Fourth island quest step by step

The quest giver is the person in the red shirt inside the bait shop, and he wants the head of the bird terrorising the island.

Fish Professional Lures ($50) for money; Bass, Halibut and Tigerfish pay $250 to $310 each, and the grill here still gives 1.5x.
Buy the Sniper Rifle ($3,800) with the Suppressor, Laser Sight, Extended Mag and the bullet tiers on sale.
Buy the Professional Boss Lure ($1,200), catch the Tuna and kill it without selling or cooking it.
Drop the dead Tuna in the middle of the grass; the Albatross lands a few seconds later.
Kill the Albatross from the house next to the grass and bring the head to the shop.

What to buy on the fourth island

The Rocks island has the widest market. The bait shop sells lures up to the Professional Boss Lure, and the gun store has the Sniper Rifle ($3,800), sharpening to 12, bullet tiers to 9 and every attachment. A third store adds the third extra slot and boat upgrades, including the second motor ($860) and the boat radar ($200).

Rifle kit first, then the boss lure; the second motor is what the I am speed achievement needs.

Fourth island boss: the Albatross

The Albatross dives on a loud screech and drops eggs on a quiet call; fight it from under the house roof with the Sniper Rifle. The Tuna before it is a separate fight on its own page.

What colour is the fourth island on the Radar?

Island 4 shows as a red dot on the Radar once the Desert tourist has given you its coordinates.

Creatures on the Rocks island

Eleven Professional Lure catches worth $250 to $380 live here, from the common Bass and Parrotfish to the rare endangered Voxelfish and Dripper, plus the Tuna and the Albatross.

	Bait	Price
Bass	Professional Lure 11.9%	$250
Sengarat	Professional Lure 11.9%	$280
Eel	Professional Lure 6.0%	$280
Red Snapper	Professional Lure 11.9%	$280
Halibut	Professional Lure 11.9%	$290
Dogfish	Professional Lure 7.1%	$310
Tigerfish	Professional Lure 11.9%	$310
Flying Fish	Professional Lure 6.0%	$320
Voxelfish	Professional Lure 3.6%	$340
Parrotfish	Professional Lure 11.9%	$350
Dripper	Professional Lure 3.6%	$380
Tuna Boss	Professional Boss Lure 100% ; Professional Lure 1.2%	$2000
Albatross Boss	Not hooked by bait: a Tuna left at the Albatross spot	Not sold whole: the 1.1.3 Fishipedia shows no price (-) for this boss; the fight drops a quest item and meat chunks instead (game data lists a nominal $13000 that players never receive).