Wildlife has been adversely affected by human impact for centuries, whether from over-harvesting, habitat encroachment, or habitat destruction, and the number of endangered species in America is growing. In the Pacific Northwest, a major issue natural resource managers face is how to best deal with our steadily declining fish populations. Fish hatcheries in the US play an integral role in maintaining population numbers for many species—most notably for salmon in the Pacific Northwest. But hatcheries are also expensive—and it looks like they may only succeed in slowing the seemingly-inevitable decline of our precious salmon population.
Recently, the Northwest Fisheries Science Center teamed up with the Washington Department of Fish and Wildlife to study the fitness levels of hatchery and wild spring Chinook salmon in Washington State’s Wenatchee River. The study, published in 2010 in the Canadian Journal of Fisheries and Aquatic Sciences, examined factors that influence the reproductive success of wild versus hatchery Chinook salmon stocks, and addressed how the physical differences between the two groups affect fitness. Was the significant investment society has made in hatchery supplementation actually contributing to the recovery of salmon populations?
Salmon have a unique life history, in which individuals hatch in rivers or streams, migrate to the ocean where they reach sexual maturity, and then migrate back up the same river or stream to spawn and die. In 2004 and 2005, from April to August, the researchers trapped and took samples from every migrating spring Chinook salmon at the Tumwater Dam. The fish were measured and weighed, and were identified as male or female, and wild or hatchery. The fish were scanned for passive integrated transponder tags (if they didn’t have one, they were given one), which can be detected and read through an antennae placed in water. This technology allows for more efficient data collection—it’s much easier to collect information on the location of fish as they swim by rather than catching every individual. Researchers were able to examine how weight, migration timing, age, origin (wild or hatchery), and spawning location influenced each fish’s reproductive success.
The researchers’ results showed that there were significant life strategy differences between wild and hatchery salmon. Hatchery-raised male fish matured from two to three years of age, while wild males matured at four. Also, hatchery fish did not migrate as far upstream or into the tributaries of the Wenatchee River like the wild salmon. This discrepancy in choice of spawning location is of particular interest, as it may be a key player in future hatchery management.
Significantly, hatchery-reared fish also displayed a considerably lower fitness level than their wild counterparts. Wild Chinook in this study produced almost two progeny per parental unit, while hatchery-reared salmon managed only 0.75 progeny. Hatchery fish in this sampling were actually failing at reproduction—according to the findings, every four parental pairs of hatchery fish are able to produce only three viable offspring, which represents a negative trend in population size. It seems that hatcheries are just a rather expensive way to make the salmon fishery disappear more slowly.
Unfortunately, this study was the “first direct estimate of the effect of general spawning location on fitness in a natural stream,” which means there is nothing to compare results against. Still, the study was immensely helpful to further the understanding of the dynamics of hatchery versus wild Chinook salmon. As the Chinook salmon continues to attempt to coexist in a human-dominated world and faces major constraints like habitat degradation and dams, hatchery fish are going to be in higher demand—hatcheries will need to produce salmon that are more viable outside the hatchery. But it seems that our already-dwindling Chinook salmon populations, even with hatchery help, may inevitably be lost to human interference. If managers can improve current practices to increase fitness, the endangered spring run Chinook salmon may have a future.
By Brendan O’Callaghan
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