I've done a little more digging into the hatchery dhad genetics issues, and this
is what I've found so far...
Adult shad cannot be held, as can some salmonids, in a hatchery for long periods
of time. Shad brood stock(s) are always wild fish, obtained on an annual basis
from select wild populations. However, little DETAILED consideration, has been
given to genetic concerns on hatchery produced American shad for east coast
stocks.
When selecting for which stock(s) to use as brood stocks, generally the thought
is to use a stock close in geographic proximity to the stream to be stocked.
Shad exhibit differences in fecundity as you move from south to north along the
coast. Obtaining eggs from a source close to the river to be stocked is trying
to maintain some resemblance genetically of the stocks in the region (i.e., VA
Fish and Game obtains their brood stock from VA rivers).
However, for restoration programs, such as what has occurred for the
Susquehanna, most of the eggs have been obtained from the Hudson, Delaware and
Connecticut and Columbia (which are of Hudson origin) Rivers, as these stocks
had more fish than those available in the Chesapeake when the program began.
One issue that has not been well discussed is why not let a population try to
recover on its own, rather than the hatchery route. For some stocks, natural
regeneration is impossible because the spawning stock is so low (fewer than 100
fish return to a particular system, as seen in several stocks). And then there
are habitat issues: rivers with dams without efficient up and DOWN stream
passage do not bode well for anadromous fish which are supposed to spawn more
than once in a lifetime. If a shad spawns once (takes a one way trip up over a
dam and can't get out), instead of 5 or 8 times then a tremendous amount of
lifetime egg production is lost.
In other systems, there are larger spawning stocks, yet they are continued to be
supplemented by doses of hatchery raised fish in an effort to boost young-of the
year production, in the hopes of getting more adults to return. For this to
happen, fishing needs to be reduced to as close to zero as you can get it. This
doesn't always work since shad continue to be fished throughout their migratory
range in the ocean on the east coast. The MD portion of the Chesapeake Bay has
been closed for 20 years, yet stocks have been relatively slow to respond.
Another point is that for hatchery production, the fish is sacrificed for its
eggs, so in same only a fraction of the lifetime egg production allowed instead
of allowing it to spawn, leave and spawn again another year.
So to address Jay's question -- what of the limited gene pool that is being
created through the use of hatchery fish? No one seems to have thoroughly
addressed this issue. For example: 4000 adults are sacrificed to produce 20
million stocked larvae annually into a river. The escapement 5 years down the
line indicate that 70% of the returns are of hatchery origin. Do this for 15
years. Is genetic diversity being limited, and in what way?
Consider the comparison to a small wild run of 4,000 fish being allowed to
repeat spawn over the same time period. Life history characteristics among
these 4,000 can be very different. Wild spawning runs are usually spread out
over a 8 to 10 week period. Broadcast spawners, like shad, use this mechanism to
maintain a wide diversity in the population (spawning over a range of temps.
etc, so that if something happens to one part of a spawn, say a severe cold
front in the spring that could wipe out a portion of the spawn, the later part
of the run could make up for it). And what of the odds of the same two fish
spawning year after year?
Genetically how different would these two populations (one-time spawning
hatchery shad vs. repeat spawning wild shad) be?
Another issue that has not received any DETAILED consideration is the extent to
which straying ocurs in the wild. Pacific salmon, it is known, stray from one
run to another, therefore mixing up the genes and keeping the runs strong.
American shad from various runs do school together while they mature in the
ocean, and when they overwinter. To what extent do shad from, say, a run in
Maine, join a run from the Susquehanna, and vice versa? If hatchery shad boost
the numbers of shad from all over the Atlantic coast, does this increase the
rate or volume of straying?
No one knows these answers, and very few are looking for them (as far as I can
tell). Right now the emphasis is on simply trying to bring the shad back through
whatever means possible -- including hatcheries, strict fishing closures, fish
lifts and passages around dams, etc. Granted, the genetics of the whole process
may prevent the shad population from returning to the millions that can once
again sustain a commercial fishery. But at least the fish won't be extinct. At
the very least, future generations of East Coast residents will be able to watch
the shad return in the spring (a rite of spring celebrated by various shad
festivals in Maryland and elsewhere).
Christopher Scharpf
Baltimore
"The secret of life is to have a task....And the most important thing is -- it
must be something you cannot possibly do!"
Henry Moore, sculptor
/-----------------------------------------------------------------------------
/"Unless stated otherwise, comments made on this list do not necessarily
/ reflect the beliefs or goals of the North American Native Fishes
/ Association"
/ This is the discussion list of the North American Native Fishes Association
/ nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word
/ subscribe, unsubscribe, or help in the body (not subject) of an email to
/ nanfa-request_at_aquaria.net. For a digest version, send the command to
/ nanfa-digest-request_at_aquaria.net instead.
/ For more information about NANFA, visit our web page, http://www.nanfa.org