TT40: The Monk Seal Moved Off Laysan, Then the First Operated On for a Swallowed Fishhook

TT40 resting on a beach. NOAA Fisheries.

A pup on Laysan

When monk seal researchers reached Laysan Island in 1984, a plump male pup got his plastic flipper tags and, with them, his name: TT40. NOAA Fisheries chose him as its monk seal of the month for August because his life touched several of the efforts to save his species.

TT40 as a yearling on Laysan in 1985, with temporary bleach marks reading "40". NOAA Fisheries.

Too many males

Laysan had long had far more adult males than females, and with it a dangerous behavior: multiple-male aggression, when several males try to mate with one seal at once. It happened elsewhere in Hawaiʻi, but most of all on Laysan. From 1983 to 1994, an average of 4 percent of the island's adult females died of the injuries every year, which skewed the sex ratio further still.

In 1994 NOAA moved 21 adult males from Laysan to the main Hawaiian Islands. Laysan's sex ratio became nearly even, and deaths of females from male aggression fell by more than 90 percent.

Choosing which males to move took care. Male monk seals have a hierarchy, and researchers knew each male's rank from careful records of their encounters. Subordinate males were the ones most often involved in group attacks, so to avoid upsetting the social order the team took only subordinates, especially those seen being aggressive toward females. TT40, then 10, had not been seen attacking females but was subordinate, so he went.

Males in temporary pens on Laysan in 1994, before transport. NOAA Fisheries.

Moving one of the males to the ship in 1994. NOAA Fisheries.

He was carried by ship and released off Hawaiʻi Island. Neither he nor any of the other relocated males is known to have taken part in a group attack since.

Kauaʻi, and a fishing line

TT40 stayed on Hawaiʻi Island for at least a year, then wandered and settled on Kauaʻi. In 2004 NOAA included him in a study of monk seal foraging and health, fitting him with a satellite tag.

TT40 on Kauaʻi in 2004, tagged for a study of foraging and health. NOAA Fisheries.

Later that year he was seen with about 15 feet of monofilament line trailing from his mouth. A rescue team caught him, and the U.S. Coast Guard flew him to Oʻahu. Under general anesthesia, veterinarians looked inside with an endoscope, a flexible tube with a camera, and found a large circle hook and its gear. Only abdominal surgery could get it out, and it was scheduled for the next day.

Preparing to anesthetize TT40. NOAA Fisheries.

Prepping for surgery. NOAA Fisheries.

The first operation of its kind

It was the first surgery under anesthesia to remove a swallowed fishhook from a Hawaiian monk seal. TT40 stayed stable through more than five hours of surgery and after it. He was eating fish 30 hours later and kept a strong appetite throughout his recovery. Three weeks on, the incision had healed; he got a new satellite tag and was released on Kauaʻi on 6 July 2004.

Recovering at a temporary holding facility on Oʻahu. NOAA Fisheries.

He was lucky that the line was spotted early: other monk seals have died from swallowed hooks or needed surgery for the complications.

TT40 lived out his years on Kauaʻi and was found dead of natural causes on a beach in 2011, aged 27, a long life for a monk seal, watched over by the many people who cared for and monitored him.

Sources

• NOAA Fisheries, "TT40: The First Hawaiian Monk Seal to Undergo Surgery for a Fishhook Removal"; rewritten in hubnx's own words. Photographs: NOAA Fisheries.