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Old 12-03-2005, 12:00 PM   #32
eyeFISH
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Join Date: Jan 2004
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Default Re: at the least be informed

Quote:
"Fish from new, conservation hatchery stock have fitness that is about equal to that of wild fish(less than wild in two years,greater than in the third year).
The actual ranges of reproductive fitness observed in the study was 85-108%.

Let's not overstate what that "85-108% fitness" figure REALLY means. All the wild broodstock proponents will naturally focus on the 108% end of that range, while the detractors will focus on the 85% end. The tables on page 17 and 18 tell the whole story.

Only one year ('97) of the three reported actually showed an apparent hatchery fitness trumping wild. Even then, the 108% figure applied only to hens.... hatchery males showed only a 90% fitness. Furthermore the authors go on to explain that the return from that '97 brood year is incomplete.... only 66% of the recruits are accounted for, leaving 2 age-classes up in the air. If a greater proportion of wild fish from '97 return at older ages than their hatchery counterparts, it will obviously bring those fitness percentages down. So it really is too early to state that their fitness equals/exceeds wild. Since that paper was dated May 2003, there should be an updated report for 2005. (I will e-mail the principal investigator Mike Blouin to see if that report has been made public yet.)

If one looks at the two years with complete data in the 2003 report, the fitness percentages defintely lean toward the 85% end of things. The '95 brood brought back 90 males with a fitness of 85% of wild and 65 females with a fitness of 87%. The weighted average for all 155 fish is a relative fitness of 85.8%.

The '96 brood brought back 95 males at 90% and 153 hens at 85%. The weighted average for all 248 fish comes out to a relative fitness of 86.9%.

The weighted average for both years combined (403 fish) is a relative fitness of 86.5%.

Again, we must remember this is only two years worth of recruits.... not much to hang your hat on. However, it does suggest that the "new and improved" hatchery fish reproduce at some level below their wild counterparts, somewhere in the neighborhood of 14-15%.

Going back to my "megapost" analysis from several days ago, the only way to make up for that reduced reproductive fitness is by allowing enough hatchery fish to escape onto the spawning gravel. Assuming a fitness of 85%, hatchery fish would have to contribute at least an additional 18% to the natural escapement to keep the population stable. Anything less than 18% would send the naturally spawning population on a downhill course. Anything greater than 18% would allow the naturally spawning population to build up.
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