Threespine stickleback fish eggs hatch in the streams formed from mountain snowmelt. The streams carry the adult threespine stickleback fish to the ocean where they live until they swim
upstream to lay eggs to begin the next life cycle. In 1964, an earthquake in Alaska turned some of the streams into ponds that were completely cut off from the ocean. Today, threespine
stickleback fish can still be found in the ponds formed by the earthquake.
How did the traits of the stickleback fish have to change
to survive?