運休なのでしょう

４月１０日から５月１９日のタイムスケジュールを見ても、火曜と木曜だけ航行となっているので、それ以前は運休のようです。客がないということなのか、気象条件によるのかは分かりません。アドリア海側は強風が吹くことがあるので。
でもアンコーナからスプリットへは便があるようです。

Note: Important info about departures from Ancona to Split:

This is a schedule for 2017
In period from 01.01 to 31.03 and 29.110 and 29.12 departures from Ancona are on Tuesday and Friday only
In period from 02.04 to 27.07 and 28.08 to 27.10 departures from Ancona are on Mondays, Wednesdays and Fridays only
In period from 28.07 to 27.08 departures from Ancona are on Mondays, Wednesdays, Fridays, Saturdays and Sundays.
In the same period on Saturdays and Sundays the ferry stops over in Stari Grad on Hvar Island before proceeding to Split.
The ferry route, run by Jadrolinija ferry company operates all year around. The ferry sails from Ancona overnight for 10 hours and arrives following morning in Split.
see current prices for this ferry route