Propagated Fish in Resource Management Symposium
Frank Thrower presented the paper "Effects of 70 Years of Freshwater Sequestration
on Survival, Growth, Early Maturation and Smolting in a Stock of Anadromous
Rainbow Trout from Southeast Alaska" at a symposium sponsored by the American
Fisheries Society in Boise, Idaho during June 2003. In the study, rainbow
trout (Oncorhynchus mykiss) from two progenies were compared for two brood
years in a hatchery environment to determine the effects of 70 years of
freshwater sequestration on growth, survival, early maturity, and smolting
proportion. One progeny was from wild, resident (freshwater) rainbow trout
descended from a stock of anadromous steelhead in 1926; these fish were
compared to progeny from wild, ancestral steelhead (anadromous) lineage
and their reciprocal crosses. The resulting smolts were tagged and released
and recovered as maturing adults to evaluate marine survival.
For the 1996 brood, 75 families were maintained in separate freshwater
raceways for 10 months. Approximately 100 fish from each family were tagged
with PIT tags, pooled by cross type, and cultured until age 2. An additional
group was tagged with CWTs and reared in the same manner. For the 1997
brood, 80 families were coded-wire tagged, separated by breeding type,
and cultured at different densities.
Size-at-age and survival rates were reduced significantly in fish from
resident females when compared with fish from anadromous females during
the first 2 months after first feeding. No significant differences were
observed in subsequent growth or survival through age 2. Higher proportions
of age-2 smolts and lower proportions of early maturing males were observed
in families from anadromous parents. Smolts produced by anadromous parents
had four to five times higher marine survival than those from sequestered
While the relative number of fish that smolted and smolt survival rates
were lower for the progeny of freshwater sequestered fish, the results
indicate significant numbers of smolts and adults can still be produced
by populations land-locked for up to 70 years and for 20 generations. The
results have substantial implications for the use of natural freshwater
environments for the preservation of endangered anadromous stocks of rainbow
trout, the rehabilitation of anadromous stocks, and the true effective
breeding size of anadromous rainbow trout populations.
By Frank Thrower.
World Summit on Salmon Conference
Simon Fraser University sponsored the conference "World Summit on Salmon"
in June 2003 in Vancouver, British Columbia. A central theme of the conference
was the need to reverse the continuing worldwide downward trend of wild
salmon populations. Bill Heard from the ABL attended the conference and
presented a poster titled "Can Wild and Hatchery Salmon Successfully Coexist?
Consider the Alaska Model."
The presentation described how Alaska salmon, the focus of major commercial
harvesting since the late 1800s, are characterized by cyclic fluctuations
in abundance resulting in varied levels of harvest. Poor catches from weak
wild stock runs cause statewide socioeconomic disruptions. Modern hatcheries,
developed in response to record low wild stock runs in the 1970s, now provide
important supplements to fisheries, even though natural runs have mostly recovered.
Hatcheries in Alaska were developed specifically to complement fisheries
under management protocols for protecting and maintaining healthy wild
stocks through protecting habitat, avoiding mixed-stock fisheries where
possible, and having hatchery stakeholders help pay costs. Hatchery siting,
capacity, general operations, and restricted brood stock origins are carefully
regulated through statewide genetic and pathology policies and statutes.
The state of Alaska's 33 production hatcheries are mostly located on nonanadromous
water sources that are not on productive salmon streams.
Collectively, these policies allow Alaska to maintain robust wild salmon
stocks balanced with integrated development of hatchery production to supplement
fisheries. A cornerstone of the Alaska model is a priority focus on escapement-based
management, where wild stocks achieve spawning goals rather than target
harvest levels. Some hatcheries release more than 100 million juveniles
annually; statewide totals have been 1.2 to 1.4 billion annually during
the last decade.
Since the late 1980s, commercial harvests of salmon have remained at or
near historic high levels, although wild stocks in western Alaska, a region
without hatcheries, remain at depressed levels. In the last decade, hatcheries
have produced 27-63 million adults annually, accounting for 14%-37% of
common property harvest. Contrary to common beliefs about permanence, 13
Alaska hatcheries have closed since 1979 for various reasons. In spite
of healthy wild stock fisheries supplemented with hatchery fish, Alaska's
commercial salmon industry, based on capture fisheries, is economically
threatened by continued worldwide production of farmed salmon.
By Bill Heard.
Quarterly April-June 2003 sidebar
April - June 2003
Auke Bay Lab