It looks blue because camouflage ability to hide like octopus. Blue ling cod is great predator. They never give up their prey. Some time when you have rock cod on you hook and you are wiring up, you would be charged by Ling cod because it thinks that fish is wounded.
I forgot to tell you. In California, the department of fishery allows to use only two hooks at a time. As you can see in video, no one uses more than two hooks.
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