What I would do is nail down the bazillion details that matter, since this is worded too vaguely to be addressed here.

Commercial or Sport or Transportation industry (DOT rules); which product; how sold; how is the boat owned and operated; is this person crewing as an employee or not; is the person paid by the boat captain or the buyer of the catch or do they sell their share of the catch on their own; what is deducted from their share, if they get a catch share from the captain; are they located on the boat overnight; are they located away from home but not on the boat overnight...A million details matter.

https://www.journalofaccountancy.com/news/2020/sep/irs-2020-2021-per-diem-rates.html

And Alaska has per diem rates based on specific location.

Start here:

https://www.irs.gov/taxtopics/tc416

https://www.irs.gov/businesses/small-businesses-self-employed/fishing-tax-center

And other web resources, such as the regional fisheries agency, and the web:

https://www.cpapracticeadvisor.com/tax-compliance/article/12425944/top-tax-tips-for-those-in-the-com...