Beside national parks, there are form of flora and fauna protections which falls into the category of Nature Reserve.

One example I know by personal experience is sectors of rivers where fishing is forbidden or regulated, usually to protect the ecosystem.

OSM holds the Nature Reserve tag already.

The class of protection is also a good way to describe, but fish reserves are not listed explicitly. Also it seems that is applies to boundaries only.

…research in progress… suggestions are welcome!