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CHAPTER 8

HECTOR’S DOLPHINS AND FISHERIES IN NEW ZEALAND: A SPECIES AT RISK

F. B. Pichler, E. Slooten, S. M. Dawson

INTRODUCTION

Incidental entanglement (‘bycatch’) in gillnets is a global prob-lem that affects at least 40 species of cetacean (Perrin et al. 1994).Small coastal cetaceans, such as some dolphins and porpoises,are particularly susceptible to entanglement mortality. In gen-eral, the impact of such fisheries mortality is difficult to deter-mine, but for a few species such as the vaquita (Phocoena sinus)there is compelling evidence that the rate of bycatch is suffi-ciently high to be causing population decline (see D’Agrosa et al.2000). New Zealand’s endemic Hector’s dolphin (Cephalorhyn-chus hectori) is considered to be another species declining due tounsustainable levels of bycatch (Dawson 1991; Martien et al.1999; Pichler and Baker 2000; IUCN 2000; Slooten et al.2000c). Calculation of the effects of fisheries upon this speciesare complicated by a variety of factors including the uneven dis-tribution of fisheries effort along the coastline, difficulty in esti-mating fisheries bycatch rates and particularly due to extremepopulation division within this species. The North Island pop-ulation of Hector’s dolphin has been proposed as distinct sub-species (C. h. maui; Baker et al. in press) and has been listed ascritically endangered by the IUCN due in part to the reports offisheries bycatch. The South Island population is widely dis-persed, and subdivided into three distinct regional sub-popula-

tions. The South Island population as a whole has been classifiedas endangered by the IUCN. The considerable effort required toprovide sufficient evidence to justify conservation managementaction for this species provides a useful case study that highlightsthe problems of managing vulnerable coastal populations ofmarine mammals.

Here we review the impact of fisheries upon Hector’s dolphin inorder to demonstrate why this species is ‘at risk’. We begin withan examination of the demographic characteristics of these dol-phins that may accentuate its vulnerability to human impacts(Figure 1). We then briefly examine the range of human-relatedimpacts that are considered to potentially threaten the long-termsurvival of Hector’s dolphins prior to discussing those fisheriesmethods thought to result in the greatest levels of bycatch. Wereview the evidence that assesses whether the impact of thisbycatch is causing population decline in this species and, takinginto consideration the other potential threats, we assess the statusof Hector’s dolphins on a regional basis. Management actionshave been undertaken in some local areas including the creationof a sanctuary and deployment of acoustic mitigation devices(‘pingers’). Further management is being considered for otherlocations and in some cases is contentious due to lack of informa-tion about either population abundance or entanglement rates.

P A R T I

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We conclude this chapter with comments about some of the man-agement strategies that may further reduce or mitigate the impactof bycatch on Hector’s dolphin.

NATURAL SUSCEPTIBILITY TO HUMAN IMPACTS

Like many island endemics, and most marine mammals, Hec-tor’s dolphins appear to be naturally vulnerable to human-related impacts. We discuss those particular characteristics ofthis species that makes them especially susceptible to suchimpacts in this section.

HabitatHector’s dolphins are found off both sandy and rocky shores(Dawson and Slooten 1988), seaward of estuaries and deepinlets (Baker 1978) and off prominent headlands (Bräger 1998).Hector’s dolphins regularly enter harbours and occasionally thelower reaches of rivers. The most detailed studies (see Dawsonand Slooten 1993; Bräger 1998; Stone 1999) of habitat use havebeen carried out at Banks Peninsula. Here, Hector’s dolphinsenter the large harbours and bays mostly during the summermonths. On the open coast their distribution also changes sea-sonally (Dawson and Slooten 1988). The proportion of sight-ings within 800 m of the shore decreases from 45.5% in summerto 21% in winter (Dawson and Slooten 1988). Research at sevenother South Island locations indicates a similar seasonal patternof distribution, with dolphins found closer to shore in summer(Bräger and Schneider 1998; Bejder and Dawson 2001). Thisalso appears to be the case for North Island Hector’s dolphins(Russell 1999).

Hector’s dolphin is a coastal species that is seldom seen beyondfive nautical miles (nm) from the shore in summer. Occasionalsightings have been made out to 9 nm offshore at Banks Penin-sula (Brown et al. 1992; Dawson et al. 2000; DuFresne et al.2001). In a recent series of surveys covering the entire SouthIsland habitat of Hector’s dolphins, sightings beyond 5 nm weremade only at Banks Peninsula and the majority of sightings inall areas were within one or two nm of the coast (Clement et al.2000; Dawson et al. 2000; DuFresne et al. 2001; Slooten et al.2001). Offshore distribution appears to be related to waterdepth with an apparent maximum depth of about 80 m (Baker1978; Bräger and Schneider 1998). The mean distance from theshore (or water depth) where Hector’s dolphins are concentratedmay also be influenced by water temperature (Bräger and Sch-neider 1998).

Stone et al. (1995) described a tendency for diurnal changes inmovement at Bank’s Peninsula’s Akaroa Harbour. In the earlymorning 47% of the dolphins were moving towards the shore orinto Akaroa Harbour. In the late afternoon, 69% of the dolphinswere moving away from the shore or out of the harbour. No diur-nal patterns were evident in a theodolite study of Hector’s dol-phins in Porpoise Bay, Southland (Bejder and Dawson in press).

Such a coastal habitat brings Hector’s dolphins into close prox-imity with many potential human-related impacts, from pollu-tion outflows to shallow-water fisheries. Risk increases oversummer when an inshore trend in dolphin distribution coin-cides with an increase in human activity. The variety of potential

Figure 1 Hector’s dolphin photographed underwater (S.M. Dawson)

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impacts in the inshore zone complicates the assessment of anyone impact.

DistributionHector’s dolphins have been found from as far north as theHokianga Harbour and the Bay of Islands to Paihia Point,South-east of Te Waewae Bay (Figures 2 and 3). Based on cur-rent knowledge, Hector’s dolphins are limited to the North andSouth islands of NZ and have never been recorded at any off-shore island. In the North Island, the population once extendedalong the entire west coast but now appears to be limited to asmall area between the Kaipara Harbour and Port Waikato(Russell 1999). Although neither small-boat nor aerial surveyshave sighted dolphins outside this range a few public sightings(C. Roberts personal communication) to the north and south ofthese boundaries suggests the possibility of either occasionalalongshore movements or some small outlying populations. In

the South Island, the distribution of Hector’s dolphins is patchy.Some sections of coast have high densities whereas they areabsent, or at very low abundance, at other locations (Dawsonand Slooten 1988; Bräger 1998; Clement et al. 2000; Dawsonet al. 2000; DuFresne et al. 2001; Slooten et al. 2001a). Hector’sdolphins are most abundant off the northern half of the east andwest coasts of the South Island (Baker 1978; Dawson andSlooten 1988; Clement et al. 2000; Dawson et al. 2000;DuFresne et al. 2001; Slooten et al. 2001a). With the exceptionof a sizeable population of dolphins at Te Waewae Bay, thesouth coast of the South Island has very few Hector’s dolphins.

Even the original reports of Hector’s dolphin distribution men-tion the possibility of population isolation. As early as 1973, itwas suggested that the east and west coasts of New Zealandmight have separate populations of Hector’s dolphin (MörzerBruyns and Baker 1973). With the lack of geographic barriers

Figure 2 Distribution of Hector’s dolphin in the North Island of New Zealand. The area of primary concentration is shown (dark stipples) with maximum current range (light stipples) and historic range (clear). Additional outlier museum specimens or sightings are shown as dots. Data source: K. Russell, 1999 and Pichler and Baker 2000.

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the most likely explanation for the isolation of dolphin popula-tions would be site fidelity resulting in isolation by distance.A.N. Baker conducted a tagging program in 1978–79 at CloudyBay to study population abundance and distribution. Plasticsheep ear tags were attached to the dorsal fins of 22 dolphins anda proportion of these were also freeze-branded. Since all re-sight-ings of marked dolphins were within a few kilometres of the tag-ging localities, Baker (1983) concluded that Hector’s dolphinsform semi-resident or resident groups within relatively confinedlocations. The results of this study are supported by numerousphoto-identification studies where high resight rates of dolphinswithin local areas are common. For example, 75% of individualsphoto-identified in the first season of study at Porpoise Bay wereresighted in the second season (Bejder and Dawson 2001). Theaverage summertime long-shore home range of Hector’s dol-

phins is about 30 km (10–60 km) with no evidence to suggesta different home range size for males or females (Bräger et al.2002). Further, there have been no reports of photo-identifiedindividuals seen in two geographic locations > 106 km apart.

Genetic analyses (Pichler et al. 1998; Pichler and Baker 2000;Pichler 2002) have shown that there are four regional popula-tions of Hector’s dolphin including a putative subspecies (Table1). The North Island population is fixed for a single mitochon-drial (mt) DNA haplotype that is unique to this population andhas significantly different microsatellite allele frequencies (FST =0.455, P < 0.0001) to the South Island population (Pichler2002). This level of divergence is comparable to that seenbetween Tierra del Feugo and Kerguelen Island populations ofCommerson’s dolphins (C. commersonii) suggesting that theNorth Island population is reproductively isolated and probably

Figure 3 Distribution of Hector’s dolphins in the South Island. The areas of greatest concentration are not necessarily continuous populations, but rather may be composed of high-density patches connected by areas of low density. Light stippling indicates areas where few dolphins are seen. Black shading indicates the Banks Peninsula Marine Mammal Sanctuary.

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a subspecies (Pichler, unpublished data). Using these geneticdata, and evidence of morphological distinctiveness, Baker et al.(in press) have formally proposed the sub-specific status (C. h.maui) of this population.

Based upon significant divergence in mtDNA haplotype fre-quencies, the South Island population of Hector’s dolphin canbe divided into three coastal regions (the west, east and southcoasts). Surprisingly, the south coast population appears to havebeen founded from the west coast rather than the east coastregional population in spite of the deep water separating thesetwo regions. These data suggest little or no female movementbetween any of the regional populations, which is consistentwith demographic evidence of small home range sizes (Bräger etal. 2002). Pichler et al. (1998) propose that the regional popu-lations within the South Island are demographically isolated andshould be managed separately and that the North and SouthIsland populations correspond to unique Ecologically Sustaina-ble Units (ESUs) (Figure 4). Bi-parentally inherited microsatel-lite data are consistent with this pattern of regional isolationindicating that male dolphins do not disperse along shore fur-ther than female dolphins (Pichler 2002). MtDNA haplotypeclines observed within the west and east coast regional popula-tions suggest that even on a local scale, long-term dispersal isvery limited (Pichler 2002). Pichler (2002) used a regression oflog Nm and the log of geographic distance as a test of isolationby distance (following Slatkin 1993) for the within-regionalcoastal populations of the South Island. The slope of the regres-sion (-1.200, 95% C.I. -0.266 – -2.13) fitted the expected slope(-1) for a one-dimensional stepwise dispersal model (Figure 5).

The patchy distribution of Hector’s dolphins coupled with theirhigh level of natal fidelity has important implications for man-agement. Localised human impacts would be expected to affectpopulations on a local (or regional) scale. The low movementrate means that dolphins in an area with little or no impact areunlikely to venture into areas of high impact. On the other hand,one would expect local depletions to persist long-term, becauseof little opportunity for healthy populations to replenish neigh-bouring impacted populations. Thus, lack of alongshore move-

ment suggests that within-region population cohesiveness mayeasily be disrupted by localised impacts.

Abundance

The first abundance estimates for Hector’s dolphin, based eitheron analysis of incidental observations (Cawthorn 1988), orextrapolation from a small part of the distribution (populationat Cloudy Bay) to arrive at a total population estimate (Baker1978), suggested a total population size between 3000–6000animals. The first quantitative boat survey was undertaken in anoutboard-powered inflatable boat in 1984/85 (Dawson andSlooten 1988). This was an alongshore strip-transect surveywhich was combined with offshore transects and simultaneousclifftop observations and boat surveys to account for availabilitybias and perception bias. The resulting abundance estimate was3408 (interpreted as being 3000–4000 individuals) with subse-quent bootstrapping (Martien et al. 1999) suggesting a 95%C.I.of 2740–3906.

Since then more sophisticated surveys have been undertakenfrom a 15 m catamaran specifically adapted for line-transect sur-veys (R.V. Catalyst), covering the north, east and south coasts ofthe South Island (Dawson et al. 2000; Clement et al. 2000;DuFresne et al. 2001). In each of these surveys transects wereplaced at 45˚ to the coast and stratified according to pre-existingdata on dolphin density. Results confirm the discontinuous dis-tribution found in the earlier boat survey (Dawson and Slooten1988) and evident in the study of mtDNA by Pichler et al.(1998). Calibration work using an independent observer in ahelicopter (following methods of Buckland and Turnock 1992)was used to quantify the effect of dolphins being attracted to thesurvey vessel, and the fraction of dolphins missed on the track-line. The combined correction was a downward adjustment ofdensity by 50%. Together, these surveys covering the north, eastand south coasts of the South Island indicated that the Hector’sdolphin population in this area was 1882 (cv = 21%; Clementet al. 2000).

A similarly designed line-transect survey was carried out inDecember 2000 off the South Island west coast. This surveywas conducted aerially, in a high-wing, twin-engine aircraft

Table 1 Genetic differentiation between the four regional populations of Hector’s dolphins. Lower diagonal is FST statistics calculated from mtDNA haplotype frequencies, upper diagonal is FST statistics calculated from microsatellite allele frequencies.* non-significant difference. Note for the south coast the sample size was low (2n = 8).

South Island

FST North Island east coast west coast south coast

North Island – 0.441 0.586 0.618

east coast 0.565 – 0.038 0.051*

west coast 0.474 0.337 – –0.025*

south coast 0.548 0.366 0.157 –

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(Partenavia p. 68) equipped with bubble windows to allowobservers to see directly under the aircraft. Aerial surveys wererequired due to the limited access and exposed nature of muchof this coastline. The west coast South Island population wasestimated at 5388 individuals (cv = 20.6%; Slooten et al. 2001).Combined with the boat surveys this estimate allowed an overallpopulation estimate of the entire South Island of 7270 (cv =16.2%; Slooten et al. 2001). The abundance of the entire SouthIsland is considerably higher than that of the 1988 estimate

(Table 2). This difference stems from the large increase in theestimated abundance of the west coast regional population. Thisis likely to be due to a more rigorous estimation of abundancerather than a dramatic increase in population abundance.

For the North Island population the abundance estimates havebeen consistently lower than those of the South Island popula-tions. The earliest estimates, based on sighting records or extrap-olation, placed the total population in the North Island as fewer

Figure 4 Hector’s dolphin may be subdivided into four genetic management units based about significant differences of mtDNA and microsatellite variation. Shaded areas indicate the sampling locations from within each region. Here all genetic samples dating to 1870 have been used to generate the four pie charts. The pie charts indicate the frequencies of the seven most common mtDNA haplotypes. Data taken from Pichler (2002).

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than 700 individuals (Baker 1978; Cawthorn 1988). These esti-mates assumed a much larger population distribution than isnow recognised. Within the area of the current known distribu-tion, these estimates were low (e.g. 100–200; Cawthorn 1988).A small-boat survey in the winter of 1985 by Dawson andSlooten (1988) sighted 22 dolphins leading to an estimate of134. From replicated small-boat transects, applying the correc-tion factors for availability bias and perception bias developed byDawson and Slooten 1988, Russell (1999) estimated the NorthIsland Hector’s dolphin population at approximately 45 indi-viduals. The only dolphins observed off the North Island werebetween the Kaipara Harbour and Port Waikato, however sight-ings and photographic information of dolphins between Raglanand Mokau compelled Russell to increase her abundance esti-mate to 80 dolphins. The estimate should be interpreted as

indicative of the size of the North Island population, rather thana robust population estimate.

The overall abundance of this species is low and two regions, theNorth Island and the south coast of the South Island have pop-ulations of fewer than 200 animals. In isolation, this fact alonesuggests that any fisheries impact is likely to be unsustainable.The east and west coast populations of the South Island havepopulations in the low to mid-thousands. However, these twopopulations are distributed over lengthy coastlines with hotspotsof abundance interspersed by zones of very low abundance. Thisimplies that localised impacts occurring within regions of lowabundance could easily result in the isolation of the populationconcentrations.

Life history, survival and population growth rates

While there may be many Hector’s dolphins within a local area,they tend to cluster into small, mixed-sex groups of about 2–8individuals (Baker 1978; Slooten and Dawson 1988). Groupsfrequently encounter each other, merge, and then split up again,following a fusion-fisson cycle typical of many small cetaceans(Slooten et al. 1993). When groups are merged there is a markedincrease in sexual behaviour (Slooten 1994). The associationpatterns of these groups are relatively fluid and individuals tendto associate with most of the other individuals in their homerange (Slooten et al. 1993; Bräger 1998).

The mating system of Hector’s dolphin has been described as‘promiscuous’ (Slooten et al. 1993). Based on behavioural obser-vations and the fact that males have large testes and are smallerthan females, Slooten et al. (1993) suggested that males do notmonopolise females but rather that they rove from group togroup to maximise the number of receptive females theyencounter. The observation of a 1:1 sex ratio (Slooten andDawson 1988) further suggests that monopolisation would be

Table 2 Summary of population estimates for Hector’s dolphin. 1) Although his total estimate for the North Island was 700 individuals, Cawthorn only estimated an abundance of between 100-200 dolphins in the area of current known distribution. 2) The bootstrapping analysis was conducted on the Dawson and Slooten (1988) sighting data. 3) This is a combination of estimates from line transect boat and aerial surveys (see text above).

Population Estimate Method Reference

North Island 100–2001 Sighting records Cawthorn 1988

134(46–2802)

Boat survey (95% bootstrap ci)

Dawson and Slooten 1988; Martien et al. 1999

80 Strip transect Boat survey and public sightings

Russell 1999

South Island 3000–4000 Extrapolation Baker 1978

3274 (2431–34762)

Strip transect Boat survey (95% bootstrap ci)

Dawson and Slooten 1988; Martien et al. 1999

72703

(5303–9966)Line-transect

(95%ci)Slooten et al. 2001

Figure 5 Log-log regression of effective migration (Nfm) derived from fixation indices (FST) against geographic distance (km) using within-region local populations of the South Island Hector’s dolphin. Data taken from Pichler (2002).

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unlikely. Such multi-male-multi-female systems appearcommon in delphinids (Evans 1987).

Dissections and tooth aging of 60 Hector’s dolphins showed amaximum age of 19 and 20 years for females and males respec-tively (Slooten 1991). Females have their first calf when seven tonine years old and males reach sexual maturity between six tonine years (Slooten 1991). Further work (now 116 carcases) hasconfirmed these estimates (Slooten and Dawson, unpublisheddata). Photo-identification studies around Banks Peninsulaindicate that females generally have one calf every two to threeyears (Slooten et al. 1992). The few cases in which females havebeen observed having a calf in consecutive years have beenattributed to the loss of the first calf (Bräger 1998). Calvingintervals for dolphins in general typically range from two to fouryears with a minimum 10-month gestation and a lactationperiod from one to two years (Perrin and Reilly 1984). Unlikepilot whales (Perrin and Reilly 1984) there is no evidence forreproductive senescence in female Hector’s dolphin (Slooten1991). The late onset of maturity and long calving interval indi-cate that the maximum female reproductive potential is onlyfour to seven calves. With a likely population growth rate ofabout 2% under ideal conditions (Slooten and Lad 1991), thisspecies will not quickly recover from population declines.

HUMAN IMPACTS

Historically, Hector’s dolphins have been taken for food, oil andfor bait. Whether these takes were more than occasional isunknown. This century, the main threat to Hector’s dolphinappears to be from indirect mortality due to entanglement ingillnets. Other threats include pollution, inbreeding of small iso-lated populations, tourism and boat strikes. Below, we reviewthe possible human impacts, historical and contemporary, sincethe vulnerability of a population to fisheries impacts alsodepends upon the effects of other non-fisheries-related humanimpacts.

A review of marine mammal remains in Maori middensthroughout New Zealand revealed evidence of extensive exploi-tation of fur seal (Arctocephalus forsteri) and sea lion (Phocarctushookeri) breeding colonies (Smith 1989). Although identifica-tion of cetacean bones is more difficult, due to the number ofspecies in New Zealand waters, pilot whale (Globicephala sp.)bone was identified from several sites known for frequent pilotwhale strandings. In addition to hunting at seal haul-outs andbreeding colonies, or the gathering of stranded cetaceans, Smithprovides evidence that dolphin species were actively hunted atsea. He reports a close correlation between the distribution ofdolphin remains and harpoons, but suggests that dolphin hunt-ing was never a common activity. Smith suggests that the targetspecies were most likely common dolphins (Delphinus delphis;Smith 1989). However, common dolphins are typically found

in deep water and are less interested in interacting with boats(Constantine 1999) than dolphins that come closer to the coastsuch as bottlenose dolphins (Tursiops truncatus), dusky dolphins(Lagenorhynchus obscurus) and Hector’s dolphin. The logical tar-gets of canoe-based hunting would be inshore dolphins that areattracted to boats.Historic impacts

In 1840, Dr Louis Thiercelin, ship’s doctor onboard the whal-ing ship Ville de Bordeaux, recorded his observations of a dolphinhunt by Maori (Thiercelin 1866). He describes ‘a large party ofporpoises’ in Akaroa harbour. Two canoes left the shore armedwith harpoons ‘made of bones fastened to wood handles andsecurely tied to the boats by flax lines’. The harpoon struck thedolphin as it was ‘blowing in front of the canoes’ and then wasrepeated stabbed by women who had jumped from the canoeinto the water. Once ashore the dolphin was promptly cookedand eaten. Although there is evidence of Maori harvestingmarine mammals about the coastline of New Zealand, there isno direct evidence that Hector’s dolphin was targeted. Unfortu-nately, Thiercelin’s (1866) memoirs do not describe the ‘por-poises’, but the location of the hunt, within Akaroa harbour andthe fact that these small porpoises approached the canoes,strongly suggest that they were Hector’s dolphins.

During European times, there are some reports of dolphinsbeing shot for sport and perhaps for oil (Diver 1933). Prior tothe introduction of the Marine Mammal Protection Act 1978there was also a low-level directed take of Hector’s dolphins foruse as bait in lobster (Jasus edwardsii) traps (Dawson and Slooten1988). The use of cetacean meat as bait in lobster or crab trapshas been a common practice worldwide, typically targetinginshore species of dolphin or porpoise (see Leatherwood et al.1988).

Non-fishery related impactsPollutionChemical pollutants, particularly Persistent Organic Pollutants(POPs), are now recognised as having one of the most poten-tially pervasive impacts on wildlife (Reijnders et al. 1999),including cetaceans. Cetaceans that are at a high trophic level areparticularly vulnerable (Tanabe et al. 1994). These animals tendto ingest most of their pollutant load from contaminated preyand to bio-accumulate toxic contaminants to high concentra-tions (Muir and Norstrom 1991; Reijnders et al. 1999). Femalestend to have lower PCB and DDT concentrations (Aguilar1983) as contaminants are passed on to offspring during gesta-tion and through lactation (Cardellicchio 1995). Contaminantlevels in cetaceans are correlated to the state of their habitat (Rei-jnders 1996). Northern Hemisphere species and coastal speciestend to have higher concentrations than in those of the SouthernHemisphere and open ocean species (Tanabe et al. 1994;Slooten and Dawson 1995; Mössner and Ballschmiter 1997;Jones et al. 1994, 1999). Hector’s dolphins have the highest bur-

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dens of NZ marine animals due to their coastal habitat and hightrophic level (McCutchen 1993; Jones et al. 1999).

Persistent Organic Pollutants (POPs), including DDTs andPCBs, are found at great distances from their release point. Forexample, DDT (dichloro-diphenyl-trichloroethane) is highlypersistent, with a half-life of 10 years in dry soil and its main res-idues changing only slightly over a period of 20 years (MfE1997). Despite more stringent regulation of the use of toxic sub-stances in the past decade, terrigenous pollution of the marineenvironment will continue (Borrel and Reijnders 1999) as mostof the POPs produced have not yet dispersed into the environ-ment (Tanabe et al.1988; Reijnders 1996).

DDTs and PCBs were heavily used in NZ between the 1940sand 1970s. To reduce levels of pollution, NZ put in place itsMarine Pollution Act in 1974 and ratified major internationalagreements (e.g MARPOL in 1994). NZ also banned DDT in1989, phased-out PCBs in 1990 and removed leaded petrolfrom sale. Global transportation of pollutants as aerosols is amajor problem (Tanabe et al. 1994; Thompson 1990) thatneeds to be managed at a global scale.

Boat strikesHector’s dolphins are boat positive and often bowride on boatstravelling at around ten knots or less; they tend to avoid fastervessels by diving (Baker 1983; Slooten and Dawson 1994).Mother-calf pairs are an exception, and seldom approach boatsclosely. Because of their adeptness at bowriding, collisionswould seem to be a small risk for slow-moving boats. The mainrisk appears to be from fast-moving vessels. Stone (1999) dis-covered two dead calves on consecutive days in Akaroa Harbour,each of which appeared to have been struck by a boat. This ledStone (1999) to suggest that mother-calf pairs are more vulner-able to boat strikes due to the reduced evasion ability and lackof experience of the calf. Boat traffic is increasing in many areasof Hector’s dolphin habitat, increasing the risk of boat strike.This negative aspect of raising public awareness (increased sight-seeing) has been taken into account in information given to thepublic about the plight of the North Island Hector’s dolphin.

TourismAt this stage, the benefits of tourism in terms of public educationare likely to outweigh the potential impacts on Hector’s dol-phin. However, continued growth in the tourism industry couldchange this balance. Short-term behavioural changes as a resultof tourism have been noted in several marine mammal popula-tions in New Zealand, and these could lead to long-term effectson individuals and populations (Constantine 1999).

A theodolite-based study of Hector’s dolphins at Porpoise Bay(Bejder et al. 1999) documented responses by Hector’s dolphinsto boats and swimmers. Dolphins were accompanied by swim-

mers for 11.2% of the time, and by boats for an additional12.4%. Hector’s dolphins were not displaced from the bay bythese activities, however dolphin response to the boat changedover time. In the initial stages of an encounter, dolphins tendedto approach the vessel. But they became less interested as theencounter progressed. By 70 minutes into an encounter, dol-phins were either actively avoiding the boat, or were equivocaltowards it, approaching significantly less often than would beexpected by chance. Hector’s dolphin groups were also signifi-cantly more tightly bunched when a boat was in the bay (as seenwith dusky dolphins also).

In contrast to Porpoise Bay, Akaroa Harbour is an easily acces-sible location near one of New Zealand’s major cities (Christch-urch). Since 1990 there has been a dramatic increase in thenumber of boats within the harbour, both directed tourism and(typically weekend) recreational boat traffic (Stone 1999). Thepeak period of boat activity is over summer, coinciding with thecalving season. Stone (1999) has voiced concern about the riskof boat strike, habituation and harassment as a result ofincreased tourism. Sustained interaction of boats and dolphinsmay prevent dolphins from engaging in normal daytime behav-iour, potentially leading to long-term effects such as increasedstress, a reduction in fecundity or dolphins avoiding the area(Constantine 1999).

Inbreeding depressionThe persistence of small populations can be compromised by theeffects of genetic drift and inbreeding. The influence of randomfluctuation of allele frequencies (genetic drift) is inversely relatedto population size. Genetic drift increases the rate of loss ofgenetic variation as population size decreases and increases therisk of accumulating mildly deleterious mutations. Inbreedingcan occur as a result of deliberate mating with kin or due to theeffect of an increase over time in the average relatedness of indi-viduals in small, closed populations. Inbreeding increases theproportion of homozygotes. Both inbreeding and genetic driftcan result in a reduction in fitness of the population termed‘inbreeding depression’ which includes effects such as anincreased susceptibility to disease, reduced fecundity, and devel-opmental or morphological defects.

Two regional populations of Hector’s dolphin may be at risk ofinbreeding depression or the accumulation of deleterious muta-tions. The North Island and the south coast of the South Islandhave small populations that are unlikely to be receiving immi-grants from other regions. Inbreeding depression or high muta-tional load may slow or prevent the natural recovery ofpopulations suffering from human-related depletions. Forexample, since the advent of gillnet fishing in the 1970s theNorth Island population has declined in abundance, geographicrange and genetic diversity (see Dawson et al. 2001, for review)and hence is at high risk of inbreeding depression. Recovery

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from small population size as fast as possible is the best strategyto avoid inbreeding depression, and this should be the goal ofmanagement of this population.

Other impacts

There are several other potential impacts on Hector’s dolphinsthat have not yet been quantified. Slooten and Dawson (1995)voice concern over entanglement of marine mammals in plasticdebris (particularly lost fishing gear). Other potential impactsinclude coastal modification (Stone 1999) and development, forexample the increase in marine farming in several areas of Hec-tor’s dolphin habitat. Some 40 mussel-farming applications arecurrently pending for the Banks Peninsula area alone. Thepotential effects of aquaculture operations on Hector’s dolphinsinclude competition for habitat, entanglement in ropes and net-ting associated with the farms, boat strikes and ecologicalchanges which could affect prey availability for Hector’s dol-phins (Clement et al. 1999; DuFresne et al. 1999; Slooten et al.2000a, 2000b, 2001b). There is an urgent need for directedresearch on the effects of aquaculture on Hector’s dolphins(Slooten et al. 2001b).

Other potential impacts include:

• reduction of prey abundance for Hector’s dolphins throughdestruction of fisheries habitat (e.g. trawling or mangroveremoval) and by over-fishing (Slooten and Dawson 1995;Stone 1999).

• increased environmental noise due to human activities(Stone 1999).

Fisheries-related impacts

This century, particularly over the last three decades, the prin-cipal human impact on Hector’s dolphin appears to be bycatchin fishing operations. The primary fishing method impactingHector’s dolphin has been identified as monofilament gillnetsset in the inshore coastal zone (Dawson 1991). In New Zealand,gillnetting is a popular fishing method for both commercial andrecreational fishers and is practised throughout the known rangeof this dolphin. Anecdotal reports of Hector’s dolphin bycatchin gillnets date back to the early 1970s coinciding with a dra-matic increase in fishing effort following the introduction ofmonofilament nylon nets (Mörzer Bruyns and Baker 1973;Gaskin 1976; Baker 1978; Cawthorn 1988). Later, interviewswith commercial fishers (Dawson 1991) and observer programs(Starr and Langley 2000; Baird and Bradford 2000) confirmedthat Hector’s dolphins were prone to entanglement in gillnets.Hector’s dolphins are also caught in trawl fisheries (Rutledge1992; Starr and Langley 2000; Baird and Bradford 2000), how-ever this fishing method is thought to pose less risk to dolphinsthan gillnetting.

GillnettingGillnets anchored to the bottom (set nets) are a commonly usedto target demersal fish stocks around the globe. Although manymarine mammal species lose individuals to gillnet entanglement,small, coastal, bottom-feeding odontocetes, like the Hector’s dol-phin, harbour porpoise (Phocoena phocoena) and vaquita appear tobe particularly susceptible to entanglement mortality (Perrin et al.1994). A review of gillnet entanglements of cetaceans (Perrin et al.1994) suggested that common factors involved in the high levelsof entanglement of small cetaceans include:

• the tendency of set nets to be used in turbid water with longsoak times,

• deployment of nets close to the shore in an acousticallycomplex environment,

• the strong construction of modern nets,

• and nets that occupy a large proportion of the water column.

Prior to 1970, there was a small-scale commercial set net fisheryin New Zealand using cotton or hemp nets. With de-licensingof the fishing industry in 1963 and the increasing availability ofcheap monofilament nylon gillnets, the number of gillnet fishersand overall fishing effort dramatically increased (Cawthorn1988; Anonymous 1994). The number of fishers in the industrypeaked in the mid-to-late 1970s and since declined due to over-exploitation of fish stocks (Cawthorn 1988), rising costs (Anon-ymous 1994) and removal of part-time fishers. Through theearly and mid-1980s, with the advent of mechanised drum haul-ing and increased net lengths, overall fishing effort remainedhigh (Cawthorn 1988; Anonymous 1994). Increased regula-tion, such as the introduction of the Quota Management System(QMS) in 1986 have helped to maintain fishing effort at a rel-atively constant level. The primary target species of this industryare small sharks; elephant fish (Callirhinchus millii), school shark(Galeorhinus australis) and rig (Mustelus lenticulatus) and to alesser extent other fish, such as spiny dogfish (Squalus acanthius)and kahawai (Arripis trutta), are also targeted (Dawson 1991;Hickford et al. 1997). These species are concentrated at a varietyof depths, and some, like the school shark fishery off the westcoast of the North Island are possibly outside the depths fre-quented by Hector’s dolphin. Fishing effort varies by seasondepending on the target species and geographic location. Over-all, both sexes appear to be equally vulnerable to entanglements(e.g. a sex ratio of 27:33 males:females was reported in Slooten1991) but in some areas it appears that male dolphins are muchmore prone to entanglement (Pichler 2002). Young dolphins(less than four years old) appear more vulnerable to entangle-ment (Slooten and Lad 1991). Some of the fin nicks used forphoto-identification are likely to have been caused by net entan-glement. So, perhaps dolphins become less prone to entangle-ment if they survive their first encounter with a net. There is no

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information on the percentage of entangled dolphins that washashore or how far dead dolphins can float before arriving onshore.

New Zealand is one of the few countries that permits recrea-tional gillnet fishing. Gillnets are readily available and inexpen-sive (roughly NZ$10 per metre). At present, there are fewregulations and no permits governing the use of recreational gill-nets, although with growing public awareness of dolphinbycatch certain recreational fishing clubs apparently ban the useof gillnets amongst their members (Russell personal communi-cation). While the majority of recreational gillnetting is a casualsummertime activity, in some areas such as poorer parts of thewest coast of the South Island, recreational gillnetting shouldmore properly be termed subsistence fishing. From time to time,these fishers are known to sell or barter a portion of their catch.This is illegal and thus may contribute to the apparent reluc-tance of recreational fishers to report bycatch. Recreationalcatches and effort are unreported and the activity occurs on anerratic, often opportunistic, basis. As such, mortality resultingfrom entanglement in recreational nets is difficult to assess andmay never be known. Assignment of beachcast dolphins thathave clear entanglement marks to amateur nets is often conten-tious in areas where commercial and amateur fishing coincide.In some respects, amateur gillnetting may pose a greater risk toHector’s dolphins than commercial netting. This is due to thegreat variability of amateur gillnet practice including poorly setnets that hang loosely in the water column and inability toretrieve nets if weather conditions deteriorate. On the otherhand, amateur fishing effort is likely to be less intensive thancommercial netting and is also probably more restricted in dis-tribution.

TrawlingA proportion of the coastal trawling industry in New Zealandfishes between the 100 m depth contour and the shore andhence overlaps with the known distribution of Hector’s dolphin.The extent of interaction between the trawl fishery and Hector’sdolphin is unknown. Dolphins entangled in trawl nets are likelyto be recovered by the fishers and thus in the absence of observerprograms information about trawl net entanglements is reliantupon reports from the fishers themselves. There are two recordsof multiple entanglements in trawl nets indicating that, even iftrawling entanglements are extremely rare, the potential impactupon small and isolated populations (i.e. North Island andsouth coast South Island) could be great.

EVIDENCE FOR FISHERIES-RELATED POPULATION DECLINE

Records of entangled Hector’s dolphins date back to the intro-duction of the monofilament gillnet to New Zealand. Initially,entanglement rates were thought to be low and mainly restricted

to the east coast of the South Island. The first survey of fisheriesentanglements (Dawson 1991) indicated that in the watersaround Banks Peninsula the bycatch rate far exceeded sustaina-ble levels (Slooten and Lad 1991). By 1988 the Banks PeninsulaMarine Mammal Sanctuary had been implemented and thepotential for unsustainable entanglement elsewhere aroundNew Zealand was being considered. By 1999, it was recognisedthat the North Island population was declining in range andabundance (Russell 1999; Martien et al. 1999; Pichler and Baker2000; Dawson et al. 2001) and that fisheries-related entangle-ments had occurred within this area. In 2000, in recognition ofthe threat of incidental mortality in fishing gear to the Hector’sdolphin population, the west coast North Island fishing indus-try proposed a mixed management strategy of closed areas, codesof practice and a logbook program. The International Union forthe Conservation of Nature has (as of 2000) classified Hector’sdolphins as ‘endangered’ and the North Island population as‘critically endangered’. Currently a survey is underway to assessthe level of fisheries-related mortality off the west coast of theSouth Island. Here we review the evidence of fisheries-relatedmortality in Hector’s dolphins.

North Island

Information relating to fisheries interactions with North IslandHector’s dolphin is limited. However it appears that this popu-lation has undergone a significant decline over the last 30–40years. Museum specimens and stranding records indicate thatthe historic geographic range of Hector’s dolphins in the NorthIsland reached from at least Dargaville to Palliser Bay on the westcoast and up to Napier on the east coast. A specimen from theBay of Islands in 1870 and reported sightings in the HaurakiGulf (Cawthorn 1988), if accurate, are probably outliers. Rus-sell’s (1999) plots of stranding records and public sightings sug-gest that range has contracted, and gradually shifted north. Inthe 1970s the sightings and strandings were widely distributedalong the west coast of the North Island with a concentration inthe Taranaki area. In the 1980s the concentration appears tohave shifted north to centre on the Raglan – Kawhia region andby the 1990s there were relatively few sightings below PortWaikato. The current distribution of Hector’s dolphin along thewest coast of the North Island coincides with the areas of min-imal fisheries effort, providing circumstantial evidence of pop-ulation decline associated with fisheries activities.

Analysis of the mtDNA haplotype diversity of North IslandHector’s dolphin (Pichler and Baker 2000) was consistent withthe declines in abundance and range indicated by Russell (1999)and Martien et al. (1999). In the same analysis as reported abovefor the East Coast South Island region, DNA was extracted frommuseum and tissue samples and then divided into a historic andcontemporary sample. These results detected three mtDNA lin-eages in the historic North Island population but only one in the

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contemporary sample. This suggests that the North Island pop-ulation was already at low diversity prior to the introduction ofmonofilament gillnets, but that the population had been furtherreduced over the last few decades. The observation of a singlematernal haplotype in the contemporary sample is suggestive ofvery low abundance. Analysis of nuclear loci (unpublished data)also indicates low heterozygosity and the presence of allelesunique to the North Island. Such low levels of diversity suggestthat this population may be inbred.Four North Island Hector’sdolphins have been reported as being entangled in set nets (Rus-sell 1999). In addition, four beachcast dolphins have beenobserved with slit stomachs or both fins and flukes removed.Finally, a further three were found beachcast, showing possiblenetmarks, and with nets next to them on the beach. The North-ern Inshore Fisheries Company, representing the commercial setnet and inshore trawl fishers released a management proposal in2000 that acknowledged that there had been a problem with netentanglements. Hence, the remaining distribution could repre-sent a relict population, isolated by the extirpation of popula-tions in the south.

South Island, east coast

By early 1973, there were reports of Hector’s dolphins ‘occa-sionally drowning’ in fishing nets in this fishery (Mörzer Bruynsand Baker 1973), however very few of these were reported to theMinistry of Fisheries (then the agency responsible for managingmarine mammals). Of the 16 reported incidental catchesbetween 1970–1977 in the east coast fishery, four were offCloudy Bay and twelve between Banks Peninsula and PegasusBay (Baker 1978). The first quantitative estimate was made inthe 1980s, from data gathered in interviews with fishers (Daw-son 1991). Adding the number of dolphin entanglementsreported by fishers involved in the interview program, Dawsonestimated that during 1984–1988 at least 230 dolphins (av. 57per year) were killed in gillnets in the Banks Peninsula area(Dawson 1991). The dolphin population in this area, at thattime, was estimated as 740 individuals (Dawson and Slooten1988). The Banks Peninsula Marine Mammal Sanctuary wascreated to reduce the level of entanglement to sustainable levels,and other management strategies such as codes of practice, anobserver program and deployment of acoustic pingers wereimplemented.

In the government review of the Banks Peninsula MarineMammal Sanctuary (Anonymous 1994), the Ministry of Fish-eries undertook to interview these same fishers again. The fisherswere re-interviewed in 1992 and asked to recall the number ofentanglements during the period 1984–1988. Their reportswere very different from the first interview series. Commercialfishers reported a total 42 entanglements between 1980–1983,approximately 86 between 1984–1988 and nine from1989–1992. The discrepancy between the MAF estimate and

that of Dawson (1991) appears to have originated from thereports of three fishers and is discussed in reviews of the sanctu-ary (Dawson and Slooten 1993; Anonymous 1994). Lien et al.(1994) show that bycatch estimates based on interviews withfishers have several serious problems including inconsistencies inreliability of reports from fishers, variability of responses due tothe type of questions asked, and age, sex and fisheries experienceof the interviewer. They found also that the fishers who reportedthe highest number of bycatch also were those most likely tochange their estimates. This may explain the differences encoun-tered between the interviews of Banks Peninsula fishers byDawson (1991) and the MAF officials.

Post-sanctuary estimates of fishery entanglements along the eastcoast arise from an industry-funded observer program. Fromobservations of 214 set nets, five incidents were observed,including three multiple captures (Starr and Langley 2000) lead-ing to an estimate of 16 mortalities in the area surveyed (Bairdand Bradford 2000). In addition, two dolphins were releasedalive (from the same net). The bycatch rate from the observerprogram (as a proportion of the population still exposed to gill-netting, outside the marine mammal sanctuary) is clearly higherthan the estimates from either of the two interview programmes.From 1988 to 1998, the Canterbury Conservancy (DOC)records include a minimum of 29 dolphins caught in nets (withthree released alive), five beachcast dolphins with slit bellies orobvious knife marks and several other incidents with dolphinsfound dead near nets or mutilated (Rutledge personal commu-nication). Over the summer of 2000/01 a mutilated Hector’sdolphin head was recovered with clear evidence of attempteddestruction. Of concern was the observation of two male dol-phins caught in the same net in 1988, where only one dolphinhad net marks (M. Rutledge, unpublished report). This suggeststhat a proportion of fresh, beachcast dolphins that do not havenet-marks in fact died due to net entanglement thus leading toan underestimate of bycatch rates. Likewise, of the dolphinscaught in commercial and recreational gillnets and brought inby fishers for autopsy only about half have any discernible gillnetmarks.

An examination of the mtDNA haplotype diversity of both theeast coast and North Island regions indicated that these popu-lations had lost significant diversity over the latter part of thiscentury (Pichler and Baker 2000). DNA was extracted fromsingle teeth of every known Hector’s dolphin museum specimenwith a known location. The samples were combined with tissuesamples and then divided into ‘historic’ and ‘contemporary’time periods based about the changes in fisheries legislation ofthe mid-1980s and the introduction of the Banks PeninsulaMarine Mammal Sanctuary. The exact point of sample subdivi-sion (the ‘midpoint’) was tested by assessing all midpoint dateswhere each sample had greater than 10 individuals. The choiceof midpoint was found to be unbiased. The east coast popula-

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tion was shown to have lost significant genetic diversity(h1925–1987 = 0.6524, h1988–1998 = 0.3498, P < 0.05).These results suggested that the east coast region had lost signif-icant diversity this century probably as a result of precipitouspopulation decline. In addition, a trend analysis based on thecumulative haplotype diversity (Figure 6) suggested that thepopulation was likely to lose all diversity within 20 years (Pichlerand Baker 2000).

Several population viability analyses have estimated the risk ofcontinued population decline for the Banks Peninsula area.Slooten and Lad (1991) compared the maximum populationgrowth rate for this population with the estimated level ofbycatch, and found that bycatch was 1.5–4.3 times higher thanmaximum population growth. Slooten et al. (1992) estimatedsurvival rates for this population, including natural and fishingmortality, and concluded that the probability of populationdecline was between 78 and 99%. Disagreement between thetwo government agencies responsible for managing marinemammal bycatch (Ministry of Fisheries and Department ofConservation) appeared to hinge on different interpretations ofhow management should proceed in the face of uncertainty. Ingeneral, some decision makers argue that uncertainty about therisk posed to a species should lead to precautionary decisions,whereas others argue for delaying protective measures until thereis strong evidence that human activity is having a serious effect

on the species. In response to this, Slooten et al. (2000c) devel-oped a population model for the Banks Peninsula populationthat incorporated uncertainty arising from parameter estima-tion, environmental (between year) and demographic (betweenindividual) stochasticity. They concluded that scientific uncer-tainty did not alter the conclusion that there is a high risk of pop-ulation decline if current levels of fisheries-related mortalitycontinue. Continuing bycatch (some inside, but especially to thenorth, south and offshore of the sanctuary) still results in unsus-tainably high mortality rates for Banks Peninsula Hector’s dol-phins (also see Cameron et al. 1999). These latest research results(Slooten et al. 2000c) indicate that the Canterbury populationis still at a high risk of population decline (77–94%).

South Island, west coast

There are significant commercial and amateur gillnet fisheriesalong the west coast of the South Island. However, the rate ofentanglement within this region is unknown. Several beachcastdolphins are recovered each year, and either netmarks or knifemarks indicating attempted destruction are not uncommon. Inone instance a completely filleted dolphin was found on a westcoast beach, indicating use of the carcase (Figure 7). Populationviability analyses for this region (Burkhart 1998; Martien et al.1999) indicate that there is a high risk of population decline forHector’s dolphins on the west coast.

Figure 6 Pichler and Baker (2000) conducted a trend analysis of change in haplotype diversity through time for the South Island east coast regional population. Each time-point represents a division in the dataset with solid circles representing the cumulative historical diversity up to and including that time-point and the clear circles representing the remaining or ‘contemporary’ diversity. Diversity is expected to initially increase and then plateau. In this case the trend in cumulative diversity (solid line) decreased leading the authors to conclude that the population was in decline.

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South Island, south coastThe south coast of the South Island has two small populationsof Hector’s dolphins that are vulnerable to gillnet or trawl-related mortality. To date, there is little evidence of fisheries-related mortality in either of these populations. Only a fewbeachcast carcases have been recovered from the south coastpopulation, perhaps due to the isolation of this region or itsexposure to extreme weather conditions. However, fishing effortin this area is moderate to high, indicating the potential for netentanglements.

Evidence of trawling-related fisheries mortality.There are a few records of trawl net entanglements with Hector’sdolphins, all of which are from the South Island. There are tworecords of multiple entanglements (three and four dolphinsrespectively) within single shots in the South Island east coastbottom trawl fishery (Baker 1978). Of 68 ‘incidents’ involvingHector’s dolphins reported to the Canterbury DOC conserv-ancy between December 1988 and April 1998, only a single dol-phin (#60, Timaru, 3/5/97) was listed as trawler bycatch(Rutledge 1992). In addition, a further three Hector’s dolphinswere caught in trawl nets off Banks Peninsula during 1985-1997and two off Greymouth on the west coast of the South Islandduring 1988 (Dawson, unpublished data).

An industry-funded observer program of 434 trawls detected asingle dolphin caught in shallow water (20 m) south of the Can-terbury Bight on 17 February 1998 (Baird and Bradford 2000).

Unfortunately, the level of observer coverage was too low toallow a quantitative estimate of the total trawl bycatch. So far,observer programs for trawling and gillnetting have only beencarried out in the Canterbury area (roughly 15% of the totalHector’s dolphin habitat).

STATUS OF HECTOR’S DOLPHIN

Analyses of the level of gillnet fishing around New Zealand indi-cate that bycatch is currently unsustainable for most Hector’sdolphin populations, and that historic population size was onthe order of two to three times the abundance observed today(Burkhart 1998; Martien et al. 1999). For both the North Islandand east coast South Island, significant declines in genetic diver-sity have occurred over the last 20–30 years (Pichler and Baker2000). Further information on fisheries interactions is urgentlyrequired for all regions in which Hector’s dolphins are found.Reliable bycatch statistics are currently available only for thecommercial gillnet fishery in Canterbury for the fishing seasonof 1997–98. Observer programs, with a sufficient level of cov-erage to provide statistically robust data, would greatly aid anassessment of the status of Hector’s dolphin populations. Giventhe available evidence we conclude that the likely status of eachregional Hector’s dolphin population is as follows:

North Island: Critically endangered. The North Island subspecies of Hector’s dolphin may numberfewer than 100 dolphins. These animals are concentrated

Figure 7 Photo of a flensed Hector’s dolphin found on a west coast South Island beach in 2001, photographer anonymous, source: Green party website.

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between a polluted river (Port Waikato) and polluted harbour(Manukau Harbour), along an isolated coastline subject toinshore trawling and both commercial and recreational gillnet-ting. The isolation of this coastline means a low risk of boatstrike or coastal modification but also a low recovery of beach-cast dolphins and few people available to report violations ofrestricted fishing zones. It is also probable that the low abun-dance and apparent clustering of this population into small, dis-crete and potentially isolated units will have resulted ininbreeding. Current work is attempting to assess if this popula-tion is suffering inbreeding depression through the geneticassessment of male fertility. Despite a voluntary code of practiceby local commercial fishers, beachcast dolphins with net marksare still being recovered. The evidence of a rapid decline in geo-graphic range and abundance together with the continuedbycatch of these dolphins leads us to conclude that this subspe-cies almost certainly will go extinct in the near future unless deci-sive and effective management actions are enacted.

South Island, east coast: Declining.The east coast, South Island, population extends from thenorthern tip of the South Island to about Moeraki. This popu-lation is divided into several concentrations connected bystretches of coastline containing small, isolated groups of dol-phins. In the north the population is very small, perhaps a fewdozen individuals and it is likely that this area is in decline. TheNelson – Marlborough region represents a potential area ofinterchange between the east and west coast populations and sothe loss of dolphins from this area is of concern. The Cloudy andClifford Bay area is subject to several potential coastal modifi-cations including a ferry terminal (to connect with the NorthIsland) and several large-scale marine farms. The next concen-tration is at Kaikoura, an area of high tourism but perhaps littleimpact upon the Hector’s dolphin population. The southernhalf of the east coast of the South Island can be divided into threeareas; Pegasus Bay, the Banks Peninsula Marine Mammal Sanc-tuary (including Akaroa Harbour) and Timaru – Oamaru. Tra-ditionally, this area has been subject to high gillnetting-relatedmortality. Creation of the sanctuary appears to be protecting thelocal Banks Peninsula population but adjacent populations stillsuffer high (perhaps increased) levels of bycatch mortality. Cur-rent levels of mitigation (the sanctuary, voluntary codes of gill-net practice and acoustic pingers) are likely to have reduced theoverall impact of the fishery. Whether the Banks Peninsula pop-ulation will recover from the effects of high bycatch in the 1970sand 80s depends on what proportion of the population is pro-tected within the sanctuary boundaries (Burkhart 1998; Mart-ien et al. 1999). The latest population viability analyses indicatethat the decline has not been arrested (Slooten et al. 2000c). Thetwo populations adjacent to the sanctuary suffer high rates ofbycatch and are in decline (Martien et al. 1999). Combined withpollution runoff, environmental modifications and increasing

tourism in the whole region, it is likely that without further pro-tection this regional population will continue to decline.

South Island, west coast: Declining?

The recent population survey (Slooten et al. 2002) has indicatedthat this regional population is more abundant than previouslythought. Poor weather conditions restrict the areas of coastlineavailable to fishers, in particular to amateur gillnetters. How-ever, the continued level of beachcast Hector’s dolphins withgillnet marks (DOC unpublished data) suggest that bycatch isunsustainable in this area. Likewise, analyses of fishing effortindicate that Hector’s dolphin populations are declining over atleast three-quarters of the west coast (Burkhart 1998; Martien etal. 1999). The lack of information about the entanglement ratesand population demographics make an assessment of this pop-ulation difficult. Based on the results of the population model-ling and bycatch information we suggest that this population isstill at risk of decline.

South Island, south coast: Vulnerable

Off the south coast of the South Island, Hector’s dolphins arefound only in Te Waewae Bay and at Porpoise Bay and its sur-roundings. Due to the distance between these two locations andlack of DNA samples from Porpoise Bay, we cannot be certainabout the relationship between these two populations. The TeWaewae Bay population is genetically distinct and demograph-ically isolated from the other South Island regional populations.The total population size of the south coast is small: < 200 ani-mals even if Te Waewae Bay and Porpoise Bay are connected.Analysis of fishing effort indicates that Porpoise Bay is decliningwhile Te Waewae Bay is of uncertain status (Burkhart 1998;Martien et al. 1999). Based on population size alone, the southcoast population should be considered vulnerable.

Summary

Overall, we conclude that this species is at substantial risk of fur-ther decline. Unless gillnet bycatch is dramatically reduced oreliminated, the North Island population is likely to decline toextinction. Thus, Hector’s dolphins may soon be restricted tothe waters of the South Island. Within the South Island, little isknown about the impacts on each population with the exceptionof the dolphins in the Canterbury area of the east coast SouthIsland. There, levels of bycatch were shown to far exceed thepopulation’s sustainable levels. Although this has been mitigatedto some extent, much of the bycatch problem was simply shiftedin location. Given the continued high risk of decline of the eastcoast region, we are concerned about the other South Islandregions. Historically, conservation management of Hector’s dol-phins has been reactive hence it is unlikely that any protectionwill be applied to the other South Island regions until evidenceof population decline is overwhelming.

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MANAGEMENT AND MITIGATION

Banks Peninsula Sanctuary

The Banks Peninsula Marine Mammal Sanctuary was estab-lished in 1988 to protect one of the greater known concentra-tions of Hector’s dolphins. The sanctuary covers an area of1170km2, extending 4 nm to sea from Sumner head to theRakaia River and prohibits commercial and amateur gillnettingfrom 1 November to the last day of February each year. Thereare further regulations within the sanctuary, including restric-tions on the size of nets and areas where fishers need to stay inattendance of their nets. The history and process of the devel-opment of the Banks Peninsula Marine Mammal Sanctuary hasbeen reviewed (Dawson and Slooten 1993; Anonymous 1994).The boundaries of the sanctuary were defined to encompasshigh densities of Hector’s dolphin, the majority of the recentreported entanglements and to enable commercial fishers tocontinue to operate outside the sanctuary boundaries (Dawsonand Slooten 1993; Anonymous 1994). The extent of dolphinentanglements within the boundaries of the Sanctuary isthought to have substantially declined, however entanglementsstill occur. By 1992, the Department of Conservation had recov-ered six carcasses from within the Sanctuary, although only onehad definite net marks (Rutledge 1992). However, also duringthis time is a sighting of a dolphin entangled in a net insideAkaroa Harbour and the reported release of another net-entan-gled dolphin (Rutledge 1992). The 1997–98 observer programrecorded an entanglement on the very boundary of the Sanctu-ary (Starr and Langley 2000). Finally, two specimens receivedfor genetic analysis in 2000 were recorded as originating fromwithin the sanctuary. There is still considerable fishing effort onthe boundaries of the sanctuary.

Aerial monitoring within the sanctuary suggested that the pop-ulation had not suffered any major decline since the creation ofthe Sanctuary (Brown et al. 1992). Further aerial surveys from1990–1994 detected a significant population increase suggest-ing that the sanctuary was effective (Young 1997). However,these surveys suffered some methodological problems (e.g.weather criteria for undertaking surveys became more stringentover the years), casting doubt on the reliability of this result.Population modelling results are consistent with a populationincrease only when the population inside the sanctuary isassumed to be completely protected from entanglement (Bur-khart 1998; Martien et al. 1999). The population inside thesanctuary is able to grow only if no entanglements occur withinthe sanctuary, and if dolphins are not at risk of entanglement bymoving outside the sanctuary boundaries. It is now clear that thedolphins are still at risk from continued entanglement inside butespecially immediately outside the sanctuary, and from bycatchin trawl fisheries (Baird and Bradford 2000). Survival rates ofHector’s dolphins in the Canterbury area are still very low

(Cameron et al. 1999) and there is still a significant risk of pop-ulation decline (Slooten et al. 2000b).

Acoustic pingers

To reduce incidental catch of cetaceans in gillnets, two forms ofacoustic modifications have been proposed; one to make gillnetsmore reflective to cetacean sonar, and another using activesound emitters in nets to alert (or deter) cetaceans to (from)nearby nets. Lack of success with the first (Dawson 1991, 1994;Jefferson and Curry 1996) has focussed attention on the second.In contrast to reflectors, 10 kHz acoustic pingers in nets havebeen shown in controlled experiments to reduce catch rates ofharbour porpoises in the Gulf of Maine by about an order ofmagnitude (e.g. Kraus et al. 1997). Clifftop-based studies of har-bour porpoises in the vicinity of moored pingers have shownthat when pingers are ‘on’, porpoises are displaced from theensonified area (Koschinski and Culik 1997; Gearin et al. 2000;Culik et al. 2001) most probably because they find the soundaversive. Pingers proved less effective when non-experimentallydeployed in the Gulf of Maine groundfish gillnet fishery (seeDawson et al. 1998 for review) but their use is now mandated.Pingers also resulted in a significant reduction in bycatch rate ofcommon dolphins in Californian driftnets for swordfish (Bar-low and Cameron 1999), and were mandatory in that fisherybefore it ceased. Probably the most important constraint onpinger effectiveness, (see Dawson et al. 1998 for review) is thepotential for habituation, which is most likely where animals areresident and frequently exposed to pinger sounds. Evidence ofhabituation was provided by Cox et al. (1999) who showed thatharbour porpoises reduced their range of displacement by 50%over five days of continuous pinger operation.

The evidence that pingers can reduce gillnet bycatch of Hector’sdolphin is much less clear than it is for harbour porpoises andcommon dolphins. Stone et al. (1997) carried out a well-designed set of trials in which hilltop observers documented thesurfacing positions of Hector’s dolphins in the vicinity of amoored pinger that was activated remotely, without observersknowing. The study reported that dolphins stayed significantlyfurther away when the pinger was active. Unfortunately, the sta-tistical analysis assumed that each of a dolphin group’s surfacingpositions is independent from the last, which is not appropriate.The plots of surfacing positions do not show a zone of displace-ment such as that clearly shown for harbour porpoises (e.g.Gearin et al. 2000). Clearer reactions of Hector’s dolphins wereseen when three different types of pinger where lowered over theside of a boat. The rate of avoidance of one pinger type was morethan four times higher than the most effective of the other twoand ten times higher than the least effective (Stone et al. 2000).The latter pinger type produced avoidance reactions no morefrequently than a silent hydrophone – suggesting that the typeof sounds made really matters.

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In the hope that pinger use would reduce entanglement, com-mercial gillnet fishers in Canterbury have incorporated pingeruse into their voluntary ‘Code Of Practice’ (COP). The COPalso encourages fishers to avoid setting in depths of less than 30m, to set nets with the tide, and to avoid setting nets when dol-phins are around the vessel. Adherence to the COP is an issue,however. Of 68 gillnet sets observed in Canterbury in1999–2000, 28% complied with the COP instructions forpinger deployment. More promising is that some gillnetters inthe 1999/2000 summer voluntarily shifted their fishing opera-tions away from high densities of Hector’s dolphins, an initiativefor which the fishers should be commended.

Insufficient observer coverage means that we cannot determinewhether these measures, even in combination, are effective. Inthe 1997–98 fishing year an observer program detected six mor-talities in gillnets from 214 sets (Baird and Bradford 2000). Nomortalities have been observed since, but observer coverage hasbeen poor (none in 1998–99, 68 sets in 1999–2000 and 24 setsin 2000–2001). One entanglement was observed in the1999–2000 season, but was released alive. If the two years withobserver coverage are combined, there is still a 14% chance thatzero bycatches would be seen if the true bycatch rate isunchanged from 1997–98 (calculation via bootstrapping).

There is no justification for seeing pingers as a panacea for theproblem of incidental mortality of small cetaceans in gillnets(Dawson et al. 1998, Stone et al. 2000). We suggest caution inthe application of pingers to mitigate Hector’s dolphin bycatch.This position is in part based on the lack of clear evidence (out-lined above) and also on our expectation that Hector’s dolphin,which shows very high site fidelity to small areas (Bräger et al.2002) is among the species most likely to habituate quickly topinger sounds.

The Scientific Committee of the International Whaling Com-mission has held several international workshops to review theeffectiveness of pingers and other measures for reducingbycatch. They have repeatedly cautioned that: 1) before imple-mentation of pingers, controlled scientific experiments shouldbe conducted to determine whether the devices significantlyreduce bycatch for the species in question; and 2) that a com-prehensive observer program with sufficient statistical power todetermine effectiveness is crucial with any use of pingers (e.g.IWC 2000). We endorse this view, and oppose pinger use unlessaccompanied by continuing observer coverage sufficient toallow statistically robust judgments of effectiveness throughtime. Pingers are one of the tools in the bycatch mitigation tool-box and are perhaps best deployed as a ‘secondary line of defense’in areas where commercial fishing continues to operate. It isimportant not to be seduced by the ‘easy fix’ that they offer, andcontinue to work on other conservation measures (e.g. area clo-sures, gear changes).

Voluntary measures (codes of practice and education)Commercial fisheries voluntary codes typically do not impactupon the fish catch but rather focus on log-books or increasedvigilance of nets or the avoidance of setting or hauling nets in thepresence of marine mammals. The primary problem of volun-tary codes is the reliance on peer pressure within fisheries tomaintain their standards, and the lack of enforcement if thesestandards are not met (Slooten and Dawson 1995). For exam-ple, on an aerial survey for North Island Hector’s dolphins, acommercial fisher was sighted setting his nets within the volun-tary exclusion zone and was further seen to hastily remove thenets and rapidly depart the area as the spotter plane circled (C.Roberts personalcommunication). However, voluntary codes ofpractice have benefits in specifying what ‘best practice’ is, andpromoting awareness of the bycatch problem. Voluntary codesof practice have been adopted in the Canterbury Conservancyand in parts of the west coast of the North Island.

Gear RestrictionIn 2000, the Northern Inshore Fisheries Company, representingthe set net fishery in the northern half of the North Island,released a proposal for managing the interaction between thecommercial fishers and the local population of Hector’s dolphin(Longland 2000). Part of this report promoted gear restrictionsbased on the experience of a commercial set netter who uses adifferent method to the other fishers in the area. It was suggestedthat within a Code of Practice area, all nets must be restricted toa maximum net height. The proposal also offered to restrict fish-ing to outside 2 nm voluntary exclusion zones about harbourentrances. This group of fishers consider that set netting is themost target-specific method possible for this region and thussuggest that changing to alternative fishing methods such astrawling would be more environmentally destructive.

Alternative suggestions for gear restriction include changing fish-ing practice from the gillnet method to long-lining (Slooten andDawson 1995), however, the fishing industry has rejected suchproposals. As all fish species targeted by commercial gillnettingcan be caught using other fishing methods, Slooten and Dawson(1995) suggest that the decision of which fishing method is appro-priate should be based on an appraisal of the environmental as wellas economic costs and benefits of the different methods. Any anal-ysis of the environmental effects of a fishing method need to eval-uate the overall environmental performance including effects onprotected species (such as marine mammals and sea birds), targetand non-target fish, and the physical environment (seafloor,spawning/breeding habitat, etc.).

Observer programsObserver programs of commercial fisheries have been under-taken in Canterbury (north and south of the Banks PeninsulaMarine Mammal Sanctuary) for both inshore trawling and

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gillnetting, and are proposed for the inshore trawl fishery of thewest coast of the North Island. Observer programs rely upon theindependence of the observers and estimate bycatch from theproportion of observed fishing events. In the Southern SquidFishery, in which bycatch of Hooker’s sea lions occurs, observermonitoring is used as a management tool to close the fisheryonce a pre-determined number of sea lions have been entangled.This management tool works well in a fishery with a smallnumber of relatively large vessels and a reasonably high catchlimit (c. 72 sea lions). This approach is not practical for Hector’sdolphin, however. Both movement and genetic data show thatlocalised bycatch could profoundly impact the local dolphinswhile having negligible impact on those 100 km away. Thisimplies that bycatch limits should apply on very small scales.Bycatch limits in any zone of 100 km alongshore would be verysmall (< 2 dolphins per year using the PBR calculation of Wade,1998), and without 100% observer coverage (almost impossiblein the NZ gillnet fishery) it will be very difficult to assess bycatchrate robustly, and hence know when a bycatch limit is reached.In many places (e.g. North Island, West Coast) the bycatch limitwould be less than one per year – raising the possibility that ifone dolphin is caught, the fishery must close for several years.

The only prudent management path that does not requirerobust data on bycatch rate is a precautionary approach (e.g.avoid use of fishing methods implicated in dolphin entangle-ments until population recovery is demonstrated). In all othercases gaining data on bycatch rate is vital. Observer programsare, for all their difficulties, the only credible way to do this. Esti-mating bycatch rate robustly will, in many areas, require highlevels of observer coverage, because it is inherently difficult toquantify rare events. New Zealand’s Conservation services Levy,which is levied on fishers to allow study of fishing impactsand development of mitigation strategies, provides a mecha-nism for funding such programmes.

CONCLUSION

Hector’s dolphin is naturally vulnerable to population declinethrough human impacts. Due to late onset of sexual maturityand low reproductive rate, the species will be slow to recoverfrom population decline. The populations are highly localised,with strong natal fidelity reducing the potential for replenish-ment of declining populations from adjacent areas. Hector’sdolphin’s inshore habitat brings it into contact with runoff pol-lution and increases its exposure to human activities. This hab-itat is also one of the primary areas for both recreational andcommercial fishers.

Clearly there are significant human impacts threatening the con-tinued existence of Hector’s dolphins. To date, the primaryfocus of conservation attention has appropriately been on theserious direct impact of unsustainable fisheries bycatch. Less

attention has been paid to less obvious or indirect impacts.However, as Stone (1999) points out, while each impact con-sidered individually may not raise concern, the combination ofall of these factors should not be underestimated. Further stressthrough either direct population reduction or lowering of fecun-dity (due to pollution load, genetic effects etc.) will only serve toincrease the vulnerability of this species to extinction. Althoughthe primary impact upon Hector’s dolphin is undoubtedly fish-eries-related mortality, it is necessary to consider the combinedeffects of the other threats when assessing a population’s vulner-ability to decline.

Scientists and managers have emphasized the need for a precau-tionary approach when deciding on an appropriate managementplan for whale and dolphin populations (e.g. Mayer and Sim-monds 1996; Thompson et al. 2000). This involves erring onthe side of caution unless there is evidence that doing otherwiseis safe. It also involves taking an integrated approach that con-siders all potential impacts on a species or an area. In the past, acommon approach to the management of threatened species wasto take action only when a particular impact had been shown tocause a decline in population size. One problem with thisapproach is that the practical challenges of studying whales anddolphins can make it difficult to detect environmental impactsunless (or until) the effects are very severe. By the time an impactcan be detected with a high level of statistical confidence, it maybe too late to halt the decline and recover to the original popu-lation size or distribution (Taylor and Gerrodette 1993). This iseven more difficult when managing a species that is subject toseveral impacts. Each individual impact may be sustainable (ortoo small to detect), but management needs to consider thecumulative and potentially synergistic effects of all of theimpacts on the species.

Hector’s dolphin is a relatively well-studied coastal species. Fish-eries-related impacts have received considerable study and somemanagement attention. However, in spite of almost two decadesof significant conservation and research effort, this species is stillat risk in most locations. Application of restrictions to fisheriespractices is often a slow and difficult process due to the greateremphasis on economic viability of fisheries relative to the viabil-ity of dolphin populations. Management action usually requiresoverwhelming evidence of population decline from a variety ofindependent sources. Such evidence now exists for at least somepopulations of this species; the purpose of this chapter was tosummarise it, and show what has been necessary to affect man-agement action. Many other coastal dolphins and porpoises aresubject to incidental or directed takes in fisheries. In many cases,little is known about these species and the impacts of fisheriescan only be speculated (e.g. Chilean dolphin, C. eutropia).Unless research on these populations is encouraged and sup-ported, significant declines in abundance due to fisheries-relatedmortality will go undetected.

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