When a seal births a two-head pup, should we be concerned?

Photo by Jeff Bradley / Burke Museum

Photo by Jeff Bradley / Burke Museum

You bet!

In the summer of 2013, Orcas Island resident Dennis King spotted a dead harbor seal on the beach near his house in Olga. He called the San Juan County Marine Mammal Stranding Network, and volunteers responded and collected the carcass for further study. Little did he know how interesting his discovery would turn out to be.

When SeaDoc interns Kay Wicinas and Liz Anderson examined the carcass they were surprised to find that the mother had died while trying to give birth. The following day when SeaDoc, The Whale Museum, and the Marine Mammal Stranding Network performed a complete necropsy, or animal autopsy, they discovered that this was no ordinary dystocia. A conjoined fetal twin that was too big to be birthed was the real cause of the problem.

Twins are very rare in marine mammals, and conjoined twins are obviously even more rare, about like hens teeth. This appears to be the first documented case of equally-developed conjoined twins in harbor seals.

Harbor seals are an important species for scientific study because they serve as good indicators of ecosystem health. They are in residence year-round and are high level predators, so studying them can help us discover emerging biotoxins or contaminants.

Because high levels of contaminants or naturally occurring toxins have been shown to cause genetic defects in domestic animals, the mother and twins were tested for a long list of known contaminants and toxins. Fortunately nothing was discovered, suggesting that these conjoined twins likely were caused by an inborn error of cellular division and not something in the environment.

The need to unravel such mysteries is one of many reasons SeaDoc puts such a high priority on investigating wildlife diseases.

Read the peer-reviewed paper by Jennifer Olson, et al., recently published in the Journal of Wildlife Diseases

(If you don't have a subscription to that journal, email us at seadoc@seadocsociety.org and we'll send you a copy of the paper.)

Join the Marine Mammal Stranding Network

If you’re interested in responding to stranded marine mammals in the San Juan Islands, please contact Jennifer Olson at The Whale Museum in Friday Harbor. (360) 472-1852 or jennifer@whalemuseum.org. Trainings happen in late Spring.

Keep your distance

Remember that the Marine Mammal Protection Act requires you to stay 100 yards away from marine mammals. If you spot a stranded marine mammal, dead or alive, please call the Stranding Hotline to report it. Their number is 1-800-562-8832.