[Fishing] Why does being on a boat make so much difference?

I was fishing around Skara on the banks. At 61.3 skill I was getting just as many of the legacy fish as I was getting the new high seas fish. About five minutes later I dropped my ship into the water to lobster fish on the deep-water side of the my ship while shallow-water fishing the same area. This time around,my catches were all high seas fish.I was targeting the same water tiles as before but there was a huge difference in what was caught. Why is there such a marked difference in shore fishing and boat fishing?

The Tokuno ship is like a +1.0 to your fishing skill.