[env-trinity] Water Deeply: Big Rains Bring Both Good and Bad News for Salmon

[Sari Sommarstrom]

WATER DEEPLY
https://www.newsdeeply.com/water/articles/2017/01/30/big-rains-bring-both-go
od-and-bad-news-for-salmon

Big Rains Bring Both Good and Bad News for Salmon

California's drought has hit fish populations hard. Now that heavy rains
have returned to the state, it would seem to be a boon for fish, such as
salmon, but actually the heavy rainfall has had both positive and negative
impacts.


Written by  <https://www.newsdeeply.com/water/contributor/alastair-bland>
Alastair Bland 

Published ons Jan. 30, 2017

 

 

The five-year-drought could hardly have been worse for some of California's
fish populations. The Sacramento River's winter-run Chinook, for example,
were nearly extinguished by low water supplies and sloppy handling of
reservoir releases during the endangered salmon's spawning season. The delta
smelt, too - a key biological indicator species - is now closer to
extinction than it has ever been. On the Klamath River, potentially deadly
parasites that thrive in low-flowing rivers infected most of the Chinook
born in 2014 and 2015.

After weeks of heavy rains and a mounting snowpack in the Sierra Nevada,
California's drought is easing, and according to the U.S. Drought Monitor,
Northern California is drought-free. That should be good news for fish.

"All this rain is definitely a good thing," says Dave Hillemeier, the
director of the Yurok Tribe's fisheries department. He says fast, gushing
flows could potentially wash out of the river system a species of worm that
serves as a host to the problematic fish-killing parasite Ceratonova shasta,
which has been linked to population declines of Klamath steelhead and
salmon.

"One day of huge flows would make life miserable for these polychaete
worms," Hillemeier says, explaining that rapid currents can not only sweep
away the creatures themselves but also the algae on which they feed.

In the Central Valley, high flows are also a boon to fish, especially when
rivers spill their banks. Research has consistently shown that numbers of
young fish spike in the months following wet winters - probably because they
create valuable, if only ephemeral, floodplain habitat for the fish.

However, too much rain at once can spell trouble for a river and its fish.
High flows can wash away gravel beds containing incubating eggs - what
biologists call "scour." Rapid increases in flow can also bury and suffocate
eggs with fine sediment or even sweep young salmon prematurely out to sea.
These impacts are especially problematic in river valleys that have been
overhauled by human activities such as logging, levees, dams and
development.

"It's not that the salmon aren't able to tolerate droughts and floods," says
Eric Ettlinger, aquatic ecologist for the Marin Municipal Water District.
"It's that their habitat has been so altered that the rivers don't work the
way they should anymore."

For example, Lagunitas Creek and its lower tributaries, which flow off the
highlands of western Marin County, have been lined with bank fortifications
and berms that confine the streams to their main channels. This looks tidy
and effective from a land use perspective, but it makes the fish that live
in the river extremely vulnerable to flooding as well as drought. That's
because water that overflows a river's banks creates slow-moving sprawls of
habitat - perfect places for young fish to take refuge from the raging
currents that may scour out the main channel. Such overflow also creates
groundwater recharge, which feeds into streams and can keep them flowing
through months, or even years, of drought. Eliminating natural flooding
cycles eradicates these ecosystem benefits.

Dams have introduced other challenges for Lagunitas Creek's coho (a member
of the salmon family). The barriers prevent the fish from spawning in the
watershed's high headwaters, where the salmon historically laid and
fertilized their eggs. Such small creeks, Ettlinger explains, are far less
susceptible to the scouring effects of flooding than the lower reaches of
the system, where tributaries merge together and create gushing torrents
during rainy periods.

Today, Lagunitas Creek's coho are barely clinging to existence, and the wet
winters that should be so welcomed can actually have drastic negative
impacts on the population. In the winter of 2005-06, heavy rains coincided
with the egg incubation period of the stream's coho. The number of spawning
adults crashed from roughly 400 to just 50 in the space of two years.
Ettlinger guesses the fish, 600 spawners strong at last count, will take a
similar hit this year.

Ted Sommer, a lead scientist with the California Department of Water
Resources, says 1,800 Chinook salmon spawned last fall in Putah Creek, a
Sacramento tributary with headwaters in Napa County. It was one of the
largest returns in memory.

But Putah Creek, like so many rivers, has been channelized with riverbank
modifications. This, Sommer says, "creates a fire-hose effect as water
shoots straight down the river channel," and he believes many or most of the
incubating salmon eggs have been lost to the heavy flows of December and
January.

However, few examples so clearly show the potential of heavy rains to
devastate rivers as the North Coast's 1964 Christmas floods. That December,
the Eel River - in recent years just a trickle of water - exploded to
one-and-a-half times the average volume of the Mississippi. Towns were swept
away, and redwood trees that had grown for a thousand years were stripped
from the earth.

Erosion was cataclysmic on recently logged mountainsides, says Scott
Greacen, executive director of the group Friends of the Eel River.

"When you take the trees off those slopes, the earth's surface melts," he
says. "When those rains fell, the mountains just came unzipped."

Rocks and sediment buried river sections where fish spawned. In some places,
pools that were 80ft (24m) deep and provided valuable year-round cold water
- essential for salmon - were filled in with rocks and sand.

"The river was structurally altered," Greacen says.

The same rainstorms clogged and buried parts of the Klamath River and its
main tributary, the Trinity. Greacen says a local geologist told him that it
might take 7,000 years for natural processes to erase - and quite literally
wash away - the effects of that rainy winter.

Fishery biologist Jacob Katz, of the group California Trout, has spent years
studying the benefits floodplains provide for fish. His work has been
focused recently on the Sacramento River. He and other scientists attribute
the long-term decline of the Central Valley's wild, self-sustaining salmon
populations in large part to the levees that have disconnected the river
from its adjacent floodplains. Today, those agricultural flatlands flood
only during extreme weather events, whereas they used to be inundated most,
if not all, years.

Katz's research has all but proven that salmon cannot survive without annual
flooding. He acknowledges the impacts that floods can deliver to some
rivers, especially those stripped of the protective wetland and woodland
buffers that soak up runoff and release it slowly and gently into the river.

Overall, however, Katz says the benefits of precipitation far outweigh the
impacts.

"It's years like this one that it's good to be a salmon in the Central
Valley," he says.

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