Central West Coast, North Island IMMA

Size in Square Kilometres

19,785 km2

Qualifying Species and Criteria

Māui dolphin – Cephalorhynchus hectori maui

Criterion A; B (i)

Marine Mammal Diversity 

Delphinus delphis, Tursiops truncatus, Orcinus orca


The central west coast North Island encompasses open, coastal waters with high levels of turbidity punctuated by a number of harbours. This is the core habitat for the Māui dolphin (Cephalorhynchus hectori maui) (Baker et al. 2002) listed by the IUCN as Critically Endangered, a subspecies whose range is now mainly restricted to a ~250km stretch of coastline between south of Kaipara Harbour and north of Raglan (Baker et al. 2016). The subspecies’ range has been significantly reduced as a result of bycatch in fisheries (Dawson et al. 2001). These dolphins favour turbid waters (Derville et al. 2016; Roberts et al. 2019a) and are exposed to risks from fishing activities (although these have been reduced with the West Coast Marine Mammal Protected Area and recent increases in set-net and trawl fishing restrictions) and disease (summarised in Roberts et al. 2019a, Roberts et al. 2019b). Harbours are rarely used by Māui dolphins now but were once important habitat (Rayment et al. 2011). The harbours along this coast are used by common bottlenose dolphins and killer whales (R. Constantine, unpublished data). The most recent Māui dolphin abundance estimate was 57 (95% CI = 44-75) dolphins aged 1+ (Cooke et al. 2018).

The turbid waters from the harbour outflows and alongshore coastal erosion form primary habitat for Māui dolphin (Derville et al. 2016, Roberts et al. 2019a). The dolphins’ preferred prey are small demersal and benthic fishes (Miller et al. 2013) in particular ahuru and sole (Roberts et al. 2019a). This IMMA incorporates feeding grounds for common dolphins particularly in the northern Taranaki region where they prey on pelagic schooling fishes such as Jack mackerel, an important fishery in the region but one that results in bycatch in this region (Abraham et al. 2017). Common dolphins also use the nearshore coastal waters. Recently, individuals assigned to the other subspecies of C. hectori, which bears the same common name as the species (which is red-listed as Endangered by the IUCN), have been observed in the primary habitat of Māui dolphins with individuals originating from the east and west coasts of the South Island (Hamner et al. 2014, Baker et al. 2016). There are no estimates for bottlenose dolphins or killer whales in the IMMA but the killer whales form part of a wider-ranging New Zealand population (Baker et al. 2019) and at least some of the bottlenose dolphins are part of the northeast coast North Island population (R. Constantine, unpublished data). The common dolphins are part of a wider-ranging population found in offshore west-coast waters. They are vulnerable to fisheries bycatch but there is no current abundance estimate for this region (Abraham et al. 2017, Stockin et al. 2014, Stephenson et al. 2020).

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

This IMMA includes the only currently occupied year-round habitat of Critically Endangered (IUCN Red List) Māui dolphins (Oremus et al. 2012, Derville et al. 2016, Baker et al. 2016, Roberts et al. 2019a). Their current range is extremely limited compared to their historical range (Dawson et al. 2001). Māui dolphins have been isolated by ~15,000 years from the South Island Hector’s dolphins (Baker et al. 2002) and their unique haplotype most likely resulted from a population bottleneck and small home range (Oremus et al. 2012, Pichler & Baker 2000). Their core range has decreased since the 1970s (Russell 1999, Baker et al. 2016).

Criterion B: Distribution and Abundance

Sub-criterion Bi: Small and Resident Populations 

The entire known range of the Māui dolphin is included in this IMMA. This is a small population (57 dolphins aged 1+ 95% CI = 44-75) facing threats from disease and fisheries bycatch (Baker et al. 2016, Cooke et al. 2018, Roberts et al. 2019a). Individuals have small home ranges averaging 35.5 km, with a maximum range of 80 km recorded for one individual (Oremus et al. 2012). A genetic and photo-identification database has identified dolphins up to 16 years after their initial identification highlighting long-term site fidelity. In 2010, there were two female Hector’s dolphins genetically identified swimming with Māui dolphins within this IMMA; one of the females was identified again in 2011 and 2015 so remained with the Māui dolphins (Hamner et al. 2014). This was considered an extraordinary event, but in 2015 a male Hector’s dolphin was also genetically identified with Māui dolphins suggesting long-range movements by Hector’s dolphins from the South Island may become a more regular occurrence (Baker et al. 2016). Surveys have been mostly conducted in summer months with neonates and calves observed in this region. Groups containing calves are larger than non-calf groups. These nursery groups contain male and female adults which differs from Hector’s dolphins (Oremus et al. 2012).

Supporting Information

Abraham, E.R., Neubauer, P., Berkenbusch, K., Richard, Y. 2017. Assessment of the risk to New Zealand marine mammals from commercial fisheries. New Zealand Aquatic Environment and Biodiversity Report No. 189, Ministry for Primary Industries, Wellington, New Zealand

Baker, A.N., Smith, A.N.H., Pichler, F.B. 2002. ‘Geographical variation in Hector’s dolphin: recognition of new subspecies of Cephalorhynchus hectori’. Journal of The Royal Society of New Zealand 32: 713-727

Baker, C.S., Steel, D., Hamner, R.M., Hickman, G., Boren, L., Arlidge, W., Constantine, R. 2016. Estimating the abundance and effective population size of Māui dolphins using microsatellite genotypes in 2015-16, with retrospective matching to 2001-16. Report to Department of Conservation, Auckland, New Zealand

Baker, C.S., Boren, L., Childerhouse, S., Constantine, R., van Helden, A., Lundquist, D., Rayment, W., Rolfe, J.R. 2019. Conservation status of New Zealand marine mammals, 2019. New Zealand Threat Classification Series 29. Department of Conservation, Wellington, New Zealand, pp 18

Cooke, J.G., Steel, D., Hamner, R., Constantine, R., Baker, C.S. (2018). Population estimates and projections of Māui dolphin (Cephalorhyncus hectori maui) based on genotype capture–recapture, with implications for management of mortality risk. Report to the 2018 International Whaling Commission, SC/67b/ASI. 15 p.

Dawson, S., Pichler, F., Slooten, E., Russell, K., Baker, C.S. 2001. ‘The North Island Hector’s dolphin is vulnerable to extinction’. Marine Mammal Science 17: 366-371

Derville, S., Constantine, R., Baker, C.S., Oremus, M., Torres, L.G. 2016. ‘Environmental correlates of nearshore habitat distribution by the Critically Endangered Māui dolphin’. Marine Ecology Progress Series 551: 261-275

Hamner, R.M., Constantine, R., Oremus, M., Stanley, M., Brown, P., Baker, C.S. 2014. ‘Long-range movement by Hector’s dolphins provides potential genetic enhancement for critically endangered Maui’s dolphin’. Marine Mammal Science 30: 139-153

Miller, E., Dawson, S., Ratz, H., Slooten, E. 2013. ‘Hector’s dolphin diet: The species, sizes and relative importance of prey eaten by Cephalorhynchus hectori, investigated using stomach content analysis’. Marine Mammal Science 29: 606-628

Oremus, M., Hamner, R.M., Stanley, M., Brown, P., Baker, C.S., Constantine, R. 2012. ‘Distribution, group characteristics and movements of the Critically Endangered Maui’s dolphin Cephalorhynchus hectori maui’. Endangered Species Research 19: 1-10

Pichler, F.B., Baker, C.S. 2000. ‘Loss of diversity in the endemic Hector’s dolphin due to fisheries-related mortality’. Proceedings of the Royal Society of London B 267: 97-102

Rayment, W., Dawson, S., Scali, S., Slooten, L. 2011. ‘Listening for a needle in a haystack: passive acoustic detection of dolphins at very low densities’. Endangered Species Research 14:149-156

Roberts, J.O., Webber, D.N., Roe, W.D., Edwards, C.T.T., Doonan, I.J. 2019a. Spatial risk assessment of threats to Hector’s and Māui dolphins (Cephalorhynchus hectori). New Zealand Aquatic Environment and Biodiversity Report No. 214. Fisheries New Zealand, Wellington, New Zealand, pp. 168

Roberts, J., Constantine, R., Baker, C.S. 2019b. Population effects of commercial fishery and non-fishery threats on Māui dolphins (Cephalorhynchus hectori maui). New Zealand Aquatic Environment and Biodiversity Report No. 215. Fisheries New Zealand, Wellington, New Zealand, pp. 18

Russell, K. 1999. The North Island Hector’s Dolphin: A Species in Need of Conservation. MSc Thesis. Auckland: University of Auckland

Stephenson, F., Goetz, K., Sharp, B.R., Mouton, T.L., Beets, F.L., Roberts, J., MacDiarmid, A.B., Constantine, R., Lundquist, C.J. 2020. ‘Modelling the spatial distribution of cetaceans in New Zealand waters’. Diversity and Distributions DOI: 10.1111/ddi.13035

Stockin, K.A., Amaral, A.R., Latimer, J., Lambert, D.M., Natoli, A. 2014. ‘Population genetic structure and taxonomy of the common dolphin (Delphinus sp.) and its southernmost range limit: New Zealand waters’. Marine Mammal Science 30: 44-63


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