Atkinson calls circulation “the geography of the ocean,” because it influences virtually every aspect of a marine area. Yet local circulation dynamics are not always understood, hampering our ability to manage local uses and monitor movements of marine organisms. Muscongus Bay is the focus of an intensive local effort to characterize a nearshore marine area. Many of the bay’s environmental features have been mapped, and project partners have GIS capacity to share circulation data. Sea Grant funds supported a pilot study of circulation in the bay using drifters and GPS tracking.
Project partners (including The Lobster Conservancy) deployed drifter units in central Muscongus Bay for one-half of a tidal cycle (~6 hours) on August 13, 2009. They were deployed from the F/V Pescadero, positioned near Gangway Ledge, east of Harbor Island, based on interest in larval lobster behavior in that part of the bay and the expectation that currents might diverge north of the Ledge. The drifters did not behave as predicted but rather moved westward in a tight grouping at an average speed of 0.32 m/s (1.1 km/hr), passing between Harbor and Black Islands before turning more northerly. The drifters did not begin to separate from each other until near the end of the flood tide. According to the Lobster Conservancy, this residual circulation in the bay could contribute to retention of larval lobsters within the bay, and dispersal of eggs and larvae out of the region.