Cheetahs are unfortunate examples of how genetics can be devastating. After a population bottleneck 10,000 years ago source, cheetahs have become so closely related that it's said you can use skin grafts from any two individuals without rejection. To put that in perspective, your own immediate family is probably too genetically distinct to do that for you. But cheetahs look like they're in great shape compared to Hawaiian Monk Seals, new research from the University of Hawaii has found.
Hawaiian monk seals (Monachus schauinslandi) were known to the native Hawaiians as Ilio-holo-i-ka-uaua, or "dog that runs in rough waters." Like the only other remaining species of monk seal, Hawaiian monk seals are considered critically endangered by the IUCN red list. The population was nearly hunted to extinction. On a single voyage in 1859, 1,500 seals were killed – more than the current total population in all the Hawaiian Islands. Despite massive conservation efforts, their numbers have dropped over 50% since the 1958, and have struggled even since being listed as endangered in 1983. Simulation models suggest that the population will decline 96% from its 2007 abundance within the next 45 years, down to less than 40 individuals, for reasons such as disease, competitors, or predators.
And part of the problem for the future, as extensive DNA testing of almost every living monk seal found in the past 25 years has found, is that these seals have the lowest genetic diversity of any mammal ever studied.
The study, published in the Journal of Heredity, estimates that the monk seals were reduced to a total population of around two dozen around 1890. Their genetic diversity is even lower than that of the Mediterranean monk seal, whose population is only 1/5 of the Hawaiian monk seal.
While the researchers found no evidence that the lack of diversity is linked to current population declines, which are blamed instead on high juvenile mortality, starvation and disease, they note that the paucity of variation is definitely a concern for the future. The poor genetic mix means that the seals are extremely susceptible to parasites other pathogens like the virus in 1998 which wreaked havoc on the seal populations. Just take cheetahs as an example – genetic problems are now limiting their ability to grow in number, and may ultimately lead to their extinction.
The Hawaiian monk seal can just look to its former Caribbean cousin to find reason to worry. Last seen in 1950 (photo from the Bronx Zoo in 1909), the Caribbean monk seal was recently declared extinct, making it the only seal to vanish due to human causes. With steady declines in the Hawaiian monk seals, it seems they may be headed for the same fate.
But there is still hope. Northern elephant seals were hunted to near extinction in the western US by the early 1920s, with less than 20 individuals surviving the slaughter. Despite the low numbers, populations have since bounced back to over 175,000 individuals – so even a species on the edge of extinction can rebound.
But yearly monk seal declines of about 4% are deeply troubling, especially considering the extensive effort put into their conservation. Some populations do seem to be growing - the seals off Maui seem fat and healthy. But others, like those off of Hawaii, are still emaciated and dropping. The researchers hope to use the DNA they've analyzed to ID thriving families and locations to better understand exactly what is killing off the ones that aren't. From there they hope to find even better ways to conserve this struggling species. If we can't improve our methods, it's likely that Hawaiian monk seals will go extinct within the next hundred years.
Schultz, J., Baker, J., Toonen, R., & Bowen, B. (2008). Extremely Low Genetic Diversity in the Endangered Hawaiian Monk Seal (Monachus schauinslandi) Journal of Heredity, 100 (1), 25-33 DOI: 10.1093/jhered/esn077