Hiya Oldsarge
The yellowtail is a pelagic specie that generally is found in open water, chasing baitfish. We normally get them by following the schools of birds which feed on the small fish that they're chasing. You simply approach the "working birds" and notice which way the school of fish is moving, plan a course to intercept them and BANG!!!

They also like reefs or pinnacles that break, as well as rocky points or headlands. They sometimes also patrol the outer edges of the kelp bed. The smaller fish is reef fish, which is found inbetween the kelp and reefs. No specific water depth. Some were found in 1-2m water whilst others in 18m water. That 3.05kg fish i took in 15m water, but i've taken a 2.6kg in 3m water on a previous occation.
Regards
miles