Dear colleagues, We are pleased to announce the publication of a set of papers that make up a special section on North Atlantic killer whales in the current issue of the JMBA. The papers are largely based around presentations at a workshop held at the 2012 European Cetacean Society meeting in Galway. This meeting marked the 25th anniversary of a previous workshop on North Atlantic killer whales and aimed to summarise the progress made during the past 25-years. We would like to thank all the authors for their valuable contributions. Please contact the corresponding authors directly with any reprint requests or enquiries. Andy Foote, Sanna Kuningas and Filipa Samarra Foreword: North Atlantic killer whale research; past, present and future Andrew D. Foote, Sanna Kuningas and Filipa I.P. Samarra Using opportunistic photo-identifications to detect a population decline of killer whales (Orcinus orca) in British and Irish waters Suzanne Beck, Andrew D. Foote, Sandra Kotter, Olivia Harries, Laura Mandleberg, Peter T. Stevick , Padraig Whooley and John W. Durban Email: biodiversityofficer@hwdt.org An assemblage of killer whales that has been sighted in waters off the west coast of the British Isles and Ireland has previously been shown to be isolated from other North Atlantic killer whale communities based on association patterns. By applying a Bayesian formulation of the Jolly–Seber mark-recapture model to the photo-identification data compiled from opportunistic photographic encounters with this population of killer whales, we show that such sparse and opportunistically-collected data can still be valuable in estimating population dynamics of small, wide-ranging groups. Good quality photo-identification data was collected from 32 encounters over 19 years. Despite a cumulative total of 77 identifications from these encounters, just ten individuals were identified and the remaining 67 identifications were re-sights of these ten animals. There was no detected recruitment through births during the study and, as a result, the population appears to be in a slight decline. The demography of the population was highly skewed towards older individuals and had an unusually high ratio of adult males, and we suggest that demographic stochasticity due to a small population size may be further impacting the population growth rate. We recommend that this population be managed as a separate conservation unit from neighbouring killer whale populations. Killer whale (Orcinus orca) occurrence and predation in the Bahamas Charlotte Dunn and Diane Claridge Email: cdunn@bahamaswhales.org Killer whales (Orcinus orca) have a cosmopolitan distribution, yet little is known about populations that inhabit tropical waters. We compiled 34 sightings of killer whales in the Bahamas, recorded from 1913 to 2011. Group sizes were generally small (mean 1⁄4 4.2, range 1⁄4 1–12, SD 1⁄4 2.6). Thirteen sightings were documented with photographs and/or video of sufficient quality to allow individual photo-identification analysis. Of the 45 whales photographed, 14 unique individual killer whales were identified, eight of which were re-sighted between two and nine times. An adult female (Oo6) and a now-adult male (Oo4), were first seen together in 1995, and have been re-sighted together eight times over a 16-yr period. To date, killer whales in the Bahamas have only been observed preying on marine mammals, including Atlantic spotted dolphin (Stenella frontalis), Fraser’s dolphin (Lagenodelphis hosei), pygmy sperm whale (Kogia breviceps) and dwarf sperm whale (Kogia sima), all of which are previously unrecorded prey species for Orcinus orca. Identifying key habitat and seasonal patterns of a critically endangered population of killer whales Ruth Esteban, Philippe Verborgh, Pauline Gauffier, Joan Gimenez, Isabel Afan, Ana Canadas, Pedro Garcia, Jose Luis Murcia, Sara Magalhaes, Ezequiel Andreu and Renaud de Stephanis Email: ruthesteban@gmail.com Killer whales have been described in the Gulf of Cadiz, southern Spain, in spring and in the Strait of Gibraltar in summer. A total of 11,276 cetaceans sightings coming from different sources (dedicated research surveys, whale watching companies and opportunistic observations) were used to create two presence – ‘pseudo-absence’ predictive generalized additive models (GAM), where presence data were defined as sightings of killer whales and ‘pseudo-absence’ data as sightings of other cetacean species. One model was created using spring data when killer whales’ main prey, Atlantic bluefin tuna, enter the Mediterranean Sea, and the other model used summer data when Atlantic bluefin tuna return to the Atlantic Ocean. Both model predictions show that killer whales are highly associated with a probable distribution of bluefin tuna during their migration throughout the study area, constraining their distribution to the Gulf of Cadiz in spring and the Strait of Gibraltar in spring and summer. Knowledge of the distribution of killer whales in the study area is essential to establish conservation measures for this population. Distribution and abundance of killer whales (Orcinus orca) in Nunavut, Canada—an Inuit knowledge survey Jeff W. Higdon, Kristin H. Westdal and Steven H. Ferguson Email: steve.ferguson@dfo-mpo.gc.ca Traditional ecological knowledge is being increasingly used in wildlife management in northern regions, and Inuit harvesters in Nunavut, Canada, have extensive knowledge about local wildlife species. We collected Inuit knowledge on killer whales (Orcinus orca) through 105 semi-directed interviews in 11 Nunavut communities from 2007 to 2010. Interviewees provided extensive information on killer whale movements, seasonal presence, distribution and abundance in the eastern Canadian Arctic. Observations from different communities were often complementary, and there was consistency in interview comments both within and among regions. Nearly all participants had seen killer whales at least once, and the whales were present every summer (July–September) in all regions, although movements depended on ice conditions. Relative abundance of killer whales varied by region, and they were reported more often in North Baffin communities than in other regions. Killer whales migrated through Hudson Strait and Lancaster Sound following their marine mammal prey. Estimates of local population sizes were variable, with suggested numbers that varied from tens to the low hundreds. Most interviewees in the Foxe Basin, Hudson Bay and north Baffin regions thought that killer whale presence was increasing. In contrast, half the South Baffin interviewees noted declines in past abundance due to the 1977 harvest of 14 whales that became trapped in a saltwater lake. Interviews provided information at a long temporal and wide spatial record. Inuit are reliable observers and continued killer whale research will be most effective if it integrates modern science approaches with the traditional skills, knowledge and experience of Inuit harvesters. Population size, survival and reproductive rates of northern Norwegian killer whales (Orcinus orca) in 1986–2003 Sanna Kuningas, Tiu Simila and Philip S. Hammond Email: sanna.kuningas@gmail.com A long-term photo-identification study of killer whales (Orcinus orca) in northern Norway was initiated in 1986, when their prey the Norwegian spring-spawning herring (Clupea harengus) started to winter in a complex fjord system. The aim of this work was to estimate population size and apparent survival rates in this killer whale population using photo-identification and mark–recapture techniques with data collected during October–December 1986–2003. Total population size was estimated to be highest in 2003: 731 individuals (SE 1⁄4 139, 95% CI 1⁄4 505–1059) using a model taking heterogeneity of capture probabilities into account. Apparent survival of adult males and adult females was estimated using the Cormack – Jolly – Seber model as 0.971 (SE 1⁄4 0.008) and 0.977 (SE 1⁄4 0.009), respectively. Calving intervals ranged from 3 to 14 years (mean 1⁄4 5.06, SE 1⁄4 0.722). These are the first estimates of northern Norwegian killer whale population parameters, allowing their dynamics to be investigated and comparisons to be made with killer whale populations globally. Historic and current distribution patterns, and minimum abundance of killer whales (Orcinus orca) in the north-west Atlantic Jack W. Lawson and Tara S. Stevens Email: jack.lawson@dfo-mpo.gc.ca This study represents the first comprehensive examination of the distribution and abundance of killer whales (Orcinus orca) in the north-west Atlantic. Based on a collation of sightings data and a multi-year photographic catalogue of killer whales, 836 sighting events have been recorded between 1758 and 2012, with most occurring in the last ten years. Killer whales were most commonly observed during June–September in Newfoundland/Labrador, Canada. Most sightings were made close to shore, although many occurred beyond coastal shelf areas and in water depths in excess of 3000 m. Relatively fewer sightings were recorded on the Scotian Shelf, in the Gulf of St Lawrence or the north-eastern USA, despite appreciable aerial and vessel-based cetacean survey effort. In the north-west Atlantic, killer whales have been sighted both alone and in groups, with group sizes ranging from 2 to 30 whales (rarely more than 15, although an aggregation of 100 was reported 43 years ago). Groups usually comprised 2–6 individuals. Based on photographic records, there are at least 67 identified killer whales in the northwest Atlantic; this is an underestimate, since a large portion of our image collection was not of sufficient quality to be considered in the analysis, and many of the whales do not have easily discernible markings. The discovery curve of newly-identified whales has not plateaued, suggesting that there are more whales to identify. These data allow us to better understand the ecology of these killer whales, and provide a baseline against which population changes and distribution patterns can be assessed. Spatial segregation and similar trophic-level diet among eastern Canadian Arctic/ north-west Atlantic killer whales inferred from bulk and compound specific isotopic analysis Cory J.D. Matthews and Steven H. Ferguson Email: cory_matthews@umanitoba.ca Killer whales in the Eastern Canadian Arctic (ECA) prey on narwhal, beluga, bowhead whales and seals, while further south in the north-west Atlantic (NWA), killer whales off the coast of Newfoundland and Labrador prey on both marine mammals and fish. Bulk and amino acid (AA) specific isotopic composition of dentinal collagen in teeth of 13 ECA/NWA killer whales were analysed to assess the degree, if any, of dietary specialization of killer whales across the region. Dentine was sampled from within annual growth layer groups (GLGs) to construct chronological profiles of stable nitrogen (d15N) and carbon (d13C) isotopic compositions for individual whales spanning 3–25 years. Interannual isotopic variation across GLGs was less than that among individuals, and median bulk d15N values differed by up to 5‰ among individuals. Significant correlation between bulk d15N values and baseline (source AA) d15N values indicates much of the observed isotopic variation among individuals reflects foraging within isotopically distinct food webs, rather than diet differences. This interpretation is supported by consistent differences in bulk d13C values between the two individuals with lowest source AA d15N values and the remaining whales. After accounting for baseline isotopic variation, comparable d15N values among individuals indicates similar trophic-level diet, although uncertainties in relative trophic 15N enrichment of individual AAs currently limits trophic position estimates for top consumers. Further research is required to clarify seasonal movement patterns and possible diet shifts of ECA/NWA killer whales to better define their role in marine ecosystems across the region. A quantitative and qualitative comparison of pigmentation features among North Atlantic killer whale (Orcinus orca) populations Pirjo Mäkeläinen, Ruth Esteban, Andrew D. Foote, Sanna Kuningas, Julius Nielsen, Filipa I.P. Samarra, Tiu Similä, Nienke C.F. Vangeel and Gísli A. Víkingsson E-mail: pirjo.makelainen@saunalahti.fi Whilst previous studies of North Atlantic killer whales have qualitatively compared pigmentation patterns, here we present the first quantitative comparison of saddle and eye patch patterns of killer whales from Norwegian, Icelandic, British, Spanish and Greenlandic waters. We found only a small amount of variation in saddle patch shapes, which may reflect a recent phylogenetic divergence from the most recent common ancestor. Eye patch shapes were more variable than saddle patches in small details. Most individuals had patches with parallel orientation, with the exception of a small group of killer whales from Hebrides, which as previously reported had angular eye patches that sloped downward at the anterior end. This differentiation in pigmentation patterns of the Hebridean killer whales from neighbouring populations may reflect one or more of several evolutionary processes, including a deeper phylogenetic divergence, low gene flow with other populations and drift. Differential rates of killer whale attacks on humpback whales in the North Atlantic as determined by scarification Jessica A. McCordic, Sean K. Todd and Peter T. Stevick Email: jamccord@syr.edu As in other populations of killer whales, Orcinus orca, prey selectivity in the North Atlantic population may indicate behaviourally or ecologically distinct types of killer whales. Some killer whale ecotypes are known to prey on large whales, but the ecological impact of such predation events is unknown. Since killer whale attacks on humpback whales, Megaptera novaeangliae, are rarely witnessed, resultant scars may be used to determine the frequency of non-fatal predatory interactions. Using images from the North Atlantic Humpback Whale Catalogue (NAHWC), we examined humpback whale flukes for the presence of rake marks from killer whales (N 1⁄4 5040). Scarring frequencies range from 2.7 to 17.4% and differ significantly among five regions of the North Atlantic (Gulf of Maine, Canada, West Greenland, Iceland and Norway). The scarring rate in the Canada region is significantly higher than all other regions, and Norway has a significantly lower scarring rate than all other regions, despite more frequently reported killer whale sightings in that region. Within the western North Atlantic, Canada has a scarring rate nearly twice that of either the Gulf of Maine or West Greenland. These data may reflect differential prey choice among killer whale ecotypes and/or the distribution of specific ecotypes across the North Atlantic basin. Prey switching by killer whales in the north-east Atlantic: observational evidence and experimental insights Dag Vongraven and Anna Bisther Email: vongraven@npolar.no Studies in the Pacific have identified distinct killer whale ecotypes that are either specialized mammal- or fish-eaters. The different types have developed hunting strategies that would suggest specialization could be more advantageous than generalism. However, it has been suggested, based on long-term dietary markers of tooth wear and stable isotope values, that lineages in the North Atlantic are generalist, but with individual variation in the proportion of prey types consumed. Here, we present the results of ten years of observational and photo-identification data of a population of killer whales that follows the Norwegian spring-spawning stock of Atlantic herring. Although the whales were predominantly observed while feeding upon herring, one pod of herring-eating whales was also observed interacting with seals. This supports the hypothesis based on the long-term markers, of a degree of specialization, with a small number of groups persistently feeding upon mammals, but switching between herring and seals. We further investigated this prey switching by conducting playbacks of herring-eating killer whale sounds to harbour seals at haul-out sites on the herring spawning grounds. We recorded changes in behaviour consistent with an anti-predator response, suggesting the seals perceived the herring-eating killer whales as a potential predatory threat and had not habituated to their calls. This could be due to the risk of herring-eating killer whales switching to mammalian prey, or the difficulty of discriminating between killer whale pods due to the large population size and number of killer whale call dialects in this population, or a combination of both.