February 9, 2006
CONTACT: Frank Smith, 508.910.6347
UMass Researchers Investigate Lobster Decline in Buzzards Bay
Water quality, shell disease among the suspects.
Researchers from UMass Dartmouth's School for Marine Science and Technology (SMAST) are working with the scientists from the Massachusetts Division of Marine Fisheries (DMF) to improve the assessment of lobsters in Buzzards Bay by using a time-tested methodologycounting.
Although a hand count of every lobster in the bay is effectively impossible, SMAST researchers are moving fishery stock assessment decisively in that direction. On the heels of their very successful methodology for video surveys of scallop stocks, the Marine Fisheries Field Research Group is taking a similarly direct approach to lobster research. As Brad Harris, the group's operations manager, puts it, "The actual observation of what's on the bottom is always the best; it's an absolute measure."
Fishery managers have long used catch data to estimate fish populations. But lobster populations in the bay have declined so much in the last decade that most lobsterman have had to move their traps offshore to catch enough to stay in business. Deprived of catch data, the DMF uses ventless traps, with no escape vent for smaller lobsters, thus giving a more accurate representation of population structure.
But what percentage of the lobsters in the area are entering the traps? One hundred percent? Fifty percent? Ten?
To address that question--i.e., to "calibrate" the traps--SMAST teamed up with the DMF and commercial lobstermen. Scuba diving on six sites in Buzzards Bay, researchers took a "hand-census" of the lobsters within a marked-off area, tagged them, deployed ventless traps, and waited to see how many tagged lobsters would end up in the traps.
Over the course of the 2005 field season, the divers logged 198 dives, tagged some 800 lobsters, and working from commercial boats provided by Fairhaven lobstermen Tom Blier, Henry and Aaron Cebula, and Larry Fowler. As they tagged each lobster, researchers recorded its size, reproductive condition, apparent health, and so forth. This information will contribute to the overall picture of the bay's lobster population, including the portion ready to reproduce in the next year and the prevalence of shell disease, helping scientists to anticipate whether the population will rebound, continue falling, or maintain its current size for the near future.
In parallel with the census effort, Prof. Jefferson Turner's Plankton Ecology Lab is conducting a study to shed light on the role that water quality may be playing in the variability of lobster populations in Buzzards Bay. As part of other scientific projects, Turner has compiled an 18-year baseline of monthly water samples at a number of sites in the bay. Eleven years of samples have already been analyzed for such things as chlorophyll, nutrients, and various kinds of plankton.
With such information, Turner can construct a timeline of Buzzards Bay water quality that straddles the lobster population crash of the past decade, and track individual parameters against changes in population size. Similarities in trend could reveal which, if any, water quality parameters have a role in lobster population decline in the bay.