Unsolicited pro tips: Hit the hanging fish with explosives on your way to the ship. They have sneaky bugs inside that will pop out and ambush your squad when they’re re running away, but not if you blast them first!
Once you get to the boat, keep your squad near the back on the top level in a defensive formation and run your fastest troop, by themselves, to the lever to pull it and run back asap. That way if they get trapped, you minimize the casualty count.
Then run like hell and get out of there.
Also, don’t use mechs lol. They’re probably about the worst troop type vs Chrysalids, so a whole squad is not going to serve you well, as you may have noticed.