I took these pictures on the evening of July 18 off a dock near northern Vancouver Island. If you look closely you will see there are sea lice on a lot of them. Sea lice on herring this small (they are about 4cm long) were never reported before salmon farms arrived. These lice appear to be Caligus, which are also found on farm salmon. There were thousands of herring, all of which are very young. For there to be this many lice, these little herring must have passed through an area with a lot of adult lice.
My guess is salmon feedlots. The lice are the light brown shapes with the "tails" which are egg strings.