Our aquatic ecosystems are important
because they are among the most pristine
that remain in North America, for sure
in the contiguous 48 United States.
These aquatic ecosystems support
functionally intact ecosystem processes,
which extend both from what's within the waters
to the terrestrial environment.
Yellowstone's aquatic ecosystems are incredibly diverse.
The one thing, also, I'd say
about Yellowstone's aquatic ecosystems is
that just about every freshwater species
that exist could probably find a place suitable
to live here, which makes it then
also vulnerable to invasion over time
if we're not protecting these places.
There are several subspecies of cutthroat trout,
of which two of 'em still persist in Yellowstone.
That's Yellowstone cutthroat trout
and westslope cutthroat trout.
They're unique because here, in Yellowstone,
they support an ecosystem that includes a lot
of important animals that other people come
to the park to see, like grizzly bears and river otters.
So the native cutthroat trout
of Yellowstone National Park are being threatened
by non-native, introduced fishes
that were brought into the park,
actually intentionally, in the late 1800s and early 1900s.
The lake trout were introduced to
what were fishless Lewis and Shoshone Lakes
in the upper Snake River, but somehow
they made their way to Yellowstone Lake.
The non-native lake trout are highly predatory species,
so the lake trout had a huge impact
on the native cutthroat population
of Yellowstone Lake, and caused a severe decline
in the cutthroat trout.
An example of the level
of the cutthroat trout decline can be seen
as one of the primary spawning streams called Clear Creek.
We have counts of the spawning cutthroat trout
at Clear Creek that date back to the 1940s.
Around 1980, nearly 70,000 fish were counted
ascending Clear Creek to spawn in the spring.
That declined over time, due to the lake trout,
to the point where, in the late 2000s,
we counted only about 600 fish ascending Clear Creek
to spawn that year.
So that's the level of magnitude of change that occurred due
to the lake trout invasion of Yellowstone Lake.
Lake trout do not ascend streams during the spring to spawn.
The spawn, actually, within the lake itself.
So the lake trout are not accessible,
then, to ospreys and bald eagles.
They're not accessible to grizzly bears,
black bears, on spawning streams
in the spring because they're not there.
So if the cutthroat trout were
to disappear, and we were to allow the lake trout
to thrive within the lake, all the animals
that have depended on the cutthroat trout would
also be displaced or gone.
We've been removing over 300,000 lake trout per year.
But now, finally, in 2018,
we were seeing a significant decline
in the numbers of lake trout in the lake,
and the numbers of lake trout that
we're catching by our netting program,
which is a huge signal to us that
this program is really working.
Anglers do play a role at suppressing lake trout
from Yellowstone Lake.
We have a must-kill regulation.
So if an angler does catch one out there,
they're required to keep it, or at least kill
it before they put it back in the lake.
We know that tens of thousands of lake trout are removed
annually by anglers from Yellowstone Lake,
which is a huge benefit to us.
Our goals here are to suppress the Lake Trout
and allow the cutthroat trout to rebound,
and recolonize naturally on their own.
What we're hoping to see, ecologically,
is a return of these animals that depend
on our cutthroat trout as a important source
of food through different times of the year,
especially our grizzly bears and black bears,
which we're already seeing come back
to some of the spawning streams in the spring.
We want to see a further rebound of those animals,
coming back to feed upon spawning cutthroat trout.
One key indicator will be our osprey population
around Yellowstone Lake, because ospreys only eat fish.
And so once the cutthroat declined,
the ospreys then were largely displaced
from the lake ecosystem.
We want to see those ospreys come back
and feed upon the cutthroat trout the way they once did.
One important thing that visitors can do
to prevent the introduction of aquatic invasive species,
is to make sure that anything they bring
into the park is totally clean.
If you're bringing a boat to Yellowstone National Park,
you need to make sure that it's
not carrying any water from any other water body.
So drain your bilge, drain your livewell,
because that water can contain,
essentially, microscopic animals
that could invade Yellowstone Park.
This park is really intact when
it comes to aquatic invasive species,
and so we still have time to prevent the introduction
of anything else that could cause
tremendous ecological harm.
It's essentially the best of what
we have in our country right now.
The majority of this ecosystem remains
naturally intact, naturally functioning,
and we need to keep it that way.
That's the mission of the National Park Service.