Monk Seal Monday #87: Metabolizing at Sea.

Have you ever wondered how Hawaiian monk seals stay hydrated? Because unlike fish, they don’t purposefully drink salty seawater, right? Nor can they absorb water through their skin and gills, known as osmosis. But what about seawater? How do monk seals cope with all that salt?

Turns out, over millennia, Hawaiian monk seals, like other marine mammals, have adapted some unique metabolic systems that allow them to live in the ocean.

To start, monk seals “drink” whenever they eat in two ways. First, their favorite foods, fish and invertebrates, consist of 60 to 80 percent water. Monk seals also produce water as a byproduct when they metabolize carbohydrate and fat. But not all food sources are equal in their hydration benefits. Interestingly, the fattier the fish, the more water and energy available to seals.

While fish possess a similar salt content to that found in the blood of marine mammals, another food source of monk seals—invertebrates—possess a much higher salt content. Too, seals may ingest seawater as they feed. This presents a challenge: what to do about the excess salt? Turns out, the kidneys of marine mammals are uniquely adapted to handle saltwater that’s upwards of two-thirds saltier than their own blood. Their kidneys are multi-lobed like cows, in which each lobe has all the components of a metanephric (single) kidney the likes of humans. This multi-lobed kidney employs a two-step filtering process that allows seals to maximize water retention while excreting salt-rich urine that’s seven or eight times saltier than their blood.

Another metabolic process that monk seals employ is something called catabolism. This is when large molecules are broken own into smaller ones, as in when fat and protein reserves are broken down to provide energy and water. This comes in handy when monk seals fast. Fasting is a normal part of the lifecycle of Hawaiian monk seals. Healthy seals fast annually when they molt; females fast for five or six weeks while they nurse young, and pups, after weaning, generally fast, too, while they figure out where to find nourishment. Amazingly, monk seals are able to fast for extended periods without critical organ failure.

Hawaiian monk seals have been called “living fossils,” likely because they figured out long ago how to survive at sea and haven’t needed to make many adaptations since then.

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Monk Seal Monday #86: When A Nap Turns Into A (Potential) Nightmare

In October 2018, a hurricane swept north of Kauai and, for a time, sunk an 11-acre sliver of sand at French Frigate Shoals, an atoll that’s part of Papahānaumokuākea National Marine Monument. On this 150-foot stretch of sand, Hawaiian green sea turtles nest and Hawaiian monk seals haul out, molt, and pup. Luckily, the storm hit late in the breeding season, and the wildlife escaped potential catastrophe.

An increase in storms such as Hurricane Walaka is one characteristic of climate change. So, too, is sea level rise. Both can result in the loss of suitable habitat necessary for Hawaiian monk seals to rest, molt, and birth pups.

Another result of increased storms and, subsequent, big wave events is a changing coastline.

Recently, a juvenile male monk seal known as R1N1 hauled out at Kiahuna Beach in Poipu. His choice of napping location was beneath a severely undercut and actively eroding stretch of ground, resulting in a seemingly perfect cave in which to sleep. (In fact, this might mimic underwater ledges where monk seals are known to rest.) Unfortunately, this spot presented the very real possibility of ground collapsing on top of the seal. What’s more, he was partially entangled in a root system that was still intact with the ground above him. As R1N1 settled in for sleep, putting pressure on the roots, he could easily have buried himself by pulling down the ground above him.

This situation was reported by one of our volunteers at 10:50 a.m. By noon, with authorization from NOAA, a trained team of DLNR and NOAA representatives and volunteers assessed the situation and crafted a creative solution that included a pair of pruning loppers, a pair of windsurfing masts, and a crowding board. The roots were cut, the seal nudged with the windsurfing masts, and the crowding board used to direct R1N1 to the water. Once there, he slowly swam away, hauling out 500 yards down the beach where he rested for the remainder of the day.

There was an additional challenge facing the efforts—the numerous bystanders always present at busy Poipu. So before any actions—filed as “haze/displace” on the subsequent “take form” that was filed with NOAA—outreach was conducted.

All this to say: there are few ordinary days in the lives of those trying to recover the species of tropical seals known as Hawaiian monk seals.

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Field Report: January 2020

Monthly Update: The Kauai team logged 319 seal sightings this month. This included 39 individually identified seals.

January 319
December: 180
November: 223
October: 258
September: 203
August: 324
July: 239
June: 179
May: 262
April: 348
March: 350
Feb: 303

New:

·       As a volunteer arrived to assess a seal that had recently hauled out, she observed a man poking adult female R1KY with a stick. The volunteer conducted outreach and found the seal resting normally.

·       The general public reported that a small seal hauled out at Shipwrecks Beach on the south shore and was quickly chased back into the water by an off-leash dog. The seal was unharmed.

Updates:

·       Subadult female R7AA, dehooked the previous month, was re-sighted 4 times in January in good condition and completely healed from the hooking.

·       Five of the six pups born in 2019 have been sighted recently and continue to thrive, the sixth is likely on the remote Na Pali Coast.

·       Displacements: RJ36 was displaced (with permission from NOAA) from the Poipu Keiki Pool for the first time. Two weeks later he hauled out on the Keiki Pool Beach again, but was in an unsafe location for displacement so was not hazed off the beach.

·       Molting: RN44 molted at a remote north shore beach and RK90 molted at a remote west side beach, requiring little volunteer response and outreach effort. Adult female R313 also appears freshly molted.

·       Bleach marking: 2 applied this month.

Research/Support of Pacific Islands Fisheries Science Center:

·       Sub-sampled scat, molt, and tissue plug samples accordingly.

·       Logged all seal sightings for PIFSC database. Organized photos and reported sightings, molt tallies, survival factors to send to PIFSC.

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Monk Seal Monday #85: Estimating Size Class and Body Condition

Last week, we reviewed ways in which a database of photography is used to identify Hawaiian monk seals. But identification of monk seals is just one way in which photography aids the recovery efforts of these endangered marine mammal.

Photography can also help scientists provide an approximate age to monk seals. In the field, NOAA scientists use codes to indicate a size class, including pups, weaners, juveniles, sub-adults, and adults. (See below.) Here in the main Hawaiian Islands, the same can be done with photographs submitted by volunteers, especially if those photos consistently show the seal’s entire body.

In addition to close ups of unusual wounds, entanglements or other abnormalities, regularly submitted photos of a seal’s entire body also allows researchers to track its health over time, possibly revealing whether a seal is losing body condition or is pregnant.

So, as a reminder, when responding to a monk seal callout, don’t forget to take whole body shots of each side of the seal, as well as, head-on and rear-on photographs, if it’s possible to do so without disturbing the seal. You may not realize it, but you’re adding to a large–and growing–database of the life history of a monk seal. Some seals may even have a larger health record than your own medical file;-)

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