February 7, 2010

John Carlos Garza
c/o Southwest Fisheries Science Center
Fisheries Ecology Division
110 Shaffer Road
Santa Cruz, CA 95060
Phone: (831) 420-3900
Fax: (831) 420-3980

((Phone: (831) 420-3903
Fax: (831) 420-3977
E-mail: Carlos.Garza@noaa.gov))

Dear John Garza,
Your name was mentioned in a recent article (In Central California, Coho Salmon Are on the Brink, Greg Miller SCIENCE vol. 327 no. 5965 January 29, 2010 page 512).  The article describes the dire plight of these wonderful endangered fish and the heroic, not to say desperate, efforts to save them from extinction.  For most of these efforts, outsiders can only cheer.  But there is one issue I think you need to know about.  It might help.

The article mentions that with the aid of two hatcheries and DNA testing you are striving to maximize genetic diversity among the endangered fish.  The expectation is, understandably, that this will maximize fertility.  Genetic diversity and fertility are a great interest to me.  Maximizing the one does not maximize the other.  What must be done is to optimize genetic diversity. 

A single word in an article by a non-specialist is a small thing, but if Greg Miller is right, then it is no small thing.  And I suspect that he is right.  You are using DNA testing to choose mates.  Unless your test is very sophisticated indeed, then in all probability any detectable difference in DNA indicates a catastrophic lowering of fertility, if not in the first generation then in the next.

The enclosed DVD will give the explanation and evidence.  The article that will be of most interest to you is the Sibly article in which he has complied over a thousand field studies of animals of a wide range of taxa.  What he found, much to his surprise, was that small gene pools produced greater fertility, and as the gene pool contracts to the smallest he could find, the fertility rises ever more steeply.  The effect is supported by two studies in humans, which find the same shaped curve.  The one from Iceland even quantitates it by using the extensive Icelandic genealogy.  In humans, couples are effectively third or fourth cousins (by their measure, which is more sophisticated than just the sharing of a great great grandparent or great great great grandparent) turn out to have the greatest number of grandchildren.

The implications for your work are not completely clear.  Obviously there is a degree of inbreeding that becomes destructive.  However the notion that maximizing genetic diversity will increase fecundity is totally false.  I have found no study that is inconsistent with that. 

I doubt that you will look at the references, get in touch with the authors to verify that they still believe what they said, and then reverse course.  But it would probably be highly desirable for you to do so.  At the very least you need to cover your bet.  Choose some populations and manage them so as to restrict gene pool size. 

After all, why do you think those salmon go to all that trouble to seek out the creek where they were spawned?  What will they find there that they will find nowhere else?  They will find relatives, pure and simple.  It is in order to mate with those relatives, to keep their gene pool size under control, that they make such mighty efforts to splash their way up to their natal brook and to no other.  If you have any other suggestion at all, I would be only too eager to learn it. 

So help them.  They are doing their best.

There is more information on my educational website nobabies.net.  If you want any more explanation or clarification from me do get in touch.  If you have anything to say addressing the issue that you would like me to post, I would be only too happy to oblige. 


M. Linton Herbert MD 

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