DETECTION OF EGG REMOVAL FROM THE OVIGEROUS LOBSTER
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DETECTION OF EGG REMOVAL FROM THE OVIGEROUS LOBSTER
FOLLOWING CHLORINE BLEACH EXPOSURE
Edward A. Cogger
Robert C. Bayer
Department of Animal and Veterinary Sciences
University of Maine, Orono
Department of Animal, Veterinary and Aquatic Sciences
The lobster (Homarus americanus) fishery in the Gulf of Maine is being
threatened by the taking of ovigerous lobsters with the subsequent removal of
their eggs by dipping their tails in a sea water and bleach solution. Solutions equal
to or greater than 20 percent (v/v) commercial bleach will cause the complete
removal of the eggs in less than 2 minutes with a 50 percent solution taking only
one minute. However, this process causes chemical damage to the plumose setal
hairs on the pleopods which can be easily detected with a light microscope. The
research reported in this paper investigates this process and provides a method
of detecting the removal of the eggs so marine enforcement officers will be able
to prosecute the offenders.
Introduction
The illegal removal of eggs from berried (egg bearing, or ovigerous) lobsters, and
subsequent harvesting of these females, will result in reduced numbers of female breeders.
As this will be followed by reduced hatchings and harvests, it is an extremely consequential
problem for the lobster industry. The problem of illicit removal of ova from the ovigerous
American lobsters (Homarus americanus) is a long-standing problem which has been referred
to as “washing” or “scrubbing”. Templeman (1940) and Hughes (1965) describe several
methods for scrubbing the ovigerous lobster including using a stiff brush, a high pressure
hose, and compressed air.
The prosecution of most “scrubbed” lobster cases depended heavily on the enforcement
officer’s ability to observe the physical act. This was usually at a great distance from a
shoreside or boat position, and at the imperilment of the officer. To alleviate these obstacles
to enforcement, Hughes, building on the work of Templeman, has described a method for
detecting the scrubbed lobster based on specific physiological and biological characteristics.
These characteristics, when taken together, provided an investigative tool for the “field”
detection of the presence of ovigerous lobsters that have had their ova removed.
The biological method, as described by Hughes, was later enhanced by the use of
biological stains (Karsson and Sisson, 1973), particularly hematoxylin, to show the presence
of the “cement” or “glue” (Yonge, 1937) which bonds the eggs to the nonplumose setae on the
pleopods. At ovulation a complex biochemical outer coat surrounds the oöcyte which,
following spawning, forms an attachment stalk to the nonplumose setae of the pleopods. This
combines with an inner coat secreted by the oöcyte in response to fertilization forming the
fertilization envelope (Talbot, 1991). The staining of the nonplumose setae on the swimmerets
of a “scrubbed” lobster dramatically demonstrates the presence of remnants of these
structures (the “cement” or “glue”) which would only be present for the attachment of ova. The
combination of the biological method and the staining technique gave New England States
marine enforcement officers the needed tools in the detection of “scrubbed” lobsters (Morejon,
1975).
Recent information raises new concerns over the problem of detecting unnatural removal
of ova from ovigerous lobsters. Now, according to marine enforcement officials in New
England, a new and widely used method of egg removal entails chemical scrubbing using a
chlorine bleach dip. Evidence gathered over the past four years suggests that some fishermen
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Fall 1996
are dipping ovigerous lobsters in chemical solutions and within minutes are completely
removing all the ova and residual glue. Inasmuch as there are no obvious external signs of
this chemical treatment, it follows that enforcement using former detection standards is futile
and these lobsters can then be sold as non-berried lobsters. As a result, the marine
enforcement officers throughout the range of the Homarus americanus are faced with the
challenging task of proving that ovigerous females have had their ova removed after having
been landed by a fisherman.
The research reported in this paper was undertaken to (1) find a method for detecting
ovigerous lobsters that have been chemically scrubbed using chlorine bleach, and (2)
determine the relationship between chlorine bleach concentration and egg release time.
Materials and Methods
Detection of Chlorine Bleach Exposure. A search for a methods to detect chlorine bleach
exposure was made utilizing lobsters held in a recirculating sea water system in the Fisheries
and Aquaculture Research Group (FARG) research laboratory at the University of Maine. The
tails of five live lobsters were immersed in a solution containing equal parts of chlorine bleach
and sea water (50% v/v chlorine bleach solution) for 90 seconds. Following immersion, the
solution was allowed to drain from the tail and the lobsters were returned to their tanks. Three
egg bearing females were also immersed in the chlorine bleach solution for the duration it took
for the eggs to be removed. Lobster pleopods (swimmerets) were removed at approximately
5 hours, 2 days, and 4 days after treatment. An equal number of untreated lobsters served as
a control from which pleopods were removed at the same times as samples were collected
from treated lobsters. The pleopods were examined immediately after their removal using a
conventional light microscope. Following examination, pleopods were preserved in neutral
buffered formalin. Selected samples were also examined by scanning electron microscopy
(SEM).
Egg Release Time. Ovigerous female lobsters were either obtained from a Maine tidal
lobster pound or wild caught from the Gulf of Maine. These were held in a recirculating sea
water system in the FARG research laboratory until utilized in this study. Five solutions (5, 10,
20, 30, and 50% v/v) were prepared by mixing commercial bleach with artificial sea water
(Instant Ocean™; salinity 28 ‰). Ten lobsters were selected and assigned to one of the five
experimental treatments (2 per treatment). Each lobster’s tail section was submerged in the
bleach solution contained in a clear two liter polyethylene vessel for videotaping egg release
using a Sony CCD-V101 Hi8 mm camcorder. The time-to-release (TTR) in seconds of all the
eggs was determined from the videotape. These data were subjected to analysis by
regressing the natural logarithm (ln) of TTR on the ln of the bleach concentration using
Statview 4.0 (Abacus Concepts, Inc.). An exopod (the lateral, distal segment of the pleopod)
was removed just prior to immersion (to serve as a reference) and at 1, 3, 5, 7, and 14 days
after immersion from each lobster to determine the extent and duration of the damage to the
plumose setal hairs using light microscopy.
Results and Discussion
Microscopic examination of pleopods revealed distinct differences in the structure of the
plumose setal hairs between bleach treated and untreated lobsters. The setae found on the
pleopods of all untreated lobsters showed a characteristic feather-like pattern with pairs of
fine, uniformly arranged hairs extending from opposite sides of a central shaft (fig. panel a).
At times bits of debris were also seen in the hairs of the setae. Pleopod setae from all lobsters
that were dipped in bleach showed a deviation from the typical feather pattern. These setae
displayed highly disorganized, bent, and even missing setal hairs (fig. 1, panel b). The
DETECTION OF EGG REMOVAL FROM THE OVIGEROUS LOBSTER
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observed differences were true for all sampling times and also easily detected in the formalin
preserved specimens. Degeneration was more apparent at 48 hours after dipping than five
hours after immersion in the bleach solution. Scanning electron microscopy further demonstrated the feather-like appearance of the untreated lobster setae and the disorganized
structure of the bleached setae (fig 2, panels a & b). The setal hairs from untreated lobsters
appear to be relatively straight 1 micron strands. It is apparent from the SEM micrograph that
the setal hairs from bleach treated lobsters either appear twisted, bent, or entirely missing.
When missing, it seems as though they have been released from the follicles where they were
attached (fig 3).
Figure 1
Figure 2
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Fall 1996
Figure 3
Regression analysis of the egg release time data indicates that there is a very highly
significant (p<0.001) effect of the concentration of the bleach solution on the TTR of the eggs
with over 96 percent of the variation accounted for by the change in bleach concentration (R2
equaled 0.965). As the concentration of the bleach increased, the TTR became shorter,
showing a TTR of 1 and 2 minutes at slightly less than 50 and 20 percent, respectively (fig.
4). We believe that scrubbing times longer than 2 minutes are probably too long to be useful
to the fisherman. The plumose setae exhibited damage as reported above though the extent
of the damage decreased as the bleach concentration decreased. At 5 percent bleach
concentration, the damage was minimal but observable by light microscopy. The plumose
setae continued to exhibit structural damage for as long as 14 days and in the opinion of the
investigators would continue to do so until the next molt was completed.
The observed differences in pleopod setae may not be specific to chlorine bleach, but are
distinct, easily recognizable indicators that the lobster has been exposed to chemical irritants,
such as bleach. The detection of exposure to bleach, using this relative simple method,
provides a highly desirable tool for law enforcement. It is hoped that with the use of this
technique, the short sighted practice of chemical scrubbing of ovigerous lobsters will stop.
DETECTION OF EGG REMOVAL FROM THE OVIGEROUS LOBSTER
500
69
TTR = 813 x Bleach (-0.674)
R2 = 0.965
TTR (sec)
2 minutes
100
1 minute
30
1
10
Bleach (%)
Figure 4. The effect of bleach concentration on the time to release of eggs (TTR).
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Acknowledgments
The authors wish thank Deanna L. Prince of the University of Maine, Orono and Roy
Morejon of the National Marine Fisheries Service, Portland, Maine for their assistance and
cooperation on this project.
References
Hughes, J. T., “How Can You Tell a Scrubbed Lobster? (Appendix I),” Mass. Div. Mar. Fish.
Annual Rep. (1965).
Karsson, J., and Sisson, R., “A Technique for the Detection of Brushed Lobsters by Staining
the Cement of Swimmerets,” Transactions of the American Fisheries Soc., Vol. 102, No.
4, (1973): 847-848.
Morejon, R., Detecting Scrubbed Egg Bearing Lobsters, Conn. Dept. of Environmental
Protection Leaflet, (1975).
Talbot, P., “Ovulation, Attachment and Retention of Lobster Eggs,” Crustacean Egg Production, Eds. A. Wenner, and A. Kuris, 9-18. Crustacean Issues, Gen. Ed. F. R. Schram, 7.
A. A. Balkema (1991).
Templeman, W., “The Washing of Berried Lobsters and the Enforcement of Berried Lobster
Laws,” Newfoundland Dep. Nat. Resources Res. Bull. (Fish.) No. 10, (1940).
Yonge, C. M., “The Nature and Significance of the Membranes Surrounding the Developing
Eggs of Homarus vulgaris and Other Decapods,” Proc. Zool. Soc. London, Sec. A, Vol.
107, (1937): 499-517