Chapter 7 · Try it yourself
Sardine Harvest
In the 1930s, Monterey’s Cannery Row canned sardines faster than anywhere on Earth. The California catch peaked around 1936–37, and by the early 1950s the sardines, and the canneries, were gone. Your turn to run the fishery. Pick how many sardines the fleet takes each year and see if the fish can keep up.
10 units a year
The ocean starts full: 100 units of sardines, its carrying capacity (K).
After 30 years
Sardines left
72 units
Caught that year
10 units
Caught in total
300 units
Sustainable
Why the middle matters
Your catch 10 a year. Balance points
The hump shows how many new sardines the population adds in a year. A nearly empty ocean has too few parents; a full one runs short of food. Growth peaks at half of K, 50 units, where it makes 12.5 units a year. That is the maximum sustainable yield (MSY). Where your catch line crosses the hump, the population can hold steady. Set it above the top and there is nowhere to hold.
Simplified model: logistic growth with r = 0.5 a year and K = 100 units, catch taken once a year, “collapse” means below 10% of K. In the cool-ocean decade r drops to 0.2. Real sardines also boom and bust with warm and cool ocean eras, which is part of what happened in the 1940s.