Rio Vista, Calif. – Rescuers stopped trying to herd two humpback whales down the Sacramento-San Joaquin Delta on Wednesday and resumed playing sounds that this time include the noises of a predator.
After 19 boats spent four hours trying in vain to get mother and calf under the Rio Vista Bridge, officials decided to return to the water at midafternoon to play three new types of sounds.
Four vessels were to roam the area until sunset as one used an underwater speaker to transmit sounds that included that of a killer whale attacking a gray whale cow and her calf.
They have held off using this tactic because there’s a risk the whales could beach themselves while fleeing, said Trevor Spradlin, a marine mammal biologist with the National Marine Fisheries Service.
A second recording is of whales feeding in Monterey Bay – humpbacks from the same group that scientists think these two whales belong to, he said.
In addition to using noises known to repel and attract humpback whales, scientists will employ computer-generated sounds at various frequencies.
Because the tones don’t exist in nature, no one yet knows how whales will react, Spradlin said.
This morning, four boats from three state and federal agencies were scheduled to begin the operation around 6 a.m. local time and continue until sundown.
At that point, officials from the National Oceanic and Atmospheric Administration will decide whether the effect of the new techniques warrant continuing through the Memorial Day weekend, said Lt. Cmdr. Jon Copley of the Coast Guard.
If the whales still haven’t responded, the vessels will honor NOAA’s request to give the creatures a temporary respite from the stimuli, he said.
The approximately 45-foot adult and her calf have open wounds believed to be caused by a ship’s propeller, keel board or skeg, a fin jutting below a boat’s outboard motor. Neither injury appears to be healing because of the creatures’ prolonged exposure to fresh water.
Also, the whales’ skins – a barrier against infection – have started to peel, Spradlin said.
Researchers are bent on saving these two whales because humpbacks are an endangered species, Spradlin said.
They are thought to belong to the Eastern North Pacific population of about 1,500, he said.
