Three-spine sticklebacks are sexually mature in only a year or two. Most will be only be just over one to three inches long when mature. Most stickleback populations are anadromous, while others live their entire lives in fresh water.
Their upright spines provide them a bit of protection from fish and bird predators as it makes them harder to swallow. Some trail cam photos make it appear the great blue herons do not have any problem eating them. Stickleback populations have been observed to be impacted when trout have been introduced into their area, so the protection of the stickleback spines appear to be limited.
Rising water temperatures appear to correlate with reduced stickleback populations.