Why Mediterranean cruisers landed their aircraft

Was replacing a cruiser's catapult with captured Italian 20-millimetre Breda guns common practice, and how was ammunition supplied?

Land-based and carrier aircraft reduced the need for cruiser seaplanes, allowing more anti-aircraft guns aboard. The ammunition-supply part of the question is left unanswered.

Land-based reconnaissance aircraft and nearby carriers supplied much of the scouting needed in the Mediterranean. Cruisers could therefore land their aircraft and fit additional anti-aircraft guns. The question cites captured Italian 20-millimetre Breda guns in the former catapult area, although the answer does not address their ammunition supply. Perth had used her aircraft earlier in the war for trade protection and operations against commerce raiders.