whale (Physeter macrocephalus) 6 15 0 UnidentiWed large whale 20 30 0 Southern bottlenose whale (Hyperoodon planifrons) 5 10 0 Gray’s beaked whale (Mesoplodon grayi) 1 5 0 Strap-toothed whale (Mesoplodon layardii) 2 6 0 Arnoux’s beaked whale (Berardius arnuxii) 1 4 0 Killer whale (Orcinus orca) 6 37 0 Rough-toothed dolphin (Steno bredanensis) & common dolphin (Delphinus sp.) 3 143 >1 UnidentiWed small cetacean 1 1 0 Total 221 650 12 123 1518 Polar Biol (2011) 34:1513–1522 for minke whales, the CART yielded an AUC of 0.96, indi- cating that the CART performed very well at classifying whether a sighting was a minke or another species, given the input predictor variables. The spatial distribution of the various cetacean species was distinct. Minke whales were encountered only in waters south of 57°S, and most sightings were made in or close to sea ice (Fig. 4). Beaked whale sightings ranged from 50°S to 61°S, with most sightings in a small area north of the South Shetland Islands. The large baleen whales were found in open water throughout the study area, but were not sighted further south than 63°. For humpback and Wn whales, two areas of high density were found: one around the South Shetland Islands (Fig. 2) and the other on the most eastern part of the survey, at latitude of about 53°S (Fig. 2 continued). Killer whales were observed at both higher and lower latitudes. Only four species were observed in ice-covered waters, mainly in the Weddell Sea and near the edge of the Larsen A and B ice shelves: Antarctic minke whale, Arnoux’s beaked whale (Berardius arnuxii), Southern bottlenose whale (Hyperoodon planifrons) and killer whale (Orcinus orca) (Fig. 2). The initial sighting cue of most of the identiWed sight- ings was the body at the surface of the water. This was fol- lowed by blows for large whales, footprints for the Antarctic minke and body under the surface for small and beaked whales (Table 2). Behaviour varied between species as well. Most animals were swimming directionally and a large proportion was logging at the surface or resting or swimming slowly (Table 2). When the helicopter passed animals in survey mode, in three cases, a visible reaction (Xuke up, increase in swimming speed, change in swim- ming direction) to the helicopter was recorded. For all these sightings, the distance to the helicopter was less than 500 m. When positioning the helicopter to take photo- graphs, reactions were observed for two beaked whale groups. Whilst lying horizontally just at the water surface, animals synchronously changed their orientation in the water towards the helicopter and dove after a few minutes. Digital photography from the helicopter oVered ability to conWrm visual estimates of group size. Mean group sizes varied between the diVerent species (Table 2). Humpback whales had a maximum group size of 11; Wn whales and Antarctic minke whales, 7 animals; sperm whales, 6 ani- mals; and sei whales, 3 animals. Killer whale group sizes ranged from 1 animal (an adult male) to 18 (Table 2). Fig. 3 CART diagram showing the relationships between three ceta- cean species and sea ice. Black bars represent Antarctic minke whales, grey bars represent Wn whales and white bars represent humpback whales. The R-squared value and number of splits are generated from the optimal recursive partitioning function to generate the best-Wt mod- el of the data. Counts indicate the total number of sightings that were used for each split, and the proportion of each species is shown in each box e.g. for sightings <142,931 m from the ice edge and ice cover >5%, 84 sightings were made and all were minke whales (black bar) Fig. 4 Photograph of a group of Antarctic minke whales taken from the helicopter in the sea ice of the Weddell Sea 123 Polar Biol (2011) 34:1513–1522 1519 Using digital photography from the helicopter, it was possible to later conWrm species (Fig. 4). This was espe- cially useful for the identiWcation of four beaked whale spe- cies seen during the survey. Digital photography was also used for individual photo-identiWcation of three humpback whales and one southern right whale mother-calf pair. Pho- tographs were then compared with existing photo-identiW- cation catalogues in South America and South Africa. One humpback whale identiWed close to the South Shetland Islands was matched with an individual identiWed oV the coast of Ecuador (pers. comm. Fernando Felix). One south- ern right whale female was matched with an individual recorded in South African waters in 1981 and 1996 (pers. comm. Peter Best). Discussion Helicopter surveys conducted from the RV Polarstern proved valuable in several respects. The helicopter allowed the coverage of a broad study area in the comparatively short period of a few hours, as opposed to ship-borne sur- veys, which would take several days to cover the same area. Also, the helicopter survey eVort was independent of the coverage of sea ice. Whilst a vessel would have to adapt survey speed and course, the helicopter can stay at a stan- dard protocol even when crossing high sea ice coverage. Thus, our surveys spanned completely open waters as well as those completely covered by ice and were not restricted to open-water habitats more easily accessed by the ship. Generally speaking, the areas surveyed in this study could not have been surveyed by conventional sighting ships as used in IWC surveys (Branch and Butterworth 2001). Whilst ship-based observations would be possible under similar sea ice conditions, ice-breaking operations generate substantial noise that has been shown to alter distribution of some whales (e.g. studies of ice-breakers and bowhead whales (Richardson et al. 1995)), which would compromise one of the major objectives of our study. To conduct a successful survey, it is essential to use a good survey design that can be challenging in complex hab- itats (Thomas et al. 2007). The design we developed can be adapted shortly before (and even during) each survey Xight, for example, to account for varying and complex sea ice conditions or in order to avoid poor local weather condi- tions. The resulting coverage results in data spanning a wide range of ice conditions, but is nevertheless spatially biased. There are spatial modelling methods that can use ice data together with the distance-sampling data to model habitat use of Antarctic cetaceans, in particular the Antarc- tic minke whale (Hedley et al. 1999; Williams et al. 2006). But methods to generate robust estimates of absolute abun- dance from such spatially biased data are still in development (Bravington and Hedley 2009). We have initiated Table 2 Overview of distribution of cues, behaviour and group sizes of large whales (Wn whale, sei whale, humpback whale, southern right whale, sperm whale); Antarctic minke whale; small whales (killer whales, dolphins) and beaked whales as observed during the ANT- XXIII/8 (2006/2007) and ANTXXV/2 (2008/2009) helicopter based surveys Large whales Antarctic minke whale Small whales Beaked whales Cue N = 94 N = 77 N = 9 N = 8 Body at surface (%) 48 71 78 62 Body under surface (%) 2 9 22 38 Blow (%) 45 0 0 0 Footprint (%) 0 20 0 0 Splash (%) 5 0 0 0 Behaviour N = 86 N = 79 N = 9 N = 9 Directional swimming (%) 57 44 89 22 Un-directional swimming (%) 2 16 0 33 Resting (%) 28 35 11 44 Feeding (%) 6 4 0 0 Other (breaching) (%) 7 0 0 0 Group size and composition N = 107 N = 94 N = 10 N = 9 Average group size 2.46 1.95 18.10 2.78 Range of group size 1–11 1–7 1–110 1–5 123 1520 Polar Biol (2011) 34:1513–1522 collaborations that will take advantage of these complex statistical models to better understand the distribution and abundance of cetaceans in the Weddell Sea after accounting for unequal coverage probability and rapidly changing ice conditions (Bravington and Hedley 2009). In the meantime, our exploratory analyses using CARTs reveal distribution patterns that can allow us to generate speciWc hypotheses regarding how diVerent cetacean species use and are aVected by changing ice conditions in the Weddell Sea. Furthermore, we can now develop an analytical framework to compare the ecological interactions between cetaceans and their environment across very diVerent Antarctic regions. The strong physical diVerences between regions such at the Weddell Sea, Western Antarctic Peninsula, and Ross Sea, for example, will have profound eVects on the community structure, distribution and abundance of ceta- ceans (and other krill predators). Understanding regional diVerences can allow for predictive models and hypotheses to be tested regarding how diVerent systems will respond to changes in environmental conditions. Recent studies have shown that the distribution of baleen whales around the Antarctic Peninsula are related to physi- cal features as well as prey availability (Thiele et al. 2004; Friedlaender et al. 2006) and that strong three-dimensional diVerences in these associations are found between hump- back and minke whales in coastal waters (Friedlaender et al. 2009). The sea ice conditions between the Weddell Sea and the Western Antarctic Peninsula are dramatically diVerent. Likewise, the oceanographic processes governing the circulation patterns and productivity of each region are very diVerent, and thus we expect diVerences in the com- munities of top predators (including cetaceans) in each region. Whilst the distribution of prey is known to have the greatest inXuence on the distribution of cetaceans on the Western side of the Antarctic Peninsula, the heavy and multi-year ice conditions found in the Weddell Sea will likely shape a very diVerent cetacean community and aVect the distribution and abundance of the species present. Whereas humpback whales are the most common cetacean species in the waters around the Western Antarctic Penin- sula in summer (Friedlaender et al. 2009) and fall (e.g. Thiele et al. 2004; Friedlaender et al. 2006), we Wnd minke whales to be the most commonly seen cetacean in the Wed- dell Sea. Similar to Friedlaender et al. (2010) from the western side of the Antarctic Peninsula, we Wnd that minke whale distribution is most inXuenced by proximity to sea ice cover in the Weddell Sea. In our current study, we demonstrate a horizontal separa- tion of minke from other baleen whales with respect to proximity to sea ice. This is in contrast to previous work around the Antarctic Peninsula that speciWcally looked at areas where minke and humpback whales were sympatric (e.g. Friedlaender et al. 2006, 2009). The diVerences in whale community structure in the current paper are likely the result of both seasonal and spatial diVerences in when and where the studies were conducted. The current study took place during the middle of summer when the marginal ice edge is retreating, and pack ice from the previous year has completely consolidated. Friedlaender et al. (2006, 2009) drew conclusions from data collected in the late autumn when ice was beginning to form for the upcoming winter. Likewise, our data were collected in the Weddell Sea, as opposed to the Western side of the Antarctic Penin- sula, and the dramatic oceanographic diVerences in these regions likely contributes to both diVerences in the physical structure of sea ice and the distribution of cetaceans in the regions. Thus, the diVerences presented here in the distribu- tion of diVerent cetacean species that rely heavily on a com- mon resource (Antarctic krill) are new and insightful. A more comprehensive analysis including measurements of prey would oVer further information regarding the regional diVerences in cetacean distribution across the Antarctic. As a survey platform, helicopters oVer a unique and eVective means of covering large areas in a short period of time. Being based on oceanographic research vessels allows helicopters to cover far-reaching areas not accessi- ble from land-based stations. Likewise, helicopter surveys can be paired with oceanographic and environmental sam- pling strategies that can only be accomplished by dedicated time on research vessels. If the research vessel stays in the same area for an extended period of time, for example dur- ing dedicated research programs, study areas can also be covered using a predetermined survey design and quantita- tive analyses can be conducted to better understand the dis- tribution and abundance patterns of cetaceans in relation to their environment. During the ANT XXIII/8 cruise two such research programs were conducted, one around Ele- phant Island investigating Wsh fauna, and one in the Larsen A and B area investigating the eVects of the collapse of the Larsen ice shelves (Gutt 2008; Gutt et al. 2011). As the ves- sel spent several weeks in each of the areas, we changed our ad hoc survey design to parallel tracklines in a way to ensure representative coverage. In the future, this will allow local whale abundance to be estimated using relatively sim- ple, conventional distance-sampling analyses. The helicopter platform allowed good observations of cetaceans above water and underneath (see Fig. 4, Antarctic minke whales surfacing and under water). For a consider- able proportion of sightings of small cetaceans and beaked whales, the main cue was the body under water, indicating that helicopter surveys are able to detect cetaceans just under the water surface when they would not be visible from an observer on a vessel. This is particularly important for species that either do not show easily recognisable sur- face cues (e.g. blows of large baleen whales) or that spend only little time at the surface (e.g. beaked whales). This is 123 Polar Biol (2011) 34:1513–1522 1521 advantageous to surveys to estimate absolute abundance, as well as for mitigation purposes (e.g. in the context of use of military sonar or seismic surveys), when it is vital to know when an animal is in the vicinity of potentially harmful human activities. As has been shown in previous helicopter surveys (e.g., dolphins in the Eastern Tropical PaciWc (Gerrodette and Forcada 2005)), one advantage of helicopters was the abil- ity to halt the survey at any time and position the helicopter in a way in which detailed information on a sighting could be collected. This was especially true for the accurate deter- mination of group size, where it was found that initial group size estimates of minke whales often increased dur- ing observation of the sighting in closing mode. The use of a digital camera from the helicopter served as an eVective tool to identify whales on a species level. In the case of beaked whales, the use of digital photography in combina- tion with the helicopter allowed the determination of spe- cies in which sightings are short and notoriously diYcult to identify. This has allowed us to obtain records of poorly known species, such as Arnoux’s beaked whale, the strap- toothed whale and Gray’s beaked whale. Even though photo-identiWcation during our helicopter survey was used as an opportunistic method, the data col- lected can provide valuable information. The matching of individual right whales between feeding and breeding grounds can oVer insight into migration patterns and habitat use. Photo-identiWcation catalogues of individual whales exist worldwide and are particularly important for those cetacean populations that occur in low numbers. In summary, conducting helicopter surveys, even from platforms that cannot follow a systematic survey design, can be an eYcient means to investigate cetacean distribu- tion and abundance in the Southern Ocean. This is espe- cially true for areas in which high ice coverage makes survey work with a non ice-breaking vessel impractical (e.g. the Weddell Sea). Nevertheless, it is diYcult to con- duct pre-designed surveys whilst working from a transiting research vessel. We see two options for overcoming this limitation. One is to be adaptive in survey design, including personnel with experience with survey design and data analysis, so that survey design algorithms can be used to lay out tracklines in more or less real time as satellite ice images become available. The second option is to come up with what is thought to represent a reasonable solution in the Weld, and accept that some principles of good survey design will be violated due to uncertainty in ice conditions. This latter approach leaves the problems of poor survey design to be addressed at the analysis stage. In our case, our future analyses are going to be complicated immensely by the unequal coverage probability that stemmed from our ad hoc survey design (Bravington and Hedley 2009). In other words, one can bring an analyst into the Weld, or be pre- pared to spend additional time and resources on analysis post-cruise. The geographic complexity and dynamic nature of sea ice will always be a challenge to the design and execution of rigorous systematic surveys for whales in these regions. However, the Xexibility and manoeuvrability of helicopters make them a powerful scientiWc tool with which to approach that challenge. Acknowledgments A large number of people have provided valu- able advice prior to the Weld work. This includes Horst Bornemann, Peter Boveng, Mark Bravington, Michael Cameron, Greg Donovan, Christian Haas, Sharon Hedley, John Jansen, JeV Laake, Russell Leap- er and Tony Warby. We would like to thank Captain Pahl and Captain Schwarze and the crew of RV ‘Polarstern’ for their logistical support. A special “thanks” goes to the helicopter crew, Jürgen Büchner, Hans Heckmann, Uli Michalski, Jens Brauer, Markus Heckmann and Car- sten Möllendorf for professional and safe Xights. We would also like to thank the meteorological oYce onboard the ‘Polarstern’, Frank-Ul- rich Dentler, Klaus Buldt, Christoph Joppich, Harald Rentsch, Edmund Knutz and Felicitas Hansen for their excellent weather forecasts. A personal thanks goes to the scientist-in-charge Julian Gutt for his con- tinuous support of this project prior to and during the ANT XXIII/8 survey. We thank Stefan Bräger, Helena Herr, Kristina Lehnert and Hans Verdaat for their dedicated observer work during ANT XXV/2. Thanks to Gunnar Spreen and his colleagues for providing AMSR-E ice concentration data. The two projects presented here were Wnanced by a number of diVerent institutions: Alfred Wegener Institute for Polar and Marine Research (AWI), Institute for Marine Resources and Ecosystem Studies (Wageningen IMARES), Johann Heinrich von Thünen Institute (Federal Research Institute for Rural Areas, Forestry and Fisheries), Research and Technology Centre Westcoast (FTZ) of the University Kiel, the Netherlands Polar Programme (NPP) of the Netherlands Organisation for ScientiWc Research (NOW), Dutch Min- istry of Agriculture, Nature and Food Quality (LNV), German Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) and the German Federal Ministry for the Environment, Nature Conserva- tion and Nuclear Safety (BMU). The responsibility of the content of this publication lies with the author. We thank Natalie Kelly, Colin Southwell, Paige Eveson and one anonymous reviewer for helpful feedback on a previous version of this manuscript. 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Accessed 20 March 2011 123 http://dx.doi.org/10.1111/j.1748-7692.2008.00263.x http://dx.doi.org/10.1016/j.dsr2.2010.11.018 http://dx.doi.org/10.1016/j.dsr2.2010.11.018 http://dx.doi.org/10.3354/meps08108 http://dx.doi.org/10.3354/meps310271 http://dx.doi.org/10.3354/meps310271 http://dx.doi.org/10.1016/j.envsoft.2010.03.029 http://dx.doi.org/10.1016/j.envsoft.2010.03.029 http://dx.doi.org/10.1029/2005jc003384 http://dx.doi.org/10.1016/j.dsr2.2004.07.007 http://www.ecologyandsociety.org/vol11/iss1/art1 http://www.ecologyandsociety.org/vol11/iss1/art1 Cetacean surveys in the Southern Ocean using icebreaker-supported helicopters Abstract Introduction Methods Helicopter surveys and whale sightings Ice covariate data and analysis methods Results Whale sightings in relation to ice conditions Discussion Acknowledgments References