Tag Archives: Harbor Seals

Mammalian Diving Reflex

Harbor Seal, Kodiak Wildlife, , ,

The mammalian diving reflex is a fantastic biological adaptation intrinsic not only to marine mammals but also to land mammals, including humans, whose ancestors once lived in the ocean. I am currently editing my wildlife book and was once again awed by how deep some marine mammals dive and how long they can stay below the surface without breathing. I think the mammalian diving reflex represents one of nature’s most incredible adjustments for air-breathing mammals required to find food in an inhospitable environment void of air.

What is the mammalian diving reflex? Biologists mostly have studied the reflex in harbor seals, so I will use a seal to explain the elements of the physiological changes. A harbor seal can dive as deep as 1640 ft. (500 m) and stay submerged for over twenty minutes. When it dives, a harbor seal’s heart rate slows from its normal rate between 75 to 120 beats per minute down to just four to six beats per minute. Blood shunts from peripheral tissues tolerant to low oxygen levels and flows to the heart, brain, and tissues dependent on a constant supply of oxygen to survive. These adaptations allow the seal to conserve oxygen while it dives and searches for food.

Seals utilize additional adaptations to conserve oxygen and withstand the rigors of increased pressure when they dive. Before a deep dive, seals exhale several times to collapse their lungs, and they then store their oxygen in blood and muscle tissues instead of in the lungs. Harbor seals have a proportionately higher blood volume than land mammals of the same size, and seals also possess ten times more myoglobin than humans. This oxygen-binding protein helps prevent muscle oxygen deficiency.

Researchers originally believed the diving reflex was an automatic response triggered by breath-holding and submergence in cool water. In recent studies, though, scientists attached a device similar to a Fitbit to harbor seals. The device records blood flow and oxygen levels in the seal’s brain, and the study produced some interesting results. Seals can control their diving reflex. Seals contract their peripheral blood vessels beginning 15 to 45 seconds before they dive, and they restore normal blood flow to their blubber several seconds before they reach the surface. When seals are feeding, they return to the surface to breathe but often don’t stay there long enough to restore normal oxygen levels. Researchers also learned that seals slow their heart rates more if they plan to stay underwater longer.

Biologists hope to learn if other animals, including humans, can also consciously control their dive reflex. The world’s top freedivers can descend to a depth of 426 ft. (130 meters) and return to the surface, and the record for breath-holding without moving tops 11 minutes. Are these free divers able to control the physiology of the diving reflex to accomplish these incredible feats?

The next time you see a harbor seal, pause for a moment to consider the rigors this animal must endure just to eat dinner.

I hope you are well and navigating our changed world. Life remains quiet here in the wilderness of Kodiak Island, and we feel oddly removed from the biological havoc wreaked by this virus. Even here, though, we have been touched by the economic disaster the world faces. I look forward to better times for all of us soon!  Take care.

Join the Battle of the Books contest, and you could win a $500 Amazon Gift Card! I am very excited to have my novel, Karluk Bones, included in this contest.

This image has an empty alt attribute; its file name is IMG_1316-4-768x1024.jpg

Robin Barefield is the author of four Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter, and Karluk Bones. You are invited to watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.

Mystery Newsletter

Sign Up for my free, monthly Mystery Newsletter about true crime in Alaska.
Open publish panel

Spring

Bald Eagle, Fin Whale, Humpback Whale, Kodiak Wildlife, Red Fox, Sitka black-tailed deer, Steller Sea Lion, Writing, , , , , , , ,

Bald Eagle in Flight

According to the calendar it is spring, but in Alaska, we won’t see much evidence of spring for another six weeks. The days are getting longer, and when the sun shines, I can feel some warmth in its rays, but it easily could snow six inches tomorrow, and no one would be surprised if the temperature dropped into the low twenties or even the teens.

After an abnormally warm winter this year, I don’t mind waiting until late May for wildflowers and leaves, but before the first forget-me-not blooms, other signs of spring will be evident. Bald eagle pairs will soar, circle, dive, and even cartwheel during their mating rituals; schools of herring will arrive to lay and fertilize eggs; and baleen whales, seals, and sea lions will follow the tasty herring into the bays. I dream about sitting on our dock on a sunny day, watching whales and other sea mammals chase and feed on herring. Some years the show is spectacular, and other years, the herring run is insignificant, and the whales are absent. The red foxes are also active in the spring, and their haunting mating screams often awaken me. By early June, we should start seeing does and their newborn fawns. By then, the eagle pairs will be tending their nests as their eggs hatch and the chicks depend on them for a nearly constant supply of food.

I am busy this time of year getting the camp ready and the meals cooked for the spike camps for our spring hunting season. I also have a trip planned to visit my family in Kansas in mid-May, so I can watch two of my nephews graduate from high school. Meanwhile, my novel, Murder Over Kodiak, is being re-released by a small publishing company in Anchorage, so I’m preparing for another round of promotion, and that is hard work. The first thing I’m planning to do is to host a “virtual” book-release party on Facebook. I’ll write more about this next week. For now, I’m trying to learn everything I can about hosting a virtual party. It’s overwhelming, and I hope I’m not in over my head! I admit that I have an uncomfortable relationship with social media.DSC_0168

Between my day job, promoting my novel, keeping up with my blog and my mystery newsletter, working on my next novel and my other writing projects, and getting ready for a trip to visit my family, my spring will be busy. No matter how rushed I am, though, if the sun is shining, and the wind is calm, you can find me sitting on our dock, craning my neck to watch eagles circle and soar, and inhaling the sweet, salty scent of the low tide while scanning the beach for foxes eating clams and mussels. I’ll also be glancing hopefully at the ocean for roiling schools of herring, and listening for the powerful exhalations of large fin and humpback whales. Spring is my favorite time of year, and I am never too busy to enjoy it. I’ll let you know what I see.

Fin Whale near Kodiak Island

Tell me about your spring. I want to hear about the beautiful tulips, daffodils and other flowers already blooming in most places, or if you live in New Zealand or anywhere else in the southern hemisphere, how is your autumn?

If you haven’t already done so, sign up for my mystery newsletter. I am working on my next edition. Also, I apologize to anyone who has recently tried to order my novel Murder Over Kodiak. As I mentioned above, it is currently being re-released, and it will be available again soon with a bright, new, shiny cover. I’ll give you a sneak preview next week and tell you about my mixed emotions going from an indie author/publisher to working with a publishing house.