Niihau great? That's an understatement!!!! If you want sharks and overall amazing diving it is not to be missed! In almost 20 years of diving throughout Hawaii I think it is the best that the state has to offer. It's simply off the charts! First and foremost it is an opportunity to dive with one of the most critically endangered marine mammals in the world - the Hawaiian Monk Seal! That in itself makes the trip worth it. If you want the chance to see sharks it's simply a great spot. I've seen whitetips, grays, galapagos, sandbar, blacktip, hammerhead and tiger sharks there (and a couple whale sharks if you count those guys). Gray and whitetip sharks are seen with the most regularity.
The trip also often includes manta and eagle rays, spinner dolphins, occasional pelagic game fish such as ono and ahi (wahoo and tuna). The small stuff there is amazing as well. Octopus, eels, ghost shrimp, lobsters, pipefish, many endemic fish species etc. If you go on the larger vessel you're likely to see amazing mammals in the channel as well i.e. false killer whales, melonhead whales, pilot whales etc...
If you stay on the south shore for local charter you will want to go in the am for your best shot at seeing sharks. Sites such as Turtle Bluffs, Fast Lanes, Zac's Pocket, Toilet Bowl, and General store are frequented by the whitetips in particular.
PM me if you have any specific questions. Though I work for SeaSports I am happy to get you contact info or just general info on the other dive shops as well. Fathom Five and Kauai down under in particular.
Have a great day
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