Dolphin Cephalorhynchus Research Articles

Postcranial axial skeletal pathology in Commerson's dolphins Cephalorhynchus c. commersonii from Tierra del Fuego, Argentina.

Commerson's dolphins Cephalorhynchus c. commersonii are the small cetacean most frequently found stranded along the coast of Tierra del Fuego, Argentina, but little is known about their pathologies. We examined the postcranial axial skeleton of 425 Commerson's dolphins collected in the period 1974-2011 for the presence of pathologies. Miscellaneous lesions were detected in 107 (25.2%) of the specimens. Among them, idiopathic hyperostosis was the most frequent pathology (73.8%), followed by spondyloarthropathy (40.2%). Traumata (25.2%), spondylitis (10.3%) and osteoarthritis (11.2%) occurred less frequently. The type of lesion was statistically associated with the region of the vertebral column. Idiopathic hyperostosis occurred significantly more frequently in the lumbar vertebrae than in other parts of the vertebral column, while spondyloarthropathy was more frequent in the thoracic and caudal vertebrae. Both conditions were predominantly seen in mature dolphins. Osteoarthritis affected the transverse processes of the thoracic vertebrae of 6 males, 3 females and 3 individuals of undetermined sex, all mature. Healed and unhealed fractures were observed in the ribs of 27 specimens and in the transverse processes of 3 others. Spondylitis of various degrees of severity affected the cervical, thoracic, lumbar and caudal regions of 11 individuals. Together these data indicate that bone lesions and traumata commonly occur in Commerson's dolphins, likely causing pain and morbidity in severe cases.

CPOD successful in trial for detecting Māui dolphin outside harbours

ABSTRACTCritically endangered Māui dolphin (Cephalorhynchus hectori maui) are found exclusively off the west coast of New Zealand’s North Island. One important data gap troubling efforts to reduce the current unsustainable level of bycatch is the limited information on the offshore and alongshore limits of their range. Passive acoustic monitoring studies could address this data gap, but Māui dolphin habitat is dominated by a sandy substrate that can shift greatly in the strong local currents. In February 2016, a short pilot CPOD deployment was thus attempted as a first step to see if the equipment could be deployed and recovered in the area and if the data collected would be viable, with a second unit deployed inside a harbour for comparison with earlier TPOD data. The pilot was largely successful, and roughly 11% of all minutes in the core habitat location contained detections of clicks attributed to Māui dolphin. A visual inspection of the data suggests some trends with diel and tidal patterns. Further work of this type is thus recommended.

Occurrence of the Commersonʼs Dolphin (Cephalorhynchus commersonii) in Fitz Roy Channel, Pacific Coast of Chilean Patagonia

Occurrence of the Commersonʼs Dolphin (Cephalorhynchus commersonii) in Fitz Roy Channel, Pacific Coast of Chilean Patagonia

Mineral and essential element measurements in dolphin bones using two analytical approaches

ABSTRACTWe explored the potential of using energy-dispersive X-ray analysis (EDX), a non-destructive technique, to assess elemental contents in dolphin bones. Specimens were deposited in museum collections, and prepared by different methodologies. Fifty eight Commerson’s dolphins (Cephalorhynchus c. commersonii) chevron bones and 24 Franciscana dolphins (Pontoporia blainvillei) were analysed. The EDX allowed us to detect the following elements: Ca, P, Na, Mg, Fe, K, Zn, S, Cl and Al; and quantify their proportion (weight percent of element). Principal components analysis differentiates two groups according to the cleaning procedures applied, supporting that cleaning methods could influence the chemical integrity of bone. No significant age-dependent increase was found for elements analysed in species, and no significant differences were found between sex and physical maturity stages. Alternative assessment was made through atomic absorption spectrophotometry, providing quantitative information on the principal elements in bones (Ca, P, Mg, Na, Fe and Zn) and allowing comparisons with other studies. A standard protocol for bone cleaning and conditioning is needed to exclude any effect on the mineral integrity of calcified tissue. This would enable future comparative studies on the bone mineral matrix over time housed in natural history museums or other scientific collections.

Accounting for Lack of Independence and Partial Overlap of Observation Zones in Line-Transect Mark-Recapture Distance Sampling

Line-transect mark-recapture distance sampling methods can be used to estimate abundance when at least two observers sight and record distances to detected groups of individuals within the survey area. However, a lack of independence between the observer’s detections will cause biased abundance estimates. Studies are also typically designed such that there is complete overlap of the regions searched by the two observers, but that may not always be possible. Here we detail an intuitive approach for line-transect distance sampling applications based upon logistic regression to account for a potential lack of independence by using the detections of one observer as a covariate in the detection function of the second observer. Partial overlap of the observer survey regions can be addressed by constraining detection probability to equal 0 for the respective observer outside of the overlap zone. We show via simulation that the method provides reliable estimates of abundance and is not affected by random unmodeled heterogeneity in detection probability. The method is illustrated by estimating abundance within the covered region of an aerial line-transect survey for New Zealand’s endemic Hector’s dolphin (Cephalorhynchus hectori hectori) conducted in the austral summer of 2013, the motivating application for this work. Supplementary materials accompanying this paper appear on-line.

Distribution and abundance of Hector's dolphins (Cephalorhynchus hectori) off Kaikoura, New Zealand

Boat-based surveys of Hector's dolphins (Cephalorhynchus hectori) were conducted throughout 2013 to evaluate their distribution and abundance off Kaikoura. We conducted a total of 48 surveys and encountered 164 groups of Hector's dolphins. This study showed that Hector's dolphins off Kaikoura preferred areas of shallow, nearshore waters with poor water clarity and that there were more sightings to the north of the Kaikoura Peninsula than to the south. Using photo-identification techniques we identified 47 distinct individuals within the study area and these known individuals were only sighted either north or south of the Kaikoura Canyon. This study, combined with opportunistic sightings data collected from 2005–2013, improves our understanding of habitat use within the Kaikoura area by Hector's dolphins. These data suggest that the canyon area, characterised by very deep waters, could act as a natural barrier dividing the Hector's dolphins off Kaikoura into two separate groups.

Abundance and Spatial Distribution of Commerson’s Dolphin (Cephalorhynchus commersonii) at a Breeding Site: Ría Deseado, Patagonia, Argentina

Abundance and spatial distribution of the Commerson’s dolphin (Cephalorhynchus commersonii) during spring and summer 2002-2004 and fall/winter 2003 were estimated in the estuary Ria Deseado, Patagonia, Argentina. To estimate the abundance, photo-identification and mark-recapture (positive method) were combined. Distribution of dolphins within the estuary was studied, and their locations were recorded using a GPS to perform a Kernel Density Analysis. Adult abundance was higher during spring (34 and 35 individuals in 2002 and 2003, respectively) and decreased during fall (7 individuals) and winter (16 individuals). Sightings of 132 adults during winter, spring, and summer (n = 12, n = 76, and n = 44, respectively) and 14 calves during spring and summer (n = 4 and n = 10, respectively) were recorded; mean school size was 2.0 ± 1.2. Distribution and abundance varied seasonally. During spring, dolphins were more equally distributed through the estuary than during summer when calves and adults remained mainly inside the estuary. The presence of dolphins year-round suggested that the inhabitants are residents of the estuary. This study offers new information on the ecology of the Commerson’s dolphin and confirms Ria Deseado as a breeding site for this species.

RANGE AND MOVEMENTS OF FEMALE HEAVISIDE'S DOLPHINS (CEPHALORHYNCHUS HEAVISIDII), AS DETERMINED BY SATELLITE-LINKED TELEMETRY

Heaviside’s dolphin (Cephalorhynchus heavisidii) is a coastal delphinid with a limited inshore distribution off the west coast of southern Africa. Knowledge of its habitat usage is an essential precursor to assessing its potential vulnerability to fisheries interactions. Six Heaviside’s dolphins (1 male and 5 females) were fitted with satellitelinked transmitters in 2004, and tracked for up to 54 days. The 5 tags fitted to female dolphins transmitted continuously, allowing for analysis of movements at a fine temporal scale. Four dolphins showed an initial avoidance of the capture site by moving over a wider area in the first 2–5 days posttagging than later in the deployment period. All dolphins had used their full home ranges (determined as 100% minimum convex polygons) 5–20 days before tag failure, suggesting measured home ranges were stable at this temporal scale. Home-range estimates using local convex hulls ranged from 301.9 to 1,027.6 km 2 (90% isopleths) and 875.9 to 1,989.6 km 2 using the 100% isopleths and scaled positively with body size but varied in shape, usage, and number of core-use areas. Although the distance from shore and depth at which individual dolphins moved varied greatly, all dolphins showed a strong onshore–offshore diurnal movement pattern, generally being closest inshore between 0600 h and noon, and farthest offshore between 1500 h and 0500 h. This pattern is assumed to be related to the movements of their principal prey, juvenile shallow-water hake (Merluccius capensis), which migrate into the upper water column at night. Movements inshore may be associated with rest, socializing, and predator avoidance.

Nouvelles données sur les cétacés des îles Kerguelen / New data on cetaceans of the Kerguelen Islands

RésuméDes observations nouvelles et quelques échouages complètent le premier bilan faunistique établi en 1989 pour les îles Kerguelen. Aux neuf espèces identifiées précédemment ( Eubalaena glacialis , Balaenoptera acutorostrata , Megaptera novaeangliae , Physeter macrocephalus , Mesoplodon layardii , Cephalorhynchus commersonii , Lagenorhynchus cruciger , Orcinus orca , et Globicephala melas ) s'ajoutent, grâce à des échouages, deux nouvelles espèces: Ziphius cavirostris et Hyperoodon planifrons . En outre, la présence occasionnelle de Phocoena dioptrica est confirmée. L'événement le plus marquant est cependant le grand nombre d'observations (n=1649) de cachalots ( Physeter macrocephalus ) faites depuis 1989 au delà du plateau des îles, dans une zone peu fréquentée autrefois par les bateaux de pêche. Pour le dauphin de Commerson ( Cephalorhynchus commersonii ), espèce la plus commune, des données biologiques et écologiques s'ajoutent aux données faunistiques. Nous faisons également état, pour trois espèces ( Physeter macrocephalus , Orcinus orca , et Globicephala melas ), d'interactions avec la pêcherie à la palangre de la légine australe ( Dissostichus eleginoides ).

Feeding Associations between White-Fronted Terns and Hector's Dolphins in New Zealand

I investigated the relationship between White-fronted Terns (Sterna striata) associating with Hector's dolphins (Cephalorhynchus hectori) while feeding in the near-shore environment of New Zealand. Associations were observed only in the austral spring and early summer. At this time up to 15.7% of all dolphin groups were accompanied by terns. The birds usually joined surface-feeding dolphins with single terns apparently hovering over single dolphins. Associated tern numbers were positively correlated with dolphin group size and increased significantly with the duration of the association. Terns were more often associated with significantly larger dolphin groups and under calmer sea conditions. Water clarity, however, appeared to have little influence in the birds' decision whether or not to associate with a group of foraging dolphins. The occurrence of feeding associations appeared to be restricted by the occurrence of small, inshore moving fish species. The associations are likely to constitute facultative commensalism by the birds and may be particularly advantageous during breeding when energetic demands are high.

Near‐shore distribution and abundance of dolphins along the West Coast of the South Island, New Zealand

Compared to other stretches of the New Zealand coast, very little is known about the cetacean fauna off the West Coast of the South Island. The purpose of this paper is to describe the near‐shore distribution and abundance of dolphins in that area by summarising the results of two major studies. Between February 1995 and February 1997, 97 day trips were undertaken from Westport, Greymouth, and Jackson Bay in a small boat to survey the near‐shore distribution of dolphins. Between July 1994 and February 1997, 283 field days were spent on the water in Doubtful Sound studying the local bottlenose dolphin (Tursiops truncatus) population of c. 63 individuals. At the same time, three longer surveys were undertaken into other fiords of Fiordland which indicated the presence of further populations. Altogether, five delphinid species were recorded in various abundances. Small‐medium‐sized groups of Hector's dolphins (Cephalorhynchus hectori) with 1–60 individuals were observed in almost all areas of Westland in winter as well as in summer. Maximum densities peaked at 5–18 individuals per nautical mile of coastline between Cape Foulwind and Hokitika. Dusky and common dolphins (Lagenorhynchus obscurus and Delphinus delphis) occurred almost exclusively in summer in groups of 2–150 individuals, often with calves, especially at Cape Foulwind and Jackson Head. Bottlenose dolphins (Tursiops truncatus) and killer whales (Orcinus orca) were observed rarely off Westland, but occurred more frequently in Fiordland.

Morphologie externe et pigmentation du dauphin de Commerson, Cephalorhynchus commersonii (Lacépède, 1804), en particulier celui des îles Kerguelen

Accurate data on the external morphology and color pattern of Commerson's dolphin (Cephalorhynchus commersonii) off the Kerguelen Islands were obtained by studying 11 individuals. The total length of the animals is 142,6 to 174 cm and their weight ranges between 55 and 86 kg. Their coloration is black, grey, and white; a sexual dimorphism exists in the form of genital patches. As far as I know, these dolphins are much bigger and heavier than South American specimens. Their coloration also differs from the typically black and white pattern of the latter. These characteristics suggest that the Kerguelen Islands population is isolated from the main stock of the species.