Off all the gamefish available to New Zealand anglers. Yellowfin Tuna would be close to the top of the catch list for many anglers.
Yellowfin Tuna usually turn up in New Zealand waters late December when the offshore waters start reaching 19-20 degrees. The main area they head to is from North Cape to East Cape although they do extend a little further south as well.

Yellowfin Tuna Information:

Yellowfin Tuna are metallic dark blue on top with a yellow-silver belly and bright yellow dorsal and anal fins and finlets. They can grow to a maximum length of 239 cm, but the largest reported in New Zealand is 164 cm.
These species tend to follow the warm water and will only really hold in an area if there is a good amount of food available.
Trolling for Yellowfin Tuna is a very productive way to find the fish and if the Tuna are very actively feeding, this will work well although Tuna of all sorts have a preference for smaller lures that match the food source. Tuna like speed when trolling so 6-8 knots is a good pace. At times these fish will happily take a popper or stickbait if offered.

Yellowfin Tuna growth rates and spawning details:

Adults reach a maximum size of 200 kg and lengths of 239 cm. First maturity is reached at 60 to 80 cm (1 to 2 years old), and the size at 50% maturity is estimated to be 105 cm. The maximum reported age is 8 years. Spawning takes place at the surface at night mostly within 10º of the equator when temperatures exceed 24-25ºC. Main spawning season is November to April. Yellowfin are multiple spawners, spawning every few days throughout the peak of the season.