With the opening of a new fish lift later this year, all 444 miles of it, plus
tributaries.
Other than the dams, the Susquehanna's water quality is sufficient for shad
reproduction. Only non-buffered streams on the eastern shore of Chesapeake Bay
have serious problems -- basically high pH and aluminum runoff during serious
storms.
>This may not maximize genetic diversity, and may have the opposite effect.
>Also, this doesn't really explain things. What about the sperm they used?
>Did they cross breed fish from different river basins?
Dunno. Shad are a homing species. Each river represents an evolutionarily
distinct stock. Whatever they're doing, though, appears to be working.
The upper Chesapeake Bay 1995 shad run of 336,000 fish represented a 159%
increase from the 1994 run of 129,500. The number of shad crossing the Conowingo
Dam on the Susquehanna have been up from about 50 -- that's right, 50! -- fish
per year in 1979 to a record 103,000 in 1997. It's estimated that anywhere from
60 to 89 percent of these returning shad were born in hatcheries. Of course,
these numbers are a long, long way from the teeming millions of centuries past,
but itıs a start.
>Columbia River? Those shad are introduced from Atlantic drainages. Why
>take Atlantic fish, transfer them to the Pacific, acclimate them there and
>use them to seed another Atlantic drainage?
Good question. To mix up the genes, I guess. It's ironic that American shad have
declined on the East Coast partly because of dams, yet are flourishing while
salmon are declining on the West Coast partly because of them. The reason for
this seeming contradiction is that shad are adapted to East Coast rivers, which
are slower-moving and warmer. Salmon are adapted to the colder, swifter-flowing
rivers of the Pacific Northwest. The warmer waters and lake-like conditions that
dams create are poor habitat for salmon, but ideal habitat for shad. Shad also
take advantage of salmon ladders to get over the dams, a feature that, until
recently, was missing from most dams on the East Coast. Apparently, sufficient
numbers of juveniles are able to survive the spillways and turbines on their way
downstream to the Pacific. In addition, shad will abort spawning attempts if
conditions are unfavorable and try again another year. Pacific salmon (except
steelhead) die in fresh water whether or not they are able to spawn.
Chris Scharpf
Baltimore
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