When considering the bookends, a totally wild spawning population vs. a spawning population comprised 100 percent of fish from hatchery origins,¬ the conclusion was stark. The hatchery populations on average produced only 12.8 percent of the recruits (the number of fish that have matured in the ocean as counted before they encounter fisheries) produced by the wild population. "The effect of hatchery fish on reproductive performance was the same among all three species. Further, the impact of hatchery fish from 'wild type' hatchery broodstocks was no less adverse than hatchery fish from traditional, domesticated broodstocks.
"We also found no support for the hypothesis that a population's reproductive performance was affected by the length of exposure to hatchery fish," the paper says. "In most cases, measures that minimize the interactions between wild and hatchery fish will be the best long-term conservation strategy for wild populations."
The analysis shows that it' wise to "keep the hatchery fish off the spawning grounds as much as possible if the goal is to rebuild the wild population," said Goodson, the ODFW's Conservation Planning Coordinator. "We kind of suggest that supplementation might not be the way to go," in many cases, Goodson said. "If the fish are going to wink out because there are problems" that won' be remedied in the shorter-term, supplementing wild populations with hatchery fish may be necessary, Goodson said. "In some cases that is all we can do." But the paper advises that such decisions should be weighed carefully.
"Supplementing natural spawning areas with hatchery fish to benefit the local wild population is a conservation tool that has seen widespread use in the Pacific Northwest (ISAB 2003)," the paper says. "The intent of this activity includes re-establishing natural production in vacant habitats, lessening the risk of demographic extinction for wild populations, ensuring the available habitats are seeded to full capacity, and maintenance of genetic lineages. "Depending on the circumstances there is a balance between risks and benefits that conservation managers must accurately assess and act on if supplementation programs are to be successful and achieve their intended effect," the paper says.
The analysis indicates that using wild fish as broodstock in so-called integrated programs does not necessarily make a more wild-friendly hatchery fish. "Surprisingly, we found that neither length of time exposed to hatchery fish nor hatchery type has any effect on a population's intrinsic productivity," the paper says. "The incorporation of wild fish into hatchery broodstocks has been undertaken with the expectation it will ensure that the hatchery fish produced will be genetically similar to the local wild fish. "Therefore, it is assumed that such genetically similar hatchery fish, if they escape capture and spawn in the natural habitat, will not harm, and may in fact benefit the conservation of the wild population.
"Use of wild fish for hatchery broodstock is a cornerstone of hatchery reforms currently being implemented for salmon and steelhead hatchery programs across much of the Pacific Northwest (USFWS 2010)," the paper says. "However, our findings call into question the effectiveness of this path as a means to lessen the impact of hatchery programs on wild populations." For the analysis the researchers selected 93 populations (four later were dropped for a variety of reasons) of anadromous salmonids from the states of Oregon, Washington and Idaho that were known to contain both wild and hatchery fish. They employed annual estimates from 1981 to 2000 of parental (spawner) abundance for each population that were based on information sources that differed by species and region. They then estimated the proportion of hatchery fish in the natural spawning population.
The next step was to estimate the "preharvest number of adult progeny (recruits) naturally produced by each brood year of spawners using the following four-step process," the paper says. "First, we estimated annual return abundance by dividing the fishery survival rate, calculated as 1 - fishery mortality rate, into the observed number of wild spawners. Next, we split each return into age categories, on the basis of the assumed proportion of different age at maturity for each population. "A table of return estimates by each age category was then constructed, and members produced by each brood year were identified," the paper says. "Finally, all members of each brood year were totaled to yield an estimate of recruits."
"Our primary finding is that across a broad geographical range and three different species, Ph (the percentage of hatchery fish on the spawning ground) was a population characteristic that is negatively associated with reproductive performance," the paper says. "Intrinsic productivity declines as the fraction of the hatchery spawners in the natural population increases. "We came to this conclusion after considering 12 different models that attempted to weigh the effect of four other covariates in addition to Ph."
This paper can be found at: http://cjfas.nrc.ca