Monk Seals on the Rise: The National Marine Fisheries Service has released a draft assessment of the populations of marine mammals in waters around Hawai`i, among other areas. The date of the publication is July 2023 and includes assessments of seals, dolphins, and whales. For the most part, the assessments are unchanged since earlier reports. However, assessments for several species, including the Hawaiian monk seal, have been updated as of 2022, based on data gathered through 2020.
For the most part, the news is good. Monk seal numbers have steadily increased since 2013, when the estimate for the population stood at just below 1,300 seals. In 2020, that number had risen to 1,465, reflecting a rate of population growth of around 2 percent.
But ongoing threats to the species remain, including intentional killings of seals in the Main Hawaiian Islands (MHI). In the time period covered by the assessment, three such killings are known to have occurred – one on Kaua`i, two on Moloka`i. Since then, at least five more seals have been deliberately killed, three on Moloka`i in 2021, two on O`ahu in 2023.
Still other threats mentioned in the report are entanglement in fishing gear, most of it of foreign origin, and toxoplasmosis. From 2016 through 2020, the death of five monk seals (four of which were females) were attributed to toxoplasmosis, the assessment states.
Comments on the draft report will be received by NMFS through April 29. For a link to the report and instructions on commenting, see the Federal Register notice of January 29.
Disease in Dolphins: Monk seals are not the only marine mammal at risk from toxoplasmosis. Researchers at the University of Hawai`i at Manoa have confirmed the deaths of at least two spinner dolphins are attributable to toxoplasmosis – one stranded on Hawai`i island in 2015, the other on O`ahu in 2019.
Among the other disease-causing agents infecting marine mammals, including those in Hawaiʻi, are morbilliviruses. These have been responsible for mass strandings of whales and dolphins, but testing populations of animals for the presence of the virus has been nearly impossible.
Or it was until recently. A team at UH’s Health and Stranding Lab, part of the Hawai`i Institute of Marine Biology, discovered that the presence of Fraser’s morbillivirus, which causes respiratory and neurological disease, can be detected in the feces of marine mammals taken from seawater, even if the fecal material is present only at very diluted levels.
“This is the first time that a pathogen responsible for mass mortalities of dolphins and whales, and that affects multiple organ systems other than the digestive tract, has been demonstrated in the feces of whales and dolphins,” Kristi West, a researcher at HIMB, stated in a news release from the university. West is the lead author of the report on the research published in Marine Mammal Science last August.
The Fraser’s morbillivirus was unknown in Hawaiian waters until 2021, when researchers were able to identify it in a Fraser’s dolphin that stranded on Maui in 2018. “The 2018 stranding … revealed that we have a novel and very divergent strain of morbillivirus here,” West stated, noting that morbilliviruses are related to human measles and smallpox.
Fraser’s dolphins “are a poorly known pelagic species found throughout the world’s oceans,” a news release from the university noted in publicizing the discovery. “This research identifies morbillivirus as a significant threat to Fraser’s dolphins, which are highly social and interact closely with other dolphins and whales in Hawaiian waters.”
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