Humpback whales learn habitat loyalty from their mothers, Alaskan study shows

The loyalty of humpback whales to their annual feeding grounds in Glacier Bay and Icy Strait, Alaska, is passed down from mothers to their calves, marine biologists have shown. Understanding these familial patterns and site preferences is critical to helping the population continue to recover from losses during heavy whaling years, according to a recent study in Endangered Species Research.

The study, led by Sophie Pierszalowski of Oregon State University in the U.S., draws from work first done in the 1970s. Charles Jurasz, a high school teacher in southeastern Alaska, recognized that humpback whales have distinctive markings on their fins and tails. He began tracking whales in the two inlets by photographing them. Today biologists commonly use photo-identification as a research tool, and they often refer to decades-old photos to trace the movements of individual whales through time.

Most Glacier Bay and Icy Strait humpbacks migrate each year between their feeding grounds in Alaska and their mating grounds near Hawaii. Because the Pacific Ocean population is rebounding from concerning lows, Pierszalowski and her colleagues set out to examine whether other humpbacks are moving into the region, or whether the resident population is expanding its clan by having more calves that stick around.

The team began by documenting humpback whales with photos and genetic sampling. For the “contemporary population” in the inlets, the scientists focused on whales arriving from 2004 to 2006. During that time, Pierszalowski used a net to collect sloughed skin samples whales that breached, or she used a modified arrow called a biopsy dart. She also used catalogued data from Glacier Bay National Park’s photo database and 25 years of genetic sampling in a southeastern Alaska whale database.

With information on 689 whales, Pierszalowski traced family lineages by comparing the whales of Jurasz’s “founders population” with her “contemporary population.” The analysis led to the most thorough assessment to date of the loyalty of humpback whales to their feeding grounds.

The results showed that the population grew from within: 96% of the females that were genetically sampled in the 1980s were also found in the contemporary population. Either the original whales were still present, or their calves or “grandchildren,” suggesting the Glacier Bay whales’ strong connections to their feeding grounds are passed down through generations from mother to calf.

Study co-author Scott Baker, associate director of Marine Mammal Institute at Oregon State University, said he observed this phenomenon during his first year working with the Alaskan whales in 1983. “There was a whale nicknamed Chop Suey. He traveled the same route day after day after day, and that’s when I began to realize that whales have a strong attachment to location,” Baker said.

Heavy losses from international whaling led to ocean-wide exploitation of humpback whales, reducing their numbers in the North Pacific Ocean to less than 1,000 whales by 1966. Now, with protections in place, there are close to 21,000 humpbacks in the North Pacific—with a population growth of about 5 percent each year.

The study shows that protecting key habitats will continue to help the species recover, especially in the areas where migratory destinations are passed down through families. Efforts to protect such whales range from rerouting shipping traffic to freeing humpbacks that become entangled in fishing gear.

The U.S. National Oceanic and Atmospheric Administration (NOAA) recently removed several populations of humpback whales from the endangered species list. “It should be a celebration of success,” Baker said, “but there is always a little trepidation as well.”

Dr. Phillip Clapham, leader of the Cetacean Assessment and Ecology Program at the NOAA Marine Mammal Laboratory in Seattle, Washington, maintains that de-listing the species isn’t a bad move. “People are upset about that. They think this is removing protection of the humpback whale,” Clapham said. “It actually isn’t because they continue to be protected under another law.” That law, in the U.S. Marine Mammal Protection Act, helps ensure that organizations charged with safeguarding whales will focus resources on populations needing the most care.

“The most exciting thing has been understanding the individual life histories of these whales and showing that they were so important for the population increase,” said Pierszalowski. “It is a really great success story.”

Citation:

Pierszalowski, S. P., Gabriele, C. M., Steel, D. J., Neilson, J. L., Vanselow, P. B., Cedarleaf, J. A., Straley, J. M., and Baker, C. S. (2016). Local recruitment of humpback whales in Glacier Bay and Icy Strait, Alaska, over 30 years. Endangered Species Research, 31, 177-189. doi:10.3354/esr00761

Teresa L. Carey is a graduate student in the Science Communication Program at the University of California, Santa Cruz. Other Mongabay stories by UCSC students can be found here.

Editor’s note: the original version of this post misspelled Dr. Clapham’s last name.