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Several penguin populations in the Antarctic Circle have dropped up to 50 percent in the last three decades, a new study finds; and the suspect in the case is most shocking of all- rebounding populations of whales. 

The brunt of the problem seems to fall on the shortage of krill –the tiny crustaceans high up on a young penguin’s menu– caused by warming seas and an increase in hungry whales. Fisheries biologist Wayne Trivelpiece has monitored population levels of Chinstrap and Adelie Penguins since the 1970s for the National Marine Fisheries Service in La Jolla, Cali.

“We see from direct measurements of krill that there's about 80 percent less out here than there was just 20 years ago,” said Trivelpiece. “So the probability of young penguins finding it often enough to survive during those first months of independence is much reduced."

Much of the collapse in krill is the result of rising sea temperatures, which actually reduces the amount of infinitesimally sized phytoplankton in the water column, starving many of the krill. The second “krill killer” is ironically an ecological success story in Antarctica- rebounding population of whales. 

"We don't have good data prior to the 1930s, but it appears that at least the 1930s to the 1970s were a real boom time for penguins, primarily because of the removal of competition in the form of whales," explained Trivelpiece. 

Now that many of the once sparse whale populations in Antarctica –species like Orca, Southern Right, Sperm and Minke– are returning, it seems the suffering of their flippered friends is just another example of the oceans ecological ebb and flow.