New Zealand is home to a plethora of marine mammal fauna, the diversity and abundance of which is often unique to the islands. Some marine mammal species are endemic to New Zealand (i.e. found nowhere else), but many live alongside cosmopolitan species (i.e. found elsewhere).
Official sighting records of dolphins around New Zealand waters vary from source to source. According to the New Zealand Department of Conservation (DOC), there are officially nine dolphin species; however, ca. 13 different dolphin species have been documented in New Zealand waters, five of which are sighted frequently. These include, bottlenose dolphin (Tursiops truncatus), dusky dolphin (Lagenorhynchus obscurus) Hector’s/Maui’s dolphin, (Cephalorhynchus hectori), divided into two subspecies (see below), Orca (Orcinus orca) and short-beaked common dolphin (Delphinus delphis). There are occasional sightings of Fraser’s dolphin (Lagenodelphis hosei), Risso’s dolphin (Grampus griseus), rough-toothed dolphin (Steno bredanensis), striped dolphin (Stenella coeruleoalba), hourglass dolphin (Lagenorhynchus cruciger), spectacled porpoise (Phocoena dioptrica), and southern right whale dolphin (Lissodelphis peronii).
Hector’s dolphin (http://en.wikipedia.org) is endemic to New Zealand, but is divided into two subspecies: Hector’s dolphin (C. h. hectori) and Maui’s dolphin (C. h. maui). Hector’s dolphin is distributed primarily around the South Island and Maui’s dolphin around the North Island. Maui’s dolphin is listed as critically endangered (CR) on the International Union for Conservation of Nature (IUCN) Red List (Reeves et al. 2013) – see http://www.iucnredlist.org. A 2012 study estimated that there were only 55 individuals > 1 year old in the entire population (http://www.doc.govt.nz).
Boat tours and beach- based swimming trips are carried out regularly around dolphins. Research carried out by Bejder et al. (1999) suggests that both swimming and boat traffic causes pods of Hector’s dolphin to pack tighter together, suggesting animals viewed boats and swimmers as a threat.
All of the odontocete (toothed) family (whales, porpoise, and dolphins) rely on active acoustics as a means of orientation, communication, predator avoidance, and foraging (www.dolphindetectors.co.uk). Both natural and man-made (anthropogenic) sources contribute substantially to ocean noise levels. Anthropogenic sound sources can be intermittent, impulsive, continuous, high or low intensity, or combinations of these simultaneously. Increased use of the marine environment for a range of activities, such as geophysical exploration (for oil and gas), wind farm construction, military exercises, and commercial shipping, has resulted in noise levels that are estimated to be ten times higher today than a few decades ago. Recent research carried out by Currey et al. (2012) estimated non-fishing-related threats (seismic activity, mining, vessel traffic, pollution) contributes to 0.27 Maui’s dolphin mortalities per annum. It was suggested death could occur directly via physical trauma from seismic air guns, boat strikes and pollution or indirectly due to reduced food availability through displacement of prey and acoustic masking (Currey et al. 2012). Empirical evidence is, however, lacking.
Considerable efforts are made by the New Zealand Government to protect Maui’s and Hector’s dolphin from commercial activities, but the species is still in a state of decline. In response to a paper presented by the World Wide Fund for Nature (WWF) to the International Whaling Commission (IWC), the scientific committee’s small cetacean working group recommended an immediate extension of a protected area surrounding Maui’s dolphin habitat. Protection now consists of a trawl ban stretching 2–4 nm, a set net ban out to 7 nm and a marine sanctuary out to 12 nm with specific limits on certain types of mining and seismic activities. For further details please refer to Bird and Palka (2013) at http://awsassets.wwfnz.panda.org/downloads/sc_65a_sm_bird_and_palka__1_.pdf.
Many different species of whales are found around the coast of New Zealand. Six sighted most commonly are humpback whale (Megaptera novaeangliae), southern right whale (Eubalaena australis), sperm whale (Physeter macrocephalus), sei whale (Balaenoptera borealis), minke whale (Balaenoptera acutorostrata), and Bryde’s whale (Balaenoptera edeni), although a further 15 species are also known to visit New Zealand’s waters. These include both the pygmy (Kogia breviceps) and dwarf sperm whale (Kogia sima), Antarctic minke whale (Balaenoptera bonaerensis), southern blue whale (Balaenoptera musculus), pygmy right whale (Caperea marginata), Cuvier’s beaked whale (Ziphius cavirostris), Giant beaked whale (Berardius arnuxii), Shepherd's beaked Whale (Tasmacetus shepherdi), bottle nose whale (Hyperoodon planifrons), Andrews' Beaked Whale (Mesoplodon bowdoini), Blainville's Beaked Whale (Mesoplodon densirostris), Ginkgo-toothed Beaked Whale (Mesoplodon ginkgodens), Gray's Beaked Whale (Mesoplodon grayi), Hector's Beaked Whale (Mesoplodon hectori) and Layard's Beaked Whale (Mesoplodon layardii). For detailed distributions of all New Zealand’s marine mammals please refer to distribution tables listed on www.osc.co.uk
New Zealand is one of the few places in the world that still permits general public to swim and dive with marine mammals. The abundance and diversity of whales in New Zealand waters feeds an expanding whale watching industry, grossing £1.27bn globally in 2008 (Sterling & Ramage 2012). One of the main whale watching centres is Kaikoura, located to the north east of the South Island, where unique coastal topography offers opportunity to observe deep diving sperm whales, only a few nautical miles offshore. Whale watching provides a platform for education and scientific research, although concerns have been raised about potential effects on New Zealand’s whales. For example, research conducted by Richter et al. (2003) indicated the presence of whale watching boats and aircraft either individually or together, appeared to increase the frequency of heading changes and reduce frequency of blow intervals of sperm whales around Kaikoura. Richter et al. (2003) suggested the boats and aircraft affected the whale’s use of echolocation as a means of orientation; however, later studies by Richter et al. (2006) suggests there is little biological impact, although eco-tourism should be maintained at current levels to reduce further strain on New Zealand’s whale populations.
Four different species of pinniped (seals, sea lions, and walruses) are found commonly around the coastal waters of New Zealand (www.doc.govt.nz). New Zealand fur seal (Arctocephalus forsteri), leopard seal (Hydruga leptonyx), and southern elephant seal (Mirounga leonina) are all cosmopolitan species. The New Zealand sea lion (Phocarctos hookeri), however, is endemic to New Zealand and is one of the rarest pinnipeds in the world, categorised by the IUCN Red List as vulnerable (VU) (Gales 2008). Primary habitat is limited to the south coast of the South Island and several of New Zealand’s sub-Antarctic islands (Chilvers et al. 2007). The New Zealand sea lion has a varied diet, preying on a wide variety of species, but those inhabiting sub-Antarctic waters target arrow squid (Nototodarus sloanii) as an essential dietary component (Chilvers et al. 2007).
The pelagic diet of sea lions and fishing methods implemented by squid fisherman off the coast of New Zealand have raised concern about levels of sea lion by-catch and possible effects on the dwindling population (Wilkinson et al. 2006). Recent research by Chilvers (2008) analysed the number of New Zealand sea lions captured on arrow squid fishing vessels between 1992 and 2007. During 16 years of observation, 226 individuals were captured, of which 130 where females and only 96 males. These data support the theory that unsustainable fishing methods are contributing to the decline of an already diminishing species. Effects of by-catch are extrapolated, as the death of a female is likely to incur the death of a pup on shore. It was suggested that relative proximity to breeding colonies on both Auckland and Campbell Island were the main cause for gender imbalance in by catch.
Since 1992 there have been several conservation initiatives of the New Zealand sea lion. In 1995, 12 nm of sea surrounding the Auckland Islands were declared a Marine Mammal Sanctuary (MMS). Following this in 2003, the area became a concurrent ‘no take’ marine reserve (Chilvers 2008). New Zealand sea lions are still declining and are set to become endangered if further action is not taken.