Ocean Watch: Honu take great lengths to find place to lay eggs

This summer, I’ve seen mostly small green turtles around my usual snorkeling place, but last week I found myself running into grown-ups right and left. Our adult turtles, it seems, have come home.

I use the term “home” in this case to mean the main Hawaiian Islands, because the turtles spend most of their time here, where they graze on seaweed and snooze on our beaches.

But every four years or so, Hawaii’s adult greens heed the call of their hormones and migrate to the small sand islands inside French Frigate Shoals Atoll in the Northwest Hawaiian Islands. About 96% of our greens nest there, a remote place about 500 miles from Oahu. While there the turtles mate, and then the fertilized females dig holes in the sand and lay eggs.

Throughout the three- to four-month summer breeding season, a female lays approximately 100 eggs in each of four or five separate sand nests that she digs, and then covers, with her flippers. It’s an exhausting effort.

Most green turtles reproduce only once every four years, resting up the three years in between for the next big push. Each year, about 25% of our turtles head northwest.

Knowing where our turtles laid eggs this year is crucial in helping them survive, because disaster struck in 2018. Soon after the turtles’ nesting season ended last year, Hurricane Walaka destroyed most of their main nesting site, East Island, an 11-acre stretch of sand inside French Frigate Shoals Atoll.

With East Island gone, no one knew where the turtles would nest this year. To find out, National Oceanic and Atmospheric Administration scientists went to Oahu’s North Shore turtle hangout in March and performed ultrasound tests on several adult females to see which had eggs developing inside.

Through skill, perseverance and good luck, the team found one and attached a satellite tag to her back. The female’s formal name is OA48, but the delighted scientists nicknamed her Motherload, as in loaded with yolked-up follicles destined to be eggs.

Shortly after, Motherload swam to French Frigate Shoals, making the journey in 2-1/2 weeks. After mating with males that also migrated, Motherload laid four batches of eggs on Tern Island, the largest of the remaining islands in the atoll.

Read Motherload’s inspiring full story at 808ne.ws/ 2kewfzP.

A team of NOAA biologists also migrated to French Frigate Shoals to study nesting activity and collect reproductive data. This included etching and painting a temporary number on adults to keep track of them during the nesting season. Now that adults have migrated to home reefs in the main Hawaiian Islands, the public (or citizen scientists) can help identify important foraging habitats by reporting these numbers.

If you see a turtle with a number on its shell, please keep a respectful distance of 10 feet and take a picture of the number, noting the beach and date. Email the photo and information to respectwildlife@noaa.gov.

If you find a turtle in distress, call the statewide Marine Animal Emergency Hotline at 888-256-9840.

Producing offspring is an energy-intensive business for all species, but for Hawaii’s green sea turtles, it’s an extraordinary achievement, as is the work of tracking these migratory animals. Congratulations to all turtle moms and to the people who study them.