Hi Roger and welcome to the forum. I'm based in the Northland, NZ near Tutukaka which is the spot from which all the diving at the Poor Knights islands is done. The Poor Knights are a marine reserve located 12 miles offshore. They are
arguably the best reef diving in NZ. The Northland is the warmest part of NZ and January/February is our warmest time of year. You can expect water temperatures of 20 - 22 degrees C and visibility of 10 - 25 metres, sometimes greater.
The underwater environment is temperate, but we have tropical visitors in the summer. I have seen sharks, dolphins, seals and turtles at the Poor Knights, but none of these are guaranteed. It's a question of being in the right place at the right time.
In the same area, there are the wrecks of the HMNZS Waikato and the HMNZS Tui. I have dived the Waikato numerous times, it is well worth doing although visibility can be variable because it is located inshore.
Further north is the wreck of the HMNZS Canterbury, further north again is the wreck of the Rainbow Warrior, both great dives.
Surprisingly, there is limited diving infrastructure in NZ.
For a Poor Knights liveaboard, I would recommend
Poor Knights Islands Scuba Diving Liveaboard dive New Zealand
They run a small, friendly liveaboard. It's not a luxury boat, but this is more than made up for by good service and food. Early booking is probably required, especially in the summer.
Alternatively,
Yukon Dive - Diving the Poor Knights, Tutukaka, Northland, New Zealand have just taken ownership of another liveaboard and I assume will be, or are already running trips.
Dive Poor Knights Islands. Diving Poor Knights Islands and shipwrecks HMNZS Tui and Waikato with Dive! Tutukaka New Zealand. / Dive! Tutukaka, Poor Knights Diving run day trips to the Poor Knights. They are a big outfit and provide a good PADI resort style service.
For the northern wrecks I mentioned, I would recommend
Diving in New Zealand, Scuba Diving NZ ? Paihia Dive
I have no financial involvement with any of these operators, but know most of them pretty well.
There is good diving in other parts of New Zealand, but I have no experience of this.
Happy to answer any other questions.