Orca (Orcinus orca) strandings are rare and post-mortem examinations on fresh individuals are scarce. Thus, little is known about their parasitological fauna, prevalence of infections, associated pathology and the impact on their health. During post-mortem examinations of two male neonatal orcas stranded in Germany and Norway, lungworm infections were found within the bronchi of both individuals. The nematodes were identified as Halocercus sp. (Pseudaliidae), which have been described in the respiratory tract of multiple odontocete species, but not yet in orcas. The life cycle and transmission pathways of some pseudaliid nematodes are incompletely understood. Lungworm infections in neonatal cetaceans are an unusual finding and thus seem to be an indicator for direct mother-to-calf transmission (transplacental or transmammary) of Halocercus sp. nematodes in orcas.

There is a paucity of information on the cetacean fauna of Guinea-Bissau in West Africa. We compiled records published in the literature and novel unpublished sighting data (2008–2014) to examine the occurrence and distribution of cetacean species. At least 10 species were verified to occur in Guinea-Bissau waters, of which eight were documented from a small number of sightings, whaling captures or skeletal remains. By far the most frequently recorded species were the common bottlenose dolphin (Tursiops truncatus) (N = 146) and the Atlantic humpback dolphin (Sousa teuszii) (N = 110). These two species were sympatric in distribution, both being found throughout coastal waters from the northern regions of Canal de Jeta and Rio Mansôa south to the Rio Cacine and around the Arquipélago dos Bijagós. However, differences were apparent in their finer-scale distribution and in the distance of sightings from shore, with bottlenose dolphin sightings generally occurring further from shore (and especially in the region of the Canal do Gêba) than Atlantic humpback dolphins. Sightings indicate that both species likely inhabit Guinea-Bissau waters throughout the year. Dedicated systematic cetacean survey work is urgently needed in coastal Bissau-Guinean waters in order to ascertain the abundance, spatio-temporal distribution, population structure and causes of mortality of bottlenose and Atlantic humpback dolphins, particularly given the Vulnerable conservation status of the latter species. Clarification of the status of cetaceans in offshore waters requires survey effort throughout the Guinea-Bissau EEZ.

Orcinus orca is a cosmopolitan species and the most widely distributed marine mammal. Its diet includes over 140 species of fish, cephalopods, sea birds and marine mammals. However, many populations are specialised on certain specific prey items. Three genetically distinct populations have been described in the North Atlantic. Population A (that includes the Icelandic and Norwegian sub-populations) is believed to be piscivorous, as is population C, which includes fish-eating killer whales from the Strait of Gibraltar. In contrast, population B feeds on both fish and marine mammals. Norwegian killer whales follow the Norwegian spring spawning herring stock. The only description in the literature of Norwegian killer whales feeding on another cetacean species is a predation event on northern bottlenose whales in 1968. Daily land-based surveys targeting sperm whales were conducted from the Andenes lighthouse using BigEyes® binoculars (25×, 80 mm). The location of animals at sea was approximated through the use of an internal reticule system and a graduated wheel. On 24 June 2012 at 3:12 am, an opportunistic sighting of 11 killer whales was made off Andenes harbour. The whales hunted and fed on a harbour porpoise. Despite these species having overlapping distributions in Norwegian waters, this is the first predatory event reported in the literature.

Here we present a 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 eye patches with parallel orientation, with the exception of a small group of killer whales from the Hebrides, which, as previously reported, had sloping eye patches that sloped downward at the posterior end. This differentiation in pigmentation patterns of the Hebridean killer whales from neighbouring populations could reflect one or more of several evolutionary processes, including a deeper phylogenetic divergence, low gene flow with other local populations and drift.

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.

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.

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.

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.

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.

The stomach contents from a killer whale stranded in north-west Ireland were examined. Siphonostomatoid copepods Cecrops latreilli and bones consistent in shape and size with those from the ocean sunfish were found. While observations of free-ranging killer whales predating on sunfish exist from the Gulf of Guinea and the South Pacific, this is the first record for the North Atlantic and the first from stomach content analysis.

Killer whales Orcinus orca are considered to be relatively uncommon in tropical waters. Few sightings have been reported from the west coast of Africa due to a paucity of survey coverage. We present data on 32 killer sightings from tropical waters off Angola (N = 18), Gabon (N = 7), São Tomé (N = 6) and Cameroon (N = 1), comprising a combination of dedicated survey sightings (N = 21) and reliable anecdotal records (n = 11). Killer whales were reported from coastal waters, the shelf edge and deep, oceanic areas. Sightings indicate a probable year-round occurrence of killer whales within the region. Mean group size was 5.6 animals. There was no difference in group size between sightings in waters >200 m deep and those on the continental shelf. No photo-identification matches were found between Angola, Gabon and São Tomé. Re-sightings of two individuals occurred annually in São Tomé during 2002–2004. Killer whales had external appearance consistent with the Type A nominate species form. Antagonistic encounters were recorded between killer whales and humpback whales Megaptera novaeangliae off Angola, Gabon and Cameroon, and with sperm whales Physeter macrocephalus off Angola. Predation on ocean sunfish Mola mola was recorded in São Tomé, and possible predation on sharks was recorded twice in Gabon.

Three killer whale (Orcinus orca) sightings were recorded during the twelve month period from March 2008 to February 2009 in the northern Indian Ocean waters around Sri Lanka. This included the first sighting of this species during a dedicated cetacean survey. In the past three decades, several dedicated cetacean surveys have revealed high species richness around Sri Lanka, but no killer whale sightings were recorded. Records thus far have been limited to two, very old, unconfirmed sightings and a few specimens in the fisheries bycatch. Due to this paucity of records despite dedicated surveys, the species has been considered to be rare in these waters. It is of interest however, that three sightings were reported during a short time span of one year, when no sightings had been reported previously despite numerous dedicated cetacean surveys and opportunistic observations of cetaceans in these waters.

The presence of Orcinus orca in Venezuelan waters has remained somewhat unclear. On 15 April 2007 a group of three killer whales was recorded on video interacting with a leatherback turtle off north-eastern Venezuela. This report is based on an extensive review of the original video taken during the sighting event and a detailed interview with the observers. This record of killer whales interacting with Dermochelys coriacea, as well as opportunistic sightings recorded in photographs between 2001 and 2008, represent the most solid confirmation of the species occurrence in Venezuelan territorial waters.