It’s that time again — time when San Diego residents don layers, pile into a boat and roll out to sea, all in the hope of catching a glimpse of one of the most spectacular migrations in the animal world. It’s time to watch some whales. Birch Aquarium, partnering with San Diego Harbor Excursion, is one of several options residents have for whale-watching this year. Featuring narration by naturalists from Scripps Institution of Oceanography, cruises happen twice daily and last 3½ hours. Observers are guaranteed to see a whale, even if it doesn’t happen the first time around. Staci Shaut, coordinator for the whale-watching program at Birch, said guests are issued a ticket for another cruise if they don’t catch a good look at a whale. Gray whales are the main attraction, since it’s their migration season, but observers can also expect to see dolphins, squid and sunfish. In past seasons, passengers have also been treated to other whale species. Fin whales, sperm whales, minkes, orcas and the largest of all — blue whales — have all been sighted recently. “Other whales that we have seen in past seasons live in these waters, but we don’t always see them because they live farther out,” said Shaut. “The gray whales stay really close to shore, so that’s why they’re so great for whale watching.” Each year, gray whales undertake a roughly 12,000-mile, round-trip migration from the Bering Sea to the lagoons of Baja California. Between mid-December and mid-April, more than 20,000 whales make the trip as temperatures drop and ice covers much of their food sources up north. Females go to give birth to their calves in the lagoons and mature whales go to mate. For San Diegans, it’s a chance to witness this phenomenon that comes around only once a year. Dylan Edwards, a former guide for Hike Bike Kayak Sports, which offers a kayak whale-watching tour in La Jolla, said that although it may seem like a risky endeavor, being on a kayak near the whales is quite a thrill. “Obviously in a kayak, you’re not as fast as you are in a boat,” he said. “On other boats, you’re out there with about 300 other people, but on a kayak, everything is peaceful and quiet. You just hear the spray of the whales. It’s really intimate.” This year, like every year, scientists are not sure what to expect from the migrating giants. In recent years, some experts have observed a later start and end date for the gray whale migration. Wayne Perryman, of the Cetacean Health and Life History Program at La Jolla’s Southwest Fisheries Science Center, said this pattern of later migrations started in the 1980s when the peak of the gray whales’ journey was in early January. Now, he said, it is in late January. Although he and other scientists are reluctant to attribute this to any one cause, theories abound. One possible hypothesis is that as temperatures rise and arctic ice doesn’t form until later in the season, gray whales may stay up north longer until their food gets scarce. “The two symptoms we’re seeing is a later arrival here in Southern California and more calves being born farther north,” said Perryman. “Really, the whole arctic system is changing, and they’re very adaptable animals, so there are going to be shifts [in their behavior]. What the cause is, it’s tough to say.” BY BOAT • Birch Aquarium with Harbor Excursions: departing at 9:45 a.m. and 1:30 p.m. from Dec. 26 to April 3, (619) 234-4111, www.sdhe.com, $30 weekdays and $35 weekends (discounts for children, seniors and military) • Hornblower Cruises: departing at 9:30 a.m. and 1:30 p.m. from Dec. 11 to April 17, (619) 686-8715, www.hornblower.com, $34 weekdays and $39 weekends for adults, $17 weekdays and $19.50 weekends for children • Seaforth Sportfishing: departing twice daily from Dec. 26 to March 31, (619) 224-3383, www.seaforthlanding.com, $34 adults • H & M Landing: 3-hour cruises departing at 10 a.m. and 1:30 p.m. from mid-December through mid-March, and 6-hour cruises to Coronado Islands departing at 10 a.m., (619) 222-1144, www.hmlanding.com, $25 adults, $20 juniors and $17.50 children ($50 for 6-hour cruises) BY AIR • Barnstorming Adventures: biplane, air combat and warbird flights, including whale watching; cost varies, (760) 930-0903 BY KAYAK • Hike Bike Kayak Sports: departing at 9:30 a.m. and 12:30 p.m. from December through March, (866) 425-2925, www.hikebikekayak.com, single-person kayak $60, tandem kayaks $55 per person BAJA TOURS • Birch Aquarium: excursions of four, five or six days following the whales down to their birthing grounds in the lagoons of Baja California, (800) 661-1325, www.andiamo-travel.com, $590-$1,095 • H&M Landing: trips of nine or 11 days, (619) 226-1729 or (619) 226-8224, cost varies