What We Learned in Chum School

Abstract Excerpt:
It is generally accepted that Pacific salmon (Oncorhynchus spp.) in the open ocean are non-schooling fishes. On March 31, 2022 in the Gulf of Alaska during a study of the winter ecology of Pacific salmon, seven juvenile chum salmon (O. keta) in their first ocean winter were caught in a 3 m x 3 m panel of gillnet with a stretched mesh size of 55 mm. This was clearly a school with fish that originated from three major locations from northern British Columbia to central Alaska and a straight-line distance between southern and northern locations of 1600 km. For these fish to be in this school in the gillnet they needed to have inherited a requirement to navigate to a particular location in the Gulf of Alaska and arrive at a particular time. They also needed to produce a chum salmon specific pheromone and have a requirement to detect increasing concentrations of the pheromone. For all of this to happen, there needed to be an evolved survival advantage to be in a school in the first ocean winter.