Friday, March 9, 2012

Hatchery Programs Mask Declines in Wild Salmon Populations

While there is broad consensus in the scientific community that large scale hatchery supplementation undermines the productivity of wild salmon populations, some in the fisheries management world remain convinced that hatchery programs can facilitate the recovery of wild fish. For instance, last year an article titled Tribes Detail Success, Promise of Supplementation to Boost Natural Spawning Salmon Populations in the Columbia Basin Bulletin quoted Yakama Tribal Biologist Bill Bosch as saying that hatchery programs in the Upper Yakima River had resulted in a 245% increase in the abundance of wild chinook. However, these estimates were derived from redd counts and biologists counting redds have no ability to distinguish between redds constructed by hatchery fish versus wild fish. The vast majority of these redds are in fact constructed by hatchery origin chinook, which now vastly outnumber wild origin fish in the Upper Yakima and have in a few generations effectively undermined thousands of years of natural selection, causing profound shifts in the life history distribution of chinook within the watershed.

This problem is not unique to the Yakima, and in many heavily supplemented systems an inability to distinguish between hatchery and wild fish allows managers to claim that they have successfully restored wild populations while continually undermining their productivity and genetic integrity. A new scientific paper out recently in PLOSone, highlights these concerns in the Mokelumne River in California's Central Valley. Using sulfur isotopes researchers were able to distinguish between hatchery origin and naturally produced chinook and found that while managers have long considered the Mokelumne one of the healthiest Fall Chinook runs in the region, only 10% of the returning fish were of natural origin. Instead, hatchery production has masked (and likely contributed to) the decline of wild chinook in the basin. This situation is not unique to the Mokelumne and highlights the need to view claims of hatchery driven "recovery" skeptically.

No comments: