LINES 551-565
The Speaker wants the Lady to actually pray for the fisherman and their sons that are going out to sea.

Fishing is a big symbol of christianity as Jesus was referred to as "the fisher of men"

"Concerned with every lawful traffic" means that the Lady is praying for good people that follow the rules.

LINES 576-570
The speaker wants the Lady to pray got the women whose husbands and sons were lost as see.

"Figlia del tuo figlio" = "Daughter of thy son"
-"Dante"

LINES 571-575
The speaker asks the Lady to pray for all the men and women that have died at sea.

"Ended their voyage in the sea's lips" means drowning in the sea

"Hearing the seas bells" refers to sailors "coming back home" spiritually when they die out at sea.