Photo by Florian Graner
In 2012, scientists discovered a dead harbor porpoise with a fungal disease that had not been previously documented in marine mammals in the Salish Sea. Over the next eight years, 20 more marine mammals were diagnosed with that same disease—mucormycosis.
Mucormycosis is caused by a group of fungi called Mucorales, commonly found in organic matter. People, terrestrial animals and marine mammals are all routinely exposed with little to no effects so long as they have no underlying health issues that weaken the immune system. However, once it takes hold, this disease spreads quickly and causes a very high mortality rate.
The harbor porpoise that died in 2012 was enough to pique the interest of Cascadia Research Collective’s Jessie Huggins and her collaborators, but the real work wouldn’t start until a few years later.
“We thought it was interesting and just sort of filed it away,” said Huggins, who worked on the first harbor porpoise case with Dyanna Lambourn of the Washington Department of Fish and Wildlife. “But then we saw some more cases in the following years and we thought it was really interesting and worth looking into further.”
Since the initial 2012 discovery, mucormycosis has been found in a total of 21 marine mammals in the Pacific Northwest. That includes 15 harbor porpoises, five harbor seals, and one Southern Resident Killer Whale (L95) - an adult male from a severely endangered population numbering just over 70 individuals.
“Once it was found in the killer whale, then it became a huge deal,” said Huggins. “That created the opportunity to look at [mucormycosis] not only in killer whales, but in a variety of marine mammals.” The broader interest that was created by the killer whale case brought researchers with additional expertise to this collaborative project, such as Linda Rhodes of the Northwest Fisheries Science Center, who analyzed tissue samples using polymerase chain reaction (PCR) to identify the exact fungal species involved.
The big question is whether there is a specific characteristic or combination thereof that makes marine mammals more susceptible to a disease that was not a threat prior to the last decade. Huggins’ study, titled “The Emergence of Mucormycosis in Free-Ranging Marine Mammals of the Pacific Northwest” and published in Frontiers in Marine Science in July of 2020, did not yield a definitive answer to that question, but it categorized all documented cases in the Salish Sea and set the stage for further study, which is happening now thanks to funding from the SeaDoc Society.
Southern Resident Killer Whales are a crucial part of the work, but with only one documented case on file, there are limitations to what can be gleaned from the necropsy data, but Huggins’ team is thinking out of the box.
“We’re looking at harbor porpoises, because they can be a good indicator species for killer whales,” she said. “We have data for 15 of them, most of them in Washington waters.”
The current study is investigating the role that chemical contaminants, metals, infectious diseases (such as brucella, morbillivirus, herpesvirus), and combinations of other conditions that might play a role in making individual marine mammals more susceptible. They’re looking at commonalities and differences between harbor porpoises that have succumbed to the disease compared to others that died of other causes. The goal is to identify factors that are associated with a higher risk of mucormycosis and use those to assess the risk of infection in Southern Resident Killer Whales.
Because the focus has been on harbor porpoises, with an eye toward how that might aid killer whale conservation, Huggins believes they are probably underestimating the occurrence of this disease in harbor seals, which strand at a higher rate but are not the subject of the funded research.
“Understanding the causes of death in marine wildlife enables us to see where human actions play a role,” says Joe Gaydos, SeaDoc Science Director. “That’s a major step in the right direction for improving the health of these animals.”