Session I: Crustaceans
Richard A. Robohm, John J. Ziskowski, George R. Sennefelder, and
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 (CL), but strongly related to location (proximity to the 106-Mile Dumpsite as well as to the 12-Mile Dumpsite).† 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 is the basis of a Disease Severity Index (DSI).† An estimate of lobster surface area could be derived mathematically from carapace length, for both male and female lobster in our database, using the formula y = 1.1034 + 1.9677 * log(CL). 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 site of lobster collection.
Regression Tree analysis of this multi-variate database indicated that, unlike prevalence, the most important variable affecting the DSI was carapace length. Overall, DSIís for smaller lobsters (CL < 95 mm), were significantly higher (p < 0.02) than larger lobsters, regardless of sex or location.† Small females had significantly higher DSIís (p < 0.04) than large females.† Males showed no significant differences when similarly compared.† A complete non-parametric regression analysis of our DSI in relation to proximity to the 106-Mile Site, may indicate whether sewage sludge dumping had any effect on the severity of shell disease lesions in offshore American lobster populations.
The decapod crustacean fauna inhabiting estuarine, neritic, and continental shelf waters off the east coast of the United States (Maine to central Florida) is rich and diverse.† Although seemingly well known, decapod faunal composition and taxonomy in this region continues to change.† The decapod fauna off the eastern United States now comprises 366 species of which 65% are crabs, 30% shrimps, 3% thalassinids, and 2% lobsters.† Ten species new to science have been discovered since 1982, when the last comprehensive review of the decapod fauna from this region was completed.† Thirty-two species have either been reassigned to different genera (15 of which are newly described) or placed in synonymy.† Sixteen higher level taxonomic changes (new superfamily, family, and subfamily designations; elevation of subfamilies and subgenera to families and genera, respectively) have also taken place.† New methods, access to new material, and recent investigations into higher level systematics provide the foundation for better understanding of evolutionary relationships and constructing more meaningful hypotheses to address questions, not only in the field of systematics, but also those in comparative biology.
The NOAA-funded "Northeast Consortium" provides support to the fishing industry to conduct collaborative research with scientist. The Environmental Monitors on Lobster Traps (eMOLT) is one such project. Phase I, beginning in year 2000, distributed temperature probes to over 50 New England lobstermen represented by four associations (Atlantic Offshore, Mass, Maine, and Downeast). These small (~3cm) instruments cost less than $100, internally record hourly temperatures with an accuracy of less than 0.1įC, and last for several years. They are deployed for multiple months at fixed locations distributed throughout the Gulf of Maine from the canyons on the southern side of Georges Bank to the mouth of the St. John River. Phase II, this year, provides a set of 9 Seabirds for monitoring salinity changes as well. The objective will be to occupy the same locations annually to obtain an index of both large-scale/long-term variability as well as a means of potentially tracking pockets of water mass that advect through the region. Phase III, next year, calls for setting up a series of computer stations/data management centers along the coast to help participants in downloading and documenting their deployments. Understanding the biological significance of the physical variability will be a secondary (but potentially worthwhile) byproduct of the results and one that the participating lobstermen enthusiastically await.† Details are posted on the project website http://www.nefsc.nmfs.gov/~jmanning/emolt.html, including links to, for example, "Results from the Field," "Data Access," and much more.
Keywords: temperature, lobster, environmental monitoring
Stehlik and Carol J. Meise
Cannibalism by large blue crabs is a well-recognized source of mortality of juveniles of the same species.† We initially determined the probability of being cannibalized with a series of experiments in 2.3 and 0.9 mm diameter tanks, pairing one adult crab >120 mm carapace width with a juvenile from one of the size classes ranging from 20-29 mm to 100-109 mm CW.† At size classes > 50-59 mm, prey crabs were almost never eaten.
Experiments were then conducted in 0.9 m diameter tanks to determine the mechanisms of attack and avoidance.† After releasing the predators, the arenas were videotaped for 24 hr.† Predator crabs exhibited behaviors such as inspect, stalk, chase while swimming, lunge with one chela outstretched, corral, consume, or maintain distance if the prey crab was large.† Prey crabs used swimming escape, maintaining distance, autotomy, and burial to avoid capture.† Prey 20-39 mm could bury completely in the sand, and if they did so before the predator detected them, they were never attacked.† If they did not bury, they were usually consumed.† Some stood behind the central standpipe where they were hard to see, and it was awkward for a large crab to reach around with its chelae.†
Several field studies of blue crab vulnerability to predation have used tethering to keep the prey in one location.† Tethering is controversial because in some studies, the tether causes unusual behavior, such as entanglement or inability to bury.† Our predation rates were lower than those from laboratory studies with tethered crabs, although the maximum size of vulnerability remained similar.