Species swims in
Waitematā Harbour, with
Auckland CBD in the background. Some particular common or known animals include
bottlenose and
common dolphins, the latter sometimes seen in "super schools" of 300-500 animals or more, while various species of whales and
orcas are a relatively common sight. Nearly a third of the world's marine mammal species live in or visit the Marine Park. with a watching vessel.Among larger
cetaceans,
Bryde's whales are residents and relatively common in the Gulf, and their presence in these busily travelled waters leads to a large number of ship strikes, with sometimes several of the whales dying each year from collisions with shipping vessels or sport boats. The population remaining is estimated to be between 100-200. In recent years, increases in numbers of migrating
baleen whales are confirmed long after the end of hunting era. These are
humpback whales, southern
blue whales,
pygmy blue whales, and
southern minke whales. Less frequently,
fin whales and
sei whales are seen as well. For
southern right whales, these whales will possibly become seasonal residents in the gulf as the populations recover (one of two of the first confirmed birth records on New Zealand's main islands since after commercial and illegal whalings were recorded at around
Milford and
Browns Bay in 2012).
Sperm whales visit occasionally. Many of the islands are official or unofficial bird sanctuaries, holding important or critically endangered species like kiwi, takahē, brown teal and grey-faced petrel. Centred on the main conservation island of
Tiritiri Matangi and
Little Barrier Island, numerous bird species that were locally extinct have been reintroduced in the last decades, while there have also been some naturally occurring bird "re-colonisations", especially after introduced pests were removed from breeding and nesting grounds.
Environmental damage The gulf is a vibrant natural environment, which has seen significant damage during the 20th and early 21st century from human use. Although major study by the Hauraki Gulf Forum in 2011 found that all environmental indicators were still worsening or stable at problematic levels, voluntary coast clean-up groups have collected about 450,000 litres of litter from the shoreline, although further conservation efforts are required to maintain the environmental integrity of the gulf. Particularly damaging were the introduction of
industrialised fishing, with for example
snapper fishing peaking in the 1970s at more than 10,000 tonnes a year (though even in the 2000s, private fishing of this species is also a considerable factor, weighing in at 400–800 tonnes a year). This severe overfishing, which unbalanced the marine environment by the removal of a main predator in the food chain, led to further degradation, such as a widespread disappearance of
kelp beds as they were overtaken by
kina barrens. Other exploitation such as the dredging of the
mussel beds of the Firth of Thames, reaching its height in 1961 with an estimated 15 million mussels taken (shortly before collapse of the industry) have led to damage which has not been recovered from forty years later, possibly due to the dredging having destroyed the seafloor, and sediment drainage from the agriculture in the Firth of Thames affecting the mussel's viability. Numerous beaches dot the shores of the gulf, many of them well known for swimming and surfing. Although environmental problems exist around urban areas, with 14 out of 52 beaches in the Auckland Region at least occasionally showing unsafe pollution levels (mostly because of untreated
sewage) for bathing, environmental groups are working to clean the beaches and restore their vitality. ==Marine Park==