Conversation so far:
What did Innis do that was so important in the 1930s?
Innis wrote extensively in the 1930s about other staple products
What other staple products did Harold Innis write about?
Innis wrote extensively in the 1930s about other staple products such as minerals
How was Harold Innis involved in fisheries?
After his book on the fur trade, Innis turned to the cod fished off the eastern coasts of North America. The result was The Cod Fisheries published in 1940.

Question: What did his study conclude about cod fisheries?
Self-contained rewrite: What did Harold Innis' study conclude about cod fisheries?