Hector's Dolphins Research Articles

Origin and radiation of Southern Hemisphere coastal dolphins (genus Cephalorhynchus).

The genus Cephalorhynchus (Gray 1846) consists of four species of small coastal dolphins distributed in cool temperate waters around the Southern Hemisphere. Each species is sympatric with other members of the subfamily Lissodelphininae but widely separated from other congeners. To describe the origin and radiation of these species, we examined 442 bp of mitochondrial DNA control region sequences of 307 individuals from the genus Cephalorhynchus and compared these to sequences from other members of the subfamily Lissodelphininae. We investigate the hypotheses that Cephalorhynchus is a monophyletic genus or, alternatively, that the four species have arisen separately from pelagic Lissodelphine species and have converged morphologically. Our results support the monophyly of Cephalorhynchus within the Lissodelphininae and a pattern of radiation by colonization. We confirm a pattern of shallow but diagnosable species clades with Heaviside's dolphin as the basal branch. We further examine the monophyly of maternal haplotypes represented by our large population sample for each species. Based on this phylogeographic pattern, we propose that Cephalorhynchus originated in the waters of South Africa and, following the West Wind Drift, colonized New Zealand and then South America. The Chilean and Commerson's dolphins then speciated along the two coasts of South America, during the glaciation of Tierra del Fuego. Secondary radiations resulted in genetically isolated populations for both the Kerguelen Island Commerson's dolphin and the North Island Hector's dolphin. Our results suggest that coastal, depth-limited odontocetes are prone to population fragmentation, isolation and occasionally long-distance movements, perhaps following periods of climatic change.

Abundance, residency, and habitat utilisation of Hector's dolphins (Cephalorhynchus hectori) in Porpoise Bay, New Zealand

Theodolite tracking and boat‐based photo‐identification surveys were carried out in the austral summers of 1995/96 and 1996/97 to assess abundance, residency, and habitat utilisation of Hector's dolphins (Cephalorhynchus hectori van Beneden 1881) in Porpoise Bay, on the south‐east corner of the South Island of New Zealand. Data are consistent with the model of a small resident population that is visited occasionally by members of neighbouring populations. Mark‐recapture analysis of photographically identified individuals, along with data on the proportion of animals bearing identifying marks, indicates a local population of 48 dolphins (95% CI = 44–55) in 1996/97. Dolphins spent a large proportion of their time in a small area inside the bay. Dolphin sightings were more congregated in successive time periods from early morning to late afternoon. No pattern of diurnal movement into and out of the bay was observed.

Accounting for Uncertainty in Risk Assessment: Case Study of Hector's Dolphin Mortality due to Gillnet Entanglement

Abstract: Uncertainties about biological data and human effects often delay decisions on management of endangered species. Some decision makers argue that uncertainty about the risk posed to a species should lead to precautionary decisions, whereas others argue for delaying protective measures until there is strong evidence that a human activity is having a serious effect on the species. We have developed a method that incorporates uncertainty into the estimate of risk so that delays in action can be reduced or eliminated. We illustrate our method with an actual situation of a deadlock over how to manage Hector's dolphin (Cephalorhychus hectori). The management question is whether sufficient risk is posed to the dolphins by mortalities in gillnets to warrant regulating the fisheries. In our quantitative risk assessment, we use a population model that incorporates both demographic ( between‐individual) and environmental ( between‐year) stochasticity. We incorporate uncertainty in estimates of model parameters by repeatedly running the model for different combinations of survival and reproductive rates. Each value is selected at random from a probability distribution that represents the uncertainty in estimating that parameter. Before drawing conclusions, we perform sensitivity analyses to see whether model assumptions alter conclusions and to recommend priorities for future research. In this example, uncertainty did not alter the conclusion that there is a high risk of population decline if current levels of gillnet mortality continue. Sensitivity analyses revealed this to be a robust conclusion. Thus, our analysis removes uncertainty in the scientific data as an excuse for inaction.

An evaluation of a management saga: The Banks Peninsula Marine Mammal Sanctuary, New Zealand

The Banks Peninsula Marine Mammal Sanctuary, Canterbury, New Zealand, was established in 1988 to protect the Hector's dolphin Cephalorhynchus hectori from accidental entanglement in set nets (gill nets). Sanctuary establishment was strongly supported by environmental groups but has continued to be strongly opposed by both commercial and recreational fishers. This paper evaluates the issues surrounding sanctuary establishment, the process of sanctuary implementation, management and review, conservation costs and benefits and identify a possible improved approach to resolving some of these identified issues. It is argued that first, a more consultative, community based and negotiated approach should have been implemented in first dealing with the dolphin accidental catch issue; second, ongoing management by the Department of Conservation should have been adaptive rather than dogmatic, and given more respect to local views; and third, that in reviewing the Sanctuary the Department of Conservation and the Minister of Conservation should have promoted a facilitated and negotiated settlement reflecting a precautionary approach and adaptive management.

Loss of genetic diversity in the endemic Hector's dolphin due to fisheries-related mortality

The endemic New Zealand Hector's dolphin is considered the rarest species of marine dolphin with a total abundance of less than 4000. The species is listed as vulnerable because of fisheries-related mortality due to entanglement in set nets. The vulnerability of this species is further increased by its fidelity to local natal ranges and the genetic isolation of regional populations. Here we present evidence, based on 108 contemporary samples and 55 historical samples dating back to 1870, of a significant loss of mitochondrial DNA (mtDNA) diversity in two regional populations of Hector's dolphin. The haplotype diversity (h) was calculated from sequences of a 206 bp fragment in the mtDNA control region, designed to identify 13 out of the 14 known maternal lineages. Over the last 20 years, the North Island population has been reduced from at least three lineages (h = 0.41) to a single lineage (h = 0; p < 0.05). Given its small size, reproductive isolation and reduced genetic diversity, this population is likely to become extinct. The diversity of the East Coast South Island population has declined significantly from h = 0.65 to h = 0.35 (p < 0.05). Based on trend analysis of the mtDNA diversity, we predict that the East Coast population will lose all mtDNA diversity within the next 20 years. This time-series of reduction in genetic variation provides independent evidence of the severity of population decline and habitat contraction resulting from fisheries and perhaps other human activities.

Hector's Dolphin Cephalorhynchus hectori calf mortalities may indicate new risks from boat traffic and habituation

Two Hector's Dolphin calves Cephalorhynchus hectori were killed by probable boat collision in 1999, indicating that boat strikes may pose more of a threat to the species than previously thought. When discovered, one dead calf was still tended by its mother. After recovery, both animals were necropsied with trauma from boat strikes as the most likely cause of death. These deaths are discussed in the context of increasing human contact with Hector's Dolphins in Akaroa Harbour, and risks to the dolphins caused by this habituation.

Bayesian inference for small-sample capture-recapture data.

We consider data on the survival of a population of Cephalorhynchus hectori, Hector's dolphins, in a marine area of New Zealand. To estimate survival probabilities of animal populations, a multiple capture-recapture sampling scheme can be used. In this paper, we propose a practical methodology to derive approximations to posterior distributions based on Laplace methods. We show how to calculate Bayes estimates and credible intervals in this setting.

Association patterns in three populations of Hector's dolphin, Cephalorhynchus hectori

Most delphinids are very social and spend much time in the presence of conspecifics. The proportion of co-occurrences of any two individuals is usually measured by means of association indices. In this study, the "half-weight index" was used to describe the association patterns in three previously unstudied populations of Hector's dolphin, Cephalorhynchus hectori, around the South Island of New Zealand. For inclusion in this analysis individuals were photoidentified repeatedly over a 2-year study period. Only about 1% of the individual associations of dolphin pairs (dyads) tested were found to be significantly different (p less than or equal to 0.01) from random distributions derived from a new constrained Monte Carlo randomisation. The overall association patterns in the two study populations off Kaikoura ( n = 48 individuals) and Moeraki (n = 24) did not differ significantly from what could be expected by chance (p = 0.07 and 0.09, respectively), whereas those in the Jackson Bay population (n = 38) were significantly different from chance (p &lt; 0.0002). Hector's dolphins appear to have a typical fission-fusion society, with many weak associations within the wider envelope of the local population.

A sensitivity analysis to guide research and management for Hector's dolphin

Hector's dolphin ( Cephalorhynchus hectori) is an uncommon endemic of New Zealand which is suspected to be in decline due to entanglement mortality. However, uncertainty in available data has led to a dispute between the New Zealand Ministry of Fisheries and the New Zealand Department of Conservation over the status of this species. We use a density-dependent deterministic model to predict the future abundance and geographic distribution of Hector's dolphin under different scenarios of fisheries management. We then examine the sensitivity of this model to a number of parameters for which few or no data are available. We find that two populations of Hector's dolphins are predicted to decline in the future even when the most optimistic parameter estimates are used. The status of the third population is dependent upon the estimate of maximum annual population growth rate. Because of the dependence of final abundance estimates on the estimates of entanglement mortality rates and maximum population growth rate, research efforts should be concentrated on estimating these parameters.

Modelling Survival of Hector's Dolphins around Banks Peninsula, New Zealand

In 1988, a marine mammal sanctuary was established around Banks Peninsula to reduce Hector's dolphin entanglement in commercial and recreational gill nets. We describe the application of a multistate mark-recapture model to data from photographic identification surveys to determine the effect of the sanctuary on dolphin survival rates. The model allows sightings to occur in three geographic strata with free movement between strata. Although we found evidence of both area and time effects on sighting probabilities we found no evidence that survival rates depended on area or time. Thus, there was no evidence that dolphin survival rates increased following establishment of the sanctuary. However, power of this test is shown to be low.

An Application of Close Range Photogrammetry In Dolphin Studies

Dolphins are agile animals and are very difficult to measure at sea. However, for the conservation of threatened or endangered species, measurement may be vital because it allows a demographic analysis of the population. Hector's dolphin (Cephalorhynchus hectori) is a rare species living only in coastal waters around New Zealand where it is studied from small boats. This paper describes a stereophotogrammetric technique developed to measure body length accurately at sea without having to capture the individual. Constant calibration with the use of a control frame allowed accurate body length measurements of dolphins to be made with this low cost system, with a measurement error of 4 per cent to 6 per cent of actual length.

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.

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.

Geographic Isolation of Hector's Dolphin Populations Described by Mitochondrial DNA Sequences

Geographic Isolation of Hector's Dolphin Populations Described by Mitochondrial DNA Sequences

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.

Conservation of marine mammals in New Zealand

New Zealand has a diverse fauna of marine mammals, comprising 35 cetacean and six pinniped species. None of these is hunted within the 200 mile Exclusive Economic Zone, but several species are killed incidentally in coastal or deep-water fisheries. Particularly affected are Hector's Dolphin, Hooker's Sea Lion, and the New Zealand Fur Seal. Detailed information on the nature and magnitude of incidental catches is patchy at best, and inadequate to assess nationally the impact on any one species. Other species are known to be caught, but a quantitative assessment of how many are caught per year is impossible. The impact of whale watching on sperm whales has attracted more attention, and impacts of tourism on other marine mammals are just beginning to be studied. We critically review the nature and management of the potential threats facing New Zealand marine mammals, including bycatch, entanglement in plastic debris, chemical pollution, and tourism. We discuss research needs and management recommendations for each conservation problem in turn.

Behavior of Hector's Dolphin: Classifying Behavior by Sequence Analysis

Behavior sequence analysis was used to classify behavior patterns of Hector's dolphin (Cephalorhynchus hectori) into five categories; feeding, sexual, aggressive, play, and aerial. Feeding behaviors were among the most closely associated behaviors, and were negatively associated with most other behaviors. Bite was closely associated with other apparently aggressive behaviors like tailsplash and chase. Copulations and possible copulations were associated with other behaviors one might have intuitively classified as sexual or social (e.g., belly present, penis out, and body contact). Aerial behaviors were most strongly associated with sexual and aggressive behaviors. Of the two play behaviors, play with weed was most strongly associated with feeding, and bubbleblow was most strongly associated with aggressive and aerial behaviors. I investigated the relationship between the sexual behavior category and social context. The rate of sexual behaviors per individual was highest in groups of 11–15 dolphins and tended to increase after groups came together.

Associations among photographically identified Hector's dolphins

Associations among Hector's dolphins photographically identified in the waters off Banks Peninsula, New Zealand, were studied using cluster analyses of simple and half-weight association indices. In addition, we carried out a temporal analysis of association patterns, plotting changes in the standardized reassociation rate over time. Some individually identified Hector's dolphins were photographed in the study area in successive seasons and years, and appeared to be resident in the area. Social organization was characterized by relatively fluid association patterns, with little stability over periods longer than a few days. Both male and female Hector's dolphins interacted with a large number of other individuals, males more so than females. Association patterns and other evidence support the hypothesis that Hector's dolphins have a promiscuous mating system.

Conservation of Hector's dolphins: The case and process which led to establishment of the Banks Peninsula Marine Mammal Sanctuary

Abstract Entanglement in gillnets constitutes the greatest known threat to populations of small cetaceans. In 1988, in response to data on the distribution and abundance, incidental catch, reproduction and population biology of Hector's dolphins, and after an extended period of public consultation, New Zealand's Department of Conservation created a 1170 km2 Marine Mammal Sanctuary. Within this area, gillnetting on a commercial scale is illegal and amateur fishers may only set gillnets in specific times and places. This paper summarizes the salient points of research that led to the creation of the sanctuary, briefly describes the process by which the sanctuary was established, and offers some comments on the information required for conservation management of small cetaceans.

SURVIVAL RATES OF PHOTOGRAPHICALLY IDENTIFIED HECTOR'S DOLPHINS FROM 1984 TO 1988

AbstractRe‐sightings of photographically identified individuals were used to estimate survival rates for a free‐living population of Hector's dolphins Cephalorhynchus hectori, a species endemic to New Zealand waters. Most individuals were identified from injuries to the dorsal fin. Consequently, the photographic catalog contained very few young individuals. Our analysis included no newborn calves or yearlings, and provided estimates of survival rates only after the first year of life. We used two complementary methods for calculating survival rates: a modified Jolly‐Seber model, and a simpler method which corrects in a more explicit way for individual dolphins being alive but not sighted. Selection of the most reliable subset of the data had a greater effect on computed survival rates than did the difference between the two methods. We conclude that careful inspection of resighting data before analysis, and, if necessary, selection of a subset, is very important in studies of this kind. Survival rate estimates came from a population which was subject to relatively heavy mortality from gillnet entanglement. Standard errors of the survival rate estimates have been used to assess the conditional probability of population decline given three fertility scenarios. The high probability that the Banks Peninsula Hector's dolphin population was decreasing during the study period (0.78 to 0.99) suggests that gillnet entanglement constituted a serious risk to this population.