ext
OBSERVATIONS ON
ON DUNGENESS
DUNGENESS CRABS
CRABS SUBJECTED
SUBJECTED TO
TO WIND
WIND STRESS
STRESS
OBSERVATIONS
INTRODUCTION
INTRODUCTION
Crab
fishing with
helicopter rather
than aa boat
introduced into
into
Crab fishing
with a
a helicopter
rather than
boat was
was introduced
Oregon
early in
in 1977.
1977. The
The new
new innovation
innovation was
was met
met with
with suspicion
suspicion and
and alarm
by'"'
Oregon early
alarm by
some.
some.
Some
boat crabbers
crabbers and
that the
Some boat
and observers
observers claimed
claimed that
the resource
resource was
was being
being
damaged
because small
sma 11 crabs
bei ng "ra
i ned" across
the wa
ter and
beach,
damaged because
crabs were
were being
"rained"
across the
water
and beach,
that the
the wind
the rotor
harmful, and
that crabs
that
wind blast
blast from
from the
rotor was
was harmful,
and that
crabs returned
returned to
to the
the
were killed.
killed.
water in
in the
the pots
pots were
water
to verify
verify these
these claims.
claims.
to
Subsequent
observations and
Subsequent observations
and experiments
experiments failed
failed
It
It was
was also
also claimed
claimed that
that prolonged
prolonged flight
flight at
at high
high speeds
speeds
would
delayed mortalities
in crabs
crabs that
that were
returned to
to the
the water.
A
would cause
cause delayed
mortalities in
were returned
water. A
done November
November 3-December
1 to
to provide
provide insight
insight into
into that
that claim.
study
study was
was done
3-December 1
claim. The
The
results of
of the
the study
study are
are covered
covered in
in this
this report.
report.
results
METHODS
METHODS
The
crabs for
for the
the study
study were
in Yaquina
because the
the small
The crabs
were caught
caught in
Yaquina Bay
Bay because
small crabs
crabs
desired were
were readily
readily available.
available. Three
Three 6-foot
6-foot diameter
diameter crab
crab pots
pots were
were borrowed
borrowed
desired
from
Bob Mathews
Mathews of
of Coos
Coos Bay.
Bay.
from Mr.
Mr. Bob
Mr. Mathews
offered the
the use
use of
of aa Hiller
Mr.
Mathews also
also offered
Hiller
3-place (conventional
(conventional power)
power) helicopter
pilot to
to set
set and
pull one
pot
3-place
helicopter and
and a
a pilot
and pull
one pot
prior to
the study
could determine
how many
in an
prior
to the
study so
so we
we could
determine how
many crabs
crabs could
could be
be caught
caught in
an
overnight
fishing period.
period.
overnight fishing
Mr. Bob
Bob Jarvis
Jarvis of
of Lake
Lake Oswego
Oswego offered
offered the
the use
use of
of his
his
Mr.
Hughes
helicopter (turbo-jet
(turbo-jet powered)
powered) and
two pilots
pilots to
to conduct
the
Hughes 5-place
5-place helicopter
and two
conduct the
flight test.
flight
test. The
The Hughes
Hughes helicopter
helicopter was
was capable
capable of
of flying
flying at
at the
the speeds
speeds we
we
desired
for the
the test,
test, whereas
whereas the
the Miller
Hiller ship
ship was
was somewhat
somewhat slower.
slower.
desired for
Our
initial plan
plan was
to fly
pots at
Our initial
was to
fly two
two test
test pots
at 100
100 mph
mph for
for four
four minutes.
minutes.
However,
only 80
80 mph
mph could
could be
be attained,
attained, and
and that
that with
with difficulty.
difficulty. As
As aa result,
result,
However, only
both
test pots
pots were
pulled from
immediately flown
flown at
of
both test
were pulled
from the
the water
water and
and immediately
at speeds
speeds of
60-80
one for
for five
five minutes
minutes and
and the
the other
other for
for seven
seven minutes.
minutes.
60-80 mph,
mph, one
Since
fewer
Since fewer
crabs
pot were
than anticipated
the crabs
both pots
pots were
crabs per
per pot
were caught
caught than
anticipated the
crabs from
from both
were
-2-
combined
in the
the holding
holding tanks.
tanks.
combined in
Crabs
a third
third pot
pot were
were used
used as
as aa control.
control.
Crabs from
from a
These
the fishing
site to
to the
the laboratory
laboratory at
These were
were flown
flown from
from the
fishing site
at speeds
speeds up
up to
to 40
40 mph,
mph,
but for
for only
but
only aa few
few seconds.
seconds.
The
control crabs
were out
The control
crabs were
out of
of the
the water
water for
for about
about
one
one minute.
minute.
The
was partly
partly sunny
sunny and
and the
the temperature
temperature 55°
55° FF during
during the
the flight.
flight.
The weather
weather was
The
crabs were
exteriorly completely
completely dry
dry when
landed, and
The test
test crabs
were exteriorly
when landed,
and were
were docile
docile
before handling.
transferred from
from the
the pots
pots to
to the
the holding
tanks in
in
before
handling. They
They were
were transferred
holding tanks
aa tub
tub of
of water
water to
to reduce
reduce fighting.
fighting.
Even with
this precaution
precaution aa few
few legs
legs were
Even
with this
were
lost
the transfer.
transfer.
lost during
during the
The
crabs were
held in
in 4x4
tanks supplied
supplied with
The crabs
were held
4x4 foot
foot fiberglass
fiberglass tanks
with aeration
aeration
and
running sea
sea water
water from
from Vaquina
Yaquina Bay.
Bay.
and running
The hardshell
hardshell and
The
and softshell
softshell crabs
crabs were
were
segregated into
into separate
separate tanks
tanks and
and fed
fed clams
clams twice
twice weekly.
weekly.
segregated
Dead
Dead crabs
crabs were
were
removed
detected, the
the shell
shell width
width measured,
measured, and
and any
any injuries
injuries noted.
noted.
removed when
when detected,
Upon
Upon
termination
termination of
of the
the study
study the
the surviving
surviving crabs
crabs were
were measured
measured and
and shell
shell condition
condition
noted.
noted.
The
study was
was run
run for
for 28
28 days.
days.
The study
RESULTS
RESULTS
Tables
Tables 11 and
and 22 summarize
summarize the
the results
results of
of the
the study.
study.
Three
Three crabs
crabs died
died in
in
each
the mortality
in the
the control
10.3%
each group,
group, but
but the
mortality rate
rate was
was 4.6%
4.6% in
control group
group and
and 10.3%
in
in the
the test
test group.
group.
The shell
shell width
of the
the crabs
crabs that
that died
died was
was 165,
165, 155
155 and
and
The
width of
153
in the
the control
control group
group and
and 155,
155, 142
142 and
and 108
108 mm
mm in
in the
the test
test group.
group.
153 mm
mm in
of the
six mortalities
mortalities occurred
first two
two weeks.
weeks.
of
the six
occurred within
within the
the first
Five
Five
Mortalities
were
Mortalities were
equal
hardshell and
and softshell
softshell crabs.
crabs. A
chi-square test
test corrected
corrected for
for
A chi-square
equal for
for hardshell
showed no
no significant
significant difference
difference in
in mortality
mortality rate
rate between
between the
the
continuity showed
continuity
and those
those in
in the
the control
control group.
group.
experimental
group of
of crabs
crabs and
experimental group
One complication
interfered with
with the
the control
c,ontrol group.
group.
One
complication interfered
On
15 of
the study
On day
day 15
of the
study
the
the
in the
the standpipe
standpipe in
the tank
tank of
of hardshell
hardshell crabs
crabs was
was dislodged
dislodged allm1ing
allowing all
all the
-3-
- 3-
water to
to drain
drain out.
out.
all
all appeared
appeared dead.
dead.
The
out of
for at
least 24
24 hours
hours and
The crabs
crabs were
were out
of water
water for
at least
and
However,
six of
of the
the crabs
crabs reacted
reacted slightly
slightly when
when stimulated.
stimulated.
However, six
These
were returned
returned to
to the
the refilled
refilled tank,
tank, and
and survived
survived to
to the
the end
end of
of the
the study.
study.
These were
We
that all
the crabs
in this
have survived
the water
We assume
assume that
all of
of the
crabs in
this tank
tank would
would have
survived had
had the
water
not drained
drained out.
out.
not
Table
1. Summary
Table 1.
Summary of
of Wind
Wind Stress
Stress Test
Test
Control
Hardshell Softshell
No. Crabs
Crabs
No.
Test
Hardshell Softshe11
17
17
48
48
17
17
12
12
121-176
121-176
90-169
90-169
131-162
131-162
121-165
121-165
Mean Size
(mm)
Mean
Size (mm)
150.6
150.6
135.1
135.1
146.0
146.0
140.7
140.7
No. mortal
i ties
No.
mortalities
1
1
22
2
2
1
%
% mortality
mortality
5.9
5.9
4.2
4.2
Si
ze Range
Range (mm)
(mm)
Size
(%)
Total mortality
mortal i ty (%)
Total
1
11.8
11.8
4.6
4.6
8.3
8.3
10.3
10.3
Table
2. Timing
of Mortalities
Table 2.
in Wind
Wind Stress
Stress Test
Test
Timing of
Mortalities in
Week
Week
Control
tàntrol
Hardshell
Softshell
Softshell
l-lardshell
Hardshell
Hirdshell
Test
Test
Softshell
Sot
tshell
11
11
00
1
1
00
22
0
0
22
1
1
0
0
33
00
00
0
0
0
44
0
0
00
0
0
1
1
One
the pots
the control
into the
the ground
One of
of the
pots originally
originally slated
slated for
for the
control crashed
crashed into
ground
in transit
transit to
to the
the landing
landing site.
site.
in
The pot
pot contained
contained nine
nine crabs,
crabs, but
but was
was not
not
The
included
in the
the study.
study. However,
However, after
after 25
25 minutes
minutes out
out of
of the
the water
water we
we decided
decided
included in
hold and
observe the
the crabs
crabs anyway.
anyway.
to hold
to
and observe
One
very soft
soft crab
crab was
was killed
killed on
on impact,
impact,
One very
-4-4-
but only
only one
one other
other died
died during
during the
the study
study period.
period.
but
The
that was
The single
single pot
pot that
was fished
fished overnight
overnight for
for 18
18 hours
hours prior
prior to
to the
the study
study
31 crabs;
crabs; 15
15 hardshell
hardshell and
and 16
16 softshell.
softshe11.
contained 31
contained
crabs had
had died
died after
after 31
31 days.
days.
crabs
Only
one of
of the
the softshell
softshe11
Only one
None
the hardshell
hardshell crabs
crabs died.
died.
None of
of the
DISCUSSION
DISCUSSION
The results
results of
of this
this study
study are
are not
not entirely
entirely conslusive.
conslusive.
The
The
close mortality
mortality
The close
rates observed
observed suggests
suggests that
repetitive tests
tests are
are necessary
necessary to
to better
better define
define
rates
that repetitive
significant difference
exists between
between crabs
crabs that
that are
flown
whether
or not
not aa significant
whether or
difference exists
are flown
and not
not flown.
flown.
and
Part
the problem
lies in
in the
it is
is difficult
Part of
of the
problem lies
the fact
fact that
that it
difficult to
to
hold live
live crabs
crabs in
in aa confined
confined space
space for
for aa prolonged
prolonged period.
period.
hold
Cannibalism,
Cannibalism,
fighting,
are a
can interand overcrowding
overcrowding are
a few
few of
of the
the factors
factors that
that can
interfighting, starvation,
starvation, and
fere
with this
this type
type of
of study.
study.
fere with
However,
two points
points stand
stand out.
out.
However, two
First, there
there will
will probably
probably be
be small
small
First,
among crabs
crabs that
that are
are carefully
carefully handled
handled because
because of
of their
their fighting,
fighting,
mortalities among
mortalities
and second,
mortalities in
crabs were
were low
wind
and
second, the
the mortalities
in the
the test
test crabs
low indicating
indicating that
that wind
stress
under the
the conditions
conditions experienced
experienced is
is not
not overtly
overtly harmful.
harmful.
stress under
According to
to the
the pilot
pilot who
who flew
flew the
the helicopter
helicopter in
in the
the study,
study, flying
flying at
at
According
80
pot trailing
trailing about
100 feet
behind and
below the
the craft
is
80 mph
mph with
with aa crab
crab pot
about 100
feet behind
and below
craft is
not only
only difficult
difficult but
but dangerous
dangerous to
to the
the flight
flight stability
stability of
of the
the helicopter.
helicopter.
not
It is
is also
proportionately more
more expensive
expensive to
to fly
fly at
at 80
80 mph
mph than
than 40-50
40-50 mph.
mph.
It
also proportionately
The
time and
speed for
for this
this study
study were
outside the
the limits
limits that
that
The flight
flight time
and speed
were well
well outside
crabs
will actually
be flown
flown in
in the
the fishery.
fishery.
crabs will
actually be
Lesser
lesser flight
flight time
time and
and speeds
speeds
stress on
on the
the crabs
crabs and
and chance
chance for
for mortalities.
mortalities.
should
also lessen
lessen the
the stress
should also
One
One factor
factor that
that has
has not
not been
been observed
observed is
is the
the effect
effect of
of freezing
freezing or
or near
near
on flown
flown crabs.
crabs.
freezing
temperatures on
freezing temperatures
those
those conditions
conditions are
are encountered.
encountered.
Observations
made when
when
Observations on
on this
this will
will be
be made
-5-5-
The
problem of
The problem
of delayed
delayed mortalities
mortalities from
from wind
wind or
or temperature
temperature stress
stress on
on
flown
if the
the method
flown crabs
crabs could
could be
be academic
academic if
method of
of fishing
fishing follows
follows the
the practice
practice
the boat
boat fishery.
fishery.
of
of the
being
pulled.
being pulled.
Most
pots are
Most crab
crab pots
are fished
fished for
for two
two or
or more
more days
days before
before
The pots
pots are
are baited
baited with
with an
an amount
amount of
of bait
bait that
that will
attract
The
will attract
crab
for about
about one
one day.
day.
crab for
Few crabs
crabs will
enter the
the pot
the second
Few
will enter
pot the
second day
day and
and most
most
of
the small
small crabs
crabs will
will probably
probably escape
escape through
through the
the escape
escape ports
ports by
by then.
then.
of the
Few
small crabs
are retained
retained in
in aa pot
pot fished
fished for
for two
two or
or more
more days.
days.
Few small
crabs are
ACKNOHLEDGMENTS
AC KNOWLEDGMENTS
II wish
wish to
to thank
thank Messrs.
Messrs. Bob
Bob Jarvis
Jarvis and
and Bob
Bob Mathews
Mathews for
for providing
providing their
their
helicopters for
this study
study and
to Harry
Harry Diack
Diack, Frank
Frank Lang,
Lang, and
and Gary
Gary aarkor,
Barker,
helicopters
for this
and to
pilots, whose
close cooperation
cooperation helped
helped get
get this
this study
study off
off the
the ground.
ground.
pilots,
whose close
" &
~ 1~l'Irll'(,
Oregon
F!sn
(jl WUfflife
"liU'iil:J
Oregon Dept.
Dept. of
of Fish
Marine
Region
Madne Region
'lne
<"';pn~o
D'I\I~
I Science
,Jl,.J""J
'_......l
Marine
Drive
Mar
Newport, Oregon
Oregon 97365
973'S5
Newport,
Ii_';