Cephalorhynchus hectori ssp. maui

Studies of mitochondrial and nuclear DNA show that North Island Hector's dolphins are genetically distinct from any of the South Island subpopulations (Pichler et al. 1998). Every sampled individual (n=11) in the contemporary North Island subpopulation has a single maternal lineage that has not been detected in the South Island (n=97).  In addition, these animals have unique microsatellite alleles at three of the ten loci surveyed.  A further four loci have alleles that are either fixed or at high frequency, yet are rare in South Island subpopulations.  Such differences over such a small geographic scale have not been observed in any other genetic studies of marine mammals (Dawson et al. 2001).  For example, two subspecies of Commerson's dolphin show less genetic divergence yet are separated by 8,500 km.  The North Island subpopulation also has morphological and coloration differences, and taken together this evidence has allowed it to be recognized as a distinct subspecies (Baker et al. 2002).

Recent surveys show that the South Island Hector’s dolphin populations collectively number about 7,270 individuals (CV=15.8%; Dawson et al. 2004), while the North Island population numbers around 111 (CV=44%; Slooten et al. 2006b). The latter’s range appears to have been drastically reduced (Russell 1999; Dawson et al. 2001; Slooten et al. 2005).

An age-structured model (Slooten et al. 2000) indicates that approximately 50% of Hector’s dolphins are mature individuals.  If about half of the estimated 111 Maui’s dolphins are mature, and half of them are females, it means that only around 28 mature females remain.

Population viability analyses using current abundance together with entanglement rates and historical and current fishing effort indicated a high risk of decline, and that gillnet entanglement had caused a decline since 1970 in the North Island subspecies population (Martien et al. 1999; Slooten 2007).  Estimated abundance in the late 1990s was around 25% of the 1970 estimate of 437 individuals (Martien et al. 1999), and the most recent estimate of depletion is that about 7% of the 1970 population remains (Slooten 2007).

The habits and biology of Hector's dolphins in the South Island have been well studied in the last couple of decades (Dawson 2002) and there has been increasing research effort on Maui’s dolphins also.  Maui’s dolphins appear to have similar behaviour and ecology to those belonging to the South Island subspecies. 

There is little information on the feeding ecology of Maui’s dolphins but it is thought to be broadly similar to that of other Hector's dolphins, which feed opportunistically on several species of small fish and squid (Dawson 2002). 

Like the species as a whole, Maui’s dolphin faces serious pressures from human activities.  The main threat is entanglement in gillnets (Dawson et al. 2001; Slooten 2005; Slooten et al. 2006b).  Of 14 stranded dolphins in which cause of death could be determined, seven had clear net markings, and an additional four had injuries suggestive of removal from nets (Dawson et al. 2001).  Recreational gillnet fishing may be a more serious problem than commercial gillnet fishing, due to the proximity of Auckland, New Zealand’s largest city. Bycatches in trawl nets also have been reported.  Additional potential threats include those listed for Hector’s dolphin, i.e. pollution, disease, vessel traffic and habitat modification (Stone and Yoshinaga 2000) although there is no direct evidence that pollution or disease is affecting this subspecies.

The species is listed in Appendix II of CITES.

The subspecies is restricted to waters of New Zealand; therefore national conservation measures are discussed here. The New Zealand Marine Mammals Protection Act (MMPA) prohibits deliberate killing or injury of marine mammals.  Bycatch in fishing gear is not illegal but can be regulated. Hector's Dolphins are listed as threatened under New Zealand legislation.

The New Zealand Government has created a protected area for C. h. maui where gillnetting is prohibited along 390 km of coastline, but the area does not extend far enough south to cover the range of recent sightings and falls well short of covering the historic range. The latter has clear implications for the prospects of recovery. Gillnetting continues inside harbors, trawling is not restricted, and there are no observer programs to estimate the number of dolphins taken (Slooten et al. 2005, 2006b).

Discussions between the New Zealand Ministry of Fisheries and Department of Conservation are currently (early 2008) underway to develop a comprehensive management plan for Hector’s dolphin (including Maui’s dolphin). Species-wide, a continuing high level of bycatch mortality indicates that stronger protection from entanglement in commercial and recreational fisheries is needed.  Protected areas, reduced gillnet fishing effort, and changes in fishing methods have been recommended as necessary to ensure the long-term persistence of Maui’s dolphin (e.g. Martien et al. 1999, Burkhart and Slooten 2003, Slooten 2007; DOC and Mfish 2007).  Meetings of stakeholders have concluded that fishery mortality must be reduced to zero to allow the subspecies to recover (Dawson et al. 2001; Slooten et al. 2006b).  Recent surveys (Dawson et al. 2004, Slooten et al. 2005, 2006a,b) indicate that restricting gillnet fisheries to waters >100m deep would have a major benefit in terms of reducing bycatch.  In waters <100m deep it would also be advisable to institute observer programs on any trawl fisheries that operate in the habitat of Maui’s dolphin habitat.