There are variants from place to place as they are so cut of from other species groups but IME they can often lose spines to make them look different, you'll have to see if they breed that is a sign that they are the same fish.
Related Species: Fourspine Stickleback (Apeltes quadracus) has 4 dorsal spines, no bony plates, occurs in similar habitat, less frequently in fresh water, from Gulf of St. Lawrence to Virginia. Blackspotted Stickleback (G. wheatlandi) has black spots, 2 soft pelvic fin rays, 3 weaker dorsal spines, and no bony plates, occurs in salt water south from Newfoundland to s. Massachusetts. I believe?
Nine Spine Stickleback - (Pungitius pungitius Linnaeus) - Native to Massachusetts, populations of ninespine sticklebacks are often found in estuaries and salt marshes. Coastal freshwater populations seem to be more common in the streams and ponds of Cape Cod and Martha's Vineyard where there is at least one land-locked population. Ninespine sticklebacks are often numerous, but they are found far less frequently than the other sticklebacks.
Three Spined
Brook Stickleback
Nine Spined
Two spined (Blackspotted Stickleback) - Grass-green above in life, mottled and finely speckled with black on the top of the head and back; sides of head and body golden with dark blotches; breast silvery; ventral fins scarlet, I think, I have only seen 3-4 specimens.