There have been many encounters with unknown creatures off the coast of New Zealand, with the East coast being particularly favoured.
There is a very good reason for this, running parallel to New Zealand's coastline is the Hikurangi Trench. A deep gouge on the ocean floor, that descends in places to depths of 3,750 metres (12,300 ft).
[ (Lewis, Collott, & Lallemand, 1998, pp. 441-468.)
New Zealands unique oceanographyThese deep troughs bring a wealth of nutrient rich organisms to the surface allowing for a mass of biodiversity to flourish in the nutrient rich upper waters.
Krill are profuse here along with smaller fish species which create a nutrient rich environment for larger predatory animals such as Giant Squid, which in turn are preyed upon by Sperm Whales. So there is no deficit of vast food supplies for large predatory animals cruising the depths of New Zealand's coastline.
Where the Hikurangi Trench joins up with the Tonga Trench, the area is heavily spotted with areas of geothermal activity which provide warm waters as well as a warm current which flows from the equatorial region.
This area of the Tonga Trench has a rich diversity of marine life previously undiscovered until recent expeditions. This is a very harsh environment where reshaping of the seafloor is happening continually, to quote from the results of a joint project between the Universities of Durham and Oxford, and funded by the National Research Centre.