Humpback whales off the West Coast consume thousands of pounds of krill, plankton and small fish each day. Research shows that humpback diets reflect their surroundings, with the truck-sized whales filter-feeding on vast amounts of krill when cold upwelling waters prevail, but switching to schooling fish such as anchovies when warmer waters take over and the fish grow abundant.
The findings presented at the Society of Marine Mammalogy's Biennial Conference in San Francisco demonstrate that humpback foraging responds to environmental changes, and illustrates how marine mammals serve as sentinels of ever-changing ocean conditions. "Whales can be great indicators but only if we know what they are indicating," said Alyson Fleming, a postdoctoral researcher at the Smithsonian Institution who is lead author of the study. "Once we know that, they can shed light on the whole ecosystem as it is today and help us predict what it might look like in the future."
The Society's conference has attracted more than 2,000 marine mammal researchers, agency representatives, educators and conservation groups to San Francisco for its first return to California in 25 years. "This is the world's largest meeting of marine mammal professionals, and the place we all compare notes and look for patterns and trends that help us piece together important changes out in the ocean," said NOAA Fisheries research scientist Jay Barlow, a co-author of the new humpback research and president-elect of the Society.
Many presentations at the meeting revealed new details about the West Coast's diverse mix of marine mammals from whales to otters, including:
Shifting conditions off the West Coast are continuing this winter with the arrival of an El Nino climate pattern, which in the past have typically affected marine mammals, their habitat and the species they prey on. Sea lions are only one example of the species affected by a changing environment, but they also may be more vulnerable than more mobile whales, dolphins and porpoises, Barlow said.
"We've seen a record warm year off California in 2014 and this year is lining up to be a huge El Nino," he said. "We are seeing many changes in the distribution of whales and dolphins. However, I worry more about climate changes affecting pinnipeds than cetaceans. Pinnipeds are tied to land sites for molting and pupping whereas cetaceans can move fluidly in response to changing conditions."
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