Marine mammals live and breed in waters all around the globe, the diversity, distribution and abundance of marine mammals play an important role in the ecosystem. Marine mammals are consumers of most trophic levels from consumers of primary producers, such as the plant eating Sirenians (dugongs and manatees), to predatory Odontocetes such as the Orca whale (Ursus maritimus) (Bowen, 1997). As major consumers, marine mammals play an important role in the flow of energy within the marine ecosystem, the interactions of marine mammals with other species also affect the ecosystem, as evidenced by changes in the ecosystem of the Antarctic caused by whaling reducing the biomass of marine mammals (Katona & Whitehead, 1988). By understanding the role marine mammals play in the ecosystem, the impact of these animals on prey populations and the structure of marine communities may be evaluated (Bowen, 1997). This essay will cover the diversity, distribution and abundance of key New Zealand marine mammal species, information which allows for further understanding of the ecological role marine mammals have in the New Zealand marine ecosystem.
Marine mammals are a polyphylectic group which spans 129 species from three different orders of Cetacea, Sirenia, and Carnivora (Pompa, Ehrlich, & Ceballos, 2011). New Zealand waters are home to an high abundance of marine mammals including whales, dolphins, porpoises, seals, and sea lions. There have been 57 species of marine mammal recorded in New Zealand waters (C. S. Baker et al., 2016).
There are two suborders of whale, Mysticeti (baleen whales) and Odontoceti (toothed whales.) Baleen whales are filter-feeders which use baleen plates to filter food from the sea. Toothed whales have conoidal teeth and feed mainly on a diet of squid and fish. Over 20 species from both suborders can be found in New Zealand (C. S. Baker et al., 2016). Four notable species of whale found in New Zealand are Antarctic and Pygmy blue whales, Southern right whales, Humpback whales, and Sperm whales.
Blue whales are famous for being the largest animal on earth (Bortolotti, 2008). Blue whales are migratory visitors to New Zealand, migrating to the Antarctic to feed in the summer months. Blue whales are baleen whales. In New Zealand waters there are two species of blue whale found: the larger Antarctic blue whale (Balaenoptera musculus intermedia) and the smaller pygmy blue whale (Balaenoptera musculus brevicauda). Blue whales are often found feeding at a foraging ground in the South Taranaki Bight (Torres, 2013). The number of Antarctic blue whales is 1700, only 1% of the pre-whaling population which was estimated to be around 200,000 whales (Branch, Matsuoka, & Miyashita, 2004). The numbers of pygmy blue whales are uncertain (Torres, 2013).
The southern right whale (Eubalaena australis) is one of three right whale species, and the only species found in New Zealand. Southern right whales are baleen whales which feed on krill and are migratory. Southern right whales reside around the subantarctic islands of new Zealand an area which the whales use as a calving ground (Patenaude, Baker, & Gales, 1998).The population is estimated to be 900 whales, only 5% or less of the abundance of the New Zealand population pre-whaling (Carroll et al., 2011).
Humpback whales (Megaptera novaeangliae) are migratory baleen whales, known for their song vocalisations. The humpback whale migrate between Antarctic summer feeding grounds and tropical Southern Pacific breeding grounds (Constantine, Russell, Gibbs, Childerhouse, & Baker, 2007). Pre-whaling, there was approximately 10,000 humpback whales around New Zealand, which was reduced to less than 5% of the original population. Currently, the number of humpback whales is estimated at 250 – 500 (Chittleborough, 1965).
Sperm whales (Physeter microcephalus) are a migratory, toothed whale (Gaskin & Cawthorn, 1967). Sperm whales sexually dimorphic, with males growing larger than females (Richter, Dawson, & Slooten, 2003). Sperm whales were named after and hunted for spermaceti, a waxy substance located in the head (Harvey & Norris, 1972). Sperm whales are mostly found around the Cook Strait (Gaskin & Cawthorn, 1967) and off the coast of Kaikoura (Richter et al., 2003). Female sperm whales and their young are rarely recording in New Zealand, rarely leaving the warm waters of the tropics (Richter et al., 2003). The sperm whales in New Zealand are often male. In any one season it is estimated there is between 60 – 108 individuals around New Zealand (S. J. Childerhouse, Dawson, & Slooten, 1995).
Dolphins and porpoises
The Delphinidae (dolphin) family has 17 species in New Zealand waters (C. S. Baker et al., 2016). There is only one species of the Phocoenidae (porpoise) family, the spectacled porpoise (Phocoena dioptricaI) (C. S. Baker et al., 2016). Notable species of the dolphin family in New Zealand are Long-beaked and Short-beaked common dolphin, Hector’s dolphin, Maui dolphin, and the Orca whale.
Two species of Common dolphin may be found in New Zealand waters, the Long-beaked common dolphin (Delphinus capensis) and the Short-beaked common dolphin (Delphinus delphis). Common dolphin are found the length of the coast from the Bay of Islands (Constantine & Baker, 1997), the Hauraki Gulf (Stockin, Lusseau, Binedell, Wiseman, & Orams, 2008), the Bay of Plenty (Neumann, 2001), and to the south of New Zealand in Kaikoura (Würsig et al., 1997). It is estimated there is a population of 1000 common dolphins in New Zealand (A. N. Baker, 1983).
Both the endangered Hector’s dolphin (Cephalorhynchus hectori) and the critically endangered subspecies the Maui dolphin (Cephalorhynchus hectori maui) are the only endemic cetaceans in New Zealand waters. Hector’s dolphins are rarely found around the North Island, usually restricted to a small west coast area (F. B. Pichler, S. M. Dawson, E. Slooten, & C. S. Baker, 1998). They are found around the coast of the South Island and in the Fiordland region. The greatest population density is off the Banks Peninsula on the South Island’s west coast (Dawson & Slooten, 1988). There is an estimated 7000 Hector’s dolphin around New Zealand (Suisted & Neale, 2004).
The Maui Dolphin is found along the west coast of the North Island. The Maui dolphin has a critically endangered status with the ICUN, which is confirmed with an estimate of only 111 dolphins in the population (Slooten, Dawson, Rayment, & Childerhouse, 2006).
The Orca or Killer Whale (Orcinus orca) is a well-known member of the dolphin family identifiable by the distinct black and white markings and prominent dorsal fin. Orca can be found throughout New Zealand waters (Visser, 1999). There is an estimated population of 200 Orcas around New Zealand (Suisted & Neale, 2004).
Seals and Sea Lions
Species from the family Otariidae (eared seals and sealions) and from the family Phocidae (earless seals) are found in New Zealand. These species include New Zealand and Subantartic fur seals, New Zealand sea lions, Leopard seals, Weddell seals, Crabeater seals, and Southern elephant seals (C. S. Baker et al., 2016). Two species of note are the New Zealand fur seal and New Zealand sea lion.
The New Zealand fur seal (Arctocephalus forsteri) is a small eared seal found in New Zealand. New Zealand fur seals inhabit the coastal waters of New Zealand and are found mainly around the South Island, but also inhabit the subantarctic islands (Crawley & Wilson, 1976). In the nineteenth century, New Zealand fur seals were hunted almost to extinction by commercial sealers, it is now a protected species and numbers are recovering (Stirling, 1968) with estimates placing population numbers at over 100,000 animals (Suisted & Neale, 2004).
The New Zealand Zealand (Phocarctos hookeri) is the only species of sea lion in New Zealand. New Zealand sea lions once inhabited the length of the coast from the North Island to the subantarctic islands, they are now restricted to only the subantarctic islands of the Auckland Islands and Campbell Island (S. Childerhouse & Gales, 1998). New Zealand sea lions hold a ICUN status as endangered, and estimates place populations numbers at less than 12,000 animals (Campbell, Chilvers, Childerhouse, & Gales, 2006).
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