Operational Plan for the Restoration of Diadromous Fishes to the ...

distributed throughout the river and stocked parr will likely be introduced in areas
with resident fish. Therefore, managers must question if they are achieving a net
gain of fish without the loss of the more desirable resident fish. Furthermore, the
need to stock parr may be indicative of a habitat problem that limits the use of fry. If
this is the case, then restoration via parr stocking is likely to fail because the habitat
cannot support all life history stages of salmon.
Parr stocking is most appropriate for reaches of stream that are not well suited for
fry. In addition, parr stocking may prove to be an effective approach in place of fry
stocking. At this point, the efficacy of parr stocking is unclear, as are the risks to the
resident population.
Smolt Stocking
Smolt stocking circumvents pre-migratory natural mortality, and is the most likely
stocking method to produce the most adult returns. However, smolt stocking has
several detractions. It requires substantial rearing space, produces more discharge,
and requires more resources at hatcheries.
Hatchery smolts do not survive as well at sea as wild fish, and therefore smolt
stocked fish must overcome this lower survival with greater numbers. Many factors
may affect the survival of hatchery smolts: size, growth rate, physiological readiness,
coloration, and behavior. Hatchery smolts have not reared in their “natal” stream,
and have been shown to have higher rates of straying than wild fish. They also may
not be as effective homing to quality spawning areas within their natal stream. They
lack rearing experience under natural conditions, and this may interfere with their
ability to reproduce. Smolt stocking avoids the resident fish interaction issues faced
with parr stocking. Some research has shown that adults derived from hatchery
smolts tend to have lower reproductive success than their wild counterparts. If this
is true in our program, then hatchery smolts would need to overcome both lower
ocean survival and lower reproductive success by returning more fish on a per
capita basis to achieve a given level of natural reproduction by adult escapement to
the rivers.
Smolt stocking is most appropriate when returning adults is paramount. However,
managers need to consider the tradeoff between adults derived from hatchery
smolts verses naturally reared smolts. Smolt stocking tends to be an immediate way
to increase adult returns, but is arguably not an effective way to restore a population,
as evidenced by the vast numbers of smolts of various salmon species stocked and
the continuing decline in the populations they are intended to support. The numbers
of smolts to stock should be calculated based on the desired number of adult
returns, but is often limited by rearing space. When other methods of stocking fail,
particularly fry stocking, managers often turn to smolt stocking. However, this failure
is likely the result of habitat deficiencies that limit survival through a complete life
history cycle. Therefore, smolt stocking may merely bypass a habitat problem, but if
this is the case, will not be effective in recovering the population.
PRFP Page 174