By Jan TenBruggencate
The Hawaiian monk seal is a mysterious species, a member of a small group of exceedingly rare or extinct seals, and the only one in the Pacific.
New genetic research has shown how it got to the Hawaiian Islands without having to swim around any of the world’s great capes: It swam across the Panama area at a time when North and South America were separated by ocean.
There were three known monk seal species, each in comparatively warm waters. The others are the Mediterranean monk seal, of which only about 400 survive, and the Caribbean monk seal, which is believed to have been extinct since it was last seen in 1952.
There are about 1,000 Hawaiian seals left. The number continues to decline in their main habitat in the Northwestern Hawaiian Islands. A small bright spot in their story is that they seem to be increasing in population in the Main Hawaiian Islands.
Most years, several pups are born to the endangered species on Kaua‘i beaches, and Ni‘ihau is reported to have an even larger population. Residents and visitors can view them from afar as they bask on the sand. It is both disruptive to the seals and dangerous to humans to approach them too closely — mother seals are big and can be aggressive. They can run to 7 feet in length and considerably north of 500 pounds.
It has always been clear they were related to the Mediterranean and Caribbean seals, but how exactly does the relationship work?
Researchers published in May a report in the journal ZooKeys based on genetic relationships of the seals. For genetic material from the extinct Caribbean seals, they collected samples from preserved seal skins in museums. The research collaborators were from Leibniz Institute for Zoo and Wildlife Research in Berlin, The Smithsonian Institution’s National Museum of Natural History, Fordham University and Marine Mammal Pathology Services.
Earlier researchers studying skull shape and other physical attributes had noted a similarity between the Hawaiian and Caribbean seals, and the DNA research confirmed they are much more closely related to each other than either is to the Mediterranean seal.
The distinctions are significant enough that the new research separates the Hawaiian and Caribbean seals into their own genus. In the new system, they will be (Hawaiian) Neomonachus schauislandi and (Caribbean) Neomonachus tropicalis, while the Mediterranean seal will remain Monachus monachus.
Genetic and other evidence suggests the original monk seal population was in the eastern Atlantic, and that the ancestors of Caribbean and Hawaiian seals swam away from Europe and Africa in the neighborhood of 6.4 million years ago.
Presumably there was a single New World population for aeons, and then the Caribbean and Hawaiian species diverged from each other about 3.6 million years ago.
Why? It was the same time the Panama isthmus closed up and formed a land barrier to seal migration. The land bridge separated the Pacific and Caribbean populations, allowing the two groups of seals to go their own genetic ways.
- Jan TenBruggencate is a Kaua‘i based writer and communications consultant.