The schooling behaviour of trout and char in the Fraser River is not really the same as what is observed in pelagic species in the ocean such as tuna, salmon, herring, etc. Pelagic species school in the ocean primarily for avoid being eaten by larger predators. Salmon travel in masses due to their specific spawning time. Trout and char in the Fraser River travel upstream during salmon spawning months and stage in tributaries throughout the winter to feed on all the food items that are available (salmon eggs, carcass flesh, invertebrates, salmon fry). They spawn in around this time of the year, but not all are spawners.
Most of the feeders also travel upstream with the spawners, but some are also found along the Fraser River down to the mouth where it enters the ocean. I've caught bull trout (but hardly many cutthroat trout) between December and February, but success rate is low. March and April are typically very hot, when fish start moving downstream from the tributaries. These fish are well fed and continue to feed on salmon fry that are migrating downstream. I find the ones I catch during spring are much more powerful than the ones in the fall.
In the Tidal Fraser River, although they don't school like what salmon would do, I find fish tend to bundle up together in the same area. That's usually where the food items are. If I catch one, I usually would spend more time in the same area. Most of the time it would result in more hook-ups. Occasionally it wouldn't, but that's fishing. I also find that if I come back to the same area on the following days, I would catch more fish, even though fish probably had moved out with the outgoing tide, They usually come back with the tide, knowing that there's probably more food to eat. I've also caught the same fish in the same area within a couple of days.