They used DEAD FISH to fertilize their crops by Native American farmers.
Explanation:
Fish was used as fertilizer Native Americans. One of the ways for the Prevention of soil fertility from soil degradation is the usage of "fish as fertilizer". The People can take fishes directly to get high quality protein and fat can be attained and avoid of waiting for the season for it to be converted to measly plant protein and starches.
Whole fish and sometimes was not taken by the people often. A few species of fish are caught in nets that may not be edible. Hence for these reasons they used Fish for improving the soil fertility.