Passage: Thrasybulus was again in command of a squadron of the Athenian fleet at the Battle of Cyzicus, a stunning Athenian victory.  In this battle, the Athenians drew the Spartan fleet out to pursue a small force led by Alcibiades; when the Spartans had gotten a good distance from land, two squadrons under the command of Thrasybulus and Theramenes appeared in their rear to cut off their retreat.  The Spartans were forced to flee to a nearby beach, where Alcibiades landed his men in an attempt to seize the Spartan ships.  The Spartans, however, with the assistance of a Persian army, began to drive this Athenian force into the sea; seeing this, Thrasybulus landed his own force to temporarily relieve pressure on Alcibiades, and meanwhile ordered Theramenes to join up with Athenian land forces nearby and bring them to reinforce the sailors and marines on the beach.  The Spartans and Persians, overwhelmed by the arrival of multiple forces from several directions, were defeated and driven off, and the Athenians captured all the Spartan ships which were not destroyed.In 409 and 408, Thrasybulus remained in command, but his actions are difficult to trace.  He appears to have spent much of the time campaigning in Thrace, recapturing cities for the empire and restoring the flow of tribute from the region.  In 407 BC, he was in command of a fleet sent to besiege Phocaea; this siege had to be lifted, however, after the Spartans under Lysander defeated the main Athenian fleet at Notium.  This defeat led to the downfall and exile of Alcibiades.  Thrasybulus was either removed from command on the spot by Alcibiades or not reelected at the end of his term; either way, he was out of office from then until the end of the war.Thrasybulus did return to action, however, at the Battle of Arginusae in 406 BC.  There, he was a trierarch in the Athenian relief fleet sent out to assist the admiral Conon, who was blockaded at Mytilene.  That battle was a major Athenian victory; after the battle, the generals in charge took the majority of...

Question: What was the intent of Alcibiades in this instance?
seize the Spartan ships