Short-finned Pilot Research Articles

Hearing Loss in Stranded Odontocete Dolphins and Whales

The causes of dolphin and whale stranding can often be difficult to determine. Because toothed whales rely on echolocation for orientation and feeding, hearing deficits could lead to stranding. We report on the results of auditory evoked potential measurements from eight species of odontocete cetaceans that were found stranded or severely entangled in fishing gear during the period 2004 through 2009. Approximately 57% of the bottlenose dolphins and 36% of the rough-toothed dolphins had significant hearing deficits with a reduction in sensitivity equivalent to severe (70–90 dB) or profound (>90 dB) hearing loss in humans. The only stranded short-finned pilot whale examined had profound hearing loss. No impairments were detected in seven Risso's dolphins from three different stranding events, two pygmy killer whales, one Atlantic spotted dolphin, one spinner dolphin, or a juvenile Gervais' beaked whale. Hearing impairment could play a significant role in some cetacean stranding events, and the hearing of all cetaceans in rehabilitation should be tested.

Cetacean diversity and distribution off Tenerife (Canary Islands)

Dedicated surveys were conducted along the south-west and north-east coasts of Tenerife (Canary Islands), between 1997 and 2006, to gather baseline information on cetacean diversity, abundance, spatial and temporal distribution. A total of 1016 sightings of sixteen cetacean species was recorded during the study period. Sightings were recorded throughout the year although the period in which the highest number of species were sighted was in spring and summer (from May through to August). The most frequently sighted species were bottlenose dolphin (Tursiops truncatus) and short-finned pilot whale (Globicephala macrorhynchus), which together comprised 82% of the total sightings. These were followed by common dolphin (Delphinus delphis), Atlantic spotted dolphin (Stenella frontalis) and dense beaked whale (Mesoplodon densirostris) which represented 9% of the total sightings. Most sightings were recorded along the south-west coast of Tenerife, where the distribution of the different species seemed to be influenced by water depth. Calves were present during sightings of almost every recorded species, especially in toothed whales. Two mother–calf pairs of fin whales (Balaenoptera physalus) were also observed. This suggests that the surveyed area, or at least the south-west sub-area, might play an important role as a calving ground for the four most frequently sighted species. The information acquired in this study indicates that the waters around Tenerife constitute an important habitat for cetaceans.

The use of stable isotope analyses from skin biopsy samples to assess trophic relationships of sympatric delphinids off Moorea (French Polynesia)

Defining trophic relationships among organisms of a community is critical in ecology. However, the access to data is sometimes difficult, particularly in remote environments. Ecological niche segregation among the most common delphinid species was investigated: the spinner dolphin ( Stenella longirostris), the roughed-toothed dolphin ( Steno bredanensis), the short-finned pilot whale ( Globicephala macrorhynchus), and the melon-headed whale ( Peponocephala electra). Resource partitioning was explored by analysing δ 13C (reflecting foraging habitats) and δ 15N stable isotopes (reflecting trophic level) from skin biopsies collected around Moorea from July to October 2002 to 2004. Results revealed that spinner dolphins had the lowest trophic level. The three other species had similar δ 15N signatures. The most significant result is the differentiation of S. longirostris from S. bredanensis and G. macrorhynchus but not from the P. electra. For the latter three species, some degrees of overlap were apparent. For S. longirostris, S. bredanensis and G. macrorhynchus, variation of δ 13C and δ 15N stable isotope was not significant between sexes. This study suggests that stable isotopes reveal some degree of segregation and overlap within this delphinid community. However, fine-scale segregation processes may be concealed by stable isotope analyses, meaning that traditional dietary analyses investigations are complementary in answering questions related to niche segregation.

The Philippine Marine Mammal Strandings from 1998 to 2009: Animals in the Philippines in Peril?

A well-maintained marine mammal stranding database can be an invaluable tool in understanding not only strandings but also changes in the marine environment. This study aimed to examine the following aspects of marine mammal strandings in the Philippines: species composition, temporal (i.e., frequency of stranding per year and seasonality) and spatial (i.e., frequency of stranding per region and province) variation, proportions of alive or dead specimens, and stranding hotspots. In 2008, a systematic collection of data on strandings, including out-of-habitat incidents, resulted in an initial 12-year database—from 1998 to 2009. A total of 178 stranding events were recorded: 163 single, 10 mass, and 5 out-of-habitat strandings, with an average of 15 observed stranding events annually. Twenty-three of the 28 confirmed species of marine mammals in the Philippines were recorded to strand, including first-recorded specimens for the Indo-Pacific bottlenose dolphin (Tursiops aduncus), pygmy sperm whale (Kogia breviceps), and Longman’s beaked whale (Indopacetus pacificus). The top five most frequent species to strand included spinner dolphin (Stenella longirostris) (n = 26), short-finned pilot whale (Globicephala macrorhynchus) (n = 14), melon-headed whale (Peponocephala electra) (n = 13), Risso’s dolphin (Grampus griseus) (n = 11), and common bottlenose dolphin (T. truncatus) (n = 10). Dugongs (Dugong dugon) stranded seven times since 2001. Strandings occurred throughout the year with frequency significantly peaking during the northeast (NE) monsoon (November to March) season. Overall, Regions III (Central Luzon) and VII (Central Visayas) had the highest number of strandings (both n = 27) followed by Regions I (Ilocos) (n = 22) and V (Bicol) (n = 18). The following provinces or local government units were considered hotspots based on high number of strandings observed at each area: Zambales, Cagayan, Zamboanga City, Negros Oriental, Bohol, Pangasinan, and Bataan. Sixty-five percent of all documented stranding events involved live (n = 116) animals. This high percentage might be linked to dynamite fishing (causing acoustic trauma), fisheries interactions, or biotoxins from harmful algal blooms coupled to their foodweb. These strandings in general validate the diverse marine mammal assemblage in the Philippines and reveal the various environmental threats with which they deal.

Long‐term abundance trends of the northern form of the short‐finned pilot whale (Globicephala macrorhynchus) along the Pacific coast of Japan

AbstractThe abundance of the northern form of the short‐finned pilot whale,Globicephala macrorhynchus, in the Pacific waters of northern Japan was estimated from a line transect survey conducted in 2006 and data from seven previous surveys collected between 1985 and 1997. To overcome the difficulty of small sample size and inconsistency in survey design, we used an adjustment method using multiple covariates and sensitivity analysis by considering several scenarios. Abundance estimates showed similar long‐term trends among scenarios. The northern form ofG. macrorhynchuswas more abundant in 1985 than in 1991–2006. The annual catch of the northern form ofG. macrorhynchusexceeded the potential biological removal (PBR), especially in the 1980s. Thus, the commercial take in the early 1980s was suspected as a partial cause of a serious abundance decrease. These results provide valuable information for interpreting the impacts of coastal whaling, and to develop future management plans.

Trends in cetacean sightings along the Galician coast, north-west Spain, 2003–2007, and inferences about cetacean habitat preferences

Since mid-2003, systematic monthly sightings surveys for cetaceans have been carried out in Galicia (north-west Spain) from observation points around the coastline, with the aim of providing baseline data on cetacean distribution and habitat use to underpin future conservation measures. Here we summarize results for September 2003 to October 2007. The most frequently recorded species were the bottlenose dolphin (Tursiops truncatus, seen during 10.7% of observation periods), common dolphin (Delphinus delphis, 3.7%), harbour porpoise (Phocoena phocoena, 1.6%), Risso's dolphin (Grampus griseus, 0.4%) and short-finned pilot whale (Globicephala melas, 0.2%). The three most common species showed different distribution patterns along the coast. In terms of habitat preferences, bottlenose dolphins were seen to be associated with more productive areas (areas with higher chlorophyll-a concentrations) where the continental shelf was wider while both common dolphins and harbour porpoises were seen most frequently in less productive areas where the continental shelf is narrowest. Possible reasons for differences in habitat use include differing diets. In Galician waters, all three main cetacean species feed primarily on fish that are common in shelf waters, and in the case of blue whiting (the most important species in the stomach contents of common and bottlenose dolphins) abundant also on the slope. All three cetaceans feed on blue whiting while scad is important in diets of common dolphin and porpoise. It is also possible that porpoises do not use areas frequented by bottlenose dolphins in order to avoid aggressive interactions. Retrospective evaluation of the sampling regime, using data from the 2500 observation periods during 2003–2007 suggests that the overall sightings rates for all species (taking into account observation time and between-site travel time) would be higher if average observation duration was increased to at least 40 minutes. On the other hand, confidence limits on sightings rates stabilized after around 1000 observation periods, suggesting that the number of sites visited or the frequency of visits could be substantially reduced.

Metazoan parasites of cetaceans off the northeastern coast of Brazil

This study represents the first survey of the parasitic fauna of cetaceans off the northeastern coast of Brazil. Parasites were collected from 82 animals rescued from the states of Ceará to Bahia, including the archipelago of Fernando de Noronha. A total of 14 species of cetaceans were evaluated: Sotalia guianensis, Stenella sp., Stenella clymene, Stenella longirostris, Stenella coeruleoalba, Stenella frontalis, Megaptera novaeangliae, Peponocephala electra, Steno bredanensis, Kogia breviceps, Kogia sima, Globicephala macrorhynchus, Tursiops truncatus, Physeter macrocephalus and Lagenodelphis hosei. The parasites were fixed and preserved in 70% ethanol or alcohol–formalin–acetic acid solution (AFA), clarified in phenol and mounted on slides for morphological identification. In total, 11 species and 8 genera of endo- and ectoparasites were identified: Halocercus brasiliensis, Halocercus kleinenbergi, Stenurus globicephalae, Halocercus sp., Anisakis sp., Crassicauda sp. (Nematoda), Phyllobothrium delphini, Monorygma grimaldii, Scolex pleuronectis, Strobicephalus triangularis, Tetrabothrius forsteri, Tetrabothrius sp., Trigonocotyle sp., Diphyllobothrium sp. (Cestoda), Campula sp. (Trematoda), Bolbosoma sp. (Acanthocephala), Cyamus boopis, Syncyamus pseudorcae and Xenobalanus globicipitis (Crustacea). The identification of some species represented novel records for the country and increased the occurrence of some parasites to new hosts. The use of standardized methodologies for collecting and evaluating a larger number of animals is essential for a better understanding of host-parasite relationships in cetaceans and their use as biological indicators in the region.

Phylogenetic analysis of a new Cetacean morbillivirus from a short-finned pilot whale stranded in the Canary Islands

Cetacean morbillivirus (CeMV) is considered the most pathogenic virus in cetaceans. Three strains have been already described: the dolphin morbillivirus (DMV), the porpoise morbillivirus (PMV) and the tentatively named pilot whale morbillivirus (PWMV). This study describes the molecular characterization of a strain of CeMV detected in the brain of a short-finned pilot whale that had stranded in the Eastern Atlantic Ocean around the Canary Islands and that showed lesions compatible with morbilliviral disease. Sequences for the nucleoprotein, phosphoprotein, fusion protein and haemagglutinin genes were obtained. The phylogenetic study showed high homology (97%) with the PWMV strain previously detected from a long-finned pilot whale stranded in the Western Atlantic Ocean. These results support the existing classification of CeMV into three principal genetic clusters.

Spinner dolphin ( Stenella longirostris) and other cetaceans in Raja Ampat waters, West Papua

Cetaceans were surveyed using ship transects across the seas of Raja Ampat (West Papua) in November and December 2007. Sighting effort reached 120 hours, over a total distance of 1561 km. The most common cetacean sighted was the spinner dolphin, Stenella longirostris (~0.238 individuals/km), most frequently in pods of 15-20 individuals, in relatively-shallow to deep waters (82-2310 m). All those spinner dolphins that were positively identified from photographs were of the pelagic form (S. l. longirostris). Other cetaceans sighted were the short-finned pilot whale, Globicephala macrorhynchus, Risso's dolphin, Grampus griseus, the bottlenose dolphin, Tursiops sp., the false killer whale, Pseudorca crassidens and the sperm whale, Physeter macrocephalus.

Species occurrence of cetaceans in Guinea, including humpback whales with southern hemisphere seasonality

An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documented primarily from specimens and photographic evidence obtained from strandings and by-catches. Seven species are fully validated, four odontocetes, Tursiops truncatus, Sousa teuszii, Stenella frontalis, Kogia breviceps and three balaenopterid whales: Balaenoptera brydei, Balaenoptera acutorostrata and Megaptera novaeangliae. Another three reported species (Globicephala macrorhynchus, Steno bredanensis and Delphinus delphis) are insufficiently supported but thought to be valid. Small cetaceans landed as by-catch and a stranded whale were used for human consumption, but no evidence of substantial takes, directed or by-catch, was found. However, concern is raised about even minimal takes of the vulnerable Atlantic humpback dolphin. The seasonal presence of three confirmed humpback whales, two strandings (July and September) and a sighting (October), is synchronous with the species' southern hemisphere wintering/breeding season in low latitudes. We hypothesize that these whales may comprise the north-westernmost range of the population that breeds/overwinters in coastal waters of the Bight of Benin, northern Gulf of Guinea.

The Cetaceans of Ghana, a Validated Faunal Checklist

The cetaceans of Ghana and the Gulf of Guinea have, until recently, remained unstudied. Periodical monitoring of artisanal fisheries for bycatches in seven Ghanaian artisanal fishing ports and landing sites over 1996-2004 has provided photographic and specimen evidence to validate occurrence of 18 species (17 odontocetes, 1 mysticete) in a tropical, predominantly pelagic cetacean fauna. At least nine species and subspecies had not previously been documented for Ghana (with asterisk), and four species are authenticated for the first time in the Gulf of Guinea (double asterisk), i.e. Tursiops truncatus, Stenella clymene, S. longirostris longirostris*, S. attenuata, S. frontalis, Delphinus capensis capensis*, Lagenodelphis hosei, Steno bredanensis, Grampus griseus, Peponocephala electra*, Feresa attenuata**, Globicephala macrorhynchus, Orcinus orca*, Pseudorca crassidens*, Kogia sima**, Physetermacrocephalus*, Ziphius cavirostris** and Megaptera novaeangliae . Also, the limited published information on distribution, natural history and conservation status is critically reviewed for each taxon. Indications are that most species encountered off Ghana may be widely distributed in the Gulf of Guinea, most notably the long-beaked common dolphin. The vulnerable Atlantic humpback dolphin, Sousa teuszii, remains unrecorded in Ghana and neighbouring nations despite apparently suitable coastal habitat. It is suggested that localized extinction may be blamed, possibly the result of accumulative bycatches and disturbance. A number of other cetacean species not yet encountered could occasionally occur in Ghana’s waters, e.g. Balaenoptera brydei, Mesoplodon densirostris, Kogia breviceps, Stenella coeruleoalba and Delphinus delphis

The odontocete community and its environment in the southwestern Gulf of California

Community structure is a function of the number of species, their relative abundance and the characteristics of the dominant, common and rare species that are part of it. It also can be described by changes in its physical and biological environment. The aim of the present work is to describe the odontocete community, its temporal changes and the relationship with environmental variability and food availability in the southwestern Gulf of California (GC). Information was obtained from 21 sampling trips from September 2003 to March 2006 between La Paz Bay and Loreto, with a sampling effort of 8769.1km. We recorded the presence, location and other biological parameters of odontocete sightings. Data on environmental variability was obtained from satellite images of sea surface temperature and chlorophyll concentration, and food availability from published reports. A total of 30201 odontocete cetaceans were recorded from 353 sightings, belonging to 10 different species. We observed a temporal lag between the peaks in productivity and an increased presence of odontocete species. The community structure showed a seasonal change in the abundance of the dominant (Tursiops truncatus and Delphinus sp.) and common species (Globicephala macrorhynchus and Kogia sp.), as well as by the absence or presence of scarce (Physeter macrocephalus and Orcinus orca) and rare species (Pseudorca crassidens and Lagenorhynchus obliquidens). This seasonal community change is in agreement with the known seasonal movements of its main prey inside the GC, which, in turn, is related to seasonal environmental variation. We observed that the community structure was dominated by fish-eating species during the temperate season and responded to the increased presence and aggregation of sardines (Sardinops sagax caerulea) in the southern GC, whereas the warm season was dominated by squid-eating species and related to the increased presence and aggregation of the jumbo squid (Dosidicus gigas) in the GC's west coast.

Mandibular fractures in short-finned pilot whales, Globicephala macrorhynchus

This study's objective was to investigate mandibular fractures in 50 short-finned pilot whales, Globicephala macrorhynchus, from two mass strandings. Based on current theories that this species is sexually dimorphic and polygynous, hypotheses were: (1) males should suffer more frequent or more substantial mandibular fractures than should females, and (2) fracture occurrence should increase with male reproductive maturity and potential correlates of maturity, such as age and length. Fractures were described and correlated with physical characteristics to infer possible explanations for injuries. Mandibular fractures were surprisingly common in males and females, being found in more than half of the animals examined (27/50, or 54% overall; 17/36 or 47% of females and 10/14 or 71 % of males). Length was the only correlate of fracture presence; the proportion of animals showing evidence of fracture increased with length. These results offer some support to initial hypotheses, but there must be another set of consequences that contribute to mandibular fractures in females. A combination of intra- and interspecific interactions and life history characteristics may be responsible for fractures. Further research from a larger sample of this and other cetacean species are suggested to help elucidate both the causes and implications of mandibular fractures.

Body Scars and Dorsal Fin Disfigurements as Indicators Interaction Between Small Cetaceans and Fisheries Around the Mozambique Channel Island of Mayotte

Cetacean bycatch in fisheries occur in all oceans of the world and may have both lethal and non-lethal consequences (body injuries). In the lagoon of Mayotte (12o50’S, 45o10’E), in the northern Mozambique Channel, two main types of fisheries occur: handlining (inside the lagoon) and longlining (outside the barrier reef, over the ‘continental’ slope). The level of interactions between small cetaceans and fisheries in this area were characterised using identification photographs taken from July 2004 to April 2008 during dedicated cetacean surveys. Photographs were taken of Indo-Pacific bottlenose dolphins (Tursiops aduncus), melon-headed whales(Peponocephala electra) and short-finned pilot whales (Globicephala macrorhynchus). Injuries on the dorsal region (especially the dorsal fin) were characterised and related to fisheries or intra-/inter-specific interactions (with sharks and other cetacean species). The results suggest interactions with fisheries involving the three species around Mayotte. The occurrence of interactions was the highest in the most coastal species, i.e. T. aduncus. This study shows that interactions between fisheries and small cetaceans occur at varying levels around Mayotte. It also confirms the utility of scars as indicators of fishery exposure to cetaceans.

Vessel noise effects on delphinid communication

Increasing numbers and speeds of vessels in areas with populations of cetaceans may have the cumulative effect of reducing habitat quality by increasing the underwater noise level. Here, we first use digital acoustic tags to demonstrate that free-ranging delphinids in a coastal deep- water habitat are subjected to varying and occasionally intense levels of vessel noise. Vessel noise and sound propagation measurements from a shallow-water habitat are then used to model the potential impact of high sound levels from small vessels on delphinid communication in both shallow and deep habitats, with bottlenose dolphins Tursiops sp. and short-finned pilot whales Globicephala macrorhynchus as model organisms. We find that small vessels travelling at 5 knots in shallow water can reduce the communication range of bottlenose dolphins within 50 m by 26%. Pilot whales in a quieter deep-water habitat could suffer a reduction in their communication range of 58% caused by a vessel at similar range and speed. Increased cavitation noise at higher speeds drastically increases the impact on the communication range. Gear shifts generate high-level transient sounds (peak- peak source levels of up to 200 dB re 1 µPa) that may be audible over many kilometres and may dis- turb close-range animals. We conclude that noise from small vessels can significantly mask acousti- cally mediated communication in delphinids and contribute to the documented negative impacts on animal fitness.

Preliminary account of cetacean diversity and humpback whale (Megaptera novaeangliae) group characteristics around the Union of the Comoros (Mozambique Channel)

Abstract Cetacean diversity and occurrence has never been investigated in the Union of the Comoros, located in the northern Mozambique Channel. Small boat-based surveys were conducted during the austral winter of 2002, primarily to assess the occurrence of humpback whales (Megaptera novaeangliae) and whether the area represents a wintering ground where the species reproduce. All other cetacean species were also recorded. Opportunistic sighting records were used to provide information on the diversity of cetaceans occurring in the area. Between 2000 and 2003, 12 cetacean species were recorded around the Comoros, including: Megaptera novaeangliae, Stenella longirostris, Peponocephala electra, Stenella attenuata, Tursiops truncatus, Globicephala macrorhynchus, Mesoplodon densirostris, Physeter macrocephalus, Lagenodelphis hosei, Grampus griseus, Mesoplodon pacificus and possibly Tursiops aduncus. During the dedicated surveys, the humpback whale was the most commonly encountered species (72% of sightings) followed by the spinner dolphin (15%). Humpback whale group composition was heterogeneous, but mother-calf pairs were the most commonly sighted (49%). This study demonstrates that the Union of the Comoros is an important site for migrating humpback whales in the southwest Indian Ocean and for a wide variety of toothed cetacean species.

Worldwide mitochondrial DNA diversity and phylogeography of pilot whales (Globicephala spp.)

Pilot whales (Globicephala spp.) provide an interesting example of recently diverged oceanic species with a complex evolutionary history. The two species have wide but largely non-overlapping ranges. Globicephala melas (long-finned pilot whale; LFPW) has an antitropical distribution and is found in the cold-temperate waters of the North Atlantic and Southern Hemisphere, whereas Globicephala macrorhynchus (short-finned pilot whale; SFPW) has a circumglobal distribution and is found mainly in the tropics and subtropics. To investigate pilot whale evolution and biogeography, we analysed worldwide population structure using mitochondrial DNA (mtDNA) control region sequences (up to 620 bp) from a variety of sources (LFPW = 643; SFPW = 150), including strandings in New Zealand and Tasmania, and whale-meat products purchased on the markets of Japan and Korea. Phylogenetic reconstructions failed to support a reciprocal monophyly of the two species, despite six diagnostic substitutions, possibly because of incomplete lineage sorting or inadequate phylogenetic information. Both species had low haplotype and nucleotide diversity compared to other abundant widespread cetaceans (LFPW, π = 0.35%; SFPW, π = 0.87%) but showed strong mtDNA differentiation between oceanic basins. Strong levels of structuring were also found at the regional level. In LFPW, phylogeographic patterns were suggestive either of a recent demographic expansion or selective sweep acting on the mtDNA. For SFPW, the waters around Japan appear to represent a centre of diversity, with two genetically-distinct forms, as well as a third population of unknown origin. The presence of multiple unique haplotypes among SFPW from South Japan, together with previously documented morphological and ecological differences, suggests that the southern form represents a distinct subspecies and/or evolutionary significant unit. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 729–744.

Additional records of metazoan parasites from Caribbean marine mammals, including genetically identified anisakid nematodes

Studies of marine mammal parasites in the Caribbean are scarce. An assessment for marine mammal endo- and ectoparasites from Puerto Rico and the Virgin Islands, but extending to other areas of the Caribbean, was conducted between 1989 and 1994. The present study complements the latter and enhances identification of anisakid nematodes using molecular markers. Parasites were collected from 59 carcasses of stranded cetaceans and manatees from 1994 to 2006, including Globicephala macrorhynchus, Kogia breviceps, Kogia sima, Lagenodelphis hosei, Mesoplodon densirostris, Peponocephala electra, Stenella longirostris, Steno bredanensis, Trichechus manatus. Tursiops truncatus, and Ziphius cavirostris. Sixteen species of endoparasitic helminthes were morphologically identified, including two species of acanthocephalans (Bolbosoma capitatum, Bolbosoma vasculosum), nine species of nematodes (Anisakis sp., Anisakis brevispiculata, Anisakis paggiae, Anisakis simplex, Anisakis typica, Anisakis ziphidarium, Crassicauda anthonyi, Heterocheilus tunicatus, Pseudoterranova ceticola), two species of cestodes (Monorygma grimaldi, Phyllobothrium delphini), and three species of trematodes (Chiorchis groschafti, Pulmonicola cochleotrema, Monoligerum blairi). The nematodes belonging to the genus Anisakis recovered in some stranded animals were genetically identified to species level based on their sequence analysis of mitochondrial DNA (629 bp of mtDNA cox 2). A total of five new host records and six new geographic records are presented.

Site fidelity and association patterns of a rare species: Pygmy killer whales (Feresa attenuata) in the main Hawaiian Islands

AbstractMost of what we know about cetacean biology and ecology comes from studies of relatively common species. Despite their distribution throughout the tropics and sub‐tropics, pygmy killer whales (Feresa attenuata) are rare throughout their range and are one of the most poorly‐known species of odontocetes. During a 22‐yr study of short‐finned pilot whales (Globicephala macrorhynchus) off the island of Hawai‘i, we opportunistically photo‐identified pygmy killer whales whenever encountered. As part of a directed multi‐species study throughout the main Hawaiian Islands from 2000 through 2007, we also photo‐identified individuals and obtained information on habitat use and behavior. This species was extremely uncommon (representing only 1.2% of odontocete sightings in directed efforts). Given the low encounter rates, assessing trends of this population cannot be feasibly done with line‐transect surveys. Despite their rarity, 80% of the distinctive individuals within groups documented off the island of Hawai‘i were seen on multiple occasions, individuals were resighted over periods of up to 21 yr, and there was evidence of year‐round use of the area. Association analyses indicate stable long‐term associations in mixed‐sex groups. High resighting rates indicate a small population of island‐associated individuals that may be at risk from anthropogenic impacts.

Comparison of odontocete populations of the Marquesas and Society Islands (French Polynesia)

Small boat surveys were organized to study cetaceans of the Marquesas (9°S and 140°W) and the Society Islands (17°S and 150°W) in French Polynesia. Prospecting took place from 12–15 m sailboats, between 1996 and 2001 with systematic visual searching. Boats moved according to sea conditions, at a mean speed of 10 km/h. Effective effort of 4856 km in the Marquesas and 10,127 km in the Societies were logged. Relative abundance indices were processed for odontocetes using data obtained with Beaufort 4 or less. In the Marquesas, 153 on-effort sightings were obtained on 10 delphinids species including the spotted dolphin, spinner dolphin, bottlenose dolphin, melon-headed whale and rough-toothed dolphin. In the Societies, 153 sightings of 12 odontocetes included delphinids (spinner, rough-toothed and bottlenose dolphins, short-finned pilot and melon-headed whales, Fraser's dolphin, Risso's dolphin and pygmy killer whale) and two species of beaked whales, the sperm whale and dwarf sperm whale. Relative abundance indices were higher in the Marquesas than in the Societies both inshore (0.93 ind/km2against 0.36 ind/km2) and offshore (0.28 ind/km2against 0.14 ind/km2). Differences in remote-sensed primary production were equally important, the Marquesas waters featuring an annual average of 409 mgC.m−2 · day−1and the Societies of only 171 mgC · m−2 · day−1. The presence of a narrow shelf around the Marquesas also accounted for differences in odontocete populations, in particular the delphinids.