BOSTON — Researchers say an ocean experiment that was accidentally conducted amid the shipping silence after the Sept. 11, 2001 terror attacks has shown the first link between underwater noise and stress in whales.

The analysis was led by a New England Aquarium researcher. It showed a drop in the stress-related hormone in right whales following the attacks.

The drop coincided with a period of significantly lower ocean noise after ship traffic came to a near-standstill for security reasons following the attacks.

The analysis combined data from two experiments that happened to be occurring simultaneously. One involved acoustic recordings of right whales in Canada's Bay of Fundy. The other collected samples of whale feces, which contain stress-indicating hormones.

It wasn't until 2009 that a researcher realized the data existed for the analysis.