quote:
Originally posted by chiselchst
I like the fact that there are efforts being made to prevent the extinction of the smelt.
However, I hope it doesn't lead to a concept where depleting smelt is acceptable, as farmed smelt can replenish those stocks.
I am curious as to how they can breed a "stronger" breed of smelt in captivity, compared to the natural occuring breed?
Not a bioligist here, but I have never heard of that one before?
This is the way I understand it from the CALFED science Workshops. It's kind of a bassackwards issue with wild smelt vs. captive smelt.
The South Delta pumps are deadliest against healthy Delta Smelt that are strong enough to swim from the Sacramento into the pump's kill zone (which is most of the Central Delta). Once into that zone the smelt are sucked south and killed off by the fish screen system or the pumps themselves.
This isn't proven yet, but evidence is strong for this theory... Pumping has killed off many (if not most) of the full-sized healthy wild smelt. The wild smelt that remain are small and weak fish that don't swim into the kill zone. Those surviving wild smelt will produce an increasing number of "dwarf" offspring. It's natural selection at work to produce smelt of any kind that will survive delta pumping long enough to produce a new generation.
Natural selection (evolution) does this all of the time in response to natural changes in the environment. Species can evolve into a larger or smaller variety in response to the environment. Those changes can be natural or man-made. That's why wild corn in South America is so much smaller that corn that was domesticated by Native Americans and the European settlers. That's how some wolves became dogs. It's why sharks and crocodiles are so much smaller than prehistoric versions.
The Delta Smelt that were captured before the population tanked are strong, full-sized smelt. If we breed them carefully, they will retain their full size and strength. But the longer we breed them in captivity the less likely they are to keep instinctual behaviors. (Ever see a hatchery trout in a small wild stream? Right after they are planted the trout will swim up to people they see on the banks looking for a fish food handout.)
If the Delta Smelt survive in the wild as a smaller, weaker-swimming fish it may not survive if Delta water circulation turns back to something more normal. The captive fish will have normal strength and size. That's another reason why it's good to have a back-up ready. The primary reason is the captive smelt may be the only ones left alive.
There are other factors that probably contributed to the Delta Smelt crash. Loss of food supply is one. That could be caused by the cross-Delta pumping or by invasive species. The loss of good spawning habitat is another possibility. Reseach is still going on to nail down the cause(s).
