Barb Wiginton , If not too deep, they can be sanded out starting with a medium wet sand paper working through to a very fine paper and finish by polishing. A headlight restoration kit can work well in removing scratches and can be inexpensive. See links below for more info. Good luck.
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http://paddling.about.com/od/kayaks/fl/How-to-Repair-Damage-to-Plastic-Kayaks-and-Canoes.htm
https://www.trails.com/how_39590_repair-scratches-polyethylene-kayak.html
https://www.youtube.com/watch?v=f3IrAUYHhuI