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NW Fishletter #215, June 8, 2006

[2] Yawning Survival Gaps Face BiOp Writers

A technical team charged with analyzing ESA-listed salmonids in the Columbia Basin has released an interim analysis that estimates just how far the region must go to bridge gaps between current fish numbers and healthy, viable populations.

In the best scenario they developed, they said Snake River spring chinook would still need an overall 29 percent boost in numbers to achieve a level that the technicians say would reduce extinction risk over the next 100 years to less than five percent.

The Interior Columbia Technical Recovery Team [TRT] has spent the past several years getting to this point, after sorting out stocks from one ESU to another and developing the viability analysis used to determine these gaps. But they say up front that their analysis needs several generations of data, so the "observed gap" between current status and viability goals don't necessarily reflect fish survival and productivity under current hydro operations.

This so-called "gap" analysis is the third step in a 10-step process to build a new collaborative BiOp. Once the gap analysis is finalized, the next step for the BiOp writers is to parse out mortality between the 4 H's of habitat, hydro, harvest, hatcheries, and the ocean, followed by development of a list of both federal and non-federal actions that can be implemented to fill the gaps.

The TRT pointed out that changes in early ocean survival rates can strongly affect estimates of the gaps, so they created three scenarios in their analyses--one using the past 20 years of data, which includes some of the poorest ocean conditions on record, another that uses the past five years' of returns, which reflects better hydrosystem conditions, and a group of scenarios that reflect different early ocean survivals. The report also said the TRT was developing a way to incorporate potential latent mortality effects from hydro passage.

The TRT report said restoration and protection measures along with other salmon recovery action measures could reduce the gaps, but they have not developed scenarios to address these issues because the data about rates and consequences of changes "are not robust." They cautioned that the effective survival needed to achieve goals may be more or less than the gaps generated by the TRT's analysis. The TRT analysis said improvements in hydropower called for in the 2004 BiOp would help but wouldn't be enough for stocks to achieve viability criteria.

But critics say the TRT's use of the basic assumptions behind population viability analysis, which was originally developed to analyze endangered birds and mammals, doesn't take into account the huge natural variation in salmon populations. And critics say the risk-averse assumptions that the TRT has built into their model aren't based on science at all, but are more related to what the team feels should be included.

Also they say the TRT's definition of extinction--a population of less than 50 individuals--doesn't jibe with reality when stocks in some Idaho creeks have actually gone to zero, then rebounded into the hundreds the following year.

Under the rosiest conditions the TRT analyzed, coupled with ocean survivals resulting from similar conditions in the past 50 to 100 years, they estimated that the Snake River Spring/Summer Chinook ESU would need a 29 percent overall improvement to achieve less than a five percent risk of extinction over the next 100 years.

Using hydro survivals based on the past 20 years, they said the springers would need a 45-percent improvement in survival to reach that 5-percent risk level in a 100-year time frame.

When a more pessimistic suite of ocean conditions was analyzed (like those encountered by the basin's salmon populations entering the ocean between 1980 and 2001), the gap goes up to 68 percent using the last 5 years' of hydro survivals, and up to 88 percent using the last 20 years' of hydro survivals.

To reach high viability, defined as less than a 1 percent chance of going extinct in the next 100 years, the TRT said it would take a 150 percent improvement in survivals for the Snake springers.

For some other listed stocks in the interior Columbia, the gaps are less severe, with ESUs like the Middle Columbia and Snake River steelhead, there may be no gaps at all.

But stocks in the upper Columbia may need more help than any of the others, according to the TRT analysis. Upper-C spring chinook suffer from a 53 percent gap at best and steelhead from that part of the basin need more than a 300-percent improvement in survival to reach the 5-percent risk level under the most optimistic analysis. Using data from the past 20 years shows that the steelhead may need more than a 500-percent improvement.

Finding ways to reduce those gaps depends in some measure on improving survival through the hydro system, but some say there isn't much room for improvement in mainstem river corridors. And controversy over how much fish mortality can be pinned on the the hydro system is heating up, with several recent papers being circulated that examine different aspects of the topic. One article currently undergoing peer review posits that the latent mortality from dam passage may not really occur at all, while another recently published paper suggests that further improvements of the in-river survival of migrating smolts may have little effect on population viability.

That paper, published this year in the peer-reviewed journal Conservation Biology and authored by four scientists from the NMFS Northwest Fisheries Science Center in Seattle, says that their sensitivity analyses show that "the survival of transported fish was deemed far more important for population viability but far fewer resources are directed at addressing how to improve this survival." -B. R.

The following links were mentioned in this story:

interim analysis

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