The historical and contemporary presence of southern right whales (SRWs; Eubalaena australis) around the Falkland Islands (Malvinas) has received little recognition. We assessed SRW occurrence in the Falklands via whaling records, a literature review, systematic surveys (boat, aerial and shore-based), and citizen science sightings. The combined data sources indicated a year-round (peaking in austral summer) presence of SRWs in pelagic areas around the Falklands. In contrast, most nearshore records originated in the austral late autumn and winter (May to August), including a marked increase in sightings along the north-east coast during 2017 compared with previous years. The data support spatio-temporal variation in the use of Falklands waters by SRWs. Pelagic waters appear to comprise summer foraging habitat, and may also be used by animals migrating between the Patagonian shelf and feeding grounds located further south and east. The peak numbers observed in nearshore waters occurred earlier in the winter (July) than those on the Argentinean or Brazilian calving grounds (Aug–Oct). Consequently, some whales may have continued migrating northwards to established breeding areas after departing Falklands waters. A component of the south-west Atlantic population could also be using the islands as a novel wintering destination, for mating and/or socializing (no calving has been confirmed to date). The importance of Falklands waters as a multi-use SRW habitat appears to be increasing. The region is important in the context of addressing current knowledge gaps regarding feeding grounds and migratory corridors highlighted in international SRW conservation and management plans for the wider South-west Atlantic.

The coastal waters of east Lewis from the Butt of Lewis to Loch Erisort are a proposed Marine Protected Area (MPA) for Risso's dolphins (Grampus griseus). A total of 100.4 h (2006.4 km) of active search effort (Beaufort sea states ≤3) was collected during 72 dedicated boat surveys between 2010 and 2017 (primarily in August and September) in the southern part of the MPA and south to the Shiant Isles. Forty Risso's dolphin sightings and 24.1 h of encounter effort were recorded, predominantly along the southern and eastern Eye Peninsula in 20–40 m water depths and at distances <1 km from shore. Group size ranged from one to 50 animals (mean = 11.8 dolphins) and calves occurred in 37.5% of sightings. A total of 2404 shore-based scans (Beaufort sea states ≤3) carried out from Tiumpan Head between September 2011 and December 2017 resulted in 271 (11.3%) ‘dolphin-present’ scans. Dolphins were present year-round, with a seasonal increase between May and October. ‘Calf-present’ scans only occurred between April and October. Photo-identification images from 28 boat surveys produced a minimum population size of 117 animals. There was evidence of high inter- and intra-annual site fidelity, with individual dolphins photographically captured in up to six of the eight survey years, and between two and seven capture dates being recorded for over 45% of individuals within most years. The combined datasets support the importance of east Lewis for Risso's dolphins, and recommendations are made for ongoing monitoring of dolphin occurrence throughout the wider MPA.

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.

A sighting of four Atlantic humpback dolphins (Sousa teuszii) was recorded and photographed close to the Benin coast on 3 November 2013. This is the first record of the species for Benin, and also represents the first verified record within a 3,065 km stretch of coast extending from Sierra Leone to Nigeria (encompassing the entire northern coast of the Gulf of Guinea). The sighting supports the possibility that some other potential range states may have remained unconfirmed to date due to a paucity of field research in suitable nearshore habitat rather than an absence of the species.

Hybrid cetaceans have been documented to occur both in the wild and in captivity. Identifying wild hybrid individuals can be problematic in the absence of genetic techniques, but published accounts indicate that intermediate morphological characteristics are often present. Between 2010 and 2013, a land-based and boat-based study of the Risso's dolphin (Grampus griseus) was carried out in nearshore waters around the Eye Peninsula located on north-east Lewis, Scotland. Three atypical individuals were photographed which exhibited morphological features intermediate between Grampus and the common bottlenose dolphin (Tursiops truncatus). These individuals were typically larger in body size than Tursiops, and had a dorsal fin shape and size consistent with Grampus. Two individuals had coloration most similar to Tursiops and the third exhibited extensive white linear scarring consistent with Grampus. The intermediate morphology was most apparent in the head shape, with all three individuals exhibiting a defined (in contrast to Grampus) but very short (compared with Tursiops) rostrum and two having an unusually steep (compared with Tursiops) forehead. On one occasion, one of the atypical individuals was observed within a mixed-species school of Grampus and Tursiops. There were four further sightings of atypical dolphins associated with Tursiops-only schools. Atypical dolphins were not recorded within Grampus-only schools. These observations are consistent with hybridization between free-ranging Risso's and bottlenose dolphins, the first such occurrence to be documented for these species in UK waters. The context and significance of these hybridization events are unknown.

The waters off north-west Scotland are known to provide important habitat for the harbour porpoise (Phocoena phocoena) and the minke whale (Balaenoptera acutorostrata). Between October 2008 and April 2011, systematic land-based surveys were carried out to assess the seasonal occurrence, group size and group behaviours of both species in a study area located off Melvaig, near Gairloch. Data were collected on 47 separate days, with a total of 4543 minutes of survey effort (in sea states ≤3) recorded during the spring months and 8204 minutes of effort during the autumn. A total of 189 sightings of marine fauna were recorded, comprising 126 cetacean sightings, 50 seal sightings and 13 sightings of basking sharks (Cetorhinus maximus). Six species of cetacean were identified, with most sightings comprising harbour porpoise (N = 72) or minke whale (N = 38). Harbour porpoise abundance was higher in autumn than in spring and there was a variation between years in numbers of minke whales sighted. In porpoises, sea state and cloud cover both influenced sightings and increasing sea state influenced survey area. Foraging behaviour was exhibited in 13% of harbour porpoise sightings and 34% of minke whale sightings. Results demonstrate a regular occurrence of harbour porpoises and minke whales in nearshore waters off Gairloch. Densities are comparable to boat surveys in the region and so support the use of land-based watches as a potential longer-term monitoring method for these species in coastal waters. Given the regular use of this area by these two European Protected Species, as well as the occurrence of a range of human activities potentially affecting them in the region, it may be appropriate to consider protecting this area for their conservation.

The cetacean fauna inhabiting the poorly-studied waters of the eastern tropical Atlantic (ETA), along the west coast of Africa, is still being described. Information on the cetacean species occurring in specific ETA range states is important for understanding their geographical distribution ranges and for implementing conservation and management measures. Here we provide photographically-verified records for the occurrence of pygmy killer whale (Feresa attenuata) off Côte d'Ivoire and of Fraser's dolphin (Lagenodelphis hosei) off Gabon. These records represent new range state records for both species, and are also the first verified at-sea sightings in the ETA and the Gulf of Guinea respectively.

The false killer whale Pseudorca crassidens is currently documented from only six eastern tropical Atlantic (ETA) range states, five of which are evidenced by strandings, by-catch or skeletal remains rather than at-sea sightings and consequently provide no information on habitat or behaviour. Here we report six false killer whale records from cetacean surveys carried out off Gabon (four records) and Côte d'Ivoire (two records) between 2002 and 2012, providing the first at-sea sightings in those two existing range states. All six sightings were located in continental shelf waters (≤103 m depth) and in relatively nearshore (mean = 13.9 km) habitat. Forty-three false killer whales were photo-identified during three encounters on the Gabonese shelf; seven individuals were matched between 2002 and 2006, including two individuals that were present during all three sightings. Observations included predation of Atlantic sailfish Istiophoms albicans and two occurrences in proximity to humpback whales Megaptera novaeangliae. Whistles recorded during one sighting had simple structure, short duration and a mean fundamental frequency of 7.8 kHz. These are the first verified records of false killer whales using continental shelf waters in the ETA, indicating that the species occupies neritic habitat in the region in addition to its previously-documented oceanic habitat. The re-sightings of marked individuals between sightings and years suggest that at least some individuals exhibit a degree of site fidelity to Gabonese shelf waters. Further information on distribution, abundance, movements, population structure and mortality rates are required for effective management of the species in the ETA.

The habitat preferences and niches of eight cetacean species inhabiting eastern tropical Atlantic waters between Angola and Gabon (1°N–11°S latitude) were examined. A total of 2873 cetacean sightings, recorded between January 2004 and June 2009, was assigned to 10 × 10 km grid cells and linked to four ecogeographical variables (EGVs): water depth, seabed slope, sea surface temperature (SST) and relative frontal strength. Classification trees revealed that the habitat preferences (in terms of the habitats sampled) of most species were primarily determined by SST (for Bryde's whale, sperm whale, short-finned pilot whale and common dolphin) and water depth (for Risso's dolphin, bottlenose dolphin and Atlantic spotted dolphin). Seabed slope was the most important EGV describing the presence of the striped dolphin. A principal component analysis was used to compare the niches of the species with respect to the four EGVs. Nineteen species pairs (68%) differed significantly in median principal component (PC) score for the first PC axis, suggesting differences in their niche centres for that axis. Sixteen species pairs (57%) differed significantly in PC score variance suggesting differences in the niche widths along the first PC axis. Water depth and SST were the most important variables for the first PC axis. Together, these results suggest that cetacean species inhabiting the eastern tropical Atlantic exhibit interspecific variation in their habitat preferences, and so differ in the niches that they occupy. These differences are most likely related to variation in prey species and foraging strategy.

The occurrence of the rays belonging to the genera Mobula (known collectively as the ‘devil rays’) and Manta is poorly documented in the eastern tropical Atlantic. Between August 2004 and September 2005, a total of 28 mobulid ray observations were recorded from geophysical survey vessels operating in the waters between Gabon and Angola. Water depth at the location of the sightings varied from 30 to 4000 m, reflecting an occurrence in both neritic and oceanic habitat. While most animals were unidentified to species level, photographs taken during two sightings facilitated the identification of two separate species/species groups of Mobula. The first individual, photographed at the surface in deep water offshore of northern Angola, was identified as belonging to the M. mobular/M. japanica species group, comprising two species that are very similar in appearance and which future evidence may reveal to represent a single species. The second animal, photographed off Pointe Noire in the Republic of the Congo, was identified as a bentfin devil ray (M. thurstoni). The previously documented southernmost records of these species in the eastern tropical Atlantic were in the Mediterranean Sea (M. mobular), Côte d'Ivoire (M. japanica) and Senegal (M. thurstoni). These observations therefore extend the known distribution ranges into the south-east Atlantic Ocean.

A total of 168.4 hours of visual cetacean survey work was carried out in association with two geophysical surveys in Montserrat waters (eastern Caribbean) during December 2007 and May 2010, using a seismic vessel as a platform of opportunity. Nine cetacean sightings were recorded: pantropical spotted dolphin Stenella attenuata (N = 2), Fraser's dolphin Lagenodelphis hosei (N = 1), sperm whale Physeter macrocephalus (N = 1), humpback whale Megaptera novaeangliae (N = 1), and sightings of unidentified dolphins (N = 1) and large whales (N = 3). A total of 73.3 hours of acoustic monitoring effort was carried out during December 2007, resulting in 19 cetacean detections. Sperm whale (N = 10) and unidentified dolphin (N = 7) detections predominated. Two acoustic detections were of pantropical spotted dolphins, corresponding with visual sightings. An opportunistic sighting of 14 pygmy killer whales Feresa attenuata during October 2008 was reported. Although the humpback whale was known previously for Montserrat waters, the sightings of other species represent the first verified records for the state.

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.

Knowledge of the whale shark, Rhincodon typus, in the south-east Atlantic off the coast of West Africa is limited to several bycatch and stranding records. Ten at-sea sightings of whale sharks from Angola (N = 9) and Nigeria (N = 1) are presented, consisting of nine sightings from offshore platforms and a single record from a helicopter. Eight of the records were from oceanic waters exceeding 1000 m, while single records originated from shelf-edge and continental shelf waters. The records support a year-round occurrence of whale sharks in offshore West African waters, although the majority (N = 8) of sightings occurred during the spring and summer months between September and January. Most sightings (N = 8) were of whale sharks estimated to be in the 5–7 m length-range. These records represent the first verified at-sea sightings in the West Africa region providing novel information on behaviour and distribution, and also confirm Nigeria as a range state for the whale shark.

Little marine mammal research has been carried out along the West African coastline, and the cetacean fauna is consequently poorly documented. Namibe Province in southern Angola was the site of several historical whaling stations, but current knowledge of the occurrence of large whales and odontocete species is lacking. A dedicated cetacean study was carried out off Flamingos, Namibe Province during the austral summer and winter of 2008. A total of 1161.2 km (96.5 hours) of boat-based search effort, 531.8 km (49.2 hours) of vehicle-based search effort and 46.6 hours of fixed-site survey effort was collected, during which 148 cetacean sightings were recorded. The 143 positively-identified sightings comprised Atlantic humpback dolphin Sousa teuszii (N = 71), bottlenose dolphin Tursiops truncatus (N = 24), Bryde's whale Balaenoptera cf. brydei (N = 37) and humpback whale Megaptera novaeangliae (N = 11). The Atlantic humpback dolphin occurred similarly in both summer and winter and occupied a strictly nearshore habitat usually within 300 m of the coast. Both the absolute number of sightings and the sighting rate of bottlenose dolphins were higher during the winter than the summer. Bryde's whale was present only during the summer survey. While present during both survey periods, humpback whales were more numerous during the winter. The dataset increases knowledge of the cetaceans occurring off southern Angola. However, further survey work is required to clarify the distribution, ecology and potential threats to cetacean species in the region.

A decline in white-beaked dolphins Lagenorhynchus albirostris had been reported in the Minch (Scotland, UK) since the 1990s, coinciding with an increasing occurrence of short-beaked common dolphins Delphinus delphis. This has led to suggestions that rising seawater temperatures are causing D. delphis to out-compete and exclude L. albirostris in this region. A total of 793 km (66.3 hours) of survey data were collected in the Minch during August 2007, to examine fine-scale habitat selection by L. albirostris and D. delphis and investigate whether their ecological overlap is sufficient to result in interspecific competition and/or habitat partitioning. Ten sightings of L. albirostris (70 animals) were recorded in a relatively small spatial area in the northern Minch. In contrast, the eleven sightings of D. delphis (1486 animals) were more widely distributed. The relative abundance per 1/4 ICES rectangle ranged from 0.41 to 0.53 animals/km for L. albirostris and 0.13 to 6.68 animals/km for D. delphis. The mean group size and group body mass were higher for D. delphis than for L. albirostris indicating D. delphis as the dominant delphinid in the Minch during August. Lagenorhynchus albirostris occurred in waters significantly deeper and further from shore than D. delphis, suggesting interspecific differences in preferred habitat. Most dolphin schools were recorded as foraging/feeding. Behaviour and seabird associations indicated that the two species differed in diet and/or foraging strategy, with L. albirostris foraging sub-surface and D. delphis exhibiting surface-feeding with associated gannets Morus bassanus. This is consistent with published information on the stomach contents of Scottish animals. The results suggest that there are subtle differences in habitat selection and diet between these two species, which may enable L. albirostris and D. delphis to coexist in the Minch. Whether these differences result from niche partitioning arising from previous/ongoing interspecific competition or are the result of genuine differences in the habitat preferences of each species, remains unclear.

The white-beaked dolphin (Lagenorhynchus albirostris) and short-beaked common dolphin (Delphinus delphis) are two of the most abundant delphinid species in shelf waters around the United Kingdom (UK) and Republic of Ireland (ROI) in the summer season (May–October). As these two species have similar habitat preferences and diets, it might be expected that they would partition their otherwise shared niche to reduce the potential for competition at this time of year. This study used 569 sightings of the two species, collected from shelf waters (<200 m water depth) in the summer season between 1983 and 1998, to investigate whether there is evidence of widespread niche partitioning based on water temperature in this area. Below 13°C, white-beaked dolphins were dominant with 96% of sightings comprising this species. In contrast, above 14°C, 86% of sightings comprised common dolphins. A classification tree analysis found that of the four eco-geographical variables analysed (water depth, seabed slope, seabed aspect and sea surface temperature), temperature was the most important variable for separating the occurrence of the two species. These results are consistent with widespread temperature-based niche partitioning between white-beaked and common dolphins in shelf waters around the UK and ROI. As temperature is important in determining the relative distribution of these species, the range of the white-beaked dolphin might be expected to contract in response to increasing sea temperature resulting from global climate change, while that of the common dolphin may expand.

The status of marine turtles in Angola, West Africa, is poorly known, and therefore during 2000–2006 a combination of both dedicated and opportunistic beach and at-sea turtle surveys were carried out, and interviews conducted with fishing communities and at markets. Green Chelonia mydas, olive ridley Lepidochelys olivacea, leatherback Dermochelys coriacea and loggerhead turtles Caretta caretta were recorded, and nesting of the first three species confirmed during September–March (peaking November–December). Green turtles nested mainly in the south, leatherback turtles in north and central Angola, and olive ridley turtle nesting was widespread. Olive ridley turtle nest density at Palmeirinhas averaged 32 nests km−1. At-sea surveys produced 298 turtle records, with peak occurrence during August. Significant anthropogenic-related mortality (including exploitation of meat and eggs and fishing bycatch) was recorded, in addition to natural predation and other threats. Maintenance of the long-term sustainability of these turtle populations should focus on the involvement of fishing communities and increasing awareness throughout Angola.

Sperm whales (Physeter macrocephalus) typically produce sharp onset, broadband pulse sounds at varying repetition rates. Acoustic recordings of different social units of sperm whales in the Mediterranean Sea included apparent non-click sounds of tonal quality, termed ‘squeals’. Quantitative analysis of the spectral signal and waveform indicate that although squeals are perceived as tonal and appear spectrally as narrowband frequency-modulated structures with harmonics, they actually consist of pulses at high repetition rates exceeding 1600 clicks/s. Squeals contained energy at between 400 Hz and 22 kHz, with mean peak energy at the relatively low frequency of 700 Hz. Five spectral forms of squeal could be recognized, with the dominant form (45%) of squeals showing a decrease in frequency along the squeal contour. Mean click repetition rate ranged between 713 and 1385 clicks/s for individual squeals, and also varied within squeals at rates of between 64 and 444 clicks/s. Variation in click repetition rate was reflected in the frequency spacing of the spectral sidebands, in a statistically significant inverse relationship. Squeals were recorded only during bouts of sperm whale social behaviour, consistent with their having a communicative social function. Sperm whale squeals are structurally and audibly similar to the burst-pulse sounds produced by many smaller odontocete species, and might fall on the continuum between distinct click trains and pure-tone whistles.

Most North Sea cetacean species are wide-ranging and consequently poorly studied. Spatial and temporal trends in the distribution of the harbour porpoise Phocoena phocoena, white-beaked dolphin Lagenorhynchus albirostris, and minke whale Balaenoptera acutorostrata were assessed at a coastal North Sea study area in Aberdeenshire, Scotland. Between March 1999 and October 2001, cetacean data were collected using both land- and vessel-based survey methods. A total of 174 sightings of these three cetacean species was recorded during approximately 330 h of combined survey effort (228 h land-based and 102 h vessel-based). Harbour porpoises were present throughout the year with peak occurrence during August and September. The presence of white-beaked dolphins and minke whales was strictly seasonal, with a peak in occurrence during August. The fine-scale distribution of all three species varied within the study area, with an apparent preference for sections of coast adjacent to deeper water. Most porpoise calves and juveniles were recorded between June and September, when 35% of harbour porpoise groups contained immature animals. The proportion of calves amongst porpoise sightings was higher during June than any other month. White-beaked dolphin calves were present in 32% of groups, and occurred in all three months that the species was recorded. Group size was higher in white-beaked dolphin pods containing immature animals. The strong seasonality in occurrence of all three species may relate to requirements for breeding habitat, movements of shared prey species and/or inter-specific competition with other species.

This study used classification and regression trees (CART) to investigate and compare the habitat preferences of marine mammals in this area. Data were collected in early summer (June/July) in 2004 and 2005 and the distribution of marine mammal species was compared to 10 ecogeographic variables (EGVs). Of 13 species of marine mammals sighted during the study, there were sufficient sightings to examine the habitat preferences of seven. For all species a measure of ‘shelf tendency’ (distance to coast or water depth) was an important variable and the species could be separated into two groups, the deep-water species and the shelf species, with little overlap between them. The occurrence of both deep-water species (long-finned pilot whales and Atlantic white-sided dolphins) was also related to dynamic variables such as sea surface temperature (SST) or primary productivity. Two of the shelf species (northern minke whales and grey seals) were only linked to topographic variables and were limited to quite specific habitats. A third species (harbour porpoise) was primarily related to topographic variables, but in the shallowest waters was also related to local variation in SST. The occurrence of the final two species (common and white-beaked dolphins) was linked to SST and local primary productivity. However, while both species preferentially occurred in areas with higher productivity, the two species differed in their preference for SST, with common dolphins preferentially occurring in warmer waters and white-beaked dolphins in colder waters.