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tank and observed ( i ) continuously for the first hour, ( ii ) at the end of each hour
for the next 6 hours, (iii) at the end of the first 24 hours, and (iv) daily for a
60-day interval. All expired fish were examined by a pathologist to determine
cause of death.

Deaths were segregated according to hooking area by identifying fin punches.
Since no two fish of a given group were the same size, hooking positions by
subarea were determined from length-weight measurements. Immediate mortal-
ity was defined as death occurring during the first 24 hours. Death thereafter was
considered delayed.

Fish were handled like the average angler might. Rough treatment, such as
jerking the hook from the fish's mouth, was avoided. However, the few fish that
fell to the ground during handling were used, since anglers often drop fish.

Study fish, subyearling largemouth bass ranging in total length from 139.8 (5.5
inches) to 264.3 mm (10.4 inches) and averaging 193.0 mm (7.6 inches), were
obtained from the Department's Imperial Valley Warmwater Hatchery, Imperial
County. These pond-reared fish were fed as many golden shiners, Notemigonus
crysoleucas, as they would consume every other day of the study. Temperatures
in the 6,800 liter (1,800 gal) test tank ranged from 9.4 C (49 F) to 15.0 C (59
F). Water in the tank was exchanged weekly to remove metabolic wastes.

RESULTS

Fifty-six percent (95% CI.; 41.0%-70.0%) of esophageally-hooked bass died
as a result of hooking. Mortalities among groups hooked in other areas were not
significantly different from the 2% (95% CI.; 0.0%-14.0%) loss in the control
group (Table 1). Twenty-one of 35 fish hooked in the ventral surface of the
esophagus died. In these cases, death resulted from hemorrhaging in the pericar-
dial cavity. The hook cut through the esophagus and pericardium and ruptured
the heart in the aortic area. According to Donald R. Manzer, examining patholo-
gist from the Department's Fish Disease Laboratory, the relative anatomy of the
largemouth bass makes it likely that death will often result when a hook embeds
in the esophagus with the barb oriented ventrally. In his opinion, similar results
would likely be recorded if the hook were left in the fish.

Seven of the 15 fish hooked in the dorsal surface of the esophagus also died.
These deaths were attributed to excessive stress associated with the compara-
tively difficult job of hook removal since they could not be related directly to
physical damage.

Of a total of 32 hooking mortalities, 20 were immediate and 12 were delayed
(Table 1). One death was attributed to bacterial gill disease.

Over 88% of the test fish survived both the stress from being crowded in the
tank for 60 days with at the most 22.7 liters (6 gal) per fish, and stress and
physical damage associated with hooking. Five of the gill-hooked fish bled
profusely, but all survived. Of the fish hooked in the roof of the mouth, the hook
penetrated an eye cavity in fourteen cases. None of these fish died.

There was no correlation between size of test fish and hooking mortality. The
mean length of the expired esophageally-hooked fish was the same as that of
the control group (Z = 0.96, P>0.05).



188 CALIFORNIA FISH AND CAME

TABLE 1. Mortality by Hooking Area and the Control Group

Hooking area Control

group
Roof of Floor of

Lip mouth Gills Tongue mouth Esophagus (50 Fish)

No. of fish hooked 50 50 50 35 50 50

No. of immediate mortalities 20

( < 24 hours)
No. of delayed mortalities.... 2 10 1 8 1

( > 24 hours)

Total mortality 2 10 1 28 ' 1

Percent mortality 4.0 0.0 2.0 0.0 2.0 56.0 2.0

95% C.I. for percent

total mortality 0.0-19.0 0.0-7.0 0.0-14.0 0.0-7.0 0.0-14.0 41.0-70.0 0.0-14.0

' Does not include one mortality attributed to disease.



DISCUSSION

While anglers using certain types of small baits (worms, salmon eggs, etc.)
hook fish in areas of the mouth unlikely to cause death, they are more likely to
deep-hook small bass than anglers using lures or minnows. However, the result-
ant mortality is probably minor since anglers using these baits catch compara-
tively few small bass. Of the sublegal largemouth bass hooked and released at
Merle Collins Reservoir during 1974 and 1975, only 12.0% were caught by
anglers using small baits exclusively. Conversely, anglers using lures or minnows
released 58.9% of their catch during the same period (unpublished data).

The size of the hook used in this study represents the average hook size used
by most anglers. It is probably larger and more damaging to fish than hooks
normally used by anglers fishing small baits. Recorded losses of esophageally-
hooked fish under study conditions may, therefore, be greater than those which
normally occur.

I did not test the effects of summertime temperatures on hooked fish. Results
of this study strongly suggest, however, that hooking mortality is not a factor
which materially reduces the value of size limit regulations.

ACKNOWLEDGMENTS

Robert R. Rawstron prompted the study and was instrumental in its design.
Stephen A. Rapp and William C. Robinson ably assisted in the hooking opera-
tion. Vida B. Wong prepared the figure.

REFERENCES

Funk, John L, ed. 1974. Largemouth bass harvest in the midwest, an overview. Symposium on overharvest and

management of largemouth bass in small impoundments. North Cent. Div., Amer. Fish. Soc, Spec. Pub. No.

3, July 1974: 116 p.
Hashagen, Kenneth A., Jr. 1973. Population structure changes and yields of fishes during the initial eight years

of impoundment of a warmwater reservoir. Calif. Fish Game, 59(4): 221-244.
Rawstron, Robert R., and Kenneth A. Hashagen, Jr. 1972. Mortality and survival rates of tagged largemouth bass

(Micropterus salmoides) at Merle Collins Reservoir. Calif. Fish Came, 58(3): 221-230.
Rutledge, William P. 1974. Performance report-hooking mortality study. Fed. Aid Proj. F-23-R-3, Hearts of the

Hills Fish. Expt. Res. Sta., Texas Parks and Wildlife Dept., Austin, Texas. 5p.



DUNGENESS CRAB CPUE 189

Calif. Fish and Came 64 ( 3 ): 1 89-1 99. 1 978

CATCH-PER-UNIT-OF-EFFORT STUDIES OF NORTHERN

CALIFORNIA
DUNGENESS CRABS, Cancer magister^

DANIEL W. COTSHALL

Operations Research Branch

California Department of Fish and Game

P. O. Box 98
Avila Beach, California 93424

Northern California commercial Dungeness crab fishermen were interviewed to
determine their catch-per-unit-of-effort. The data were used to calculate population
size and mortality rates of legal sized crabs and to predict season landings. Generally,
the mean catch per trap increased as the number of fishing days increased. As the
season progressed, fishermen tended to fish their traps for longer periods. The
calculated weight of legal male crabs at the beginning of the season ranged from a
low of 1.1 Mg (2.4 million lb) in November 1971 to a high of 7.5 Mg (16.5 million
lb) in November 1969. Instantaneous total mortality rates (z) ranged from —0.00490
during the 1966-67 season to —0.18300 during the 1971-72 season. The fishermen
probably harvest a greater percentage of the available crabs during seasons of high
abundance.

INTRODUCTION

Accurate and consistent catch-per-unit-of-effort data are vital to population
dynamics studies. California Dungeness crab fishermen are not required to
submit records of daily catch and effort. In December 1964 we initiated inter-
views with commercial crab fishermen in Eureka to determine the number of
traps fished and the weight of crabs caught. A similar study was undertaken at
Crescent City in January 1966 (Gotshall and Hardy 1969). Data were collected
from both areas through the 1971-1972 season. Originally, these data were used
to obtain estimates of the abundance of legal sized crabs and to predict season
landings. It soon became apparent from the data that population size estimates
and mortality rates of legal sized crabs could be calculated. We also distributed
log books (voluntary) to cooperative fishermen beginning in 1966. Unfortunate-
ly, very few of the fishermen kept consistent data and this experiment was
terminated during the 1968-69 season.

METHODS

Commercial fishermen were interviewed whenever possible as they were
unloading the day's catch at the dock. Eureka interviews were conducted by
Department of Fish and Came biologists and seasonal aids.

Crescent City interviews were conducted by the Pacific Marine Fisheries
Cooperative Port Sampling Project biologists (Public Law 88-309) from January
1966 through May 1968. From December 1968 through February 1972 these
interviews were conducted by Department biologists from Eureka.

The information collected during each interiew included: number of traps
pulled that day, number of days traps had fished (1 day equals approximately
24 hr of fishing), location, depth traps were fished, and weight of crabs landed.

RESULTS
From December 1964 through February 1972, 1,460 interviews were con-



' Accepted for publication March 1978.



190



CALIFORNIA FISH AND GAME



ducted at Eureka, and 1,230 at Crescent City (Tables 1 and 2). These numbers
do not include interviews where the fishermen had pulled traps fished for two
or more different time periods. Generally, the Eureka fishermen fish an area
bounded on the south by Cape Mendocino and on the north by Dry Lagoon
( Figure 1 ) . Crescent City fishermen do most of their fishing between Big Lagoon
and the Oregon border. Monthly mean catch per trap for one day's fishing at
Eureka ranged from a high of 9.8 kg (21.7 lb) per trap in May 1966 (one
interview) to a low of 0.4 kg (0.9 lb) per trap in February 1972. These figures
represent 14.3 and 0.5 crabs per trap, respectively, based on mean weight data
(Table 3).



TABLE 1. Number of Crab Fishermen Interviewed and Mean Catch (Kg) of Crabs Per
Trap by Days Fished, Cape Mendocino to Big Lagoon, December 1964 - February 1972.











Days fished












1






2


3




4




5






No. of




No. ot


No. of




No. of




No. of






Inter-


Kg/


Inter-


Kg/ Inter-


Kg/


Inter-


Kg/


Inter-


Kg/


Month


views


trap


views


trap views


trap


views


trap


views


trap








1964-


65 Season














December


23


5.3


-


-


1


10.1


-


-


-


-


January


13


3.8


12


5.6


2


4.6


2


5.1


3


9.6


February


4


3.1


9


4.1


2


3.7


2


2.8


10


4.5


March


13


4.4


4
1965-


2.6
66 Season


2


1.7








1


3.9


December


-


-


11


10.8


-


-


-


-


1


-


January


7


9.5


4


10.7


5


12.8


2


12.7


4


11.8


February


3


7.8


9


9.8


1


9.4


1


7.8


4


11.0


March


3


6.5


7


5.6


6


6.5


6


8.9


1


5.8


April


1


7.9


1


10.9


-


-


-


-


1


19.1


May


1


9.9


4
1966-


12.2
67 Season











_








December


80


6.9


21


7.8


4


7.0


-


-


2


6.6


January


17


4.4


5


6.9


1


10.9


1


8.5


2


4.7


February


7


3.8


2


6.2


1


1.6


1


7.6


1


8.1


March


4


5.9


1


3.2


-


-


-


-


-


-


April


5


3.3


5


2.7


1


8.4


-


-


1


6.7


May


1


1.0


3
1967-


3.5
68 Season





~~






1


5.4


December


20


7.6


3


6.6


5


8.9


1


6.0


4


8.1


January


31


5.6


6


8.5


2


6.5


-


-


3


7.3




23


4.7


4


4.3


3


4.0


-


-


3


6.5


March


15


3.4


7


3.1


4


3.7


1


1.7


3


2.8


April


10


2.1


9


5.1


5


5.0


10


5.6


10


3.7


May


5


2.6


7


3.3


4


2.6


1


3.2


8


5.6








1968-69 Season














December


27


6.0


15


11.7


4


9.8


-


-


2


7.7


January


65


5.9


42


5.5


11


6.0


4


4.4


5


4.5


February


10


3.5


8


3.0


8


2.5


9


2.8


14


3.2


March


19


2.3


20


2.0


22


2.3


4


2.0


5


2.8


April


-


-


5


3.6


6


4.0


-


-


8


2.2


May


8


3.9


2


8.6


1


11.4


-


-


6


13.6


June


-


-


1


3.9


1


1.5


-


-


-


-








1969-70 Season *














January


120


8.8


1


9.0


-


-


-


-


-


-


February


71


4.6


48


5.3


7


5.5


4


5.3


2


1.9


March


17


4.3


29


3.2


21


3.1


4


3.2


12


27


April


3


1.5


2


2.9


5


2.7


-


-


8


2.5



DUNGENESS CRAB CPUE

1970-71 Season **

February 48 5.5 17 5.7 1

March 25 2.6 16 2.5 10

April 5 1.6

May - - 1

1971-72 Season

December 20 3.2 13 3.9 14

lanuary 2 1.0 3 1.3 3

February 2 0.4 1 0.8

* Season opened December 1, fishing did not begin until January.
** Season opened December 1, fishing did not begin until February.



191



9.4


-


-


-


-


2.9


7


2.8


5


2.1


-


1


1.5


4


1.2


2.7


-


-


-


-


5.0


2


5.6


7


3.3


1.7


2


0.7


6


1.5


-


-


-


1


0.3



TABLE 2. Number of Crab Fishermen Interviewed and Mean Catch (Kg) of Crabs Per

Trap by Days Fished, Dry Lagoon to Oregon Border, December 1966-December 1971

Days fished

1 2 3 4 5

No. of No. of No. of No. of No. of

inter- Kg/ inter- Kg/ inter- Kg/ inter- Kg/ inter- Kg/

Month views trap views trap views trap views trap views trap

1966-67 Season

December 38 6.1 9 6.3 6 8.5 3 6.8 1 10.7

January 9 9.4 26 6.4 10 6.0 10 6.1 12 6.4

February 36 6.5 25 5.5 10 6.0 6 6.0 6 8.9

March 18 5.9 13 4.3 15 6.6 2 6.5 4 11.0

April 1 0.8 1 1.1 1 2.8 1 1.9 1 0.9

May - - - - -

June - 3 2.8

1967-68 Season

December 49 9.3 17 11.7 7 10.8 1 25.0 31 12.5

January 40 7.6 24 9.8 9 12.2 8 11.8 11 11.0

February 25 3.6 55 5.0 18 5.3 9 7.9 20 9.2

March 1 4.3 6 4.9 4 3.6 4 3.4 10 5.6

April - 4 2.8 8 4.1 2 3.7 13 4.1

May 1 1.4 1 1.4 3 2.9 9 3.5

1968-69 Season

December 41 9.5 9 9.4 1 12.5 2 11.9 6 12.0

January 26 6.3 12 5.8 8 4.8 4 5.8 7 5.4

February 4 2.0 4 3.1 5 2.5 2 3.4 13 4.4

March 3 1.8 14 2.5 16 2.4 5 3.5 18 3.9

April 3 3.3 7 2.9 4 2.4 9 4.0

May 3 2.2 4 7.1 1 1.7 2 7.2 18 7.0

June - - - - -16.4

1969-70 Season *

lanuary 46 10.5 16 15.2 10 15.8 2 22.1 8 17.4

February 17 4.9 12 3.4 4 5.5 3 4.7 7 5.3

March 1 1.3 4 3.6 8 1.5 3 1.7 7 3.5

April 4 4.3 9 4.1 5 3.3 9 5.8

May - 1 3.0 - - - 1 5.7

1970-71 Season **

February 43 10.9 2 7.4 3 17.4 2 17.2 1 19.1

March 31 5.7 9 6.1 3 5.1 2 4.3

April 2 4.5 1 5.6 1 4.3

May 1 5.4

June - 1 4.2

1971-72 Season

December 16 8.9 15 2.7 6 3.1 2 3.7 3 0.4

* Season opened December 1, fishing did not begin until January.
** Season opened December 1, fishing did not begin until February.



192



CALIFORNIA FISH AND GAME



4:



41.



40°.



39'



v Point St. George
.Crescent City



) Stone Lagoon
'Dry Lagoon
'Big Lagoon




Albion



30



Nautical Miles




Point Arena



125" 124°

FIGURE 1. Northern California fishing areas and landmarks.



123



DUNCENESS CRAB CPUE 193

TABLE 3. Monthly and Seasonal Mean Weights (Kg) of Dungeness Crabs Landed at

Crescent City and Eureka, 1964-1972

Season

Month 1964-65 1965-66 1966-67 1967-68 1968-69 1969-70 1970-71 1971-72

Eureka

December 0.91 0.94 0.85 0.91 0.82

January 0.88 0.91 0.94 0.74 0.91 0.73 0.83

February 0.86 0.88 0.98 0.84 0.93 0.80 0.92

March 0.89 0.78 0.90 0.73 0.86

April - - 0.99 0.71 0.94 0.77 0.83

May 0.69 0.91 0.82 0.94

June ______ -

Mean for Season 0.87 0.86 0.95 0.78 0.92 0.75 0.86 0.83

Crescent City

December 0.94 0.83 0.89 0.77

January 0.94 0.99 0.84 0.92 0.89 0.81

February - 0.77 0.94 0.82 0.91 0.85 0.96

March 0.84 0.93 0.78 0.93 0.84 0.94

April - 0.78 0.89 0.79 0.86 0.84 0.92

May - 0.76 0.84 0.94

June 0.75 0.84 -

Mean for Season 0.81 0.94 0.79 0.90 0.86 0.94 0.78

The highest monthly mean recorded by Crescent City fishermen for 1 day's
fishing occurred in February 1971 and was 10.8 kg (23.9 lb) or 11.3 crabs per
trap (Table 3).

Generally, the monthly mean catch per trap increased as the number of fishing
days increased, particularly during the first month of the season. During most
seasons the catch-per-unit-of-effort declined steadily each month and then in-
creased again in March, April, or May.

As the season (December 1 to July 15) progressed, fishermen tended to fish
their traps for longer periods. Approximately 70% of the fishermen pulled their
traps every day during the 1 st month of the season ( Figure 2 ) . However, by the
5th month this figure dropped to 12.3% and increased slightly to 19.1% during
the 6th month. Conversely, only 8.1% fished their traps 5 or more days during
the 1st month but, by the 7th month, this figure increased to 66.7%. It appears
that the fishermen could have caught more crabs had they pulled their traps
every day, particularly after the 1st month of the season. For example, in March
1969 Eureka fishermen averaged 2.3 kg (5.1 lb) or 2.6 crabs per trap overnight
and 2.3 kg (5.1 lb) per trap after three nights. If they had pulled their traps every
day, they could have averaged 6.9 kg ( 1 5.3 lb ) or 7.7 crabs; assuming, of course,
that weather conditions permitted fishing every day.

Population Size

A population size estimate of legal sized crabs at the start of the fishing season
was calculated from the combined Eureka and Crescent City catch per trap data
for 1 day of fishing, and cumulative landing data (Table 4).

The following equations were used, based on Leslie's least square method
(Ricker 1975):

Y = a + bX
and

N„ = a/c
and c = —b



194



CALIFORNIA FISH AND CAME



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i— fN O C^ O^ O ^"



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i- K N CN



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fN fN



DUNCENESS CRAB CPUE



195





695


First M


onth


8.1


460


Second Month


92


25.8


Third Month


19 5


246


Fourth Month


193


50
















28.6




305




UJ




98 61






pili, 23 5




> A










62


en


16 2








1-
Z


12


8 7

| 1 7




80


U_














o
o


Fifth Month


32.6


19 1


Sixth Month


447





Seventh Month


66 7


1


2 3 4


54


<
§»

LlI

Q.










25-




22 ? 203






223








12 3






123






74 64


16 7 16.7



























, 1






1


2


3


4


5 +


i


2


3


4


5+


1


2


3


4


5+







DAYS TRAPS FISHED

FIGURE 2. Percentage of crab fishermen interviews and number of days traps were fished, Cres-
cent City and Eureka dates combined, 1964 through 1972.

Where:

Y = mean catch in pounds per trap for 1 day of fishing
a = intercept of line on Y axis
b = slope of line
X = cumulative landings

a — productof the original population, N and the catchability, c
— b='catchability, c
N„ = estimated population in pounds of legal sized crabs at the start of the
fishing season
Population estimates were calculated for the 1966-67 through the 1971-72
season (Table 5). The largest calculated population estimate, 7.6 Mg (16.7
million lb), was present at the beginning of the 1969-70 season, the lowest
population estimate, 1.1 Mg (2.4 million lb), was obtained from data collected
during the early part of the 1971-72 season.

TABLE 5. Calculated Population Estimates of Northern California Dungeness Crabs by
Weight (Kg) at the Beginning of the Fishing Season, Cape Mendocino to Oregon Border.*











Lower 95%


Upper 95%


Total Exploitation




Intercept


Slope


Population


confidence


confidence


catch


rate


Season


(a)


(b)


(mean no.)


limit


limit


Mg


(u)


1966-67


16.34318


0.00000102


7,274,318


3,257,893


41,044,989


4.597


63.2


1967-68


20.85992


0.00000140


6,764,575


4,624,158


10,504,761


4.859


71.8


1968-69


25.29165


0.00000185


6,206,707


3,625,982


11,863,158


5.321


85.7


1969-70


22.40918


0.00000134


7,592,363


6)684,943


8,962,693


6.118


80.6


1970-71


17.84373


0.00000217


3,733,205


1,674,335


7,153,291


3.258


87.3


1971-72


12.29002


0.00000505


1,104,886


793,287


3,120,111


0.804


72.8



* Fort Bragg area landings not included.

Based on these population estimates, fishermen were harvesting between 63
and 87% of the available crabs during the seasons considered (Table 5). Jow



196 CALIFORNIA FISH AND CAME

( 1 965 ) estimated that fishermen harvested 85% of the available crabs during the
1962-63 season. He also speculated from tag recovery data that fishermen
harvested a higher percentage of the population during years of low abundance
than during years of high abundance. From my data it appears that fishermen
are harvesting a higher proportion of the legal males during years of high abun-
dance, and a year or so after the population begins to decline, than during years
of low abundance and years when the population is increasing. Fishing effort
(numbers of boats) follows a similar pattern, thus supporting catch-per-trap


1 2 3 4 6 8 9 10

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