Ovigerous Dungeness crabs were collected from the San

Francisco and Eureka-Crescent City regions and maintained at

the Department's Marine Culture Laboratory near Monterey.

Hatching success, expressed as viable larvae released, was

measured and compared by region. Larval counts were made from 15 Dungeness crabs, 5 from the San Francisco region, 7 from the Eureka-Crescent City area and 3 of unknown origin. Mean hatching success exceeded 80% in the San Francisco region, and averaged more than 90% in the Eureka-Crescent City area. However, a Student's t-Test showed this difference in hatching success was not significant.  (16pp.

Ebert, Earl E.

Haseltine, Arthur W.

Kelly, Randolph O.

Aquatic Commons

OBSERVATIONS ON THE
LARVAL HATCHING SUCCESS OF
DUNGENESS CRAB, CANCER MAGISTER,
FROM THE SAN FRANCISCO
AND EUREKA-CRESCENT CITY REGION
-~
II
r
by
Earl E. Ebert,
Randoph O. Kelly and
Arthur W. Haseltine
MARINE RESOURCES
TECHNICAL REPORT NO. 29 1975
CALIFORNIA DEPARTMENT OF FISH AND GAME
MARINE RESOURCES TECHNICAL REPORTS
**************************************
Marine Resources Technical Reports are research
documents by Department personnel that are of sufficient
importance to be preserved, but which for some reason
are not appropriate for primary scientific publication.
No restriction is placed on subject matter.
These Reports may be cited in publication, but
care should be taken to indicate their manuscript status.
The material in these Reports may eventually appear in
the primary scientific literature.
Inquiries concerning the Reports should be directed
to The Editor, Robson A. Collins, Operations Research
Branch, 350 Golden Shore, Long Beach, California 90802.
•"'-:.:..
OBSERVATIONS ON THE LARVAL HATCHING SUCCESS OF
DUNGENESS CRAB, CANCER MAGISTER, FROM THE SAN FRANCISCO
AND EUREKA-CRESCENT CITY REGIONS
by
Earl E. Ebert, Randolph O. Kelly and
Arthur W. Haseltine
Operations Research Branch
MARINE RESOURCES TECHNICAL.REPORT NO. 29
California Department of Fish and Game
- 1975 -
- LDA -
!'"
ABSTRACT
Ovigerous Dungeness crabs were collected from the San
Francisco and Eureka-Crescent City regions and maintained at
the Department's Marine Culture Laboratory near Monterey.
Hatching success, expressed as viable larvae released, was
measured and compared by region. Larval counts were made from
15 Dungeness crabs, 5 from the San Fran9isco region, 7 from
the Eureka-Crescent City area and 3 of unknown origin. Mean
hatching success exceeded 80% in the San Francisco region, and
averaged more than 90% in the Eureka-Crescent City area. How-
ever, a Student's t-Test showed this difference in hatching
success was not significant.
(2)
..
..........
ABSTRACT •••.
ACKNOWLEDGMENTS
INTRODUCTION . •
MATERIALS AND METIIODS
RESULTS • • • • •
CONCLUSIONS
TABLE OF CONTENTS
(3)
Page
2
4
5
6
7
14
ACKNOWLEDGMENTS
Ovigerous crabs were obtained through the cooperative efforts of several
Departmental personnel. Ron Warner and Nancy Nelson supplied specimens from
the Eureka-Cr~scent City area. San Francisco region crabs were obtained
through Walter Dahlstrom, Patrick Collier and Paul Wild.
Dr. Harold Orcutt, Robert Tasto, Timothy Farley and Rob Collins reviewed
the manuscript and offered helpful suggestions.
Rollin "Mike" Burgoon assisted in maintenance of the ovigerous adult
crabs in tanks, and helped in making crab larval counts.
Corinne "Connie" Clarke typed the original manuscript draft and the
final typing was done by Nancy Durell.
We gratefully acknowledge and appreciate the assistance of these people.
This study was conducted in cooperation with the Department of Commerce,
National Oceanic and Atmospheric Administration, National ~furine Fisheries
Service, under Public Law 88-309, Project 4-20-R.
(4)
INTRODUCTION
The decline in the San Francisco region of the Dungeness crab, Cancer
magistep, fishery in recent years has been of major concern to scientists,
fishermen and the general public alike. Yet, until 1974 there had been
almost no support to launch a major study to identify possible causative
factors.
Crab investigations for the most part have been limited to population
dynamics and basic life history studies., both essential to management of
the resource; but data are also needed on crab ecology, larval distribution
and abundance, and the effects of pesticides and heavy metals on crab popu-
lations.
In 1970 the Department established a marine culture laboratory to in-
vestigate the mass culture feasibility for selected marine shellfish species,
including the Dungeness crab. In the process of developing mass culture
techniques for the crab we encountered high larval mortalities, particularly
with early developmental stages. This caused speculation about the viability
of newly hatched crab larvae. The nagging thought persisted that environ-
mental pollutants had been transmitted from parent to offspring, at sublethal
levels, but sufficient to affect larval viability.
To test this hypothesis we collected ovigerous crabs from the San Fran-
cisco region and the Eureka-Crescent City area to compare hatching success.
The latter fishery had not experienced the long term decline in landings
suffered in central California. Presumably differences in crab larval hatch-
ing success could account for the difference in the magnitude of the resources.
During the crab mass culture studies conducted in 1972-73, incidental
data were gathered on size of the hatch and on larval release periods for
(5)
- 6 -
individual females. This report includes that data, but is comprised
principally of data collected during the 1973-74 breeding season.
The objective of this study is to measure and compare crab hatching
success from the two regions of the fishery and possibly relate these find-
ings to the status of the resource.
MATERIAL AND METHODS
Ovigerous crabs, caught by commercial fishermen, were wrapped in sea-
water-saturated cheesecloth and packed in styrofoam containers for shipment
to the laboratory. Refrigerant bags were placed in each container to main-
tain cool temperatures, alleviating possible heat stress to the crabs.
Transit time to the laboratory did not exceed 24 hours.
Crabs were measured and examined upon arrival at the laboratory. Par-
ticular attention was focused on each egg mass, its size and coloration.
Crabs were then placed in 75 liter (20 gal) aquaria, one per aquarium, and
supplied with 15 ~- filtered, continuously flowing seawater.
Crabs were maintained on a market squid, LoZigo opaZescens, diet sup-
plied fresh on alternate days. However, when larvae commenced to hatch,
the market squid diet was discontinued.
Daily observations were made of egg shedding and egg mass coloration,
coloration being indicative of embryo development within the egg capsules.
Three color descriptions were used: yellow-orange, orange and brown. As
developing embryos approached maturity, aquaria water inflows were shut off
during non-observation periods (night hours) to insure larval retention.
Aeration was substituted during these hburs. A static, aerated system was
maintained during the larval hatching period.
7 -
Upon hatching, the crab larvae (zoeae) were removed daily by siphoning.
Zoeae were next concentrated in a sieve, transferred to a glass container,
and brought to a final volume of 1, 2, or 3 liters (1.06, 2.12 or 3.18 qt),
depending on larval density. Dense concentrations were brought to the 3
liter volume to facilitate counting. Two 25 m1 (0.02 qt) aliquot samples
were taken, and each was distributed into a separate dish. Live larvae were
immobilized with 5% formalin, counted, and the counts from each dish averaged.
Average counts were then multiplied by the appropriate factor for 1, 2, or 3
liter sample size to obtain the larval estimate. Dead larval counts were ob-
tained similarly; however, these larvae accumulated on the aquaria floors,
and did not require formalin treatment.
A coefficient of correlation was calculated to determine the relation-
ship between adult crab size and the size of the larval hatch.
A Student's t-Test was used to determine if the mean hatching success
of crabs from the two California regions was significantly different.
RESULTS
Ovigerous crabs were relatively easy to maintain in the laboratory al-
though a few died. Cause of death may be attributable to shock stress while
in transit, injuries in handling, or a combination of these.
Adult crabs displayed variable behavior in their feeding habits during
the egg bearing period; feeding voraciously at times, and on other occasions
exhibiting total indifference to introduced market squid.
Egg sponge coloration proceeds from a yellow-orange to orange to brown
phase. The darker coloration is indicative of embryo chromatophore develop-
ment, concomitant with maturation. We preferred to receive ovigerous
specimens having orange to brownish egg sponges because maintenance time
- 8 -
in the laboratory prior to the zoeal hatch was abbreviated. Conversely,
specimens having immature (yellow-orange) egg sponges required extended
maintenance periods prior to hatching larvae. During this period the crabs
constantly tended their egg masses, often tearing away substantial portions.
Similar behavior probably occurs in situ, but it may be more pronounced in
captivity. No attempt was made to measure the extent of this egg loss.
Duration of larval hatch per adult averaged about 8 days, ranging from
5 to 12. Hatching durations were similar for crabs originating from the San
Francisco and Eureka-Crescent City regions.
The number of larvae hatched daily per adult followed a characteristic
pattern; however, it did vary. Typically the first day's hatch was small
«4% of total), increased markedly on the second day, peaked on the third
or fourth day, then tapered off to approximate the first day's hatch by the
sixth day. Both the San Francisco and Eureka-Crescent City area crabs fol-
lowed this hatching sequence (Figure 1).
Larval estimates were initially obtained from four crabs in January
1973. Origin data from three of these crabs were lost. The remaining crab,
originating from the Eureka region, measured 169 mm (6.7 inches) shoulder
width, hatched an estimated 574,100 larvae, of which 97.1% were alive.
Hatching success of the three crabs with unknown origins also exceeded
90% (Table 1).
During the December 1973 - January 1974 period larval estimates were
obtained from five crabs from the San Francisco region and six from the
Crescent City area.
San Francisco region crabs had yellow-orange to orange colored egg
sponges when first received. They were maintained for periods ranging
.
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SAN FRANCISCO
CRESCENT CITY - EUREKA
432
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FIGURE 1. Larval release patterns for San Francisco and Eureka-Crescent City area ovigerous Dungeness crabs.
TABLE 1. Hatching Success of Dungeness Crab Larvae, Cancer magister, from Eureka and Unknown
Origins, January 1973.
Origin
~ ,J
Female
Shoulder
Width, nnn Hatching Period
Larval Counts
Live Dead Total
[i
% Survival
(~ , \)
- 11 -
from 14 to 36 days before the onset of larval release. Larval hatching suc-
cess of three crabs exceeded 93%, another produced slightly better than 82%
viable larvae, and the remaining crab had approximately 65% larval survival.
This latter specimen, in addition to having poor larval survival, hatched
a comparatively small number of larvae (Table 2). This crab did have a full,
orange colored egg sponge when received. However, the egg retention time in
the laboratory (36 days) to attain larval maturation and release exceeded
that of other ovigerous crabs. Extensive egg shedding apparently occurred
during the long egg tending period.
Crescent City area crabs had full brownish colored egg sponges when
received, and with the exception of one individual, commenced to hatch larvae
on the following day. Good larval hatching success was obtained, ranging
from 92% to nearly 99%; averaging about 95% (Table 3).
Although Eureka-Crescent City area crabs exhibited slightly better
hatching success than did crabs from the San Francisco region, the differ-
ence was not significant. Using an arc sine transformation of the percent-
ages, and testing with Student's t-Test, t = 2.12 where t.05,lO = 2.228.
Total larval estimates per adult varied widely for similar sized crabs
from both regions (Figure 2). A positive correlation would be expected
between crab size and fecundity, and presumably the size of the larval
hatch. Calculations disclosed a low to moderate positive correlation co-
efficient (r = 0.44). Egg shedding from handling of adults and, in some
cases, extended periods in the laboratory prior to hatching larvae ·undoubt-
ed1y affected hatching success.
TABLE 2. Hatching Success of Dungeness Crab Larvae, .Cancer magister, Originating from the San
Francisco Region, December 1973 and January 1974.
Female Larval CountsShoulder
Width, mm Hatching Period Live Dead Total % Survival
158 1/16/74 - 1/23/74 1,122,400 67,600 1,190,000 94.9
169 1/4/74 - 1/15/74 1,088,900 53,200 1,142,100 95.1
162 1/14/74 - 1/19/74 349,000 61,300 410,300 82.4
151 12/6/73 - 12/10/73 314,700 21,000 335,700 93.3
I
145 1/15/74 - 1/23/74 61,200 33,600 94,800 64.6 f-I
tv
TABLE 3. Hatching Success of Dungeness Crab Larvae, Cancer magister, Originating from the
Crescent City Region, January and February 1974.
Female Larval CountsShoulder
Width, nnn Hatching Pe_riod Live Dead Total % Survival
151 1/25/74 - 1/31/74 1,108,600 13,000 1,121,600 98.8
149 1/25/74 - 1/31/74 893,100 28,600 921,700 96.8
151 1/25/74 - 1/31/74 633,500 36,200 669,700 94.3
153 1/25/74 - 1/31/74 540,800 42,500 583,300 92.1
152 2/1/74 - 2/8/74 478,700 15,700 494,400 96.7
137 1/25/74 - 1/31/74 230,500 15,500 246,000 93.3
!, (.,
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- 13 -
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SAN FRANCISCO - •
CRESCENT CITY- EUREKA - 0
14 0 150 160 170
CRAB SHOULDER WIDTH (mm)
FIGUP~ 2. Dungeness crab larval hatch compared to adult crab size.
- 14 -
CONCLUSIONS
Because Dungeness crabs hatch-out viable larvae equally well from both
coastal regions it would appear that other factors are involved in the over-
all fishery decline occurring off San Francisco. It is possible that sub-
sequent larval stages become contaminated and succumb, via biological
magnification through the food chain; or oceanographic conditions unfavor-
able to larval crabs could be responsible. These and other factors require
investigation if we are to interpret the fishery decline and, if possible,
bring the fishery back to former abundance levels.
4-29-75 350 RAe


Observations on the larval hatching success of dungeness crab, Cancer magister, from the San Francisco and Eureka-Crescent City region

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Observations on the larval hatching success of dungeness crab, Cancer magister, from the San Francisco and Eureka-Crescent City region

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