Oops: "Between July 27 and August 19, 2010, while conducting development testing of its Nationwide Automatic Identification System (NAIS), the Coast Guard inadvertently tele-commanded most AIS users transiting the Eastern United States between lower Connecticut and North Carolina to switch to AIS frequencies other than the AIS default frequencies (161.975 MHz - Channel 87B - 2087 and 162.025 MHz - Channel 88B - 2088)...""As a result, those users within uniquely defined channel management
regions (as shown in the picture) will neither see nor be seen by
vessels operating on the default AIS channels when within these regions.
Similarly, vessels operating on default frequencies will not see or be
seen by those vessels that were inadvertently switched to other frequencies." You can download the USCG Alert 0710.pdf here.