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Yukon
River Chum Salmon Freshwater Ecology and Environmental Influences On
Their Survival:
Ongoing research and analyzes
Recent
developments have demonstrated that some western Alaska salmon stocks
may be in trouble. Weak returns during the 1990’s have resulted in both
restrictions and closures on commercial and subsistence fisheries.
Subsistence and commercial fishing were closed on much of Yukon River
during 1993 and 1998. The
returns of summer-run chum (Oncorhynchus keta) and chinook (O.
tshawytscha) salmon over much of western Alaska during 2000 were the
worst ever recorded. At the USGS Alaska Science Center - Biological Science Office
(ASC-BSO) we are
conducting research addressing critical information gaps concerning the
spawning ecology of Yukon River drainage summer-run and fall-run chum
salmon. Our study focuses
on the freshwater portion of the chum salmon’s lifecycle.
Compared
to other, more southerly stocks of chum salmon, little is known about
the ecology, behavior, and productive capacity of Yukon River chum
salmon. It is generally understood that there are two major runs:
"summer" chum tend to spawn in lower and middle Yukon
tributaries during July and August; while "fall" chum are
found more frequently in upper Yukon tributaries during September,
October and November. Summer chum salmon spawning is usually associated
with run-off type streams while fall chum salmon spawning usually occurs
in areas having upwelling groundwater. Escapement indices, and weir- or
sonar-derived population estimates are available for some significant
spawning populations. However, little else is known about the extent or magnitude
of production or the factors limiting production of Yukon River chum
salmon.
The
ASC-BSO initiated this study in 1996 to identify factors affecting or
controlling the abundance of Yukon River chum salmon.
Two study sites were selected because they were thought to be
representative of other Yukon River tributary stocks, and were readily
accessible. Both sites are
located in Interior Alaska within the Tanana River Drainage.
The summer-run site is located within Hodgin’s Slough on the
Chena River and the fall-run site is in Bluff Cabin Slough on the Tanana
River, near the town of Delta Junction.
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Project
Goal
We
are attempting to fill information gaps concerning the freshwater portion
of the chum salmon’s lifecycle, provide input for production models, and
help managers to better assess the consequences of proposed conservation
and rehabilitation activities. To
this end, our research is focused on describing freshwater production in
terms of numbers of smolts produced per spawning female and the
investigation of mechanisms, both physical and biological, mediating and
controlling survival from egg deposition through smolt emigration.
Project Objectives
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Determine the numbers of spawning fish.
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Estimate the numbers of eggs delivered to each study
site.
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Estimate the intergravel survival of eggs and alevins
(yolk-sac bearing fry).
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Estimate the numbers of emigrating smolts each spring.
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Develop detailed maps of available habitat and spawning
locations.
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Determine
the environmental mechanisms (e.g., intergravel flow patterns,
temperatures, and dissolved oxygen) affecting spawning site selection
and reproductive success.
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