None of the rescue crews spotted the dolphins in searches Thursday as they patroled the Shrewsbury River in central New Jersey, and it was feared that the bottle-nosed dolphins died in the extremely cold waters.
Dolphins can suffer from frostbite and even pneumonia.
The plight of the dolphins, who had made the river their home since the summer, attracted wide public attention. A team of rescuers tried to coax them to swim north toward the Atlantic, but dolphins have an internal clock that tells them to swim south when the weather gets cold, and the Shrewsbury River has no southern outlet. The rescue crews included representatives from the U.S. Coast Guard, the state Marine Police and the National Marine Fisheries Service. For the last few days, only three of the four dolphins were seen in the river and it was believed that one had already died. Marine police stationed in Sea Bright had unofficially adopted the dolphins, which had been frolicking in the river since July.