Chum Salmon Supplementation: Bane or Boon?

The decline of a number of wild salmon populations in Washington State over the last two decades has caused salmon managers to increasingly employ hatchery supplementation to facilitate recovery of salmon stocks that are at risk of extinction. However, this practice has frequently been criticized as having unacceptable negative consequences on salmon populations, and has been described as a failed approach for recovering depleted populations. An early successful application of hatchery supplementation involved two wild summer chum salmon stocks in south Puget Sound. These stocks experienced a severe decline in the late 1970s, in part because of high harvest rates which were directed at hatchery coho salmon. Artificial production techniques were utilized to supplement the three largest spawning populations of summer chum in the region. The supplementation program operated from 1976 to 1991, contributing to summer chum runsizes that returned to and exceeded pre-decline abundance. Harvest rates were reduced in the early 1990s, and the two stocks are currently sustaining themselves without aid of supplementation. Average post-supplementation runsizes, now 2^nd and 3^rd generation natural origin recruits, are higher than average returns of the pre-decline years.