Sea otters are known to be more aggressive than river otters but I do not think they view humans as preys. It is probably a territorial or mating reason in your

Sea otters are known to be more aggressive than river otters but I do not think they view humans as preys. It is probably a territorial or mating reason in your case. I have read different reports of what the OP mentioned. The official statement by the park is that he (as reported to them by himself) ran through the pack of otters because of poor visibility (early morning) and tried to get them to do something about the otters. That is quite different from what the OP claims.