Two points:
1.  British Columbia wants us to eat more farmed Atlantic salmon...in keeping with the province's financial goals...is pleased that wild "king" ("spring" or "chinook" to Canadians) salmon are depleting.  (After 36 summers fishing northern Vancouver Island coastal waters, I have observed first-hand the province's "push-pulls" involving Atlantic salmon farms.) 
2.  The science indicates that the combination of three years of drought curbing spawning in rivers and streams AND hot water resulting from global warming clobbering food (e.g., bait fish) caused massive starvation of what would have been three-five year old kings, ergo smaller kings ("teenagers").  (In August, 2017, I was told by one British Columbia Department of Fisheries and Oceans employee that, "smaller wild springs are a blessing because they eat less food;" I had to bite my lip!)
Dr. Eldon Baker
Sequim, WA