Shell Disease Prevalence In Offshore American Lobster Populations     Diane Kapareiko, Richard A. Robohm, John J. Ziskowski, George R. Sennefelder and Anthony Calabrese   NOAA, National Marine Fisheries Service, Milford Laboratory, Milford, Connecticut 06460 USA     During the period 1990-1992, 15,004 lobster from 146 commercial catches at nine offshore canyon sites surrounding the 106-Mile Sewage-Sludge Disposal Site were examined for signs of shell disease.  Overall, 1,184 lobster (7.9%) had lesions.  Females were more affected by this condition than males.  Shell-lesion occurrence was independent of carapace length.  Disease prevalence in female lobsters from canyons within the “Potential Area of Influence” of the 106-Mile Site were significantly higher than those found on lobster populations from canyons outside of this area.  However, logistic regression tests showed an equally strong regression of shell lesion occurrence with proximity to the old 12-Mile Dumpsite as that shown by proximity to the 106-Mile Dumpsite.  The possibility of multiple influences from both the 106-Mile Site and the 12-Mile Site on offshore shell-disease prevalence could not be discounted.  Data collection for the shell-disease study included not only evaluation of presence or absence of disease, but also measurements of lesion size and carapace length.  This was done in anticipation of developing a method that would determine the percentage of total surface area of each lobster affected by shell disease; this percentage would be the basis of a Disease Severity Index (DSI).  Twenty-six healthy, intact female lobster ranging 2.0 to 17.5 cm in carapace length were selected to establish a relationship between carapace length and total surface area.  Approximately 20,000 measurements were taken at 0.5- or 1.0-cm increments on individual body parts.  Using these measurements, circumferences were calculated at each increment using the formula for the length of a parabolic arc.  Areas were calculated for each body part by applying Simpson’s Rule to the circumferences and the totals were summed.  The mathematical relationship between carapace length and the total surface area of these female lobster was found to be a power function of the formy = 12.6889 X1.9677.  Surface area can now be derived and applied to our database.  The percentage of surface area covered by shell lesions, multiplied by 103, provides a DSI that may allow better statistical correlations between mean disease severity and the site of lobster collection.