Layer 4: Stocks and flows
4.01. Extraction: Fishing
How much fish is being caught inside your boundaries? If your system of study is located along the coast, then fish landed at the ports (even if they were caught out at sea) is also of interest. Also be sure to include aquaculture production (fish farming). In most countries there are measurements in place to track how much fish is being caught. Find out what authority is in charge of this, and start there. People in the industry will also be able to point you in the right direction.
Note that this category should include any type of aquatic catch or harvest, including crustaceans, seaweed (kelp), etc.