From time spent in British Columbia and Northwest Territories working for Dept. Fisheries and Oceans, I had multiple occasions to see stomach contents of trout species containing different types of Sticklebacks.
They do not cause any problems to larger species and are mostly shore line, shallow water, species feeding on phytoplankton and micro-organisms.
The stickle part is not as much a danger to any fish eating them, I gather from readings that it�s a sign of sexual maturity for the adults to have their stickles showing and their coloration also becomes bright.
Another observation; I believe the three-Spined Sticklebacks "Gasterosteus aculeatus" are endemic to North America, so they are an indigenous species common to most areas.
I would not be concerned over sticklebacks myself!
my two cents...
