4
T he C olumbia P ress
July 19, 2019
Crabs: Crustacians
travel far for food
Continued from Page 1
with them the tags that cost $300 each.
Crabbers usually target sandy areas
with their pots because they’re less like-
ly to get tangled on the sea floor.
“There just isn’t a lot of food down
there,” said Henkel, who works out of
OSU’s Hatfield Marine Science Center
in Newport. “There’s usually only very
small worms and clams, yet there’s an
enormous crab harvest each year and
most of that is from sandy-bottomed
regions.”
Henkel tagged an additional 20 crabs
and dropped them into the water near
Cape Falcon, which has rockier habitat
and is about 10 miles south of Cannon
Beach. Only four crabs left the region
right away; the other 16 stayed an aver-
age of 25 days. One stayed for 117 days.
“Even though it’s a small sample size,
it’s clear that habitat can influence crab
movement,” Henkel said. “The crabs
in the rocky areas had more to eat,
but they often also have mossy bellies,
which may not be as desirable commer-
cially. Commercial crabbers like to tar-
get migrating crabs in sandy areas that
tend to have smooth bellies.”
Henkel’s theory is that Dungeness
crabs may travel far and wide in search
of food, and when they find it, they’ll
stay put.
“We heard from a fisherman who
caught one of our tagged crabs in 70 me-
ters of water near Astoria Canyon, who
then let the crab go,” Henkel said. “A
few days later, another crabber caught
the same crab in Grays Harbor, Wash.”
Studies by Henkel and others have
shown that Dungeness crabs will
range an average of 11.5 miles, and
some extend that range to more than
50 miles.
While listening for crabs, Henkel and
her colleagues picked up other signals
from the transmitters. When they con-
tacted other researchers, they learned
that 35 of the acoustic “pings” came
from green sturgeon that had been
tagged for other studies.
Seven additional “pings” came from
great white sharks near Cape Falcon.
“The great white sharks were tagged
in Northern California and we detected
them – up here in December and Janu-
ary,” Henkel said. “They were very close
to shore, which is interesting. In the
three years we had acoustic receivers
at a site about seven miles off the coast
near Newport, we never detected a sin-
gle shark.”