In recent years, it
has become apparent that the growth and survival of local salmon populations
can be profoundly affected by fluctuations in ocean conditions caused
by two ocean processes; the Pacific Decadal Oscillation (PDO) and the
El Niño-Southern Oscillation (ENSO).
The PDO is a pattern
of climate and ocean condition regimes occurring in the north Pacific
Ocean that results in shifts in sea surface temperatures and plankton
abundance on a long time scale (20 to 40 years). The PDO regimes have
been shown to relate directly to the abundance of salmon populations that
spend their marine lives in the Gulf of Alaska. A shift occurred in 1977,
which resulted in warmer coastal sea temperatures, cooler central Pacific
sea temperatures, and more abundant plankton resources. These ocean conditions
likely contributed to general increases in production of those Washington
salmon populations that migrate to the Gulf of Alaska, most notably pink
and chum salmon. The PDO can also have a major influence on the local
freshwater environment, and since 1977 coastal Washington has experienced
a general stream flow pattern that includes summer/fall droughts and extreme
flooding in early winter.
While the environmental
conditions since 1977 have been generally favorable for chum and pink
salmon, the warmer coastal sea temperatures and freshwater drought conditions
have had negative consequences for local populations of chinook and coho
salmon. Overlaid on the PDO effects are ENSO events, which begin as warming
episodes in the tropical Pacific zone and can result in large scale intrusions
of anomalously warm marine water northward along the PNW coastline. The
impacts of these warm water intrusions are felt along the Washington and
British Columbia coast for a one to two year duration in an irregular
periodicity of every two to seven years. The combined impacts of the 1977
PDO shift and frequent recent ENSO events have created generally hostile
freshwater and ocean environments for the coastally oriented chinook and
coho populations over the last two decades. When combined with the effects
of altered freshwater and estuarine habitats, dams, and fishing impacts
these environmental changes have contributed to the recent low abundance
of chinook and coho salmon.
There is increasing
evidence that the PDO has recently shifted to a regime of different ocean
and climate conditions. Local patterns of salmon production are now consistent
with environmental conditions similar to those that existed prior to the
1977 regime shift. In general, over the last several years chinook and
coho populations have shown increased abundance, while chum and pink populations
have contracted somewhat from the large returns of the last two decades.
These changes, if they continue, are a normal part of the long-term abundance
cycles of local salmon populations, and should not be considered to reflect
a change in the status of the various salmon species.
sockeye salmon ecosystem includes the interrelated complex of biological
communities and environment conditions that contribute to population
Sockeye salmon generally spawn
in streams that are tributaries to large lakes. These streams can vary
in type, ranging from small tributaries to large mainstem rivers and side-channels.
Additionally, some sockeye stocks spawn along the shorelines of lakes.
Sockeye spawning in Washington State begins as early as August and can
extend through February. Those stocks spawning from August through October
need adequate stream flows to provide proper spawner distributions on
the spawning grounds. All sockeye stocks require extensive, quality spawning
riffles for optimum production. Successful egg and alevin survivals are
dependent on clean spawning gravels and low to moderate winter stream
flows. Those sockeye that spawn on lake shores need access to undisturbed
shallow water shorelines, and clean gravels with upwelling ground water.
Sockeye migrate downstream
to the deep waters of nursery lakes upon emergence from spawning sites,
at a size of approximately 25 to 32 millimeters (1.0 to 1.25 inches).
At this small size, sockeye fry are vulnerable to predation by other fishes
and birds, and survivals can be lowered substantially by aggregations
of natural or artificially produced predators Juvenile sockeye rear in
the nursery lake for 1 or 2 years, and continue to be subjected to predation
by other fish species. They also face competition for available food resources
with other fish. The production of food organisms is particularly important
at this life stage because faster growth rates can increase the survival
of the young sockeye.
Sockeye smolts emigrate to
sea in spring at a length of approximately 4 - 6 inches and are subjected
to intense predation by a variety of fish and bird species. Squawfish
and trout have been identified as especially significant predators during
this outmigration life phase, and gulls and grebes are some of the significant
avian predators of sockeye smolts.
The freshwater/saltwater transition
zone provided by estuary habitat can be important to the success of sockeye
smolts. A natural, productive estuary provides the food resources necessary
for the smolts to transit the area, and can offer refuges from numerous
fish and bird predator species. In the near shore and open ocean environments,
predation by fish, birds, and marine mammals, and competition for food
resources with other fish species affects growth and survival of sockeye
salmon. Ocean growth and survival of all species of Pacific salmon can
be affected by periodic warm water events (El Nino) in local waters, and
by cyclic changes in ocean Click here to read about climate conditions
in the North Pacific Ocean.
stream flow can impede summer-run spawners, and high flows can disrupt
the spawning of fall and winter sockeye.
Low stream flows can limit
early run sockeye spawner distribution to sub-optimal stream reaches,
and force fish to spawn in the center of the stream channel, which can
increase egg and alevin mortalities during winter floods. Sockeye that
spawn after mid-November are frequently affected by high flows, which
can disrupt upstream migration and interfere with spawning activities.
All sockeye stocks can be negatively impacted by high flows during the
fall and winter incubation period. The erosion and downstream movement
of spawning gravels is a major cause of egg and alevin losses, and severe
flooding can cause mortalities exceeding 90%.
Land use practices and natural
events that introduce substantial amounts of silt into spawning streams
affect sockeye intergravel survivals by reducing the permeability of the
gravel, which can affect the survival of incubating eggs and alevins by
interfering with the delivery of oxygenated water and the removal of metabolic
wastes. Channelization and bank armoring reduces the amount, quality,
and diversity of sockeye spawning areas by narrowing and deepening the
limitations of food supplies during lake rearing can reduce growth rates,
which in turn can lower survival of the juvenile sockeye in the lake
and during their early marine life.
Juvenile sockeye rear for 1
or 2 years in lake habitats before migrating to sea. Limnetic habitats
are especially critical because sockeye spend most of their time in these
habitats. Good water quality and production of food organisms are important
because survival in lakes can depend upon how fast sockeye grow to a size
that reduces their vulnerability to predators. In addition, the size of
sockeye leaving freshwater has a direct affect on their subsequent marine
The freshwater migration corridors
used by emigrating sockeye juveniles (smolts) and by returning adults
are generally medium to large sized mainstem streams, providing a direct
route between the outlet of the home lake and marine waters. This mainstem
habitat on the Columbia River and Lake Washington systems has been altered
by the construction of dams, which has had negative impacts on sockeye
salmon success. The impacts of Columbia River mainstem dams on the local
sockeye stocks have included factors such as: total extirpation (in the
case of stocks above Grand Coulee Dam); turbine passage mortalities of
outmigrating juveniles; water quality problems (nitrogen supersaturation
mortalities); predation on smolts in reservoirs; and between dam losses
of upstream migrating. The dam and ship locks on the outlet of Lake Washington
causes some impacts on sockeye salmon survivals; primarily through increased
susceptibility to predation, and facility related (physical injury) mortalities
of outmigrating smolts.
sockeye smolts emigrate to salt water after one or two years, and early
marine survival is dependent on healthy estuaries providing good quality
water, and abundant food resources.
Juvenile sockeye salmon spend
the first part of their marine lives in estuarine and near shore areas
adjacent to their natal streams, although their residence time in these
areas may be the shortest for any of the salmon species. Most of the estuaries
in Washington have been altered by changes including channelization, dredging,
diking, filling of wetlands and tidal areas, and degraded water quality.
This alteration and/or loss of estuarine habitat by factors such as urbanization,
agriculture, forest land management, and industrial and water resource
development has been extensive. It has been estimated that 39% of the
coastal wetlands and 70% of the Puget Sound emergent wetlands have been
lost. These habitat modifications tend to reduce the overall amount of
habitat, and reduces the general productivity of estuaries (and food production),
which limits overall utility of these areas for sockeye rearing.
and competition for food resources with other fish species in the near
shore environment and open ocean can reduce sockeye survivals and abundance.
A variety of predator species
feed on sockeye salmon throughout their life cycle. Juvenile sockeye are
preyed upon by fish (including other salmonids) and birds in both the
freshwater and marine environments. This type of predation does not normally
threaten the success of sockeye populations unless they are subjected
to unusual aggregations of predators. The release of hatchery salmonids
can cause large aggregations of species that are potential predators,
and in some situations, this practice has generated concerns about the
possibility of negative impacts on the production of each of the salmon
species. Adult sockeye are subject to predation in marine areas by sharks,
lampreys, and marine mammals, and in freshwater by bears and large predatory
Temporal and spacial overlap
of spawning sockeye with other salmon spawners can result in reduced survivals
caused by the loss of eggs due to redd superimposition. Competition for
food with other fish stocks and species in the marine environment has
been shown to influence sockeye survivals. In particular, the abundance
of sockeye salmon originating from different regions and sharing common
marine areas with other sockeye stocks can negatively impact sockeye survival
Instream flows sufficient to
meet the needs of sockeye salmon for migration, spawning, incubation,
and juvenile outmigration are essential for successful production. Man-made
barriers to migration should be removed or made passable wherever possible.
Land use practices must be compatible with the maintenance of quality
instream conditions such as; minimal siltation, stable stream banks, natural
flow regimes, extensive spawning riffles, and stable and diverse stream
beds. Lacustrine and estuarine habitats supporting sockeye should be managed
to maintain or restore good water quality1 and populations
of predator species should not be enhanced either directly or indirectly.
In areas frequented by juvenile sockeye salmon, releases of hatchery salmonids
should be managed to minimize their potential impact as both predators