You could be right man. I just know that every year around this time of we get fish that are beat up with scars not unlike this. Granted this is one of the more severe cases. Knowing most of the locals I can't think of anyone who would use an outboard on this river as there's just not much need. But I'm not there everyday and it could be possible.
What typically happens during the spawn is a big female will swim a slow serpentine pattern. The smaller males ram and bite her inducing her to drop eggs. They are pretty rough on them and the females get really beat up in the process.
