I don't think it should be taken at face value because those ways could be the main ways to earn money, but it could probably be the least reliable or successful ways. This sentence could just be a lie taken literaly in which has a hidden meaning. This could be a meaning that you might not get, in which will leave you ripped off.
All of them are necessary
Dominate trade in atlantic basin
In result of wet conditions and also poor hygiene, a lot of the soldiers would suffer from 'trench foot'. hope this helped :)
