Risso's Dolphin Research Articles

Disseminated Toxoplasmosis in a Mediterranean Pregnant Risso's Dolphin (Grampus griseus) with Transplacental Fetal Infection

Fatal disseminated toxoplasmosis was diagnosed in a Risso's dolphin (Grampus griseus) dam and its fetus on the basis of pathologic findings, immunohistochemistry, and structure of the parasite. The dolphin was stranded alive on the Spanish Mediterranean coast and died a few hours later. At necropsy the dam was in good condition. From the standpoint of pathology, however, it had generalized lymphadenomegaly and splenomegaly, enlargement of and multifocal hemorrhage in the adrenal glands, diffuse mucosal hemorrhage of the glandular and pyloric stomach, ulcerative glossitis and stomatitis, focal erosions and reddening of the laryngeal appendix, and severe paraotic sinusitis with intralesional nematodes Crassicauda grampicola. The dolphin was pregnant, most probably in the first gestational trimester. The most prominent microscopic lesions were multifocal granulomatous encephalomyelitis, diffuse subacute interstitial pneumonia, mild multifocal necrotizing hepatitis and nonsuppurative cholangiohepatitis, gastritis and adrenalitis, mild lymphoid depletion, medullary sinus and follicular histyocitosis, and systemic hemosiderosis. The fetus had foci of coagulative and lytic necrosis in the kidneys, the lung, and the heart. Most lesions were associated with tachyzoites and tissue cysts of Toxoplasma gondii. The diagnosis was confirmed immunohistochemically. This is the first report on toxoplasmosis in a Risso's dolphin (G. griseus) and on transplacental transmission to an early-stage fetus in any cetaceans.

Disseminated Toxoplasmosis in a Mediterranean Pregnant Risso's Dolphin (Grampus griseus) with Transplacental Fetal Infection

Disseminated Toxoplasmosis in a Mediterranean Pregnant Risso's Dolphin (Grampus griseus) with Transplacental Fetal Infection

SPATIOTEMPORAL PREDICTION MODELS OF CETACEAN HABITATS IN THE MID‐WESTERN NORTH ATLANTIC OCEAN (FROM CAPE HATTERAS, NORTH CAROLINA, U.S.A. TO NOVA SCOTIA, CANADA)

AbstractHabitat prediction models were developed for 13 cetacean species of the mid‐western North Atlantic Ocean: beaked whale, fin whale, humpback whale, minke whale, pilot whale, sperm whale, bottlenose dolphin, common dolphin, Risso's dolphin, spotted dolphin, whitesided dolphin, and harbor porpoise. Using the multiple logistic regression, sightings of cetaceans during the 1990–1996 summer (June‐September) surveys were modeled with oceanographic (sea surface temperature, monthly probability of front occurrence) and topographic (depth, slope) variables for the same period. Predicted habitat maps for June and August were created for each species using a Geographical Information System. The predicted habitat locations matched with current and historic cetacean sighting locations. The model also predicted habitat shifts for some species associated with oceanographic changes. The correct classification rate of the prediction models with 1997–1998 summer survey data ranged from 44% to 70%, of which most of the misclassifications were caused by false positives (i.e., absence of sightings at locations where the models predicted).

Evolution of group size in the dolphins and porpoises: interspecific consistency of intraspecific patterns

I investigated group size variability in dolphins and porpoises using intraspecific comparisons. Explanatory factors considered in the analysis were variables of the physical environment, the diet, and the life history of the species. Open habitat and small body size were viewed as increasing predation risk. This pattern was apparent in Risso's dolphins (Grampus griseus) and weakly apparent in bottlenose dolphins (Tursiops spp.). Group size was negatively correlated with body size in pilot whales (Globicephala spp.) and positively correlated with the openness of habitat in killer whales (Orcinus orca), striped dolphins (Stenella coeruleoalba), and common dolphins (Delphinus spp.). No such relationship was found for harbor and Dall's porpoises (Phocoena phocoena, P. dalli). Group size also seemed to vary depending on other physical measures of the habitat, which may indirectly reflect diet; group size showed U-shaped patterns if related to temperature. The predictive power of variables comprising detailed prey information on group size was variable. For example, pilot whales had smaller group sizes when they fed more on mesopelagic fish and less on mesopelagic cephalopods, and common dolphins had larger groups if they fed on varying types of fish. In most Delphinoidea species, group size could be described by the variables considered in this study. But each species showed its own pattern of correlations between group size and a specific set of explanatory variables. Thus, no general and consistent relation between group size and the other variables was found. It remains unknown whether these species-specific patterns result from a historical process or whether they are specialized adaptations. Copyright 2002.

Risso's dolphin ( Grampus griseus) stranding on the coast of Israel (eastern Mediterranean). Autopsy results and trace metal concentrations

The stranding of Risso's dolphin ( Grampus griseus) on the Mediterranean coast of Israel is reported in this study. High concentrations of trace metals (Hg, Cd, Zn, Fe and Se) were found in the various tissues analyzed, while Cu and Mn concentrations were naturally low. The specimen was found alive, but died a day later. The cause of death was attributed to bacterial bronchopneumonia in combination with endotoxemia, resulting in disseminated intravascular coagulation. Plastic bags found in its stomach contributed to the dolphin's poor physical condition. No connection was found between the high concentrations of trace metals in the internal organs and the cause of death. It is assumed that the high concentrations were a result of the high trophic level of this species, its diet and its advanced age. Anthropogenic influence could not be assessed due to the sparse database of trace metals for this species, in particular knowledge of the natural levels.

Mercury, organic-mercury and selenium in small cetaceans in Taiwanese waters

Total Hg (∑Hg), organic-Hg (O-Hg) and Se bioaccumulations in small cetaceans distributed in Taiwanese waters of the Taiwan Strait and the southwestern Pacific have been investigated for the first time. The results could represent the baseline metal concentrations of marine mammals in the southwestern Pacific, where volcanic activities are possibly the major source of mercury to the environments. Muscle samples of four species of small cetaceans were collected from animals accidentally caught by tuna-longline fisheries from 1994 through 1995. In total, 53 pantropical spotted dolphins, Stenella attenuata, nine spinner dolphins, S. longirostris, five bottlenose dolphins, Turiops truncatus and four Risso's dolphins, Grampus giseus were analyzed. In addition, two stranded pantropical spotted dolphins were investigated. Cold vapour AAS and ICP-MS were used in the analysis of Hg and Se, respectively. Significant species difference was found in the four species of small cetaceans. Among them, the pantropical spotted dolphin showed the highest mean concentration (mg/kg wet wt.) of both ∑Hg (3.64±2.19) and O-Hg (2.79±1.23), whereas the Risso's dolphin had the highest mean concentrations of Se (1.77±1.29). There was no significant sex difference with respect to metal bioaccumulation in the samples of S. attenuata. Significant correlations between body length (BL) and ∑Hg, as well as O-Hg concentrations were observed in pantropical spotted (Sa) and spinner dolphins (Sl). The linear relationships were Sa: ∑Hg=−8.290+0.066BL, r=0.421; Sl: ∑Hg=−2.735+0.025BL, r=0.875; Sa: O-Hg=−3.723+0.036BL, r=0.408; and Sl: O-Hg=−3.017+0.025BL, r=0.870. However, a demethylation phenomenon that decreasing the percentage of O-Hg coupled with increasing levels of Se was observed when the ∑Hg concentrations in the muscle tissues of dolphins reached 4 mg/kg wet wt.

A morphological study of the thyroid gland in Risso's Dolphin, Grampus griseus.

To accumulate histological information of cetaceans and basic information about metabolic systems of marine mammals, the thyroid gland of Risso's dolphins was examined by gross anatomical and light and electron microscopic observations. Gross anatomically, right and left lobes of the thyroid were not clearly discriminated, and no isthmus was observed. By light microscopy, irregular or oval follicular lumens were seen, and surrounded by follicular epithelial cells. By electron microscopy, the rough endoplasmic reticulum (rER) was seen adjacently to mitochondria at the basal and lateral regions of the follicular epithelial cells. RERs at the basal side of the cells sometimes contained flocculent material with the same electron density as the follicular lumen component. Microvilli were poorly developed at the apical surface of the cells. In the apical regions of the cells, there were typical Golgi complexes, multivesicular bodies, and granules with various size and electron density. The parafollicular cells were recognized among the follicular epithelial cells and in the interstitial regions but never protruded into the follicular lumen. These cells were present singly and/or formed clusters among the follicular epithelial cells, and often located adjacent to capillaries. They were obviously discriminated from follicular epithelial cells by higher electron density of their granules. In their cytoplasm, well-developed rERs, primary lysosomes, secondary lysosomes, multivesicular bodies, and phagosomes were recognized.

Distribution of Risso's dolphin (Grampus griseus, Cuvier 1812) in Chilean waters

En este trabajo se revisa la informacion del calderon gris Grampus griseus en aguas chilenas. En base al analisis de 44 registros, la distribucion a lo largo de la costa chilena parece ser continua entre los 20o13' S y 40o S, sugiriendo que los registros mas australes en Chile (~52oS) podrian corresponder a calderones grises provenientes del Oceano Atlantico. Los registros en Chile muestran un aumento durante el verano austral e indican una preferencia por aguas sobre los 1000 m de profundidad. Varamientos masivos, interacciones con pesquerias y asociaciones con otras especies de cetaceos son tambien revisadas.

Comparative external morphology of cetacean spermatozoa

SUMMARY: To compare size and morphology of spermatozoa in cetaceans, sperm and epididymis samples were collected from 10 species in four families and spermatozoa were observed with phase-contrast and scanning electron microscopes. According to the average total length of the spermatozoa, the 10 species examined were classified into the following four groups in order of increasing size: (i) Baird's beaked (Ziphiidae) and Bryde's whales (Balaenopteridae); (ii) Dall's and finless porpoises (Phocoenidae); (iii) common, bottlenose, and Pacific white-sided dolphins (Delphinidae); and (iv) killer and short-finned pilot whales, and Risso's dolphin (Delphinidae). Spermatozoa head length of Bryde's whale and the finless porpoise were shorter than those of the other species. Spermatozoa head width was widest in the killer whale and thinnest in the Baird's beaked whale. The lateral aspects of sperm heads from the 10 species were characterized as the ‘anterior region of the sperm head is thin and flat while the posterior region is thick.’ The dorsal aspects of sperm heads were ‘paddle-shaped’ in Bryde's whales, ‘bowling pin-shaped’ in Baird's beaked whales, ‘Japanese fan-shaped’ in killer whales, an ‘elongated ellipsoid shape’ in Delphinidae except for killer whales, and ‘ellipsoid shaped’ in Phocoenidae. Size and morphology of the spermatozoa showed interspecific differences among the 10 species examined, which correspond to cetacean taxonomic classification.

Cetaceans of the Atlantic Frontier, north and west of Scotland

Surveys carried out to the north and west of Scotland have recorded 15 species of cetacean between 1979 and 1998. These were fin whale ( Balaenoptera physalus) , sei whale ( B. borealis) , minke whale ( B. acutorostrata) , humpback whale ( Megaptera novaeangliae) , sperm whale ( Physeter macrocephalus) , northern bottlenose whale ( Hyperoodon ampullatus) , Sowerby's beaked whale ( Mesoplodon bidens) , killer whale ( Orcinus orca) , long-finned pilot whale ( Globicephala melas) , Atlantic white-sided dolphin ( Lagenorhynchus acutus) , white-beaked dolphin ( L. albirostris) , Risso's dolphin ( Grampus griseus) , bottlenose dolphin ( Tursiops truncatus) , common dolphin ( Delphinus delphis) and harbour porpoise ( Phocoena phocoena) . Atlantic white-sided dolphin was the most abundant species in the region with a total of 6317 animals recorded. Harbour porpoise was the most frequently sighted cetacean species. The geographical distribution of sightings indicate that cetacean species have varying ecological requirements, with species such as sperm whale, pilot whale and white-sided dolphin favouring deep water off the continental shelf edge, while minke whale, white-beaked dolphin and harbour porpoise were apparently limited to the continental shelf. The diversity of species recorded in the region suggests that the Atlantic Frontier is an important habitat for cetaceans.

Vocalizations of eastern Australian Risso's dolphins, Grampus griseus

Recordings were made from a group of Risso's dolphins (Grampus griseus) off the coast of Newcastle, Australia, between 30 Hz and 22 kHz. Risso's dolphins exhibited seven separate vocalisation types: broadband clicks, barks, buzzes, grunts, chirps, whistles, and simultaneous whistle + burst-pulse sounds. Broadband clicks were highly variable in duration, with a frequency range of 6 to >22 kHz. Bark vocalisations consisted of highly variable burst pulses, with durations ranging from 0.2 to 7.4 s and a frequency range of 2-20 kHz. Buzz vocalisations were clearly stereotyped, consisting of a short burst pulse of around 2 s and a frequency range of 2.1 to >22 kHz. Low frequency narrowband grunt vocalisations (0.4–0.8 kHz) were short in duration. Chirp vocalisations were slightly higher in frequency than the grunt vocalisations, ranging in frequency from 2 to 4 kHz. There were at least five different whistle types, ranging in frequency from 4 to 22 kHz. We recorded a combined tonal and burst-pulse vocalisation. The rising whistles ranged from 6 to 18 kHz, while the burst-pulse sounds ranged between 3 and 21 kHz. This combined whistle + burst pulse sound appears to be unique to Risso's dolphins.

Vocalizations of eastern Australian Risso's dolphins, <i>Grampus griseus</i>

Recordings were made from a group of Risso's dolphins (Grampus griseus) off the coast of Newcastle, Australia, between 30 Hz and 22 kHz. Risso's dolphins exhibited seven separate vocalisation types: broadband clicks, barks, buzzes, grunts, chirps, whistles, and simultaneous whistle + burst-pulse sounds. Broadband clicks were highly variable in duration, with a frequency range of 6 to >22 kHz. Bark vocalisations consisted of highly variable burst pulses, with durations ranging from 0.2 to 7.4 s and a frequency range of 2-20 kHz. Buzz vocalisations were clearly stereotyped, consisting of a short burst pulse of around 2 s and a frequency range of 2.1 to >22 kHz. Low frequency narrowband grunt vocalisations (0.4–0.8 kHz) were short in duration. Chirp vocalisations were slightly higher in frequency than the grunt vocalisations, ranging in frequency from 2 to 4 kHz. There were at least five different whistle types, ranging in frequency from 4 to 22 kHz. We recorded a combined tonal and burst-pulse vocalisation. The rising whistles ranged from 6 to 18 kHz, while the burst-pulse sounds ranged between 3 and 21 kHz. This combined whistle + burst pulse sound appears to be unique to Risso's dolphins.

Killer Whales (Orcinus orca) Sighted West of Ni'ihau, Hawai'i

A rare sighting of five killer whales (Orcinus orca), including one juvenile, occurred on 20 March 2000 during an aerial survey of waters west of the Hawaiian island of Ni'ihau. The sighting occurred ca. 11 km west of Kamalino Bay on Ni'ihau, at 21049' N, 160020' W. Killer whales are not unknown in Hawaiian waters, but the most recent confirmed sighting on record for Hawaiian waters was in 1979. ON 20 MARCH 2000 during an aerial survey of marine mammals in Hawaiian waters, four large delphinids and one juvenile were sighted approximately 11 km west of Kamalino Bay on Ni'ihau (21049' N, 160020' W) in waters approximately 1830 m (1000 fathoms) deep. The animals were circled for 7 min at an altitude of 244 m, during which time two photographs (Figure 1) were obtained through a belly window using a Pentax 645 camera with a 206-mm lens. Simultaneously, altitude measurements were obtained with a radar altimeter (Collins 50A). Positive identification of species at the time of sighting was hampered by glare. One observer (M.W.N.) commented that the animals appeared unusually robust. In the absence of positive identification, the sighting was recorded as unidentified delphinids. Subsequent inspection of the photographs revealed clear diagnostic features of killer whales (Orcinus orca), including evidence of white eye patches on three individuals, white anus patch on two individuals, a relatively tall dorsal fin on one individual, and light gray saddle marking behind the dorsal fin of one 1 Manuscript accepted 30 October 2000. 2 Social Sciences, University of Hawai'i-West O'ahu, 96-129 Ala Ike, Pearl City, Hawai'i 96782. 3 National Marine Mammal Laboratory, 7600 Sand Point Way NE, Seattle, Washington 98115-0070. 4 Kewalo Basin Marine Mammal Laboratory, 1129 Ala Moana Boulevard, Honolulu, Hawai'i 96814. 522371 Hartman Drive, Los Altos, California 94024. Pacific Science (2001), vol. 55, no. 3:301-303 © 2001 by University of Hawai'i Press All rights reserved individual. The clearest diagnostic feature evident in the photographs was the characteristic wide, paddle-shaped flippers that are almost as wide as they are long (Leatherwood et al. 1988). Leatherwood et al. (1988) noted that killer whales can sometimes be confused with false killer whales (Pseudorca crassidens) and Risso's dolphins (Grampus griseus). However, the paddle-shaped flippers distinguish them from both of these species, and the dark coloration and larger body size (~9 m) distinguish them from Risso's dolphins (~4 m). By knowing the precise altitude via the radar altimeter, combined with the use of a calibrated camera system, we were able to apply standard photogrammetric techniques (Baker 1960, Perryman and Lynn 1993) to the two photographs. We estimated that the adults ranged in length from approximately 4.7 to 6.5 m, and the juvenile was approximately 3.8 m in length. In the first photograph, the four adults were arranged two abreast, with the juvenile trailing behind. In the second photograph, taken several minutes later, the adults were spread farther apart and the juvenile appeared to be swimming either canted to one side or inverted (based on the greater proportion of white coloration) just behind and below the right pectoral flipper of the largest adult. It is likely that this adult was a male, due to the larger flippers and flukes (Dahlheim and Heyning 1999). Killer whales are not unknown in Hawaiian waters, but are sufficiently rare to be worthy of note. The earliest record appeared in the Honolulu Star-Bulletin of 26 February 1938 (cited in Tomich 1986), which described a sighting off Olowalu, Maui. Because

Isomer‐specific polychlorinated biphenyl determination in cetaceans from the mediterranean sea: Enantioselective occurrence of chiral polychlorinated biphenyl congeners

AbstractIsomer‐specific concentrations of 41 polychlorinated biphenyls (PCBs) and the enantiomeric ratios (ER) of nine chiral PCBs were determined in the liver of four cetacean species—Risso's dolphin (Grampus griseus), bottlenose dolphin (Tursiops truncatus), fin whale (Balaenoptera physalus), and long‐finned pilot whale (Globicephala melaena)—found dead in the Mediterranean Sea. The total PCB concentration (sum of 41 congeners) ranged from 484 to 63,200 ng/g wet weight. The 2,3,7,8 tetra‐chlorodibenzo‐p‐dioxin (TCDD) toxic equivalents (TEQs), as defined by the World Health Organization (WHO), ranged from 4.3 to 1,454 pg/g wet weight. The contribution of mono‐ortho PCBs was consistently higher than non‐ortho PCB congeners, in whale species, whereas in dolphins this predominance was not so clear. The PCB profiles were dominated by congeners 138, 153, and 180 in almost all the investigated samples. Comparison of PCB profiles by using principal component analysis allowed to separate the species into different groups. Polychlorinated biphenyls 170 and 180 seem to be eliminated by the two whale species, and PCB 180 also seems to be eliminated by Risso's dolphins. The PCBs 95, 132, 149, and 176 revealed an enantiomeric excess of the second eluted enantiomer in almost all the cetaceans investigated, where 136 and 174 were racemic or almost racemic. It is the first time that an enantiomeric excess of PCB 84 and 91 has been reported in biological samples. Although it was only possible to calculate them in two dolphin liver samples, the high values of enantiomeric excess found are surprising (86.3 and 32% for PCB 91 and 84, respectively).

Ovarian histology of minke whale and Risso's dolphin stranded on the coast of Niigata district, Sea of Japan

Ovarian histology of minke whale and Risso's dolphin stranded on the coast of Niigata district, Sea of Japan

Histopathological and immunohistochemical studies on cetaceans found stranded on the coast of Italy between 1990 and 1997.

Detailed histopathological and immunohistochemical studies were carried out on 24 cetaceans, 17 of which were striped dolphins (Stenella coeruleoalba), four bottlenose dolphins (Tursiops truncatus) and three Risso's dolphins (Grampus griseus), all found stranded on the Italian coast between 1990 and 1997. The most frequently detected lesions were chronic pneumonia (73.7% of the examined lungs), focal chronic pancreatitis (71.4%), non-purulent encephalitis (50%), chronic hepatitis (42.1%), and chronic focal interstitial nephritis (31.2%). The skin and the subcutaneous panniculus were often (33.3%) affected by parasitic diseases (Phyllobothrium delphini and Pennella sp.). An appreciable percentage of animals showed lymphoid depletion in their lymphatic organs (47.2%), as well as a high rate of parasitic infestations in their alimentary tracts (25%).

Distribution of mercury in the organs and tissues of five toothed-whale species of the Mediterranean

Mercury levels were determined in the tissues and organs (lung, liver, kidney, skin, muscle, bone) of five toothed-whales stranded along the Corsican coast between November 1993 and February 1996. The species taken into consideration were the bottlenose dolphin Tursiops truncatus, the common dolphin Delphinus delphis, the striped dolphin Stenella coeruleoalba, the pilot whale Globicephala melas and the Risso's dolphin Grampus griseus. The variation in mercury levels between the different tissues and organs (lung, liver, kidney, skin, muscle, bone) of the cetacean species are discussed as regards storage, biotransformation and elimination. In all cases, the liver appears to be the preferential organ for mercury accumulation (with concentrations as high as 4250 μg Hg/g dw and 3298 μg Hg/g in the livers of Tursiops truncatus and Grampus griseus, respectively). The kidney and lung are the next organs in terms of mercury uptake followed by the muscle, bone and skin. The stomach contents of Grampus griseus and D. delphis were determined and consisted of cephalopods for Grampus griseus, and of sardines Sardina pilchardus and mackerels Trachurus sp. for D. delphis. Cephalopods had higher mercury concentrations (25.4 μg Hg/g dw) than fish (ca 1 μg Hg/g). These contents represent only one meal and mercury levels found in livers may integrate mercury uptake having occurred during the whole life span of animals.

NEW HOST RECORD FOR THE WHALE LOUSE ISOCYAMUS DELPHINII (AMPHIPODA, CYAMIDAE)

Isocyamus delphinii (Gu?rin-M?neville, 1836) was described from the com mon dolphin, Delphinus delphis L., 1758. It has subsequently been recorded from Risso's dolphin, Grampus griseus (G. Cuvier, 1812), the long-finned pilot whale, Globicephala melas (Traill, 1809), the short-finned pilot whale, Globi cephala macrorhynchus Gray, 1846, the white-beaked dolphin, Lagenorhynchus albirostris (Gray, 1846), the false killer whale, Pseudorca crassidens (Owen, 1846), the rough-toothed dolphin, Steno bredanensis (Lesson, 1828), the harbor porpoise, Phocoena phocoena (L., 1758), the bottlenose dolphin, Tursiops trunca tus (Montagu, 1821), and the Antillian beaked whale, Mesoplodon europaeus Ger vais, 1855. For documentation of the above host records, the reader is referred to Martin & Heyning, 1999 (their table 1 and Literature Cited section) and to Haney (unpubl.). The killer whale, Orcinus orea (L., 1758), is also listed as a host for /. delphinii in Sedlak-Weinstein (1992), who cites Best (1969) for the host record. One of the present authors (Haney), however, found no such reference in Best's report, so the record of this cyamid species from the killer whale is considered doubtful. Although Isocyamus delphinii has been reported on the aforementioned ceta cean hosts from various localities in the North Atlantic and Pacific oceans, it has only once been previously recorded from a cetacean in the Gulf of Mexico (Bowman, 1955).

Heavy metals and methylmercury in tissues of Risso's dolphin (Grampus griseus) and Cuvier's beaked whale (Ziphius cavirostris) stranded in italy (South Adriatic sea).

Heavy metals acquired through the food chain or absorption via the water as a result of marine pollution are a potential threat to dolphins. In fact, marine mammals are known to accumulate these contaminants with extremely high concentrations because they occupy a top trophic position in the ecosystem. Mercury is one of the heavy metals to cause most concern in the marine ecosystem because its elevated toxicity, especially when present in the organic form(s). Since toxic heavy metal and methylmercury concentrations can vary considerably among and within species depending upon factors such as growth, lactation, parturition, tissue analysed, etc, it is important to determine baseline data for both species.

Quantitative analysis of tonal calls from five odontocete species, examining interspecific and intraspecific variation

Whistle vocalizations of five odontocete cetaceans, the false killer whale P. crassidens, short-finned pilot whale G. macrorhynchus, long-finned pilot whale G. melas, white-beaked dolphin L. albirostris and Risso's dolphin G. griseus, were analysed and summarized quantitatively. Recordings were acquired from a number of locations and encounters. Significant differences were found between species and, to a lesser extent, between locations. The calls of the two pilot whale species are distinct despite their close relatedness, and similar size and morphology. This may be due to selection pressures to maintain distinctiveness. The variance was partitioned into between-species, between-location (within species) and within-location factors. For the frequency variables, variation between-species is high relative to variation between locations. Thus geographic variation is a relatively minor effect, compared to the many processes which cause interspecific differences. The within-location component includes such factors as social context, behaviour and group composition. This component is of a similar magnitude to the between-species component, indicating that whistles vary considerably with these factors. Significant between-location differences may be attributable to these confounding factors. For whistle duration, most of the variation occurred within location. There is less significant variation in duration across species compared with the frequency measures. This study highlights the need to collect samples across all potential strata whenever possible, and provides a framework for future, more comprehensive work.