Stage 4 of 6
Island 4: the casino, the sniper and the Albatross
The rocks island adds roulette, the best Reel of Fortune pool so far, the sniper rifle and a boss that only lands when a tuna is on the ground.
Checked against Patch 1.0.11.

Your route through Rocks Island (the casino)
6 people are here, with 8 stations, and the shore drops clam, radio and seagull. The island ends with the Albatross. Every detail of the island is in the islands lookup.
Buy what this island adds
New here: Professional Lure ($50), Professional Boss Lure ($1,200), Sniper Rifle ($3,800), Dual Motors for the boat ($860). Whether the Professional Lure is worth it now: Which lure to buy. Whether to buy the Sniper Rifle: Which weapon to buy. The boat's own ladder is in the upgrades lookup.
Start the grill
The grillmaster is here as well and offers the same grill quest as on island 3. He wants Blue Shark or Goblin Shark. Unlocking and using the grill.
Open island 5
The islander scared of the bird wants Albatross Head, which opens island 5. The whole chain.
Use the stations
Boat motor upgrades, Boat radar, Bullet damage upgrades, Grill, Melee sharpness upgrades, Reel of Fortune slot machine, Roulette table, Weapon attachments. Every ladder and price is in the upgrades lookup.
Decide about the casino
A roulette table and the Reel of Fortune. Is roulette worth playing, and which island to spin on. What each spin can land on is in the skins lookup.
Beat the Albatross
Leave a dead Tuna on the ground in its zone for 3 seconds. 7,800 health on Default, five minutes before it leaves. How do I summon and beat the Albatross? Its stats are in the creatures lookup. What the Albatross Head is for: What do the boss drops do?
Then: Island 5: Volcano
The volcano island sells the top lure and the assault rifle. Five creatures buy the whale bait, the whale drops the fin, and the lava turns it into the final fight. Go to the Island 5: Volcano route.