One moment they're in a loose ball with only the ambient weavings of the outer fish noticeable. Then, something, a shadow or movement in the water, causes them to pull in tightly. Light pulses off their bodies, a submerged flashing silver strobe. On-going exploratory surveys continue to discover new, unreported surf smelt spawning areas. Surf smelt spawn in the upper intertidal during high tides.
Females glue their eggs to coarse sand or fine gravel as males swim through, fertilizing the eggs.
Incubation takes two to five weeks depending on water temperature. Hatching most likely occurs at high tide too, so that the newly hatched fish are carried off the beach by the ebb tide into the cover of eelgrass or algae beds. Their average age is two to three years, five years maximum. Fisheries biologists are learning that stocks of surf smelt are similar to salmon and other extensively studied fish stocks in that each stock is believed to be genetically distinct with it's own set of biological variables, including dependence on a specific spawning location. This means that faced with a loss of habitat, the local Kilisut Harbor stocks most likely would not re-establish in another location.