That's sort of what I was thinking. Instead of a "straight line" from long spawn in the south to short spawn in the north, I wondered about a "triangle" shape. Down south, can spawning range from short duration to long duration in various waters. Then, as you move north, the duration has to get narrower just out of necessity with the short growing season. If this was true, then it would be fun to see what causes the "range" in durations at southern or mid-latitudes.
