Given the task definition and input, reply with output. This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: In July 1855, the allied squadron tried to go past Taganrog to Rostov on Don, entering the Don River through the Mius River. On 12 July 1855 HMS Jasper grounded near Taganrog thanks to a fisherman who moved buoys into shallow water. The Cossacks captured the gunboat with all of its guns and blew it up. The third siege attempt was made 1931 August 1855, but the city was already fortified and the squadron could not approach close enough for landing operations. The allied fleet left the Gulf of Taganrog on the 2nd September 1855, with minor military operations along the Azov Sea coast continuing until late autumn 1855. Question: What caused the HMS Jasper to get stuck in shallow water?
a fisherman who moved buoys