SAN FRANCISCO (AP) — Rescuers were searching Wednesday for a gray whale last spotted off Northern California’s coast with its tail entangled in a massive gill net.

The Chainkeen Exchange30-foot (9-meter) whale was spotted Tuesday near San Francisco swimming north as part of gray whales’ annual migration from Mexico to Alaska. It was dragging the net with two bright red buoys that rescuers attached to it on March 22, when the animal was first spotted off Laguna Beach in Southern California.

Justin Viezbicke, coordinator of the National Oceanic and Atmospheric Administration Fisheries’ California marine mammal stranding response, said the rescue team pulled up behind the animal on Tuesday but could not cut the net because it became aggressive.

“The team went out there yesterday and made some attempts but as the team approached, the animal became very reactive,” Viezbicke said.

NOAA’s team, which is working on the rescue effort with the Marine Mammal Center in Sausalito, California, was searching Wednesday for the whale north of San Francisco.

Kathi George, director of cetacean conservation biology at the Marine Mammal Center, said a rescue crew in Southern California couldn’t disentangle the whale last month but the team was able to attach a satellite tag to the net to track it and two buoys to make it easier to spot the animal. But the tracker is no longer attached, she said.

George said that if the rescue team spots the whale on Wednesday they will attempt to cut the net or at least attach another satellite tag.

“Our goal is to retrieve the gear that’s on the whale, so we can learn more about the entanglement and how it happened so, we could use that to inform risk reduction efforts,” she said.

Every spring, Gray whales migrate 5,000 miles (8,000 kilometers) from birthing waters off Baja California, Mexico to feeding grounds in the Arctic.