Monk Seal Monday #138: Morbillivirus, Mobbing, and No More Fish Hooks

A news report broadcast earlier today confirmed a novel strain of morbillivirus killed a Fraser’s dolphin that stranded on Maui in 2018. Elsewhere in the world morbillivirus has killed hundreds of dolphins and/or whales. While only one dolphin has been confirmed to die of the highly infectious morbillivirus, it’s for the potential to spread to monk seals that NOAA vaccinates Hawaiian monk seals against morbillivirus.

Good news: KP1 has thrown his hook. Last week, on the heels of the news of a hooked Temp 606, KP1 turned up with a fish hook in his mouth. In both cases, the hookings were determined to be non-life-threatening. Rather than risk handling–and injuring–a wild animal, the seals were left untouched. And in both cases, the animals managed to help themselves by throwing their own hooks without the aid of human intervention.

WARNING: But not all monk seals seem to be helping themselves and their own species’ survival. The video below illustrates the phenomenon known as “male mobbing” in Hawaiian monk seals. It’s a disturbing turn of events, and you may not wish to watch it.

This interaction generally but not always takes place between a group of males, generally competing sub-adult males, and a single female and is called male mobbing.

In 2016, RK28 was observed with large wounds and abscesses on her back. It was determined these wounds were caused by male monk seals who had attempted to mount her and while doing so, biting her repeatedly on the back. The wounds can be severe and certainly disturbing-looking to our eyes. For good reason, it turns out.

According to the NOAA Pacific Islands Fisheries Science Center’s website, “Events involving multiple and single adult male Hawaiian monk seals exhibiting aggression towards adult females and immature seals has led to a significant number of severe injuries and deaths. Unfortunately, the loss of even a single female, and the loss of her lifetime reproductive potential, represents a significant setback to population recovery of this endangered species.”

Also from the NOAA PIFSC website:

Over an 11 year period from 1984-1994, 37 male seals were selectively removed from Laysan Island to restore a balanced sex ratio. These seals were translocated to Johnston Atoll (n=9) or the main Hawaiian Islands (n=21), placed into captivity (n=5), or died (n=2). Following removal, instances of injury or death from multiple male aggression events drastically declined. The removal of these males from the Laysan Island population has contributed to the restoration of a balanced sex ratio and has proven a valuable mitigation strategy.

Single male aggression events have most notably occurred at French Frigate Shoals and more recently at Kure Atoll. Intervention efforts include hazing of identified aggressors, translocating pups from areas where aggressive males frequent, treating injured seals when appropriate and removal of the adult male. The 3 adult males at French Frigate Shoals observed to repeatedly target pups, were translocated to Johnston Atoll (n=2 in 1998) or euthanized (n=1 in 1991). One adult male was brought into permanent captivity in 2013 after he had been observed injuring pups at Kure Atoll. This mitigation strategy effectively reduced pup deaths as a result of adult male aggression at this site.

To read more about adult male aggression, click here. And if you see a female with fresh wounds on her back, please report it to the Kauai Hawaiian Monk Seal hotline at 808-651-7668. This will allow the animal’s health to be assessed. If the injuries are severe, she may be treated with antibiotics to prevent the wounds from becoming infected. Keep in mind, Hawaiian monk seals have an amazing natural ability to heal. We’ve seen it time and again.