"I will have lost two hundred fathoms of good Catalan cardel"
Catalonia, Spain
Creative Commons Attribution Share AlikeCatalonia, Spain (in red) - Credit: Mutxamel, subido por Rastrojo

Catalan is a reference to Catalonia, Spain, an autonomous community within the Kingdom of Spain.

The term cardel is rather obscure. It is likely that Hemingway meant cordel, which is "a thin rope or line used on board a ship." Thus, Catalan cardel would be fishing line made in Catalonia.