The Idaho Captive Rearing program collects naturally produced Chinook salmon parr or eyed eggs, and then rears them in captivity to adults for release to increase the number of naturally spawning salmon.

The proposal indicates that this experimental effort will be terminated by 2012. The sponsors request funding to complete the evaluation of this captive rearing strategy. The ISRP raised several questions in the preliminary response.

The principal query was for an outline of the timeline of juvenile rearing and adult release, and the subsequent natural parr, smolt, and adult production, to ensure that the time frame for the data collection and analysis was sufficient. The sponsors provided an answer to this question that was sufficient.

A secondary question was about the natural spawning performance of the captive stock. In earlier proposals, the sponsors reported asynchrony in the spawning of natural and cultured adults, and poor egg viability in natural redds produced from captive stock. No mention of this was in the current proposal and the ISRP requested an update. The sponsors provided a review of the recent observations on asynchrony, reporting that during the last funding cycle this was not a problem. Egg viability was not tested during this time period. No explanation was provided for the improvement in synchrony between natural and cultured spawning adults.

Finally, the ISRP asked about the quantitative benefits from a program like this to an entire ESU, under circumstances such as the spring and summer run Chinook in the Snake River that consist of an appreciable number of spawning units. That is, assuming there is a demographic benefit in the treated tributary, what are the quantitative consequences in the Viable Salmonid Population metrics for the ESU, from these improvements in individual sites.

Sponsors responded that:
"It remains difficult for us to comment on whether the potential added adult production from this program will elevate VSP abundance or productivity parameters to a status level more desirable than the current ‘High Risk' standing. Nevertheless, added adult production will help ensure that a continuum of spawning from one generation to another occurs. Preventing cohort loss will slow the loss of critical population genetic variation and preserve future recovery options."

The ISRP appreciates this candid appraisal, but emphasizes that addressing this larger issue is critical when considering using this technology to support ESUs consisting of multiple independent populations or spawning aggregates. When you have 30 to 40 independent populations in an ESU, what aggregate demographic benefit are you getting if you can improve the status by these intensive actions in one or two of the individual populations? What is the short and medium term benefit from this type of action?

The final reports and analyses should include this later consideration of the quantitative benefits at the ESU level if benefits are demonstrated at the independent population level.