It's time for the southward migration of humpback whales down the Pacific coast, and these huge marine mammals need to feed as much as possible as they swim to pack on blubber before reaching warmer waters in Mexico with little to eat for months.

There have been a lot of whales passing by Monterey Bay recently, and as whale-watch guide Captain Michael Sack tells KPIX, there have been an unusually large number of calves spotted this year.

"Seems like this year we’ve had more calves than I believe we’ve had in past years," he tells the station. "For us it’s pretty neat to see. We’re as excited as can be to just be seeing it every day."

Videos from other whale-watch boats like the one below show the abundance of surfacing humpbacks in the Bay this past week.

As Sack explains, calves aren't the ones feeding around Monterey — these babies likely born around December are still not eating solid food, and are still breastfeeding — but there are plenty of anchovies and sardines in the ocean right now to feed the adults, which he says is a good sign of a healthy ocean.

The whale sightings are abundant, Sack says, about seven miles from shore and they have been passing by in droves since he reopened his tour business in mid-June. Due to the pandemic, he's only filling his boats to 50-percent capacity, but he is still doing tours.

The whales make a 10,000-mile round trip each year between their breeding grounds in Mexico and their feeding grounds in Alaska, spending the winter down south and the spring up north. In between, they're swimming — and when they don't get enough to eat in the spring and summer, it can mean they die of malnutrition on the trip north the following year.

That is what marine biologists have been observing among the gray whale population in the last few years, with malnutrition being a leading cause of whale beachings. And hunting for food sources each spring has brought humpback and gray whales into San Francisco Bay recently, where they typically would not have ventured, and which puts them at risk for ship strikes.

Related: Blue Whales Make Rare Appearance Off San Francisco Coast, Prompting Warning For Ships