Do you have the ability to do SI? If so, maybe make a few passes from different angles at about 3 mph with chart speed set at 3-4 and sensitivity set to 11-12. I think you would be able to read more off it and possibly see fish shadows if taken from different angles.

Other option is to really study it with sonar by playing with settings and going over at different angle passes looking for arches.

Curious to know what you find, good luck!

-Scuba