DISCUSSION
ON TUE
THE USE
USE DISCUSSION ON
OF
PORTS IN
IN OF ESCAPE
ESCAPE PORTS
CRAB TRAPS
TRAPS CRAB
"
by by
Nelson
E. Stewart
Nelson E.
Stewart INTRODUCTION INTRODUCTION
One of
objectives of
of the
State/Federal Dungeness
Crab
One
of the
the initial
initial objectives
the State/Federal
Dungeness Crab
Management
by certain
Management Program
Program is
is to
to evaluate
evaluate crab
crab mortality
mortality caused
caused by
certain fishery
fishery
practices and
recommend changes
in existing
regulations
practices
and to
to develop
develop methods
methods or
or recommend
changes in
existing regulations
to reduce
or eliminate
eliminate that
that mortality.
mortality.
to
reduce or
One
area of
of major
concern is
is reducing
reducing
One area
major concern
caused by
by sorting
sorting and
and discarding
discarding female,
female, sublegal
sub1ega1 male,
male, and
and softshell
softshell
mortality caused
mortality
crabs
from the
the catch.
catch.
crabs from
Escape ports
ports in
in crab
traps provide
provide aa means
by which
Escape
crab traps
means by
which smaller
smaller crabs
crabs can
can
escape.
Reasons for
for requiring
requiring escape
escape ports
ports include:
include:
escape. Reasons
(1)
to
(1) handling
handling mortality
mortality to
sub1ega1
(2) injury
injury to
sublegal male
male and
and female
female crabs
crabs is
is reduced;
reduced; (2)
to small
small crabs
crabs resulting
resulting
from
(3) loss
is reduced;
reduced; (4)
(4) if
if traps
traps
from fighting
fighting is
is reduced;
reduced; (3)
loss from
from cannibalism
cannibalism is
are
to escape;
(5) they
they benefit
benefit
are lost
lost the
the sublegal
sublegal crabs
crabs have
have an
an opportunity
opportunity to
escape; and
and (5)
fisher~men
legal-sized crabs
reducing the
the amount
fishermen by
by retaining
retaining the
the legal-sized
crabs and
and reducing
amount of
of sorting
sorting
needed
to remove
remove the
the sublegal
sublegal crabs
crabs from
from their
their catch.
catch.
needed to
At the
the present
present time
time virtually
virtually all
all crab
crab traps
traps are
are provided
provided with
with at
at least
least
At
one
escape port.
port.
one escape
However,
is that
that there
there is
is no
no uniformity
uniformity as
However, a
a major
major problem
problem is
as
to
of the
the escape
escape opening.
opening.
to size
size of
The
purpose of
report is
is to
to summarize
sUITIllarize and
and evaluate
the available
available
The purpose
of this
this report
evaluate the
information regarding
ports in
in use
use in
in the
the coastal
information
regarding the
the size
size of
of escape
escape ports
coastal crab
crab
~ inch
inch minimum
minimum size
size limit.
limit.
fishery in
in relation
relation to
to the
the present
present 6¼
fishery
-2-2­
REGULATIONS ON
ESCAPE PORTS
PORTS
REGULATIONS
ON THE
THE USE
USE OF
OF ESCAPE
Washington and
and Oregon
Oregon have
have no
no regulations
regulations requiring
requiring escape
escape ports.
ports.
Washington
California law
law requires
requires that
that north
north of
of Point
Point Conception
Conception each
each crab
crab trap
trap shall
shall
California
have
have at
at least
least two
two rigid
rigid circular
circular openings
openings of
of not
not less
less than
than four
four inches
inches inside
inside
on the
the top
top or
or side
side of
of the
the trap.
trap.
diameter
located on
diameter located
If side
openings are
are used,
used,
If
side openings
at least
least one
least one-half
at
one of
of them
them shall
shall be
be located
located so
so that
that at
at least
one-half of
of the
the opening
opening
is
(Edgerton, 1971).
1971).
is in
in the
the upper
upper half
half of
of the
the trap
trap (Edgerton,
SIZE OF
ESCAPE PORTS
PORTS IN
IN USE
USE IN
IN THE
THE COASTAL
COASTAL FISHERY
FISHERY
SIZE
OF ESCAPE
Washington
Washington
In December
December 1973,
1973, the
In
the Washington
Washington Department
Department of
of Fisheries
Fisheries collected
collected data
data
on
the size
escape ports
ports in
in crab
crab traps
traps employed
employed in
in the
the Washington
Washington coastal
coastal
on the
size of
of escape
crab
(Anonymous, 1974).
1974). A
total of
442 rings
rings in
in traps
traps belonging
belonging to
to 41
41
crab fishery
fishery (Anonymous,
A total
of 442
fishermen
were measured.
measured. The
ring arrangements
arrangements encountered
encountered were
were aa single
single ring,
ring,
fishermen were
The ring
two rings
rings on
on opposite
sides of
of the
the pot,
pot, two
two rings
rings adjacent
adjacent to
to one
one frame
frame upright,
upright,
two
opposite sides
and
half-rings in
in frame
frame corners.
corners.
and half-rings
Escape ring
ring inside
diameters ranged
ranged from
from 3.4
3.4
Escape
inside diameters
to
inches.
to 4.6
4.6 inches
Inches with
with an
an average
average of
of 4.23
423 inches.
close
to
close to
The majority
of the
the rings
rings were
The
majority of
were
~ inches
inches (82
(82 percent
percent of
of the
the rings
rings were
were from
from 4.2
4.2 to
to 4.3
4.3 inches).
inches).
4¼
Oregon
Oregon
There
the size
ports in
in
There is
is no
no 'recent
recent information
information available
available on
on the
size of
of escape
escape ports
use in
in Oregon.
Oregon.
use
However, the
the results
results of
of various
various interviews
interviews conducted
conducted by
by Fish
Fish
However,
Commission
Coninissionbiologists
biologists indicate
indicate that
that the
the majority
majority of
of Oregon
Oregon fishermen
fishermen use
use at
at
least
least
~
inch escape
escape ports.
ports.
4¼ inch
California
California
The
size of
in use
in California
vary from
from about
about 3.9
3.9 to
to 4.6
4.6
The size
of escape
escape rings
rings in
use in
California vary
inches.
However, in
in the
the San
Francisco area
area the
the majority
of escape
escape rings
rings are
are
San Francisco
majority of
inches. However,
inches.
from about
about 4.1
4.1 to
to 4.3
4.3 inches.
they range
range from
4
and In
in the
the Bodega
Bodega Bay
Bay area
area they
4 inches
inches and
,
1
I
I
I
I
I
~
-3-3­
STUDIES
STUDI ES
Length-Hidth Measurements
/'~easurements
Length-Width
The
legal measurement
measurement of
of Dungeness
Dungeness crab
crab is
is the
the carapace
carapace width.
width. This
is
The legal
This is
the
the straight-line
straight-line distance
distance measured
measured across
across the
the carapace
carapace directly
directly in
in front
front of
of
the
tenth anterolateral
anterolateral spines.
spines.
the tenth
Although crab
crab lengths
lengths are
are not
not normally
normally measured,
measured,
Although
they
they are
are the
the best
best measurement
measurement to
to use
use for
for determining
determining the
the proper
proper size
size of
of escape
escape
ports.
ports.
Crabs
they are
Crabs normally
normally move
move about
about laterally,
laterally, although
although they
are capable
capable of
of moving
moving
forward
and backward
backward (Jow,
(Jow, 1961).
1961). The
smallest opening
through ''''hich
forward and
The smallest
opening through
which a
a crab
crab
can crawl
crawl is
is about
about equal
equal to
to his
his length,
length, which
which is
is the
the smallest
smallest dimension.
dimension.
can
Therefore,
to determine
the size
size of
ports the
the relationship
relationship between
between
Therefore, to
determine the
of the
the escape
escape ports
carapace width
and length
length is
is needed.
needed.
carapace
width and
California biologists
biologists collected
collected length-width
length-width data
from 1,556
1,556 male
and 373
California
data from
male and
373
female crabs
crabs taken
taken in
in the
the San
San Francisco
Francisco area
area in
in 1954-55
1954-55 (Figure
(Figure 1)1".
1)11.
female
Jow
(1961)
Jow (1961)
gives data
data from
from measurements
measurements on
on 268
258 male
male and
and 63
63 female
female crabs
crabs (Figure
(Figure 2).
2).
gives
Oregon
Oregon
biologists
length-width data
data from
from 1,000
1,000 male
male crabs
crabs in
in 1967
1967 (Figure
(Figure 3).
3).
biologists collected
collected length-width
In
In each
each case
case the
the length-width
length-width relationship
relationship shows
shows that
that aa legal
legal male
male crab
crab of
of
~
6¼
inches in
in width
width has
inches
has aa length
length very
very close
close to
to 44~ inches.
inches.
Escape Opening
Opening Experiments
Experiments
Escape
Jow (1961)
(1961) presents
presents data
data from
from several
several escape
escape opening
opening experiments
experiments done
done in
in
Jow
between 1955
1955 and
and 1959.
1959.
California between
California
Following is
is aa suninary
summary of
of the
the
Following
of results
results of
more
pertinent experiments.
experiments.
more pertinent
Comparison
of Traps
with NoOpeninQs,
Escape Openings,
Two 4-Inch
Escape
Ports,oror Two
Two
?5?_T.with
No Escape
Two 4-Inch
Escape
Ports,
41-Inch Escape Ports
The fishing
fishing qualities
qualities of
the three
three types
types of
of traps
traps were
were tested
tested at
at Bodega
Bodega Bay
Bay
The
of the
in
fathoms of
of water.
water.
in seven
seven fathoms
11J Eight
sets were
were made
made at
at five
five different
different fishing
Eight sets
fishing
A length-width
length-width relationship
relationship was
also determined
determined for
for crabs
crabs collected
collected from
from
A
was also
the Eureka
Eureka area
in 1956
1956 which
in close
the
area in
which is
is in
close agreement
agreement with
with that
that determined
determined for
for
However,
that
data
is
not
included
here
crabs
from
the
San
Francisco
area.
However,
that
data
is
not
included
here
crabs from the San Francisco area
because it
it Is
is not
not known
known how
how many
many crabs
crabs were
were measured.
measured.
because
-4­
stations
each type
type of
of gear.
gear. 'The
traps were
pulled and
and emptied
emptied every
stations with
with each
The traps
were pulled
every
two days.
days.
two
No significant
significant difference
difference was
was found
found in
in the
the legal
legal male
male catch.
catch.
No
The average
average
The
catch
catch of
of legal
legal males
males per
per trap
trap for
for the
the three
three types
types of
of gear
gear ranged
ranged from
from 1.1
1.1 to
to 1.4.
14.
However, the
greater in
in those
those traps
traps
However,
the mean
mean size
size of
of malE::
niak ,crabs
crabs was
was significantly
sinificantl,Ygreater
having
having
4¼-inch
~-inch escape
escape ports.
ports.
The traps
traps with
with 4¼-inch
~-inch ports
ports were
were also
also the
the most
The
most
efficient
(sublegal males
plus females)
females) to
to
efficient in
in allowing
allowing non-marketable
non-marketable crabs
crabs (sublegal
males plus
escape.
escape. Traps
Traps with
with
~-inch ports
ports took
took on
on the
the average
average four
four non-marketable
non-marketable crabs
crabs
4¼-inch
every legal
legal male
male while
traps with
with 4-inch
4-inch ports
ports and
and those
those without
without escape
escape
for every
for
while traps
openings took
took 88 and
and 17,
17~ respectively.
respectively.
openings
Comparison of
of Traps
with One
One 4-Inch,
4-Inch, One
One 4¼-Inch,
~-Inch, or
or One
One 4½-Inch
f)-Inch Escape
Escape Port
Port
Comparison
Traps with
Equal numbers
traps with
the three
three escape
escape port
port sizes
sizes were
set at
at 10
10
Equal
numbers of
of traps
with the
were set
stations in
in productive
productive fishing
fishing areas
areas off
off Crescent
Crescent City,
City, Eureka,
Eureka, Bodega
Bodega Bay,
Bay, and
and
stations
San
Francisco. Traps
Traps were
were pulled
pulled and
and emptied
emptied every
every two
two days.
days.
San Francisco.
No significant
significant difference
difference was
was found
found in
in the
the numbers
numbers of
of legal
legal males
males caught.
caught.
No
The average
catch of
legal males
males per
per trap
trap for
for the
the three
three types
types of
of gear
gear ranged
ranged
The
average catch
of legal
from 2.2
with a
a
from
2.2 to
to 2.5.
2.5. Traps
Traps with
4- or
or
with
a 4with a
~-inch port.
port.
4¼-inch
4½-inch port
port caught
caught larger
larger male
male crabs
crabs than'did'traps
than didtraps
~-inch
Significant
differences existed
existed in
in the
the numbers
numbers of
of
Significant differences
female and
and sublegal
sublegal males
males the
the different
different traps
traps caught.
caught.
female
Traps
with aa
Traps with
~-inch
4½-inch
port
legal male
traps
port caught
caught only
only two
two non-marketable
non-marketable crabs
crabs for
for every
every legal
male while
while the
the traps
with
4-inch and
and
with 4-inch
~-inch ports
ports caught
caught five
five and
and six
six crabs,
crabs, respectively.
respectively.
4¼-inch
Comparison of Traps with One 4-Inch.
4-Inch, T\,/o
4-Inch, Two
Two 4k-Inch.
tPi-Inch, ,or
Two 4½-Inch
41a-Inch
Two 4-Inch,
or Two
Escape Ports
Eight
with each
each type
type of
of trap
trap at
at seven
seven stations
stations off
off central
central
Eight sets
sets were
were made
made with
California.
were pulled
pulled and
and emptied
emptied every
every two
two days.
days.
Traps were
California. Traps
The legal
legal male
catch did
did not
not differ
differ significantly
significantly between
between the
the four
four types
types
The
male catch
of traps
traps fished.
fished.
of
The
average catch
The average
catch of
of legal
legal males
males per
per trap
trap ranged
ranged from
from 1.3
1.3
-5­
to
to 1.8.
1.8.
The mean
size of
of male
male crabs
crabs increased
increased with
with escape
escape port
port size.
size.
The
mean size
The
The
numbers of
by the
the different
types of
numbers
of female
female and
and sublega1
sublegal males
males caught
caught by
different types
of traps
traps
differed
considerably. Traps
two
differed considerably.
Traps with
with two
crab
every legal
1egal male.
male.
crab for
for every
~-inch ports
ports caught
caught one
one non-marketable
non-marketable
4½-inch
Traps with
ports caught
caught two
two non-marketable
non-marketable
Traps
with two
two ~-inch
4-inch ports
crabs for
legal male,
traps with
4-inch ports
ports caught
crabs
for every
every legal
male, while
while traps
with 4-inch
caught four
four to
to six
six
non-marketable crabs.
crabs.
non-marketable
DISCUSSION AND
AND CONCLUSIONS
CONCLUSIONS
DISCUSSION
At
the present
present time
time most
used in
in the
the Dungeness
At the
most traps
traps used
Dungeness crab
crab fishery
fishery have
have at
at
least
port for
the purpose
purpose of
of allowing
allowing small
small crabs
crabs to
to escape.
escape. The
The
least one
one escape
escape port
for the
problem is
is that
that there
there is
in the
the size
problem
is considerable
considerable variation
variation in
size of
of escape
escape ports
ports
used
it is
is permissible
permissible to
to fish
ports in
used and
and it
fish traps
traps without
without escape
escape ports
in Washington
Washington and
and
Oregon.
California requires
requires that
that crab
crab traps
traps have
have at
at least
least two
two escape
ports of
Oregon. California
escape ports
of
than four
four inches
inches inside
inside diameter.
diameter.
not
less than
not less
However,
this size
size of
of port
port does
does
However, this
not appear
large enough
not
appear to
to be
be large
enough to
to allow
allow adequate
adequate escapement
escapement of
of sub1egal
sublegal males
males
and
female crabs.
crabs.
and female
Length-width
than 2,800
2,800 male
that aa crab
Length-width measurements
measurements from
from more
more than
male crabs
crabs show
show that
crab
in width
length close
the smallest
smallest opening
opening
of
of ~
6¼ inches
inches in
width has
has a
a length
close to
to 4~
4 inches.
inches. Since
Since the
8
through
to his
his length,
length, it
it appears
through which
which a
a crab
crab can
can crawl
crawl is
is about
about equal
equal to
appears that
that the
the
optimum
ports with
to the
the present
present
optimum size
size of
of escape
escape ports
with respect
respect to
minimum size
6~-inch
6¼-inch minimum size
be 44: inches.
inches.
limit should
limit
should be
Escape
reported by
by Jaw
(1961) indicate
indicate that
that traps
traps with
Escape opening
opening studies
studies reported
Jow (1961)
with
escape
ports of
escape ports
of 4,
4,
~,
in diameter
4¼, and
and ~
4½ inches
inches in
diameter will
will catch
catch approximately
approximately the
the
same
number of
of legal
legal crabs.
crabs.
same number
However, the
the larger
larger the
the escape
escape openings
openings the
the more
However,
more
efficient
the traps
In actual
actual
efficient the
traps are
are for
for releasing
releasing sublegal
sublegal male
male and
and female
female crabs.
crabs. In
3
inches,
legal crabs
through an
port of
fishing
fishing operations
operations some
some legal
crabs may
may escape
escape through
an escape
escape port
of 48
4 inches,
but
loss would
potential savings
but it
it appears
appears the
the loss
would be
be minimal
minimal and
and the
the potential
savings of
of sublegal
sublegal
male
and female
female crabs
crabs could
could be
be much
much greater.
greater.
male and
-6­
Crabs reportedly
reportedly often
often get
get caught
caught in
in escape
escape ports
ports while
while trying
trying to
to get
get
Crabs
out
of the
the trap.
trap.
out of
each trap
trap should
should have
have at
at least
least two
two escape
escape ports.
ports.
Therefore,
Therefore, each
The
ports should
should be
located in
in the
the upper
upper half
half of
of the
the trap
trap so
so that
that they
they
The escape
escape ports
be located
can
still function
function if
if the
the trap
trap becomes
becomes partially
partially sanded
sanded in.
in.
can still
RE
COI4r~ENDAT
OATII ON
RECOMMEN
ON
Because of
the desirability
of providing
providing protection
protection to
to sublegal
sublegal male
and
Because
of the
desirability of
male and
female
crabs, it
it is
is reconinended
recommended that
female crabs,
that all
all Dungeness
Dungeness crab
crab traps
traps be
be required
required to
to
have aa minimum
two circular
ports of
of at
at least
least 44~ inches
inches inside
inside diameter
diameter
have
minimum of
of two
circular escape
escape ports
.~::-~'-~"--'-"-"-
located
top or
side of
of the
the trap.
trap.
located on
on the
the top
or side
If escape
ports are
are placed
placed on
on the
the side
side
If
escape ports
trap, they
they should
should be
be located
located in
in the
the upper
upper half
half of
of the
the trap.
trap.
of
the trap,
of the
It
is also
also
It is
recommended that
that aa period
period of
least 55 years
be allowed
recommended
of at
at least
years be
allowed for
for altering
altering crab
crab
conform with
with this
this regulation.
regulation.
traps to
to conform
traps
LITERATURE
CITED
LITERATURE CITED
Anonymous. 1974.
Escape
in use
pots in
in the
the Washington
Escape rings
rings in
use on
on Dungeness
Dungeness crab
crab pots
Washington
1974.
Anonymous.
coastal
fishery. Wash.
Dept. Fish,
Fish. Prepared
Prepared Rept.
Rept. 33 p.
p.
Wash. Dept.
coastal fishery.
Edgerton,
L.F. (Compiler).
(Compiler). 1971.
State
California Department
Department of
of Fish
Fish and
1971.
State of
of California
and
Edgerton, L.F.
Game,
Fish and
and Game
Game Code.
Code. 47th
Ed.
Game, Fish
47th Ed.
Jow,
T. 1961.
Crab trap
trap escape-opening
escape-opening studies.
studies.
Crab
Jow, T.
1961.
No.5,
110. 5, pp.
pp. 49-72.
49-72.
Pac.
Fish. Comm.
Comm. Bull.
Bull.
Pac. Mar.
Mar. Fish.
Prepared
Program, Policy
Policy
Prepared for
for the
the State/Federal
State/Federal Dungeness
Dungeness Crab
Crab Management
Management Program,
Committee Meeting,
Meeting, April
April 1974.
1974.
Committee
130
130
.
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.
120 , 4-3/8
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140
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160
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180
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WIDTH
NILLIMEThRS
relationship of
of male
male and
and female
fe~ale Dungeness
Dungeness crabs.
crabs. Regression lines based
based
Lengthwidth relationship
Figure
1. , Length-width
Figure 1.
on
neasurementa of
of 1~556
1556 male
Francisco area
on measurements
male and
and 373
373 female
female crabs
crabs taken
taken in the San Francisco
area in
1954·55.
D!ta compilid
compilod by
by Walt
Walt Dahistrorn,
Dahlstrom, California
Fish and
and Game.
Game.
1954-55. . flta
California Oepurtment
Department Fish
120
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SHOULOER-WIOTH MILLIMETERS
SHOULER-WIOTkMILUMTER$
"
Figure
Figure 2.
2.
The lergth
leqgth '$dth
width relationship
relationship of
of male
male and
and female
f~lale market
market crabs.
crabs. Regression
Regression lines
lines
The
derived from
from measurements
of 258
258 male
male 'and
63 female
fenlale crabs
crabs taken
taken from
from central
central California
California
derived
measurements of
and 63
waters during
during 1958.
1958. (From
(From Jow,
Jow, 1961)
1961)
waters
"
, I
"
Shell
width in
in inch
inches
Sh11 'iidth
3.9'
4.3
39 4.3
,*
4.7
4.7
5.5
55
5.1.
5.1
150
15
6.7
6.7
5.9
6.3
5.9 6.3
7.S
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Width
in
Width in
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170
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g""
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siza.
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2.8
2.4­
2.4
1
180
160
190.
200
210
llm •.
.'
1igure.
3. Lengthwidth
Length-widthrelationship
relationship of male
ure3.
male Dungene~s
Dungenes crabs;­
crab."
Data
compiled· by
by Dale
Dale Snow,
Snow, Oregon
Oregon Fish
Fish Comiiission1
Commission, 1967.
Data compiled
1967.
.
..c
u
3.1
3.1
legal
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60'
. ~0
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