Hoku endured some rough days before he died last spring. Three dogs chased him off one of his resting beaches, and he battled a minor tsunami that left him wedged between a pair of boulders in a lava field far from shore.
Observers noticed him looking thin in the few months before fishermen found him dead on a beach near the east Kaua`i town of Kapa`a.
In the end, disease took him.
Nicknamed “Star” in Hawaiian for the small white spot on his forehead, Hoku was a large, 10-year-old Hawaiian monk seal, an endangered species.
Hoku may likely have been the second Hawaiian monk seal to die this year from Toxoplasmosa gondii, a parasite transmitted primarily through cat feces and carried to the ocean in polluted runoff and sewage.
The first suspected toxoplasmosis case of the year came in January. While conducting his weekly seal search along the coastline of Moloka`i’s Kalaupapa National Historical Park, marine ecologist Eric Brown discovered a stillborn pup in a tide pool. His mother, apparently in good health, lay nearby.
David Schofield, marine mammal response coordinator for the National Oceanic and Atmospheric Administration’s Pacific Islands Regional Office, believes the pup may have been the first Hawaiian monk seal to die from a toxoplasmosis infection transmitted in the womb.
With only about 1,100 monk seals left in the wild, the deaths are “very concerning and put toxo as one of our primary concerns” for the species, says Charles Littnan, lead scientist for NOAA’s monk seal research program.
The overall population of monk seals is declining at a rate of about 4.5 percent a year. The good news is that in recent years, their numbers have been growing in the main Hawaiian islands. Now resource managers worry that in the midst of so many humans, interactions will likely increase, as will the seals’ chances of encountering diseases and contaminants.
No studies have been done in Hawai`i on how and where toxoplasmosis reaches the ocean and there are few efforts to control it. In California, however, researchers have found that it infects sea otters mainly though runoff from urban areas.
Flushing cat litter down the toilet is one pathway, since sewage treatment does not always kill the parasite’s hardy eggs, called oocysts. Studies have found that oocysts can live for at least two years in sea water.
Over the past ten years, the cat parasite has killed at least four monk seals in the main Hawaiian islands - two from Kaua`i, one from O`ahu, and one from Moloka`i - and perhaps six, experts estimate.
Those deaths “should be considered an absolute minimum since there are dead seals we never know about and ones we sample but are unable to determine a cause of death for,” Littnan said.
“We are only just beginning to understand the prevalence of the disease in the population and determine ways to mitigate the impact.”
Hunted to near extinction in the late 19th century, the Hawaiian monk seal was federally listed as endangered in 1976, after populations plummeted during the 1960s and 1970s, largely due to military disturbance.
Today, it is considered the most endangered pinniped in the United States. With a potential peak population of about 3,000 seals, NOAA predicts numbers will drop below 1,000 in the next few years.
The population’s core has long been in the remote, largely uninhabited Northwest Hawaiian Islands, but more and more, conditions there are killing them. Low juvenile survival due to starvation is by far the biggest problem facing monk seals. Some researchers speculate that overfishing may have caused a shift in predator dominance that is now making it nearly impossible for young seals to compete for food.
But diseased cats also are among the seals’ worst enemies, since their feces flow into the ocean via runoff and sewage.