i've had similar white stress marks in my portabote (which is probably made of the same stuff as your yak) for quite some time now after i hit unlit bridge abutment in Mexico HARD when returning from night expedition. i just ignore em and they don't seem to have affected anything....had the bote out in 8-9' swells with bad wind chop since then, and no structural effect as far as i can see.
just come up with a good story to hide the embarrassment...."Oh that? that's from when i hit the surfacing submarine"
