ABSTRAC
Squid boats in the Monterey squid fishery utilize Italian lampara nets
that have chains as lead-lines. Two experimental half-purse seine nets are
the other type of gear used (spring, summer 1987). Squid egg cases were
collected and then damaged with the assumption that gear net lead-lines
drag across/through egg masses and potentially cause an increase in squid
egg mortality. Egg cases traumatized mid-way through development
experienced a higher estimated percentage of mortality (EPM) than those
damaged at early or late stages, for low levels of damage (0 and .21 kg).
Misdeveloped embryos occurred most frequently in these mid-stage egg cases,
Higher levels of damage (1.2, 2.1 and 3.0 kg) resulted in significant
increases of EPM for all three stages. Field work included an observation
aboard one of the squid boats that had a half-purse-seine net. Pelagic
organisms were 100 a of this catch, suggesting that this net did not drag
the bottom significantly during this particular set. Variation of
developmental stages within three egg clusters suggests that larger egg
masses may have variation within. Attempts to restrict fishing above egg
masses in mid-stages would be futile because of the mixture of stages
within these egg clusters or egg masses.
INTRODUCTION
Variable squid landings have caused the squid fishery in Monterey Bay
to become an unstable business. The reasons for such fluctuations in
catches per year are difficult to ascertain because little is known about
the market squid's population density and distribution. Hardwick & Spratt
(19/9) correlated 4th quarter sea elevations and corresponding Davidson
currents to low catches the following summer and McInnis & Broenkow (1978)
have shown that high water temperatures may precede high squid landings and
that the converse may be true, yet there are no physical explanations for
these phenomena.
The past two years have been especially difficult for the squid
fishery. Low demand for market squid has made it difficult to maintain the
8-10 person crew needed for the lampara net (Figures 1, 2) and the rising
concern about the chain's effect on the egg masses has resulted in the
issuing of two experimental permits for the use of half-purse seine nets
(Figure 3). These purse seines have nylon encased lead-lines so that the
only metal in the net is the rings that guide the purse line (Figure 4)
Life History of the Squid
Eggs of the market squid (Loligo opalescens) have a developmental
period of 3-5 weeks depending upon temperature. Fields (1965) reported that
embryonic development takes 3-4 weeks in aquaria at approximately 16 °C.
while McGowan (1954) incubated eggs at an average temperature of 13.6 %
and found that they hatched in 30-35 days
During this incubation period embryos reside in gelatinous egg cases,
the jelly-like matrix of which deters most predators. As the chorions of
individual embryos expand through development, the case and its tunic
layers expand and by the time of later stages, the egg case is
approximately five times larger in volume than it was at time of deposition
(Fields 1965)
If late stage embryos are forced to hatch prematurely, they are able
to swim (with the yolk sac extending from their arms), but these premature
hatchlings have an increased chance of early mortality (Boeletsky & Hanlon
1983). Hatchlings must learn how to eat within the 2-4 days before their
internal yolk supply is depleted. Once they learn how to eat, hatchlings
will prey upon other planktonic organisms such as larval fish (Hanlon et,
al. 1979). During their planktonic lives, they are swept to deeper waters
via currents and grow rapidly until they reach a mature size in 1-2 years
(Spratt 1979). Near the end of its life cycle, the market squid returns to
the Bay (or other sheltered areas running along the Pacific coast line) to
spawn and then die soon after. Spawning squid can be found in Monterey Bay
from April to November and peak during summer months,
During the spawning season, females deposit egg cases into large
aggregated egg masses that are usually attached to the sandy bottom. These
egg masses can be nearly an acre in area (Okutani and McGowan 1969) and 1.3
meters in height above the bottom (Fields 1965)
Market squid are obligate schoolers and they prefer shallow waters for
spawning (Fields 1965). These characteristics make them ideal for
commercial fishing. Monterey Squid Fishery
The current squid boat fleet of Monterey Bay's squid fishery utilizes
lampara nets, introduced to the fishery in 1905 by Italian fishermen,
Originally, these nets lacked lead lines and were operated by hand. They
were eventually pulled aboard with large drums and lead weights were often
strung along anchor lines to increase sinking time. As the anchoring line
sinks it causes the net to take a U-shaped configuration with two
enveloping wings:
By 1980, lampara nets began using lead chains to increase the sinking
speed of the net. When the net is pulled aboard, this chain is dragged
along the bottom. Although it has been assumed that these chains simply
bounce over egg masses that may be underneath the schooling squid, tons of
squid eggs have been pulled up in the net as part of incidental catches
(Hardwick, pers. comm., 1987). It is also possible that egg masses or parts
of them are being pulled up from the substrate by these chains. This would
leave them prone to drifting into an area where eggs die (i.e., beaches) or
where hatchlings could not survive (i.e., extremely shallow or polluted
waters).
The purse seine is another type of fishing net that has been used
effectively to catch market squid, especially in Southern California. It
has been illegal in Monterey Bay because the lampara net has been so
traditional and because of the concern that the purse seine's lead-lines
(made of steel cables) would be detrimental to the egg masses that it may
come in contact with. The setting time for this type of net is less than
that of the lampara and it can be twice as efficient in terms of catch and
stacking time.
Little is known about what actually occurs at the bottom when a
lampara or purse seine net is set. While observations of eggs caught
incidentally suggest that chains have been dragging the bottom, the actual
amount of damage issued is unclear. The half-purse seine spends less time
on the bottom, so it should drag less, but there is currently no evidence
to suggest that it does not come in contact with egg masses,
Simulation of the hypothetical damage that an individual egg case
experiences is difficult because it is such a complicated issue, However,
if a chain or lead-line is being dragged over an egg mass, the damage may
take the form of pressure. This can be simulated by subjecting individual
egg cases to various weights. In this study, egg cases were damaged
individually by rolling a cylinder of different weights along the length of
each case, thereby inflicting varying degrees of pressure upon each case to
test the egg cases level of sensitivity.
MATERIALS AND METHODS
Egg cases were obtained from laboratory aquaria containing spawning
market squid (Loligo Opalescens) and from Monterey Bay via SCUBA. The egg
cases from the Bay were collected as clusters from a depth of 20-25 ft. off
Wharf #2.
A direct count of embryos per egg case was obtained with the aid of a
dissecting microscope. Light passed through each case from below allowed
adequate visibility of individual embryos,
Egg cases were damaged individually by rolling a cylinder of varying
weight along their length. The cylinder, a hollow section of
polyvinylchloride (PVC) pipe (length (L) - 250 mm, diameter (D) - 48 mm.
weight (W) -.21 kg) accommodated up to three 2 1b. (0.94 kg) dive weights,
This afforded four increasing levels of damage: zero (control), cylinder
only (D), cylinder plus .94 kg (D1), cylinder plus 1.88 kg (D2), and
cylinder plus 2.79 kg (D3).
Inflicting damage upon an individual egg case required 1) keeping the
egg case immobilized by covering/securing it with a fine mesh, 2) running
sea water (enough only to keep the egg case from desiccating or sticking to
the mesh), and 3) an inclined surface that allowed consistent rolling of
the cylinder. The inclined surface was provided by a block of styrofoam (L
- 1035 mm, width - 250 mm, height - 50 mm), with one end resting upon a
small section of PVC pipe (D - 33.65 mm). The cylinder accelerated down the
4.4° - 5° incline where it reached the stalk end of the egg case
approximately 450 mm from the starting point,
Egg cases were damaged at three different stages in development: TIME¬
ZERO, MID-STAGE, and LATE-STAGE. TIME-ZERO egg cases were up to 10 days old
(at 11-12 °0) and characterized by a lack of organ development at the
animal pole of the egg. MID-STAGE egg cases were 13-16 days old and
contained embryos with colorless organs (arms, eyes, mantle). LATE-STAGE
egg cases contained embryos that resembled hatchlings with yolk sacs
extending just past their arms. These egg cases were 24-28 days old and
within a week of hatching.
Once counted and damaged, TIME-ZERO, MID and LATE STAGE groups (n = 4
to 5 egg cases/group) were incubated at 15-16° C (to decrease hatching
latency) in aerated sea water that was changed every 2-3 days. The volume
of sea water per egg case was 250 ml.
An estimated percentage of mortality was obtained by dividing the
number dead after damage by the original number of embryos per egg case,
TIME-ZERO and MID-STAGE egg cases were assessed 1-2 weeks after damage,
while LATE-STAGE mortality was determined by counting the number of viable
hatchlings and obtaining the number dead via subtraction. Embryos were
counted as dead if they were 1) visibly dead, 2) fertilized yet
undeveloped,3) misdeveloped, or 4) hatched prematurely,
Estimated percentage of mortality of damage level groups D, D1, D2,
and D3 were compared to control groups for each stage. The Mann-Whitney U.
test was used for statistical analysis.
RESULT
Lab Study
The number of embryos per egg case ranged from 14-220 with a mean of
104 for the 100 egg cases counted. There were 37 Time-Zero (T-O) egg cases
with mean length (L) - 45.08 mm and mean number of embryos (n) - 142, 21
Mid-Stage (MS) egg cases with mean L - 48.82 mm and mean n = 82, and 42
Late-Stage (LS) egg cases with mean L - 70.47 mm and mean n = 89. Length
measured the portion of the egg case that contained embryos. Of the 100
cases counted, 21 were used for T-O, 20 for MS, and 25 for LS groups that
were damaged.
For each stage in development the number of embryos per egg case is
dependent upon the length. Figures 5, 6 and 7 depict the linear regression
lines for T-O, MS and LS egg cases respectively. By using an un-paired t.
test to determine significance of the regression lines, it is clear that
the number of embryos per egg case is positively correlated with length for
each stage.
Damaged egg cases from T-O and LS groups experienced an
increase in estimated percentage mortality (EPM) with increasing weight
(Figures 8, 10), while MS egg cases had a relatively high EPM throughout
all five levels of damage (Figure 9). T-O and LS groups from damage levels
DI, D3 and Dl, D2, D3 respectively showed a significant increase in EPM.
while control and Dl groups were nearly 1008 viable. T-O and LS groups had
similar EPM's (Figure 8), but differed dramatically from MS eggs,
especially in the lower levels of damage (control, D, and D1) (Figures 7.
9).
Field Study
Three clusters of egg cases were collected from Monterey Bay via
SCUBA. They were located off Wharf No. 2 at a depth of 20-25 feet.
Cluster No. 1 had approximately 200 egg cases that were mainly in later
stages of development or otherwise completely hatched and deteriorating
In a laboratory aquarium of running sea water (11-13 C) hatchlings were
observed from this cluster three days after they were collected and for
the subsequent 18 day period (hatchlings were removed weekly to
determine total hatching period). Cluster No. 2 had 163 egg cases that
were at the T-O stage in development when collected. They did.
however, differ 2-4 days in developmental stages (water temperature
approx. 12 C). Clusters 1 and 2 were both attached to the sea weed
Cystoseina. Cluster No. 3 was found resting on the ocean floor,
unattached to any substrate. It contained 259 egg cases that were
visibly in two different stages of development. 123 of them were T-O
and 136 were brownish, LS egg cases. This represents a 2-3 week
difference in developmental stages.
One observation was made on May 19, 1987, aboard the EL DORADO.
one of the two squid boats in the Monterey fleet that had an
experimental half-purse seine net. A single netting was made in the morning
just beyond the Cannery Row kelp beds at an approximate depth of 100 feet.
7Os of the unmarketable small catch was Pacific Mackeral, 153 market squid.
and 108 sardines. The incidental catch consisted of approximately 20 Barrel
Salps (Thetys Vagina) and 5 electric rays. One small clump of mud and sea
plant was pulled aboard but no squid eggs were observed. The other squid
boats in the fleet were also unsuccessful in netting a marketable amount of
squid.
DISCUSSION
The numbers of embryos per egg case reported from previous studies
(Fields 1965, Okutani & McGowan 1969) were larger than the mean number per
egg case (104) obtained in the present study. Fields described his method
as "counting the eggs in a measured part (of the casel and then estimating
the total content." When this method was tested at the onset of the present
study overestimates were obtained. Counting the embryos directly seems to
be the most accurate method, yet it was very time consuming and would be
impractical in a field study,
Regression lines obtained from data in the current study may be of use
to future studies on market squid eggs because they allow a reasonable
estimate of the number of embryos per egg case from the length. For T-O, MS
and LSs in development, the number per case is dependent upon length,
Critical to the regression lines is the separation of the three stages
because they have different number/volume ratios. For example, LS egg cases
are inherently larger than T-O eggs and thus have a smaller number/volume
ratio.
Results from the present study suggest that MS egg cases are more
sensitive to trauma than T-O or LS egg cases. The relatively high EPM
values of 81.753 and 75.388 obtained from Control and D MS groups (lowest
levels of damage) were due to the trauma elements involved in counting
(temperature change, stress of handling), that did not effect T-O or LS
eggs. Egg cases used in MS and T-O groups were from the same cluster and
eggs from this batch that were not counted went on to hatch normally, This
suggests that they were not from a cluster of egg cases that had a pre-
determined high level of mortality,
MS egg cases thus seem to contain embryos at a critical point in
development. When perturbed at this stage in development, there is an 8-
fold increase in EPM. The relatively high EPM values for the lower damage
groups and the highest occurrence of misdeveloped embyros support this
hypothesis. Misdeveloped eggs were characterized by the extraneous tissue
(1-3 mm in radius) that surrounded the eye and optic lobe regions of the
embryo and by other obvious, yet less frequent anomalies (i.e.,
insufficient mantle growth).
1-O eggs had a much smaller occurrence of misdeveloped embyros and
appeared to be at a stage in development preceding the critical point that
the MS range includes. Increasing weight of the cylinder seemed to be the
sole cause of the increase in EPM for these egg cases; significant
increases of EPM occurred in Dl and D3 damage groups. The D2 group included
egg cases that had tunic layers removed as a result of damage, which may
have increased the amount of aeration received by the embryos and resulted
in an insignificant increase in EPM at this level of damage. Tunic layers
of DI egg cases remained intact, but often bunched up, which may have
decreased aeration at these areas of the egg case where a large percentage
of the dead embyros were observed. Tunic Layers of D3 egg cases were
removed leaving the embyros exposed, yet this high level of damage may have
surpassed the physical limitations of the chorion sacs and resulted in the
significant increase in EPM,
LS eggs also showed an increase in EPM with increasing weight of the
cylinder, yet the mortality of these egg cases was due mainly to the
occurrence of premature hatchlings. Embryos that were not physically
squeezed out or hatched prematurely nearly all went on to hatch normally,
Egg cases from Control and D groups were also nearly 1008 viable. This
suggests that, while sensitive to damage as demonstrated by the occurrence
of pre-mature hatchlings, these egg cases contain embryos that have
developed beyond the proposed time of critical damage,
Data obtained from the three egg clusters from the field study
suggests that egg clusters and possibly larger egg masses contain egg cases
at varying stages in development. Possible explanations for this phenomena
are: I) egg clusters are not created all at once. This notion is supported
by the results of experiments in which real or artificial egg clusters
placed in laboratory aquaria containing market squid acted as a stimulus
for spawning (Hurley, 1977). 2) egg clusters contain egg cases that develor
at different rates. This may occur because egg cases experience varying
levels of exposure to sea water depending upon the amount of crowding or
covering by other cases. 3) a combination of varying deposition times and
10
developmental rates. Clearly, further studies with data from larger egg
masses needs to be obtained.
If it is the case that egg masses have a high variability of
developmental stages then it would be difficult to place regulations on
squid fishing times based on the stage of development at which egg masses
are reported (by divers or incidental catch observations).
Based on physical properties of the lampara net's chains and the
purse-seine's lead line, the comparative level of damage would fall between
the D and Dl levels of damage of the lab study described above, It is
unlikely that the level of net damage would fall in the range of levels D2
D3. This would indicate that the optimum time for fishing would be in an
area with an egg mass that is known to be at T-O or LS, and restrictions
could productively apply to the period at which the egg mass was at its MS
in development. Because such a non-variation situation seems highly
unlikely, such a regulation would be impossible to use,
The squid boat observation, afforded some information information
about the half-purse seine net. The incidental catch consisted of pelagic
organisms and lacked squid egg cases. Further observations by the Calif,
Dept. of Fish and Game will support or refute this single observation and
will be the basis of the decision of whether or not to use half-purse
seines in the Monterey Bay squid fleet. While setting time for this type of
net is less than the lampara and thus spends less time on the bottom,
further studies, involving SCUBA and/or under-water video technology will
be essential to determine what is actually occurring at the bottom and on
the egg masses themselves,
CONCLUSIONS
Future studies on market squid eggs may benefit from the regression
11
lines obtained incidentally from the data of this study. Reasonable
estimates can be made, for T-O, MS and LS egg cases, by measuring length
(x-value) and using the equation of a line (y-bxta) to obtain the number of
embryos.
MS egg cases appear to be more sensitive than T-O or LS egg cases, It
is hypothesized that egg cases in this range of developmental growth are at
a critical/vulnerable stage.
Although a change in the squid fishing industry's use of nets may be
eminent, further studies are needed to support or refute the small sample¬
size observations of the field aspect of this study. The issue of squid
landing variability remains a complicated one. Even if the half-purse seine
becomes accepted by the squid boat association and Fish & Game as less
detrimental than the lampara net, there may be additional or unknown
factors contributing to this dilemma that the industry currently faces
ACKNOWLEDGMEN
Warm thanks to my T.A. and dive buddy Carol Marzuola and to my
advisors Chuck Baxter and William Gilly. Thanks also to Mark Denny for
extensively proof-reading the paper. Special thanks to developmental
specialists Tasha Fraley and Bruce "Del Monte Beach" Hopkins and to Steve
Kernie and Tom Otis for their patience on my third Monterey Wharf dive, The
field study was made possible largely because of the help I received from
Jim Hardwick of the California Department of Fish and Game in meeting the
squid fishermen. I would also like to thank Vince Aliotti and the crew of
his boat The El Dorado for their cooperation during my squid boat
observations. Extremely warm thanks to my classmates of BIO 175H for a
memorable spring quarter "under seas.'
12
LITERATURE CIT
Boeletzky, S.V. and R.T. Hanlon. 1983. A review of the laboratory
maintenance of Cephalopod Molluscs. Mem. Nat. Mus. Victoria
No. 44. 147-187.
Fields, W.G. 1965. The structure, development, food relations,
reproduction, and life history of the squid Loligo Opalescens
Berry. Calif. Dept. Fish Game, Fish Bull. 131: 44-64.
Hanlon, R.T. et. al. 1979. Rearing experiments on the California
market squid, Loligo Opalescens Berry, 1911. The Veliger
(21)4, 428-421.
Hardwick, J.E. and J.D. Spratt. 1979. Indices of the availability of
market squid, Loligo Opalescens, to the Monterey Bay fishery,
CalcOFI Rep. Vol XX, 35-39.
McGowan, J.A. 1954. Observations on the sexual behavior and spawning
of the squid, Loligo Opalescens Berry, at La Jolla California,
Calif. Fish Game, 40: 47-54.
Okutani, Takashi and J.A. McGowan. 1969. Systematics, distribution.
and abundance of the epiplanktonic squid (Cephalopoda, Decapoda)
larvae of the California Current, April 1954- March 1957, Bull.
Scripps Inst. Oceanogr., 14: 1-90.
Spratt, J.D. 1979. Age and growth of the market squid, Loligo
Opalescens Berry, from Statoliths. CalcOFI Rep. Vol. XX, 58-64.
EIGURE LEGEND
Figure 1. Side view of a squid boat using its lampara net. The chain
is shown at the bottom; its purpose is to sink the net quickly, The cork
line rests on top of the water and allows the net to span the depth of
water. The drum at the stern of the squid boat pulls the net in. Lampara
nets require an 8-10 person crew.
Figure 2. Top view of the lampara net, showing the wings that come
together to form a pocket when the net is drawn in. Throughout this slow
and steady process, the lead chain drags the bottom,
Figure 3. Side view of the half-purse seine, which is currently
restricted in Monterey Bay. When the purse lines are pulled in on the boat.
the bottom of this net closes up like a satchel and all of its metal rings
coming together.
Figure 4. Top view of half-purse seine, showing purse line, metal
rings and lead line. While traditional purse seines have lead-lines made of
steel cables, the modified half-purse seine (experimental gear net) has a
lead-line that is encased in nylon. This may reduce damage to egg masses
compared to the chains of the lampara. Half-purse seines require a 3-4
person crew.
Figure 5. Linear Regression Analysis of Time-Zero eggs. 37 egg cases
were counted for number of embryos; mean L - 45.08 mm and mean n - 142.
Number is dependent on length because the slope of the regression line (b -
3.323708) is significantly different from zero (ts - 8.23, P § ,001), For
estimates of y - bx +a, a = -8.2561.
Figure 6. Linear Regression Analysis of Mid-Stage eggs. 21 egg cases
14
were counted for number of embryos; mean L - 48.82 mm and the mean n - 82.
Number is dependent upon length because the slope of the regression line (b
- 2.0962) is significantly different from zero
(ts - 3.883, P « .01).
For estimates of y - bx + a, a - -19.8536.
Figure 7. Linear Regression Analysis for Late Stage eggs. 42 egg cases
were counted for number of embryos; mean L - 48.82 mm and mean n - 89.
Number is dependent upon length because the slope of the regression line (b
- 1.26318) is significantly different from zero
(ts - 9.81, P « .001).
For estimates of y - bx + a, a - .312621.
Figure 8. Damage of Time-Zero eggs. Estimated Percentage of Mortality
(EPM) is given for five levels of damage (Control, D, D1, D2 and D3), Cross
hatchings show s.d. (if « 5 then s.d. is not shown). Significant increases
in EPM were observed in Dl and D3 groups (Us = 16) compared to the control
group.
Figure 9. Damage of Mid-Stage eggs. EPM is given for five levels of
damage (Control, D, D1, D2 and D3). Cross hatchings show s.d.. All groups
are above 408 EPM and egg cases receiving 2.1 kg of weight (D2) showed a
significant decrease in EPM (Us - 16) compared to the control group. Notice
that Control and D groups had EPM's » 753.
Figure 10. Damage of Late-Stage eggs. EPM is given for five levels of
damage (Control, D, D1, D2 and D3). Cross hatchings show s.d. (if § 5 it is
not shown). All groups with egg cases receiving upper levels of damage (D1.
D2 and D3) showed a significant increase in EPM (Us - 25) compared to the
control group.
Figure 11. Damage comparison between Time-Zero and Mid-Stage eggs: EPM
15
with increasing weight. Mid-Stage eggs are significantly higher than
Control, D, Dl and D2 groups of Time-Zero egg cases,
(Us - 16 for C, D
and D1; Us - 19 for D2).
Figure 12. Damage comparison between Time-Zero and Late-Stage eggs:
EPM with increasing weight. Only one significant difference occurred; at
2.1 kg of weight (D2) Late-Stage eggs had a significantly higher EPM (Us -
25)
Figure 13. Damage comparison between Mid-Stage and Late-Stage eggs.
Mid-Stage eggs have significantly higher EPM's for Control, D and DI groups
(Us = 20).
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