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.

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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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


·       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.


·       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.

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.

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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.

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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;-)

It’s not uncommon for monk seals from Niihau–where they aren’t tagged–to venture over to Kauai. Earlier this month, an untagged Hawaiian monk seal male showed up on the north shore, hanging out in the same general area for seven straight days, and it was assumed he was from Niihau. Volunteers managed to take pictures pinpointing several unique scars that should have made it easy to identify him. But his scars didn’t match any such seals in the NOAA database, and he was given the identification of R406. Then, seemingly as soon as he appeared, he disappeared, presumably back to Niihau. But last week, he was sighted hauled out on the shores of Oahu. Is this just the beginning of his journey? Or did his journey start farther northwest of Niihau? And where will he venture next? At least, he’s now well identified and logged in the database.

Langley 1

PC: Langley

Honnert 1

PC: Honnert

Honnert 3

PC: Honnert

Langley 2

PC: Langley

Honnert 2

PC: Honnert

Monthly Update: The Kauai team logged 180 seal sightings this month. This included 32 individually identified seals.

December: 180
November: 223
October: 258
September: 203
August: 324
July: 239
June: 179
May: 262
April: 348
March: 350
Feb: 303
Jan: 284


  • Subadult female R7AA was sighted with a medium sized circle hook in her left cheek. The Kauai team responded and were able to capture her on the beach and remove the hook without complications. A 2-foot heavy gauge monofilament leader and pigtail swivel was attached to the hook which presented a serious entanglement and drowning hazard. The seal was immediately released and has been sighted since with no signs of infection.
  • An untagged adult female that has not been sighted on Kauai previously hauled out at Poipu and has since become a somewhat regular seal on the south shore. This seal was previously sighted on Niihau in 2017 with a pup and has an ID of R371. She has numerous scars and can be easily identified, even without flipper tags.
  • Another untagged Niihau adult female was sighted for the first time on Kauai’s north shore. Her ID is R367.
  • Another untagged likely Niihau seal molted at a remote east side beach. He is a new seal to Kauai and has a temp ID of Temp361.
  • Yearling RL58 observed with a large fresh cookie cutter shark bite very close to the genital slit. The seal was closely monitored for possible infection, and the seal has quickly recovered.
  • A volunteer observed a tourist attempt to pet the large adult female RK90 at a west side beach. The seal responded by leaving the beach. Outreach was conducted by the volunteer.


  • RH38, the seal rehabbed at KKO and released in July, continues to thrive on north shore. Her tracking tag remains attached, however the battery has died so no further data is being transmitted.
  • All of the 6 pups born this year have been sighted recently and continue to thrive.
  • Displacements: No displacements this month.
  • Molting: Adult male RN02 spent 3 weeks at the busy Poipu Beach in pre-molt, molt, and post-molt which required extensive volunteer coverage. One other seal molted this month in less busy areas.
  • Vaccinations: A booster morbillivirus vaccine was given to new juvenile seal R1NI.
  • Bleach marking: none this month.

Research/Support of PIFSC

  • 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.

Here’s some year-end data that might make for some interesting reading and analysis the next time you’re at the beach. So, have at it!

Grand sightings total:

o   3,154 or 8.9/day monk seal sightings on Kauai in 2019

o   3,253 or 8.9/day in 2018

o   3,621 or 9.9/day in 2017

o   3,236 or 8.9/day in 2016

o   3,321 or 9.1/day in 2015

o   2,516 or 6.9/day in 2014

Kauai population:

o   67 unique individual seals sighted on Kauai in 2019

o   60 in 2018

o   60 in 2017

o   56 in 2016

o   53 in 2015

o   47 in 2014)

Other stats:

  • Births: 6 total born on Kauai.
  • Mortalities: one confirmed mortality in 2019 and one suspected.
  • Niihau Seals: sighted a minimum of 5 new seals in 2019 likely from Niihau.The Kauai team flipper-tagged 2 of these.
  • Displacements: 21 total displacements occurred.

o   15 displacements from unsafe or unsuitable locations (boat ramps, beach roads, sidewalks, etc).
o   6 displacements from the Poipu Keiki Pool.

  • Vaccination for morbillivirus efforts:

o   4 seal pups and 1 new juvenile seal were fully vaccinated on Kauai.

  • Bleach marking effort:

o   9 bleach marks were applied

Stranding Responses in 2019:

  • 7 monk seal stranding responses:

o   RH38 – captured and transported to Ke Kai Ola for rehabilitation. The seal was emaciated due to unspecified blunt trauma to the rear flippers resulting in a systemic infection and a cascade of medical complications. The seal recovered and was released back on Kauai.

o   RKA6 – captured on the beach and a large circle hook was removed from the mouth.

o   NG00 – captured on the beach and a large circle hook was removed from the right cheek. The seal had been hooked for over 2 years but was never sighted in a location safe for capture and handling.

o   R7AA – captured on the beach and a medium size circle hook was removed from the left cheek.

o   Unknown adult carcass – discovered on Niihau and transported to Kauai for partial necropsy.

o   RH58 and pup – assisted pup by cutting the umbilical cord which remained attached to the placenta. This posed a hazard to the pup near the wave wash which could have pulled the pup out to sea.

o   Adult Female – closely monitored and evaluated for emaciation in the months after weaning her pup. The seal most likely died of natural causes and old age.