When fish biologist Eva Schemmel gets an early morning phone call from the Honolulu Fish Auction, it means something exciting has landed at Pier 38, the center of Hawai‘i’s commercial fishing village.
Recently, it was a record-sized gindai.
Weighing in at 4.95 pounds, the deepwater snapper may not look like a trophy fish to some (especially next to 100–200 pound tunas!). But it's worth much more than its weight thanks to a collaboration between fishermen and NOAA life history scientists.
Understanding Fish Populations
Schemmel is part of a NOAA Fisheries team that studies the life history of fish species across the Pacific Islands—how they grow, reproduce, and die. These “fish detectives” collect clues from some of the region’s most valuable (and tasty!) commercial fish species to reveal the mystery of fish population structures. This information helps scientists maximize harvest opportunities for fishermen.
“It’s the key piece to understanding if your fishery is healthy,” Schemmel said. “With the best scientific information possible, you can maximize how much fishing you can do, while keeping fish populations reproducing at the same level.”
Healthy fish populations depend on reproductive adults, and it’s often the oldest, largest fish that play the biggest role in keeping their numbers going. By collecting enough samples from larger fish—like the recent gindai—scientists can determine the average and maximum lifespan of fish in a population. This data helps scientists create more accurate stock assessment models—the foundation for management measures.
Tick Tock: Fish With Hidden Clocks
The science of aging fish relies on a key piece of evidence: otoliths. Most fish have these tiny, jewel-like bones in their inner ears. They help fish hear and balance in their surroundings underwater. They also carry information about the fish’s growth, similar to growth rings in a tree. These lines provide a reliable estimate of the fish’s age.
Collecting otoliths is quick and doesn't harm the catch. In return for this effort, NOAA Fisheries scientists gain a literal lifetime of data.
“What are they eating? Where are they going? How big do they get? How fast do they grow? It helps us understand the fishery better. Get inside the mind of the fish, and you can catch more.” —Eva Schemmel, Fish Biologist with NOAA Fisheries
Otolith samples from the gindai showed the fish was about 30 years old, in line with the maximum age on record for this species in Hawaiʻi.
The Case of the Hāpu‘upu‘u
Hāpu‘upu‘u, or Hawaiian grouper, is another fish Schemmel and colleagues study. And its life history is more complicated than others.
Hāpuʻupuʻu are all born as female. However, they can transition to males: Female gonad tissue gets absorbed, and male gonad tissue develops. This happens when they reach a certain size or social condition, such as when there are few to no males around to mate.
When fisherman Ed Watamura called the lab to bring in a 35.5-pound hāpu‘upu‘u, the team expected the fish to be male. It was well outside of the typical size range for main Hawaiian islands catches. Plus, it was larger than the typical size when hāpu‘upu‘u change to male (a key metric for monitoring hermaphroditic fishes). To their surprise, it was a 40-year-old female!
Understanding how old hāpuʻupuʻu females are when they start reproducing and when they turn male can help fishermen and resource managers understand the status of the population. It also helps them identify appropriate management strategies.
For Watamura, that’s a powerful incentive. He has been donating samples to the program for more than 20 years. Watamura is a skilled angler, former Western Pacific Fishery Management Council advisor and member, boat club president, and advocate for fishermen in Hawai‘i. He’s the kind of person who really understands different perspectives in fishing.
He sees the need for fishermen and scientists to work together—but he didn’t always feel this way.
“When we started in fisheries management, [as fishermen] we felt, the more fish that we catch and report, it's coming out of the ocean and the stock,” he said. Some fishermen are reluctant to share catch info with scientists and managers, fearing it might lead to less fishing. “Once we got involved more, we [saw] it was exactly the opposite.”
Sharing catch information helps scientists understand whether a fishery is healthy or in trouble, which is key to keeping fish stocks sustainable for the long haul.
“I always encourage other fishermen, that if they catch something of note … to contact the Science Center … [They] pick what they need, and then you get back the food.”
Schemmel speaks highly of this partnership: “We love working with [the fishermen] because we have the same questions.”
Ready to learn more about your catch? Email pifsc.lifehistory@noaa.gov.
