Dusky Dolphins Research Articles

Multi-locus phylogeography of the dusky dolphin (Lagenorhynchus obscurus): passive dispersal via the west-wind drift or response to prey species and climate change?

BackgroundThe dusky dolphin (Lagenorhynchus obscurus) is distributed along temperate, coastal regions of New Zealand, South Africa, Argentina, and Peru where it feeds on schooling anchovy, sardines, and other small fishes and squid tightly associated with temperate ocean sea surface temperatures. Previous studies have suggested that the dusky dolphin dispersed in the Southern Hemisphere eastward from Peru via a linear, temperate dispersal corridor provided by the circumpolar west-wind drift. With new mitochondrial and nuclear DNA sequence data, we propose an alternative phylogeographic history for the dusky dolphin that was structured by paleoceanographic conditions that repeatedly altered the distribution of its temperate prey species during the Plio-Pleistocene.ResultsIn contrast to the west-wind drift hypothesis, phylogenetic analyses support a Pacific/Indian Ocean origin, with a relatively early and continued isolation of Peru from other regions. Dispersal of the dusky dolphin into the Atlantic is correlated with the history of anchovy populations, including multiple migrations from New Zealand to South Africa. Additionally, the cooling of the Eastern Equatorial Pacific led to the divergence of anchovy populations, which in turn explains the north-south equatorial transgression of L. obliquidens and the subsequent divergence of L. obscurus in the Southern Hemisphere.ConclusionOverall, our study fails to support the west-wind drift hypothesis. Instead, our data indicate that changes in primary productivity and related abundance of prey played a key role in shaping the phylogeography of the dusky dolphin, with periods of ocean change coincident with important events in the history of this temperate dolphin species. Moderate, short-term changes in sea surface temperatures and current systems have a powerful effect on anchovy populations; thus, it is not infeasible that repeated fluctuations in anchovy populations continue to play an important role in the history of coastal dolphin populations.

Functional significance of bronchial sphincters in two Southwestern Atlantic Dolphins: Pontoporia blainvillei and Lagenorhynchus obscurus: a comparative approach

The existence of myoelastic sphincters in the terminal airways of some cetaceans is well established. Although several studies have tried to explain the functional role of these structures, none of them has been based on a comparative analysis. The present study was initiated with the purpose of investigating whether differences in the morphology of myoelastic sphincters are related to different diving patterns. We have compared serial histological lungs sections from two dolphin species with different diving patterns. In Pontoporia blainvillei, a shallow diving dolphin, myoelastic sphincters are thin rings with irregular distribution, which occasionally strangle the airway. Lagenorhynchus obscurus, with deeper dives and faster vertical displacements, presents thicker sphincters with regular distribution, generally strangling the airway completely. We conclude that these morphologies could be related to different functional demands. We suggest the existence of two groups of dolphins, one shallow diver, comprising small cetaceans with less developed sphincters whose functional activity is uncertain, and another group with a wider diving range, having strong and functional sphincters.

Population structure of nuclear and mitochondrial DNA variation among South American Burmeister’s porpoises (Phocoena spinipinnis)

Little is known about the biology of Burmeister’s porpoises (Phocoena spinipinnis), a small cetacean species endemic to South American waters. Information on stock structure, however, is urgently needed, as the species suffers from considerable mortality due to local fishery activities throughout its distribution range. Using mitochondrial control region sequences and 11 species-specific microsatellite loci, we assessed the genetic differentiation among 118 stranded, incidentally or directly-caught Burmeister’s porpoises from different localities in Peruvian, Chilean, and Argentine waters. F-statistics and Bayesian clustering analyses indicate a major population differentiation along the South American Pacific coast, separating Peruvian from both Chilean and Argentine individuals. Interestingly, this population boundary is consistent with the population structure found in another sympatrically-occurring cetacean species: the dusky dolphin (Lagenorhynchus obscurus). Given that vulnerability to local depletion for South American coastal porpoises and dolphins is probably highest in the Peruvian population (due to high exploitation levels and recurrent El Nino events), the genetic data reported here considerably strengthen the need for conservation efforts focused on regulation of catches in local waters. Moreover, we discuss possible genetic differentiation among Burmeister’s porpoises (i) from the Atlantic and Pacific Ocean and (ii) from different Peruvian harbors. Finally, cross-species amplifications suggest that our newly-developed microsatellite markers will be useful in population genetic studies in the five other extant porpoise species.

Evidence for male dispersal along the coasts but no migration in pelagic waters in dusky dolphins (Lagenorhynchus obscurus)

Using nine nuclear species-specific microsatellite loci and two mitochondrial gene fragments (cytochrome b and control region), we investigated the processes that have shaped the geographical distribution of genetic diversity exhibited by contemporary dusky dolphin (Lagenorhynchus obscurus) populations. A total of 221 individuals from four locations (Peru, Argentina, southern Africa, and New Zealand) were assayed, covering most of the species' distribution range. Although our analyses identify a general demographic decline in the Peruvian dusky dolphin stock (recently affected by high natural and human-induced mortality levels), comparison between the different molecular markers hint at an ancient bottleneck that predates recent El Niño oscillations and human exploitation. Moreover, we find evidence of a difference in dispersal behaviour of dusky dolphins along the South American coast and across the Atlantic. While data in Peruvian and Argentine waters are best explained by male-specific gene flow between these two populations, our analyses suggest that dusky dolphins from Argentina and southern Africa recently separated from an ancestral Atlantic population and, since then, diverged without considerable gene flow. The inclusion of a few New Zealand samples further confirms the low levels of genetic differentiation among most dusky dolphin populations. Only the Peruvian dusky dolphin stock is highly differentiated, especially at mitochondrial loci, suggesting that major fluctuations in its population size have led to an increased rate of genetic drift.

Echolocation signals of wild dolphins

Most of our understanding of dolphin echolocation has come from studies of captive dolphins performing various echolocation tasks. Recently, measurements of echolocation signals in the wild have expanded our understanding of the characteristics of these signals in a natural setting. Measuring undistorted dolphin echolocation signals with free swimming dolphins in the field can be a challenging task. A four hydrophone array arranged in a symmetrical star pattern was used to measure the echolocation signals of four species of dolphins in the wild. Echolocation signals of the following dolphins have been measured with the symmetrical star array: white-beaked dolphins in Iceland, Atlantic spotted dolphins in the Bahamas, killer whales in British Columbia, and dusky dolphins in New Zealand. There are many common features in the echolocation signals of the different species. Most of the signals had spectra that were bimodal: two peaks, one at low frequencies and another about an octave higher in frequency. The source level of the sonar transmission varies as a function of 20logR, suggesting a form of time-varying gain but on the transmitting end of the sonar process rather than the receiving end. The results of the field work call into question the issue of whether the signals used by captive dolphins may be shaped by the task they are required to perform rather than what they would do more naturally.

Echolocation signals of dusky dolphins (Lagenorhynchus obscurus) in Kaikoura, New Zealand.

An array of four hydrophones arranged in a symmetrical star configuration was used to measure the echolocation signals of the dusky dolphin (Lagenorhynchus obscurus) near the Kaikoura Peninsula, New Zealand. Most of the echolocation signals had bi-modal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 80 and 110 kHz. The low-frequency peak was dominant when the source level was low and the high frequency peak dominated when the source level was high. The center frequencies in the dusky broadband echolocation signals are among the highest of dolphins measured in the field. Peak-to-peak source levels as high as 210 dB re 1 microPa were measured, although the average was much lower in value. The levels of the echolocation signals are about 9-12 dB lower than for the larger white-beaked dolphin (Lagenorhynchus albirostris) which belongs to the same genus but is over twice as heavy as the dusky dolphins. The source level varied in amplitude approximately as a function of the one-way transmission loss for signals traveling from the animals to the array. The wave form and spectrum of the echolocation signals were similar to those of other dolphins measured in the field.

DUSKY DOLPHIN (LAGENORHYNCHUS OBSCURUS) FORAGING IN TWO DIFFERENT HABITATS: ACTIVE ACOUSTIC DETECTION OF DOLPHINS AND THEIR PREY

AbstractActive‐acoustic surveys were used to determine the distribution of dusky dolphins and potential prey in two different New Zealand locations. During seven survey days off Kaikoura Canyon, dusky dolphins were found within the DeepScattering Layer (DSL) at 2000 when it rose to within 125 m of the surface. As the DSL rose to 30 m at 0100, the observed depth of dolphins decreased, presumably as the dolphins followed the vertical migration of their prey. Acoustically identified subgroups of coordinated animals ranged from one to five dolphins. Time, depth of layer, and layer variance contributed significantly to predicting foraging dusky dolphin subgroup size. In the much shallower and more enclosed Admiralty Bay, dolphins noted at the surface as foraging were always detected with the sonar, but were never observed in coordinated subgroups during the brief (two‐day) study there. In Admiralty Bay dolphin abundance was correlated with mean volume scattering from potential prey in the water column; and when volume scattering, an index of prey density, was low, dolphins were rarely present. Ecological differences between the deep waters of Kaikoura Canyon and the shallow nearshore waters of Admiralty Bay may result in differences in how, when, and in what social groupings dusky dolphins forage.

Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand

Abstract Marine farms have the potential to affect dolphin foraging in the coastal environment, yet this issue has been largely omitted from aquaculture management models. Data on the subject are minimal. This study was conducted to examine potential overlap between dusky dolphin habitat use and New Zealand's growing green‐lipped mussel farming industry. Data on dusky dolphin occurrence, distribution, abundance, and behaviour were collected from small vessels over five successive winters in the Marlborough Sounds, the centre of New Zealand's mussel farming industry. Locations and movements of dolphin groups were recorded at 2 min intervals with a global positioning system receiver to examine the overlap of dusky dolphin use of coastal areas with existing and proposed marine farms. All cases of dolphins entering the boundaries of mussel farms and total time spent in farms were recorded. Over 8500 dolphin dorsal fin photographs were analysed to develop a catalogue of 421 marked individuals utilizing the area. All instances of dolphin feeding were noted, and focal group behaviour was recorded at 2 min intervals for groups observed ⩾1 h. Within the Marlborough Sounds, dusky dolphins were most often encountered during the winter in Admiralty Bay, the area with the greatest density of proposed farming activity in the region. Mark‐recapture data indicate that more than 1000 dusky dolphins used Admiralty Bay over the course of the 5 year study, with an average of 220 individuals inhabiting the bay on any given week during the winters of 1998–2002. As many as 55% of individuals returned to Admiralty Bay in consecutive winters. Overlap of dusky dolphin habitat use with proposed marine farms is high, and dolphins rarely used areas within the existing farms. If dusky dolphin distribution with respect to farms were random, an expected 18plusmn1;0.5 of 436 groups would be encountered in existing inner Admiralty Bay farms; however, no dolphin groups were first encountered in farms. In 5 years, only eight of 621 dusky dolphin groups monitored in Admiralty Bay were observed to enter the boundaries of mussel farms at any point. Dolphins entering mussel farms moved rapidly up the lanes between rows of lines and floats. Dolphins were observed a total of 14.2 min inside farms versus 147.5 h outside of farms in Admiralty Bay. Correcting for area, dolphins were observed spending significantly less time per survey inside than outside of farms. Most dusky dolphin groups in Admiralty Bay were observed feeding on small schooling fish, often associated with seabirds and/or fur seals. Movement and diving patterns indicate much foraging when not actively feeding. Regular seasonal migration of dusky dolphins and frequent feeding associations with other apex predators make management of marine farming a wider socio‐economic and ecological issue. Copyright © 2004 John Wiley & Sons, Ltd.

INCIDENTAL CATCH OF DOLPHINS IN TRAWLING FISHERIES OFF PATAGONIA, ARGENTINA: CAN POPULATIONS PERSIST?

The incidental mortality of dusky dolphins (Lagenorhynchus obscurus) in the Patagonian trawling fishery is a well-known problem, especially in mid-water trawl fisheries for shrimp and anchovy. Therefore, it is necessary to determine if recent levels of dolphin bycatch are compatible with the persistence of the dusky dolphin population. This was assessed by comparing annual bycatch rates with a sequence of critical values. These values were based on the maximum rate of increase (rmax) = λ − 1, where λ is the finite rate of increase. The finite rate of increase was estimated from a Leslie matrix where Monte Carlo procedures were employed to incorporate parameter uncertainties (age at first reproduction, survival rates, and fertility). Model life tables were used for survival, and reproductive parameters were estimated from available data on calving interval and age at sexual maturity. Uncertainties associated with annual bycatch rates were also included in the analysis through another randomization procedure that incorporated the variability in dolphin catch per unit effort, nominal fishing effort, and population size. This modeling approach rendered frequency distributions for the parameters of interest. Considering the critical values for incidental mortality rate as (1/2)R = (1/2)rmax and (1/4)R = (1/4)rmax, and a 2-yr calving interval scenario, the probability that recent dolphin bycatch rates exceed the maximum annual removal rates were higher than 0.3. These results suggest that incidental mortality due to fishing could be, or may become, a threat for the dusky dolphin population off Patagonia. Therefore, a more accurate and intense monitoring program is needed to avoid the decline of this population. Also, this issue should be included in the fishery management strategies to be implemented in the near future.

GENETIC STRUCTURE, DIVERSITY, AND HISTORICAL DEMOGRAPHY OF NEW ZEALAND’S DUSKY DOLPHIN (LAGENORHYNCHUS OBSCURUS)

Although generally limited to coastal waters of South America, South Africa, and New Zealand, dusky dolphins (Lagenorhynchus obscurus) show high potential for dispersal over large distances. In New Zealand, photographic identification data indicate a seasonal shift in residency of dolphins between Kaikoura and the Marlborough Sounds as well as changes in group size and behavior. The effect of this seasonal variation on the genetic structure of New Zealand's dusky dolphins was examined by sequencing a 473-base pair fragment of the mitochondrial DNA control region for 169 individuals from 4 regions along the New Zealand coast. A neighbor-joining phylogeny and an analysis of molecular variance did not support genetic subdivision among regions (ϕsr = −0.041, P = 0.13). However, nested-clade analysis demonstrated significant evidence for contiguous range expansion and fragmentation along the New Zealand coast. Seasonal movement patterns from Kaikoura to either Otago or the Marlborough Sounds and West Coast are presented as an alternative explanation of nested clade results. New Zealand-wide diversity indices and rate of substitution among sites were used to estimate effective female population size. Lineages-through-time analysis was used to test hypotheses of population growth. Structure of the neighbor-joining phylogeny, the nested haplotype network, and results of the lineages-through-time analysis suggest that the New Zealand dusky dolphin population underwent at least 1, if not 2, historical population expansions.

Behavior of dusky dolphins foraging on the deep-scattering layer in Kaikoura Canyon, New Zealand

Little is known of foraging habits of sound-scattering layer consumers. A 200-kHz echosounder was used to survey dusky dolphins and the sound-scattering layer in winter 2002, in Kaikoura Canyon, New Zealand. Visual observations of dolphin surfacings occurred 84% of the time that dolphins were acoustically detected, confirming identifications from the acoustic data. Dusky dolphins were within the layer at 2000 h (about 1.5 h after dusk), within 125 m of the surface. As the layer rose to within 30 m of the surface at 0100 h, the observed depth of dolphins decreased presumably as the dolphins followed the vertical migration of their prey. The mean depth of dolphins was within the scattering layer except when the top of the layer was deeper than 125 m. Dusky dolphins often forage within large groups. Acoustically identified subgroups of coordinated animals ranged from 1 to 5 dolphins. Subgroup size varied with time of night, minimum depth of the scattering layer, and the variance of the food resource. The largest subgroups occurred when the scattering layer was closest to the surface, and when the layer was most heterogeneous. Time, depth of layer, and layer variance contributed significantly to predicting foraging dusky dolphin subgroup size.

Population Structure and Habitat Selection by Anisakis simplex in 4 Odontocete Species from Northern Argentina

We described the population structure and habitat selection of Anisakis simplex in 46 franciscanas, Pontoporia blainvillei, 8 Burmeister's porpoises, Phocoena spinnipinis, 2 Dusky dolphins, Lagenorhynchus ob- scurus, and 2 common dolphins, Delphinus delphis, caught incidentally in the coastal fisheries of northern Argentina. Prevalence ranged from 50% to 100%, but mean intensities were low (1.0-3.6), suggesting that A. simplex has low recruitment rates to coastal dolphins in this area. Adult nematodes were found exclusively in the main stomach of 64.5% of franciscanas (the first stomach of this species) and the forestomach of 50% of Burmeister's porpoises and Dusky dolphins. Other developmental stages occurred in the first stomach but were also found in posterior digestive chambers. The median worm of the distribution among chambers was more anterior for preadults than for L4s and more anterior for L4s than for L3s. Our data are compatible with the hypothesis that individuals of A. simplex tend to select the site where digestion begins. This preference is more pronounced in adult worms. The greater restriction of adults to the first chamber could be viewed as a strategy to enhance mating opportunities. Alternatively, it might indicate that adults have stronger requirements for the resources provided by the first chamber.

Catch and Bycatch of Sea Birds and Marine Mammals in the Small‐Scale Fishery of Punta San Juan, Peru

Abstract: Between 1991 and the present, we have had observers stationed at the port of San Juan in southern Peru to interview fishers as they landed their catch. They observed the landings of 922 Humboldt Penguins ( Spheniscus humboldti), 510 dusky dolphins ( Lagenorhynchus obscurus), 214 Burmeister's porpoises ( Phocaena spinnipinnis), and 75 bottlenose dolphins ( Tursiops truncatus) between November 1991 and June 1998, although the retention of penguins and small cetaceans is banned by Peruvian law. Most of these animals were captured in 1992–1994, when the fishers were mainly using surface‐drift gillnets to target a pelagic schooling fish called cojinova ( Seriolella violacea). Capture rates were much lower in 1995–1998, when fishers were mostly using fixed demersal gillnets and shellfish diving, due apparently to a lack of surface‐schooling cojinova in the vicinity. We used generalized linear models to examine the effect of year, gear type, area, and target fish species on the probability of capturing either penguins or dolphins. We found that the probability of a fishing vessel capturing a penguin or a dolphin increased when drift gillnets were used instead of fixed gillnets. Fishing area, year, and the species of fish caught also significantly affected the probability of capture. A population model ( Vortex) applied to Humboldt Penguins showed that the high levels of mortality seen in the early 1990s are not sustainable and could lead to local extinction in a few years. The mortality levels seen in the late 1990s are more likely to be sustainable, but a return to the use of drift gillnets would rapidly result in unsustainable levels of mortality.

Serological evidence of Brucella species infection in odontocetes from the south Pacific and the Mediterranean

Sera from 58 odontocetes taken in fisheries off Peru in 1993 to 1995 and from 24-cetaceans stranded along the Spanish coast of the Mediterranean in 1997 to 1999 were tested...

Genital Diseases in the Peruvian Dusky Dolphin (Lagenorhynchus obscurus)

Ovarian cysts and one ovarian tumour, uterine tumours, vaginal calculi, abscesses of the broad ligament or undetermined testicular lesions were observed in 25 out of 502 female and male dusky dolphins (Lagenorhynchus obscurus) caught off Peru in 1985–1987 or 1993–1994. Tentative or definitive diagnoses included Graafian follicle cysts, luteinized cyst, ovarian parasitic granulomatous inflammation, dysgerminoma, leiomyoma, fibroleiomyoma and chronic fibrino-suppurative inflammation of the broad ligament. All lesions described represented first reports for L. obscurus, and the diagnosis of dysgerminoma was the first in a cetacean. It is also the first time that trematode eggs have been reported in the ovaries of cetaceans and that a vaginal calculus has been encountered in a sexually immature cetacean. The finding of struvite as a major component in two vaginal calculi suggested an infectious aetiology. Of 11 mature females with ovarian tumour or cysts or uterine tumours, only one (9·1%) was pregnant, i.esignificantly less than the expected pregnancy rate (53·3% in a random sample of Peruvian dusky dolphins). Several females with ovarian or uterine lesions and males with aberrant testes were large animals. It is possible that some of these lesions were associated with normal senescence of the reproductive system.

Food consumption and growth of a female dusky dolphin (Lagenorhynchus obscurus)

Food consumption, body measurements, weight changes, and body temperatures of a female dusky dolphin are presented for the 13 years that she was at Sea World, Durban. Her annual food consumption increased from 1,870 kg at the age of 3 years to 2,170 kg when she was 5 years old. During her sixth year, her annual food intake increased to approximately 2,900 kg. This increase coincided with the installation of a cooling system that was used in the summer in the years thereafter. After her sixth year, her food consumption fluctuated between 2,400 and 2,800 kg per year. The dolphin's body weight increased gradually from approximately 52 kg at the age of 2 years to approximately 66 kg at the age of 6 years. Thereafter, her weight fluctuated between 61 and 74 kg. As body weight increased, daily food consumption as a percentage of body weight decreased. In general, her food intake was above average during autumn and winter, and below average during spring and summer. The average pool water temperature fluctuated seasonally. Gastrointestinal initial passage time was measured using carmine red dye. The median passage time was 150 minutes. The average rectal temperature was 36.9°C. Zoo Biol 19:131–142, 2000. © 2000 Wiley-Liss, Inc.

Food consumption and growth of a female dusky dolphin (Lagenorhynchus obscurus)

Food consumption, body measurements, weight changes, and body temperatures of a female dusky dolphin are presented for the 13 years that she was at Sea World, Durban. Her annual food consumption increased from 1,870 kg at the age of 3 years to 2,170 kg when she was 5 years old. During her sixth year, her annual food intake increased to approximately 2,900 kg. This increase coincided with the installation of a cooling system that was used in the summer in the years thereafter. After her sixth year, her food consumption fluctuated between 2,400 and 2,800 kg per year. The dolphin's body weight increased gradually from approximately 52 kg at the age of 2 years to approximately 66 kg at the age of 6 years. Thereafter, her weight fluctuated between 61 and 74 kg. As body weight increased, daily food consumption as a percentage of body weight decreased. In general, her food intake was above average during autumn and winter, and below average during spring and summer. The average pool water temperature fluctuated seasonally. Gastrointestinal initial passage time was measured using carmine red dye. The median passage time was 150 minutes. The average rectal temperature was 36.9°C. Zoo Biol 19:131–142, 2000. © 2000 Wiley-Liss, Inc.

GASTROINTESTINAL HELMINTHS OF THE DUSKY DOLPHIN, LAGENORHYNCHUS OBSCURUS (GRAY, 1828), OFF PATAGONIA, IN THE SOUTHWESTERN ATLANTIC

AbstractThe stomachs and intestines of 23 dusky dolphins incidentally caught in a trawl fishery off Patagonia were surveyed for helminths. All the dolphins were parasitized, with a total of 3,936 helminth individuals. Only five species occurred, of which three were common (prevalence ± 10%): Anisakis simplex, Braunina cordiformis and Hadwenius sp. A. simplex was present in all the dolphins and showed the highest abundance and mean intensity (104.9 individuals/infected host). B. cordiformis was next most common (87%), and Hadwenius sp. third (52.2%). A. simplex was found mostly in the stomach (94.8%), B. cordiformis in the duodenal ampulla (51.4%), and Hadwenius sp. in the stomach (64.5%). The rare species Corynosoma australe (immature specimens) and Pholeter gastrophilus occurred in the stomach. A. simplex and B. cordiformis showed a clumped distribution along the intestine. Brillouin's diversity and evenness indices for the intestinal helminth community were 0.329 and 0.393, respectively. The diversity values and the number of parasite species were within the range for other small cetaceans.

SKIN SWABBING FOR GENETIC ANALYSIS: APPLICATION TO DUSKY DOLPHINS (LAGENORHYNCHUS OBSCURUS)

AbstractExfoliated skin was collected from bowriding dolphins with the use of a sterilized nylon scrub pad affixed to a wooden dowel. Initial tests of the effectiveness of the technique and dolphin behavioral responses were conducted on dusky dolphins off Kaikoura, New Zealand. During 14 sampling days, 128 contacts using this procedure were made with bowriding dolphins, of which 114 showed behavioral response. Responses during sampling were mild, with 11% of contacted individuals showing no visible response, and 66% of individuals which could be monitored for 30 sec after contact returning to bowride within 30 sec. Mean return time was 10 sec postcontact and did not vary significantly for groups of different sizes. Behavioral controls suggest that a proportion of responses could be explained by typical dolphin behavior in the presence of boats. Seventy‐eight percent of contacts resulted in successful collection of tissue samples. Sample time was three minutes on average. Size of group and behavioral state did not appear to influence sample time. Preliminary genetic analyses revealed that tissue collected by this technique was suitable for amplification and sequencing of mitochondrial DNA (mtDNA) via PCR. Comparisons of mtDNA control region sequences with those from known L. obscurus and other delphinid samples verified that this technique was robust against contamination from elements in sea water.

Polychlorinated dibenzo-p-dioxins, dibenzofurans and polychlorinated biphenyls in New Zealand cetaceans

Limited information is available on the concentrations of halogenated aromatic hydrocarbons (HAHs) in cetaceans from the Southern Hemisphere. This paper presents data on blubber concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in Hector's dolphins, dusky dolphins, southern right whale dolphins, blue whales, minke whales, Gray's beaked whales, Cuvier's beaked whales and pygmy right whales stranded in New Zealand. Both HAH concentrations and toxic equivalents (TEQs) are found to be higher in Hector's dolphins, a species with an inshore distribution, than in other odontocetes, which are more oceanic. Baleen whales, which are oceanic and feed at lower trophic levels, present the lowest levels of pollutants, with PCDD and PCDF concentrations usually below detection limits. The PCB profiles of the various species suggest that they are exposed to different PCB sources. Overall, HAH levels detected are lower than those reported for comparable species in the Northern Hemisphere. The relative abundance of low chlorinated PCB congeners in New Zealand cetaceans, as compared to those from northern waters, suggests that the origin of these compounds is mostly atmospheric deposition.