Hector's Dolphins Research Articles

Seasonal changes in distribution of Hector's dolphin at Banks Peninsula, New Zealand: implications for protected area design

Abstract The efficacy of protected areas for wildlife management is largely dependent on appropriate design. It is therefore crucial that the distribution of target species is well understood. The Banks Peninsula Marine Mammal Sanctuary (BPMMS) was designed to protect Hector's dolphins from bycatch in gillnets. However, the Banks Peninsula dolphin population is likely to be still declining, partly due to continued bycatch outside the boundaries of the BPMMS. A three year series of aerial line‐transect surveys around Banks Peninsula was carried out to investigate seasonal changes in distribution of Hector's dolphins out to 20 nautical miles (37 km) from the coast. Dolphin sightings were concentrated close to shore in shallow water in summer, but were more evenly distributed throughout the study area in winter. A greater proportion of dolphins were sighted outside the 4 nautical miles (7.4 km) offshore boundary of the BPMMS in winter (mean=56%) than in summer (mean=19%) (G=88.25, df=1, P<0.001). Partial Mantel tests revealed the effects of distance offshore and depth on dolphin occurrence while controlling for spatial autocorrelation and multicollinearity within the data. Distance offshore had the strongest and most consistent effect on dolphin presence, while depth had a strong effect in summer only. It is proposed that restrictions on gillnetting around Banks Peninsula must be extended in order to reduce bycatch of Hector's dolphins to a sustainable level, and that a new offshore boundary of the BPMMS would be best defined by distance from the coast. Copyright © 2009 John Wiley & Sons, Ltd.

Use of T-PODs for acoustic monitoring of Cephalorhynchus dolphins: a case study with Hector’s dolphins in a marine protected area

The 4 dolphin species in the genus Cephalorhynchus have small populations, restricted distributions and are threatened by anthropogenic activities. It is therefore essential that tools be developed for assessing these threats and the effects of management actions. The T-POD is a com- mercially available acoustic data logger. We evaluated the efficacy of the T-POD for addressing habi- tat use questions relevant to management by passive acoustic monitoring of Hector's dolphins C. hec- tori in the Banks Peninsula Marine Mammal Sanctuary (BPMMS), New Zealand. Three T-PODs were deployed at 3 inshore locations in summer and winter over a 2 yr period (n = 431 d). Acoustic detec- tion data were summarised by detection-positive minutes per day. A linear regression model indi- cated that season had the largest effect on detection rate (F = 81.95, p < 0.001), with T-POD ID (i.e. variation in sensitivity between individual instruments) also having a significant effect (F = 9.45, p < 0.001). There was no significant difference between acoustic detection rates at night and during the day (paired t-test, t = 0.55, p = 0.59). The present study provides further evidence to support the year- round ban on all gill netting within the BPMMS. We demonstrated that T-PODs can be used to inves- tigate temporal differences in habitat use by Cephalorhynchus dolphins. However, several issues must be considered when designing such experiments; namely the mode of deployment, accounting for variation in sensitivity between individual T-PODs and the possibility of false positive detections from non-target species.

Feeding at a high pitch: Source parameters of narrow band, high-frequency clicks from echolocating off-shore hourglass dolphins and coastal Hector’s dolphins

Toothed whales depend on echolocation for orientation and prey localization, and source parameters of echolocation clicks from free-ranging animals therefore convey valuable information about the acoustic physiology and behavioral ecology of the recorded species. Recordings of wild hourglass (Lagenorhynchus cruciger) and Hector's dolphins (Cephalorhynchus hectori) were made in the Drake Passage (between Tierra del Fuego and the Antarctic Peninsular) and Banks Peninsular (Akaroa Harbour, New Zealand) with a four element hydrophone array. Analysis of source parameters shows that both species produce narrow band high-frequency (NBHF) echolocation clicks. Coastal Hector's dolphins produce clicks with a mean peak frequency of 129 kHz, 3 dB bandwidth of 20 kHz, 57 micros, 10 dB duration, and mean apparent source level (ASL) of 177 dB re 1 microPa(p.-p.). The oceanic hourglass dolphins produce clicks with mean peak frequency of 126 kHz, 3 dB bandwidth of 8 kHz, 116 micros, 10 dB duration, and a mean estimated ASL of 197 dB re 1 microPa(p.-p.). Thus, hourglass dolphins apparently produce clicks of higher source level, which should allow them to detect prey at more than twice the distance compared to Hector's dolphins. The observed source parameter differences within these two NBHF species may be an adaptation to a coastal cluttered environment versus a deep water, pelagic habitat.

Confirmed expression of MHC class I and class II genes in the New Zealand endemic Hector's dolphin (Cephalorhynchus hectori)

AbstractWe provide the first description and confirmation of expression for three Major Histocompatibility Complex (MHC) genes (DQA, DQB, and class I) in the New Zealand endemic Hector's dolphin (Cephalorhynchus hectori). Sequences were derived from cDNA generated from peripheral blood leukocyte mRNA collected during a temporary live capture of two Hector's dolphins. The complete exons 2 and 3 of DQA, DQB, and class I were amplified from cDNA to confirm their expression. The same primers proved reliable for amplification from genomic DNA. Locus identity was supported by phylogenetic relationships to MHC molecules from other closely related species. No evidence was found for duplication of DQ loci, but cloning of amplified exon 2 of the class I gene indicated duplication or triplication of this locus. However, the expression of multiple class I loci was uncertain as only one allele could be detected from clones of cDNA. Balancing selection was indicated by a significantly greater ratio of nonsynonymous to synonymous substitutions at all three loci and by the apparent transspecific sharing of alleles for DQA and DQB.

Sustainable Levels of Human Impact for Hector's Dolphin

Hector's dolphin is endemic to New Zealand, and listed as endangered on the IUCN Red List and equivalent New Zealand list of threatened species. The main threat to the species is entanglement in fishing gear, in particular gill- nets. The Potential Biological Removal (PBR) method developed by the US National Marine Fisheries Service is a com- monly used standard for determining a level of bycatch for marine mammal populations which, if exceeded, is likely to cause population decline. For Hector's dolphin, PBRs are less than one individual per year for most populations and the total for the whole species is less than 10 per year. Current estimated bycatch is on the order of 10-35 times higher than these PBRs. This is consistent with several Population Viability Analyses indicating that under current management Hec- tor's dolphin populations are declining rapidly.

Application of decision theory to conservation management: recovery of Hector's dolphin

Decision theory provides an organised approach to decision making in natural resource conservation. The theory requires clearly stated objectives, decision alternatives and decision-outcome utilities, and thus allows for the separation of values (conservation and other societal objectives) from beliefs. Models express belief in the likely response of the system to conservation actions, and can range from simple, graphical representations to complex computer models. Models can be used to make predictions about likely decision-outcomes, and hence guide decision making. Decision making must account for uncertainty, which can be reduced but never eliminated. Uncertainty can be described via probabilities, which in turn can be used to compute the expected value of alternative decisions, averaging over all relevant sources of uncertainty. Reduction of uncertainty, where possible, improves decision making. Adaptive management involves the reduction of uncertainty via prediction under two or more alternative, structural models, comparison of model predictions to monitoring, and feedback via Bayes’ Theorem into revising model weights, which in turn influences decision making. As part of a 3-day workshop on structured decision making (SDM) and adaptive resource management (ARM), we constructed a prototypical decision model for the recovery for Hector’s dolphin (Cephalorynchus hectori), an endangered dolphin endemic to New Zealand coastal waters. Our model captures several steps in the process of building an SDM/ARM framework, and should be useful for managers wishing to apply these principles to dolphin conservation or other resources problems.

Trace elements, PCBs and organochlorine pesticides in New Zealand common dolphins (Delphinus sp.)

Trace elements, polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticide levels were determined in tissues collected from stranded and bycaught common dolphins (Delphinus sp.) from New Zealand waters between 1999 and 2005. The concentrations of mercury (Hg), selenium (Se), chromium (Cr), zinc (Zn), nickel (Ni), cadmium (Cd), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), tin (Sn), lead (Pb), arsenic (As) and silver (Ag) were determined in blubber, liver and kidney tissue. PCBs (45 congeners) and a range of OC pesticides including dieldrin, hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) and its metabolites DDE and DDD were determined in blubber samples. Cr and Ni were not detected in any of the samples and concentrations of Co, Sn and Pb were generally low. Concentrations of Hg ranged from 0.17 to 110 mg/kg wet weight. Organochlorine pesticides dieldrin, HCB, o,p'-DDT and p,p'-DDE were present at the highest concentrations. Sum DDT concentrations in the blubber ranged from 17 to 337 and 654 to 4430 microg/kg wet weight in females and males, respectively. Similarly, Sigma45CB concentrations ranged from 49 to 386 and 268 to 1634 microg/kg wet weight in females and males, respectively. The mean transmission of SigmaDDTs and ICES7CBs between a genetically determined mother-offspring pair was calculated at 46% and 42%, respectively. Concentrations of organochlorine pesticides determined in the present study are within similar range to those reported for Hector's dolphins (Cephalorhyncus hectori) from inshore New Zealand waters.

Vessel collisions with small cetaceans worldwide and with large whales in the Southern Hemisphere, an initial assessment

Collisions with vessels are a well-documented conservation problem for some populations of large whales (LW) in the Northern Hemisphere. Less attention has been given to incidents in the Southern Hemisphere or to small cetaceans (SC) worldwide, therefore an experimental database was compiled (N=256; 119 LW, 137 SC) to allow a rapid assessment. Confirmed collision records were identified for 25 species (7 LW, 18 SC) and unconfirmed but probable records for 10 other species (2 LW, 8 SC). Among LW, ship-caused mortality and traumatic injuries seem to affect primarily southern right (56 reported cases), humpback (15) and Bryde's whales (13), but also sperm (8), blue (5), sei (4) and fin whales (2) are involved, and probably Antarctic minke and dwarf minke whales. Southern right whale populations off South Africa and off eastern South America (Brazil, Uruguay and Argentina) suffer significant mortality. Incidence and potential population impact vary widely among the 26 small cetacean species for which collision records exist. Vessel strikes in at least two populations each of the Indo-Pacific humpback dolphin (Xiamen and Hong Kong/Pearl River, possibly western Taiwan), Irrawaddy dolphin (Mahakam River, Chilika Lagoon, possibly Laos) and finless porpoise (Yangtze River, Hong Kong) may directly compromise long-term survival. Annual vessel-caused mortality (min. 2.9% of population) for Irrawaddy dolphins in the Mahakam River may not be sustainable. The quasi-extinction of the baiji warns for a potential similar fate for the Yangtze River finless porpoise and Ganges river dolphin. Two calves of the endangered Hector's dolphin are known killed by boats. All highly impacted species have a neritic, estuarine or fluviatile habitat, areas where vessel traffic is concentrated. Species that may receive a moderate impact from collisions but which may be sustainable at species level (because many strikes are nonlethal), include common bottlenose dolphins, killer whales, short-finned pilot whales and pygmy sperm whales. Almost 2% of common bottlenose dolphins in the Gulf of Guayaquil showed propeller-inflicted injuries and scars. Propeller guards should be made compulsory for all boat-based cetacean tourism, as habituation to boat traffic seems a contributing factor in accidents. Low impact occurs in 15 small cetacean species with only few reported vessel strikes. However, vast underreporting is thought to be the norm and there is a need for a global, standardised database.

Conservation and the genetics of populations

Conservation and the genetics of populations

Offshore distribution of Hector's dolphins at Banks Peninsula, New Zealand: Is the Banks Peninsula Marine Mammal sanctuary large enough?

Aerial surveys of Hector's dolphins were carried out to evaluate the effectiveness of the Banks Peninsula Marine Mammal Sanctuary. In summer, the proportion of sightings inside the 4 nautical mile offshore boundary of the sanctuary was 79%. This dropped to just over 35% in winter. These estimates were used in a population viability analysis to determine whether the sanctuary needs to be extended to reduce dolphin bycatch to sustainable levels. We followed the standard procedure for setting limits on marine mammal bycatch in the United States to calculate a bycatch limit of 1.6 or 2.8 dolphins per year (depending on whether the sanctuary population is included). If the offshore boundary was extended to 15 nautical miles, the sanctuary would need to be extended alongshore north and south by more than 30 nautical miles to reduce bycatch to 2.8, or north and south by 60 nautical miles to reduce bycatch to 1.6 dolphins per year.

CAPTURE-RECAPTURE ESTIMATES OF HECTOR'S DOLPHIN ABUNDANCE AT BANKS PENINSULA, NEW ZEALAND

Capture-recapture techniques have been extensively used to estimate survival rates of Hector's dolphins at Banks Peninsula, but not abundance. We analyzed nine seasons of photo-identification data using a model-fitting approach in the computer program MARK, and then used MARK's estimates of capture probabilities to calculate the abundance of distinctive individuals. We extrapolated these estimates to include unmarked individuals using five seasons of data on the proportion of identifiable individuals in this population, obtained from “random photography.” This capture-recapture approach suggests a 1996 population of about 1,100 (CV = 0.21). This is very similar to the 1997 line-transect estimate of about 900 (CV = 0.28), especially considering that the two techniques do not necessarily measure the same thing. An important advantage of the capture-recapture approach stems from the inherent versatility of photo-ID data. If the sampling design is appropriate, an unbiased abundance estimate can be achieved as a spin-off from work directed at other questions. However, in our view, line-transect estimates are easier to interpret because the sampling design is explicit.

AERIAL SURVEYS FOR COASTAL DOLPHINS: ABUNDANCE OF HECTOR'S DOLPHINS OFF THE SOUTH ISLAND WEST COAST, NEW ZEALAND

AbstractLine‐transect surveys of abundance depend critically on the estimation of detection probability, which includes corrections for availability and visibility. In this aerial line‐transect survey for Hector's dolphin (Cephalorhynchus hectori) we recorded dive times from a helicopter to estimate the proportion of time that dolphins could be seen at or near the water surface and were therefore “available” to be counted. The proportion of available sightings that were counted on transect lines was estimated by comparing sightings by two independent teams of two observers in the fixed‐wing plane. The survey covered the area between Farewell Spit and Milford Sound, off the west coast of the South Island of New Zealand. Survey effort was stratified according to existing distribution data. A total of 142 separate sightings was made on 1,355 km of trackline. Average availability for fifty Hector's dolphin groups observed from the helicopter (161 dive/surface cycles) was 46.3% (CV = 4.2%). Data from the two independent observer teams indicated that 96.2% (CV = 2.3%) of the dolphin groups that were at the surface and on the trackline were seen. The abundance estimate for the South Island west coast, corrected for visibility and availability, was 5,388 Hector's dolphins (CV = 20.6%). The total population estimate for South Island Hector's dolphins is 7,270 (CV = 16.2%).

A Classical Study of Catch-Effort Models for Hector's Dolphins

Effective management is the key to the protection of many endangered species. Identification of the primary factors that affect their survival often lead to the introduction of strategies to improve survival rates. In this article, we consider a small population of Hector's dolphins located off the coast of New Zealand and the impact that the establishment of a seasonal sanctuary has on their survival and migration rates. Using Akaike's information criterion and an extension of the simulated annealing algorithm, we distinguish between a wide range of competing models that correspond to different assumptions as to the region and temporal dependence of the survival rates. We also examine the impact of the inclusion of catch-effort information and demonstrate the added value that these data provide in terms of both model discrimination and parameter estimation. In particular, we find a whole class of models that provide a far better fit to the data (and therefore better prediction and ultimately better management) than those adopted for previous analyses.

Bayesian analysis of the Hector's Dolphin data

In recent years there have been increasing concerns for many wildlife populations, due to decreasing population trends. This has led to the introduction of management schemes to increase the survival rates and hence the population size of many species of animals. We concentrate on a particular dolphin population situated off the coast of New Zealand, and investigate whether the introduction of a fishing gill net ban was effective in decreasing dolphin mortality. We undertake a Bayesian analysis of the data, in which we quantitatively compare the different competing biological hypotheses, determining the effect of the sanctuary upon the dolphin population.

Population viability analysis for Hector's dolphin (Cephalorhynchus hectori): A stochastic population model for local populations

Mortality of Hector's dolphin (Cephalorhynchus hectori) in gill‐net fisheries is a threat to local populations throughout its range. This population viability analysis extends previous work by exploring a wider range of fishing levels and population growth rates, by incorporating year‐to‐year and environmental variability and by reporting results for smaller population units. Ten of the 16 populations are likely to continue to decline, five are indefinite, and one is likely to increase. All populations subjected to high fishing effort are declining. The only population predicted to increase is partly protected by a marine mammal sanctuary (created in 1988) which reduces the amount of gill‐net fishing. Conservation measures are most urgently needed for the highly threatened North Island population, in particular the dolphins at the northern and southern end of this range.

Habitat selection in a coastal dolphin species ( Cephalorhynchus hectori )

Hector's dolphin (Cephalorhynchus hectori )i s a small New Zealand delphinid with a coastal distri- bution. Within a strip of 1 km from shore, the present study quantified the habitat used by the dolphins (n=461 groups) over a 19-month period (216 field days with 966 survey hours) by recording the abiotic factors sea surface temperature (SST), water depth and water clarity. Resource selection functions were used to dis- tinguish the properties of 461 ''used'' sites (dolphins present) from 425 ''unused'' sites (no dolphins present) in six different study areas. Most dolphins were encountered in waters 14� C temperature. The preference of Hector's dolphins for warm and turbid waters was tested using eight models. Water depth, water clarity, SST and the study area explained dolphin presence to a very significant degree (p<0.001), and the model al- lowed the creation of probability plots for a variety of combinations of the variables. Habitat selection by dolphins differed between study areas, particularly between east and west coasts, in summer (December- February) and winter (June-August). Dolphin abun- dance appeared to change seasonally in some study areas, possibly due to a more offshore distribution of their prey in the winter, with its lower SSTs. This was so especially in summer (the main reproductive season), when dolphins (frequently with calves) occupied shallow and turbid waters, whereas in winter less use was made of this habitat.

High concentrations of isovaleric acid in the fats of odontocetes: variation and patterns of accumulation in blubber vs. stability in the melon.

Isovaleric acid (iso5:0) is an unusual fatty acid that is important for echolocation and hearing in acoustic tissues of some odontocetes, but its functional significance in blubber is unknown. We examined patterns of accumulation of this compound in blubber in 30 species of odontocetes ( n=299). Iso5:0 concentrations in blubber varied with phylogeny, ontogeny and body topography. Iso5:0 accumulated in greater quantities in superficial/outer blubber than in deep/inner blubber. In the outer blubber of northern right whale and Hector's dolphins, iso5:0 accounted for one-third to one-half of all fatty acids. Total blubber burden of iso5:0 in harbour porpoises represented up to 15 times the amount deposited in the melon. The composition of the melon does not change during starvation in harbour porpoises, supporting the hypothesis that lipids in melon are conserved for a specific function. Some odontocetes continually deposit iso5:0 in blubber after levels in melon have reached asymptotic levels, suggesting independent control of iso5:0 synthesis and storage in these compartments. Dolphins and porpoises inhabiting cold waters possess higher concentrations of iso5:0 in their outer blubber layers than species from warmer regions. We propose that this relationship represents an adaptive secondary role for iso5:0 in maintaining blubber flexibility in cold environments.

Sex-biased dispersal in a salmonid fish.

We tested the hypothesis that dispersal is sex biased in an unexploited population of brook trout, Salvelinus fontinalis, on Cape Race, Newfoundland, Canada. Based on the assumptions that trout are promiscuous and that reproductive success is limited primarily by either number of mates (males) or fecundity (females), we predicted that males would disperse greater distances than females. We also tested the hypothesis that trout populations comprise stationary and mobile individuals, predicting that males have greater mobility than females. Based on a mark-recapture study of 943 individually tagged fishes, 191 of which were recaptured over 5 years, we find strong support for our hypothesis of male-biased dispersal in brook trout. Averaged among all 11 resampling periods, males dispersed 2.5 times as far as females; during the spawning period only, male dispersal exceeded that by females almost fourfold. Both sexes were heterogeneous with respect to movement, with a lower incidence of mobility among females (29.6%) than males (41.1%); mobile males dispersed six times further than mobile females. We conclude that this sex bias reduces mate competition among male kin and decreases the probability that males will reproduce with related females.

Geographical variation in Hector's dolphin: Recognition of new subspecies of Cephalorhynchus hectori

The endemic New Zealand dolphin Cephalorhynchus hectori has been shown through genetic analyses to consist of four regional populations separated to various degrees both geographically and reproductively. A morphological study of skull and mandible features was undertaken to examine variation between the most genetically distinct population, occurring on the west coast of the North Island, and the populations around the South Island. Univariate and principal component analyses demonstrate that the North Island population can be differentiated from the southern populations on the basis of several skeletal characters. These characters, plus the genetic evidence of haplotype differences and absence of gene‐flow between populations, enable us to formally describe the North Island population of Hector's dolphin as a new subspecies, C. hectori maui, and the nominate South Island populations as C. hectori hectori.

Site fidelity and along-shore range in Hector's dolphin, an endangered marine dolphin from New Zealand

To document site fidelity and the alongshore range of individual Hector's dolphins we analysed sightings of 32 photographically identified dolphins, each seen ⩾10 times at Banks Peninsula, New Zealand, between 1985 and 1997. The furthest two sightings of an individual were 106 km apart. All other individuals ranged over less than 60 km ( x̄=31.0 km, SE=2.43) of coastline. Gender did not significantly influence alongshore range (female x̄=30.4 km, SE =3.21, n=18; male x̄=27.4 km, SE=5.68, n=5). Site fidelity was high: for example, on average, individuals were seen in Akaroa Harbour for about two thirds of the years they were known to be alive. These data suggest that impacts on Hector's dolphins are most appropriately managed on a small spatial scale.