This is a myth; we forget the more logical option. Krill shrimps are edible also, there is plenty in the sea and you just need a net. Is by far much less dangerous option for sea workers and human consumers. In famine times you need to save as many energy as you can, and use the precious fuel wisely. In any case, not enough strong fishermen would be available to go to a dangerous and demanding fishing trip, because the men will be at thousand km of home, doing war.