user: Question: When was Stellbrookmoor established?
Columns: ['NSG Nr.', 'Name of the nature reserve', 'District / Town', 'Area (ha)', 'Date established']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Nord-Sylt', 'Nordfriesland', '1.785,87', '19800523 23.05.1980']
SQL:

assistant: SELECT "Date established" FROM "Table" WHERE "Name of the nature reserve" = 'Stellbrookmoor';