Orca killings of gray whale calves in California's Monterey Bay have increased substantially in the last week of April.
According to marine biologists, the killing spree has been unprecedented and the frequency went up after April 20.
Since the said date, four gray whale calves haven killed in a span of 8 days, said marine biologist Nancy Black. The unprecedented Orca attack also surprised many scientists.
"This has never happened in my thirty years," said Black.
Shawn Johnson, director of veterinary science at California's Marine Mammal Center said it is not unusual for orcas to hunt for calves of gray whales.
A family of killer whales is mounting the attacks with 33 orcas involved in it, according to Black.
She also noted the unusual speed the orcas had been killing the calves this year. In the past, it took several hours. This year, in just 20 minutes, a pod of orcas was pulling down a calf from its mother's care and killing it.
Killer whales also train juniors in the pod on attack methods. Faced with the risk of counter attack by the mothers of gray whale calves, including harder slamming, training the younger ones is essential in enhancing their predatory skills.
Calves Migrating From Mexico
The calves and mothers migrate from Mexico and they travel to California and beyond. This year, their arrival in California was late by many days and hungry killer whales seemed to have been waiting for them, Black said.
According to another scientist, Alisa Schulman-Janiger, the late arrival of gray whales was evident from the ACS/LA annual census count which noted only 2-5 calves did pass Pt. Vicente until April 20. However, 14 calves were spotted a day after.
The migration gets a late start for mothers and calves because they would wait for the calves to grow up and gain weight before taking the long migration trip, Black added.
Killer Whales And Mysterious April 20
It appears that killer whales of California have a mysterious date of April 20. It is usually the date on which mammal-eating whales are consistently spotted in Monterey Bay.
This has been a regular fixture since 2009. According to Black, it looks like a "luck of the draw kind of day."
On April 20, 2016, some whale watchers also noted a family of killer whales training the younger ones with hunting tactics.
Monterey Bay Favorite Of Orcas
From the breeding grounds, the new calves accompanied by mothers swim toward the feeding grounds near Alaska. The gray whales also try to traverse through shallow waters to avoid the attack of killer whales.
However, the deep submarine canyon off Monterey Bay is a favorite hub for the orcas as it's easy for them to prey upon the calorie rich gray whales to feed their families.
According to a study by Robert L. Pitman with co-authors Black and Schulman-Janiger, unlike the fish-eating killer whales, mammal-eating killer whales are silent while hunting because their preys have strong hearing abilities.
Good Time For Whale Watchers
Certainly, the killings of gray whale calves by orcas have given whale watching enthusiasts a good time. Many bought front-row seats to witness it live. For them, it was a great opportunity to see the action seen only in movies.