The ongoing story of the European green crab invasion offers us
scientific, social and even psychological drama, which I would like
to update by mentioning four new developments:
The somewhat mysterious finding of a partially eaten green crab
on the Bellingham waterfront,
A “story map” that spells out much of what we know about
European green crabs in Puget Sound, including maps, photos and
videos.
Information about Harper Estuary in South Kitsap and other
areas where groups of citizen scientists are on the lookout for
green crabs, and
Reports of a new breed of European green crab in Maine that
attacks people and may prove to be more destructive than the green
crabs that have lived in the area for a very long time.
The war against the invasive European green crab continues in
Puget Sound, as this year’s Legislature offers financial support,
while the Puget Sound Crab Team responds to crabs being caught for
the first time in Samish Bay in North Puget Sound and at Kala Point
near Port Townsend.
In other parts of the country where green crabs have become
established, the invaders have destroyed native shoreline habitat,
diminished native species and cost shellfish growers millions of
dollars in damages. See
Environmental Protection Agency report (PDF 1.3 mb).
European green crab trapping
sites in Puget Sound.
Map: Washington Sea Grant
In Puget Sound, it’s hard to know whether the crabs are being
trapped and removed rapidly enough to defeat the invasion, but so
far humans seem to be holding their own, according to Emily Grason,
who manages the Crab Team volunteer trapping effort for Washington
Sea Grant.
“The numbers are still in line with what we saw the past two
years,” Emily told me. “Since the numbers have not exploded, to me
that is quite a victory. In other parts of the world, they have
been known to increase exponentially.”
The largely volunteer Crab Team program is focused on placing
baited traps at 56 sites in Puget Sound, as shown in the first map
on this page. About 220 trained volunteers are involved in that
work, with various federal, state and tribal agencies adding about
40 additional people.
I heard some legitimate questions about how to identify European
green crabs and what to do if you find one. The main thing is to
get a photograph and send it to the Washington Sea Grant Crab Team,
which is leading the war on green crabs. I’m reminded that it is
illegal to possess a green crab without a permit.
Here are some links from the Crab Team website that could be
helpful:
I’m also pleased to see the announcement of a free online
webinar on July 10 to help people identify European green crabs.
The two-hour “First Detector
Training Webinar” is co-sponsored by the Crab Team and
Washington Invasive Species Council. Register ahead of time to get
information about the event.
Nearly 100 invasive European green crabs were trapped along
Dungeness Spit near Sequim this past spring and summer — far more
than anywhere else in Puget Sound since the dangerous invaders
first showed up last year.
European green crabs started
showing up in traps on Dungeness Spit in April.
Photo: Allen Pleus, WDFW
Despite the large number of crabs found in this one location,
green crab experts remain undeterred in their effort to trap as
many of the crabs as they can. And they still believe it is
possible to keep the invasion under control.
“In a lot of ways, this program is functioning much as we had
hoped,” said Emily Grason of Washington Sea Grant, who is
coordinating volunteers who placed hundreds of traps in more than
50 locations throughout Puget Sound. “We look in places where we
think the crabs are most detectable and try to keep the populations
from getting too large, so that they are still possible to
control.”
After the first green crabs were found on Dungeness Spit in
April, the numbers appeared to be tapering off by June, as I
described using a graph in
Water Ways on June 24. The numbers stayed relatively low, with
three caught in July, two in August, three in September and two in
October. But they never stopped coming.
The total so far at Dungeness Spit is 96 crabs, and more can be
expected when trapping resumes next spring. The good news is that
all the crabs caught so far appear to be just one or two years old
— suggesting that they likely arrived as free-floating larvae. That
doesn’t mean the crabs aren’t mating at Dungeness Spit, but the
trapping effort has reduced the population to the point that males
and females are probably having a tough time finding each
other.
Officials with the U.S. Fish and Wildlife Service, which has
taken charge of trapping at Dungeness Spit, will need to decide
whether to attempt a complete eradication of the local green crab
population, according to Allen Pleus, coordinator of Washington
State’s Aquatic Invasive Species Program. That would involve
managing a large number of traps until no more crabs are seen. The
alternative, he said, would be to manage the crab population with
fewer traps and make further decisions down the line.
During one three-day stretch last year, 126 traps were deployed
in areas on and near Dungeness Spit, part of the Dungeness National
Wildlife Refuge managed by the Fish and Wildlife Service.
Even with the most exhaustive trapping program, there is no
guarantee that green crabs won’t be found again, Allen said. The
likely source of the crab larvae is an established population of
green crabs in Sooke Inlet on Vancouver Island, just across the
Strait of Juan de Fuca from Dungeness Spit.
Allen said he is disappointed that crabs continued to be caught
on or near Dungeness Spit — mainly in one small area near the
connected Graveyard Spit. “But I am very impressed with the
dedication of the U.S. Fish and Wildlife Service, which continued
to trap throughout the summer,” he said.
While there is no evidence so far that the invading crabs have
reproduced at Dungeness Spit, it is possible that mating took
place. If so, everyone involved in the green crab effort could face
a whole new group of young crabs next year.
I have to admit that I was worried last spring that funding for
the essential volunteer effort would run out as officials scrambled
to finance the start of trapping season. But the Environmental
Protection Agency agreed to fund the project through next year
under the Marine and Nearshore Grant Program.
Meanwhile, Allen said he is working with Canadian officials to
see what can be done about reducing the population of green crabs
in Sooke Inlet, which is likely to remain a source of the invasive
crabs coming into Washington state. The Canadians have their own
concerns about green crabs, which can severely damage commercial
shellfish operations and disrupt critical eelgrass habitats.
“Sooke Inlet is the only known population established in the
Salish Sea,” Allen said. “We are working with Canada and setting up
meetings this winter to continue our discussions.”
Canadian officials are monitoring for green crabs on their side
of the border, but the effort is much less than in Puget Sound. It
appears that only limited efforts have been made so far to control
the Sooke Inlet population and reduce the amount of invasive crab
larvae heading to other areas in the Salish Sea.
Researchers are still investigating the conditions that allow
green crab larvae to survive long enough to grow into adult crabs.
It appears that larvae move up the coast from California during
warm years and particularly during El Niño periods, Emily told me.
That may explain why the Puget Sound traps began catching so many
crabs the past two summers.
“The signal we are seeing does point to 2015 and ‘16 as being
the first arrivals,” she said. “Our working hypothesis is that warm
years are spreading larvae.”
That could offer renewed hope for the immediate future, since El
Niño is over and we may be going into cooler La Niña conditions
next year.
No new crabs have shown up in the San Juan Islands, where Puget
Sound’s first green crab was discovered last year. But two more
were found about 30 miles away in Padilla Bay, where four crabs
were caught last fall.
New areas with green crabs this year are Lagoon Point on Whidbey
Island, where two crabs were caught, and Sequim Bay, not far from
Dungeness Spit, where one crab was caught.
The latest concern over green crabs is Makah Bay on the outer
coast of Washington near the northwest tip of the Olympic
Peninsula. In August, a beach walker spotted a single green crab on
the Makah Tribe’s reservation and sent a picture to the Puget Sound
Crab Team, which confirmed the finding. Tribal officials launched a
three-day trapping effort last month and caught 34 crabs — 22 males
and 12 females — in 79 traps.
An aggressive trapping effort is being planned by tribal
officials for the coming spring. Interested volunteers should
contact Adrianne Akmajian, marine ecologist for the Makah Tribe, at
marine.ecologist@makah.com
The Makah effort is separate from the Puget Sound Crab Team,
which encourages beach goers to learn to identify green crabs by
looking at photos on its website. Anyone who
believes he or she has found a green crab should leave it in place
but send photographs to the crab team at crabteam@uw.edu
Emily said she is most proud of all the people and organizations
that have come together as partners to quickly locate the invasive
crabs and advance the science around the issue. Such cooperation,
she said, makes the impact of the program much greater than it
would be otherwise.
State biologists are holding out hope that the European green
crab invasion at Dungeness Spit can be contained. We may now be
going through a critical period, which could result in a permanent
infestation or possibly the final throes of the invasion.
Green crabs, an invasive species known to displace native
species and cause economic devastation to shellfish growers, were
first discovered on April 12 in a marshy area on Graveyard Spit,
which juts off from the larger Dungeness Spit in the Strait of Juan
de Fuca.
The total number of green crabs caught in an ongoing intensive
trapping program has reached 76. The weekly numbers have been
declining, as shown in a chart on this page. That could be a good
sign, but biologists are quite reserved in their predictions.
“The numbers are tapering off,” said Allen Pleus, coordinator of
the state’s Aquatic Invasive Species Program, “but in my view the
numbers are still too high. Eradication would take several weeks of
zero. At this point, our main objective is to bring down the
population to a point where spawning would not be successful.”
So far, all of the crabs caught are young and small — about 1 to
2.5 inches across their backs. This means that they have not been
in the area for long, probably arriving on last year’s currents in
the Strait of Juan de Fuca.
Another good sign is that no other crabs have been caught
elsewhere along the Strait, although officials acknowledge that
they would like to deploy more traps to capture any early invaders.
Also, I am happy to report that no new crabs have been captured
this year in Padilla Bay or on San Juan Island, where the state’s
first confirmed green crab invasion took place last year. See
Water Ways, Sept. 24, 2016.
Update: I’ve been informed that one green crab was caught in
April in Padilla Bay where others were caught last year.
The decline in captures at Dungeness Spit may be a sign that
some of the crabs have entered their reproductive phase, a period
when they don’t eat and so are not attracted to the baited traps.
Males and females get together to mate after molting, a phase of
development in which they shed their exoskeletons. The trapping
effort has reduced the crab numbers and made it more difficult for
reproductive males and females to find each other, but each female
can produce hundreds of thousands of eggs — so even one successful
mating could expand the invasion.
This small male crab is one of
the 76 European green crabs caught in traps at Dungeness Spit. //
Photo: Allen Pleus
Because the baited traps may not work at this time, officials
are experimenting with substrate traps, which are pieces of plastic
pipe ranging in size from a half-inch to 2 inches, Allen told me.
Young crabs may seek shelter in the tubes. So far, no crabs have
been captured that way.
Another idea yet to be tried is baiting traps with pheromones,
which are sexual attractants that lure crabs looking for a mate.
Allen said he also would like to experiment with electrical
stimulation, in which an electrical current is discharged in the
muddy substrate to drive crabs out of their burrows. With proper
control, no permanent harm comes to them or other creatures in the
vicinity, Allen said.
When it comes to controlling future crab invasions in Puget
Sound, experts would like to know where the crab larvae are coming
from. The leading suspect is a population of green crabs that
appear to have settled into Sooke Inlet, just west of Victoria on
Vancouver Island in Canada. It is also possible that the larvae
drifted in from coastal waters in British Columbia, Washington or
even Oregon or California. Experts hope that genetic tests of green
crabs from the various locations can be used to identify where the
crabs on Dungeness Spit originated.
Emily Grason of Washington Sea Grant coordinates a group of
volunteers who monitor traps placed throughout Puget Sound with a
goal of stopping the next invasion.
“The presence of green crab in Dungeness Bay, though
unfortunate, offers a unique opportunity to test how effective the
EDRR (Early Detection-Rapid Response) model is for intervening in a
potential green crab invasion,” Emily wrote yesterday in a blog
post on the Crab
Team website.
“Generally speaking, invasive species are rarely noticed in a
new spot until they have already become too abundant to eradicate,”
she said. “Though 76 crabs at Dungeness Spit is more than we would
ever like to see, the population hasn’t yet reached the numbers
that are seen in areas of greatest infestation. And they are, as
far as we know, still confined to a relatively small location….
“Preventing and managing biological invasions is similar to
planning for a wild fire season: The best thing to do is prevent
either invasions or wildfires from taking hold in the first place,
but we know that some will occur despite our best efforts. It’s
difficult to forecast exactly where, when or how severe they will
be when they do pop up, and yet it’s imperative to respond quickly
and aggressively as soon as they are detected.”
Emily added that we are fortunate in this area to have the
tremendous support of volunteers, partners and beachgoers, all
involved in the effort to prevent a permanent invasion of green
crabs. Staff and volunteers at the Dungeness National Wildlife
Refuge have been instrumental in placing and tending the traps
placed in that area.
An invasion of the European green crab, which started last
summer in northern Puget Sound, appears to be continuing this
spring with 16 green crabs caught in traps at one location on
Dungeness Spit near Sequim.
European green crab
Photo: Gregory C. Jensen, UW
The new findings are not entirely unexpected, given that
invasive green crabs have established a viable population in Sooke
Inlet at the southern end of Vancouver Island in Canada. From
there, young crab larvae can move with the currents until they
settle and grow into adult crabs. Last summer and fall, green crabs
were found on San Juan Island and in Padilla Bay.
The big concern now is that a growing population of invasive
crabs could spread quickly to other parts of Puget Sound, causing
damage to commercial shellfish beds and disrupting the Puget Sound
ecosystem.
“It knocks the wind out of your sails for sure,” said Emily
Grason when I asked how she felt about the latest discovery. “You
feel kind of powerless, and you want to get out there and start
doing things.”
Padilla Bay, an extensive inlet east of Anacortes in North Puget
Sound, could become known as an early stronghold of the invasive
European Green crab, a species dreaded for the economic damage it
has brought to other regions of the country.
Trapping sites for crabs (gray
markers) during this week’s rapid assessment in Padilla Bay. Red
markers show locations where three more invasive European green
crabs were found.
Map: Washington Sea Grant
After one young green crab was found in Padilla Bay on Sept. 19
(Water
Ways, Sept. 24), three more crabs were found during an
extensive trapping effort this past week. All four crabs were
captured at different locations in the bay. These four live crabs
followed the finding of a single adult green crab in the San Juan
Islands — the first-ever finding of green crabs anywhere in Puget
Sound. (Water
Ways, Sept. 15).
With these new findings in Padilla Bay, the goal of containing
the crabs to one area has become a greater challenge. Emily Grason,
who coordinates a volunteer crab-surveillance program for
Washington Sea Grant, discusses the difficulty of putting out
enough traps to cover the entire bay. Read her report on the
fist day of trapping:
“Similar to our trip to San Juan Island, we are conducting
extensive trapping in an effort to learn more about whether there
are more green crabs in Padilla Bay. One difference, however, is
scale. Padilla Bay is massive, and it’s hard to know exactly where
to start. On San Juan Island, the muddy habitats where we thought
crabs would do well are well-defined, and relatively limited.
Padilla Bay, on the other hand, is one giant muddy habitat — well,
not all of it, but certainly a huge portion. We could trap for
weeks and still not cover all of the suitable habitat!”
In all, 192 traps were set up at 31 sites, covering about 20
miles of shoreline. The crab team was fortunate to work with the
expert staff at the Padilla Bay National Estuarine Research
Reserve, a group of folks who know the area well and had worked
with shoreline owners to get approval for access.
Three of the four green crabs caught in Padilla Bay were young,
probably washed into the bay during last winter’s warm currents,
Emily said in her wrap-up
report of the effort.
“All of the detections of European green crabs occurred on the
east portion of the bay,” she wrote. “Though the sites varied
somewhat in the type of habitat, all of the crabs were found
relatively high on the shore, in high salt marsh pools, or within a
few meters of the shore.
The first of four European
green crabs found in Padilla Bay.
Photo: Padilla Bay National Estuarine
Reserve
“Padilla Bay has about 20 miles of shoreline, and, at last count
in 2004, there were 143 acres of salt marsh habitat in the bay,”
she continued.”These numbers suggest that there are a lot of places
European green crabs could live in Padilla Bay, and protecting the
bay from this global invader will undoubtedly require a cooperative
effort.”
Yesterday, the response team held a conference call to discuss
what to do next. Team members agreed that no more intensive
trapping would take place this year, Sean McDonald of the
University of Washington told me in an email.
Winter is a tough time to catch crabs. Low tides shift from
daytime hours to nighttime hours, making trapping more difficult.
Meanwhile, crabs tend to lose their appetite during winter months,
so they are less likely to go into the traps to get food, experts
say.
Researchers, shellfish growers and beach walkers are being asked
to stay alert for the green crabs, not only in Padilla Bay but also
in nearby Samish and Fidalgo bays.
The Legislature will need to provide funding to continue the
citizen science volunteer monitoring program, which provided an
early warning that green crabs had invaded Puget Sound. Whether the
crabs will survive and in what numbers is something that demands
more study and perhaps a major eradication effort.
Meanwhile, Washington Department of Fish and Wildlife would like
to expand its overall Aquatic Invasive Species Program with
additional efforts to prevent invaders from coming into Puget
Sound. For information, check out my story on invasive species in
the Encyclopedia
of Puget Sound — specifically the section titled “Biofouling
still mostly unregulated.”
A second European green crab has been found in Puget Sound, this
one in Padilla Bay — about 30 miles southeast of where the first
one was discovered about three weeks ago.
A second European green crab
has been found in Puget Sound, this one in Padilla Bay.
Photo: Padilla Bay National Estuarine Research
Reserve
Green crabs are an invasive species known to devour a variety of
native species and alter habitats where they have become
established. Keeping green crabs out of Puget Sound has been a goal
of state officials for years.
After the first green crab was caught in a volunteer trapping
program three weeks ago, experts mounted an intensive trapping
effort to see if other green crabs were in the area around Westcott
Bay in the San Juan Islands. (Water
Ways, Sept. 3). No live crabs were found, but one cast-off
shell (molt) was discovered nearby (Water
Ways, Sept. 15).
The latest find is a young female crab, 34 millimeters across,
which may have grown from a larva dispersed last winter.
“We were relieved to find very little evidence of a larger
population of invasive European green crab in Westcott Bay,” Emily
Grason of Washington Sea Grant said in a
news release (PDF 371 kb). “But finding an additional crab at a
site more than 30 miles away suggests that ongoing vigilance is
critical across all Puget Sound shorelines. WSG’s Crab Team is
committed to continuing the efforts of volunteer monitoring as
resources allow, but we also rely on beachgoers to keep a watchful
eye out for this invasive species.”
A second rapid-response effort will get underway Monday with
more traps being deployed over a larger area than last time. The
goal is to locate any crabs that may have made a home in the area
and determine where the crabs might be gaining a foothold.
The advice for beachgoers remains the same:
Learn how to how to identify green crab. Check out the
Crab Team webpage at wsg.washington.edu/crabteam or Facebook and
Twitter
@WAGreenCrab.
Take a photo and report sightings to the WSG Crab team at
crabteam@uw.edu.
Shellfish collected in one location should never be released or
“wet stored” in another location unless authorized by WDFW.
Clean, drain and dry recreational gear or other materials after
beach visits.
No European green crabs were caught this week during an
intensive two-day trapping program designed to see if any of the
invasive crabs have gained a foothold in the San Juan Islands.
These are the locations and
number of traps placed in the northern San Juan Islands on Monday.
// Map: Washington Sea Grant
If you recall, a single adult green crab was trapped Aug. 31 by
a team of volunteers in the San Juan Islands. It was the first
green crab ever found in Puget Sound, but experts have been worried
about the crab for years. (See
Water Ways, Sept. 3.) The volunteers are involved in a citizen
science monitoring program to locate green crabs when they first
arrive in Puget Sound and before they become a breeding
population.
The response by professional leaders of the Crab Team was to
place 97 traps in and around the location where the first crab was
found. The effort was started on Monday and repeated on Tuesday.
The maps on this page show the locations and the number of traps
place at site on the two days. Hundreds of native crabs were
trapped and inspected, but no green crabs were found.
These are the locations and
number of traps placed in the northern San Juan Islands on Tuesday.
// Map: Washington Sea Grant
Although no live crabs were found, one molt (cast-off shell)
from a green crab was found by Jeff Adams, a marine ecologist for
Washington Sea Grant who manages the Crab Team of volunteers. The
molt was close to where the live crab was found. The experts have
not determined if the molt came from the first crab or if there
might be other crabs in the area.
The next step is still being planned. It could involve another
intensive trapping effort, perhaps in the spring, as well as
increasing the number of volunteer trapping sites in the San Juan
Islands. The volunteer program takes a hiatus in the winter, when
the crabs are less active, but it will resume in the spring.
The next green crab training program is scheduled for March,
when new and former citizen science volunteers will be taught how
to identify green crabs and conduct an effective trapping effort in
up to 30 locations throughout Puget Sound. To learn more about the
volunteer program, check the Washington Sea Grant webpage
“Get Involved” or sign up for a free email newsletter called
“Crab Team News” (click “Newsletters”).
Emily Grason, Crab Team coordinator for Washington Sea Grant,
was involved in the two-day intensive trapping program. Emily blogs
about the effort on the Crab Team website:
Sean McDonald of Washington Sea
Grant heads out to check on crab traps on Henry Island, not far
from where the first green crab was found in Puget Sound. //
Photo: Emily Grason, WSG
A European green crab, one of the most dreaded invasive species
in the world, has finally arrived in Puget Sound.
Caught in a crab trap on San
Juan Island were these fish, along with the first European green
crab ever found in Puget Sound.
Photo: Craig Staude, courtesy of Washington Sea
Grant
A single adult green crab was caught in a trap deployed on San
Juan Island by a team of volunteers involved in a regionwide effort
to locate the invasive crabs before they become an established
population.
Until now, green crabs have never been found in Puget Sound,
although they have managed to establish breeding populations along
the West Coast — including Willapa Bay and Grays Harbor in
Washington and the western side of Vancouver Island in British
Columbia.
Here’s what I wrote: “Puget Sound has so far avoided an
invasion of European green crabs — at least none have been found —
but the threat could be just around the corner….
“Green crabs are but one of the invasive species threatening
Washington state, but they are getting special attention because of
fears they could seriously affect the economy and ecosystem of
Puget Sound. Besides devouring young native crabs and shellfish,
they compete for food with a variety of species, including fish and
birds.”
Along the beach, careful
observers may find weathered crab molts of all sizes. The green
crab, upper left, can be distinguished by the five points on each
side of the carapace. (Click to enlarge.)
Photo: Jeff Adams, Washington Sea Grant
In Canada, one breeding population has been identified in Sooke
Inlet near the southernmost tip of Vancouver Island. That’s about
40 miles away from Westcott Bay, where Puget Sound’s first green
crab was found on Tuesday.
It is likely that the crab traveled to San Juan Island in its
early free-swimming larval form by drifting with the currents, said
Jeff Adams, a marine ecologist for Washington Sea Grant who manages
the Crab Team of volunteers. This crab likely settled down in
suitable habitat and located enough food to grow into an adult.
Based on the crab’s size, it probably arrived last year, Jeff told
me.
European green crab //
Photo: Gregory Jensen, UW
Finding a green crab in Puget Sound is alarming, Jeff said, but
it is a good sign that the first crab was found by the volunteer
monitors. That suggests that the trapping program is working. If
this first crab turns out to be a single individual without a mate,
then the threat would die out, at least for now.
The concern is that if one crab can survive in Puget Sound, then
others may also be lurking around, increasing the chance of
male-female pairing. The next step is to conduct a more extensive
trapping effort in the area where the first green crab was found,
then branch out to other suitable habitats in the San Juan Islands,
Jeff said. The expanded effort is planned for the week of Sept. 11
and will include a search for molts — the shells left behind when
crabs outgrow their exoskeletons and enter a new stage of
growth.
Green crab
Researchers and others who work with invasive species quickly
recovered from their initial surprise at finding a green crab in
Puget Sound, then got down to business in planning how to survey
for crabs and manage their potential impacts.
Allen Pleus, coordinator of the Aquatic Invasive Species Program
at the Washington Department of Fish and Wildlife, told me several
weeks ago that if green crabs show up in Puget Sound, one idea
would be to conduct an extensive trapping program to eradicate or
at least reduce their population. First, however, the extent of the
infestation must be identified. I expect that more extensive
trapping will be planned next spring and summer to look for
offspring from any successful mating in the San Juan Islands.
This video shows a green crab found in Willapa Bay on the
Washington Coast.
Typically, green crabs are found in marshy areas, which are
habitats extensively used by our native hairy shore crab. But Jeff
tells me that some populations of green crabs seem to be expanding
their habitat into more exposed rocky areas.
With roughly 400 suitable sites for the crabs in Puget Sound,
invasive species experts are calling for everyone who visits a
beach to look for green crabs and their molts. One can learn to
identify green crabs from the
Washington Sea Grant website. The volunteer trapping program is
funded by the Environmental Protection Agency with a grant to Fish
and Wildlife.
A public discussion about green crabs and how people can help
protect Puget Sound from an invasion is scheduled for Sept. 13 at
Friday Harbor Laboratories on San Juan Island. See Crab
Team Public Presentation.
