As many as 15 dolphins were spotted in the Shrewsbury and Navesink rivers.
But now just somewhere between seven and 10 remain.
Teri Frady, a spokeswoman with the National Oceanic and Atmospheric Administration, stressed today that a decision hasn't yet been made on whether to intervene.
But she says the matter will be decided by the end of the month.
The agency's considering two options: using a U-shaped flotilla of boats to try to herd the dolphins back out to sea, or using recorded "socialization sounds" of other dolphins to lure them from the river into Sandy Hook Bay and ultimately the ocean.
