To fishermen in Hawaii, Pacific mahimahi stomachs hold no particular value and are discarded. But to National Oceanic and Atmospheric Administration scientists researching mahimahi diet, each stomach tells a unique story and provides an opportunity to help the fish and its environment.
Mahimahi is a federally managed fish popular among recreational and commercial fishermen in Hawaii, but there’s still much to learn when it comes to their diet and role in marine ecosystems.
NOAA Fisheries scientists and managers are enlisting the help of fishermen to collect mahimahi stomachs for research.
The stomach contents will help NOAA scientists understand what these predatory fish are eating, and reveal how much of the fish’s diet comes from pelagic (open-ocean) life stages of coral reef animals.
“Collaborating with the fishing community is an important component of this work,” said Keith Kamikawa, fishery management specialist, NOAA Fisheries Pacific Islands Regional Office. “We’re conducting science while getting Hawaii fishermen and anglers involved.”
Under the Magnuson-Stevens Act, NOAA Fisheries must prevent overfishing of federally managed fish, and rebuild overfished stocks. Part of this work involves protecting their habitat.
The stomachs may provide information about inshore coral reef habitats and could be a key factor when it comes to keeping the mahimahi population stable.
“While coral reef fish live their adult lives near shore, when they mature and spawn, their larvae drift out to sea and develop in the open ocean,” Kamikawa explained. “There they grow from tiny plankton to pelagic juveniles just a couple of inches long.”
These juvenile reef fish may become prey of mahimahi (and other pelagic predators) while on their way back to the reef to grow into adults.
“From the 180 stomachs processed to date, preliminary results have shown that the majority of prey items found in mahimahi stomachs are juvenile stages of reef-associated animals, such as goatfish and surgeonfish,” Kamikawa said.
The stomach samples are donated from recreational, subsistence, and charter fishermen who provide scientists with stomach samples year-round.
To encourage participation, NOAA is piloting a “punch card” program. Along with the fish stomachs, fishermen must share the catch location, type of bait used, and size of the fish, and other catch-related information.
Fishermen then receive one point for every stomach donated with a full set of data, and for every 10 points, they get a $50 gift card to a local fishing supply store. So far, fishermen have donated more than 300 stomachs.
NOAA scientists use genetics to identify digested prey, and so far they have found: malu (sidespot goatfish), moano (manybar goatfish), nunu (flat needlefish), snake mackerel and gilded triggerfish.
Scientists have identified more than 500 prey items and the results will be shared with the fishing community. Fishermen can verify patterns found in the lab with what they see out on the water, and adjust the bait or lure color they are using.
In addition to the fishing community, members of the public can contribute to healthy fish populations by choosing sustainably harvested seafood when at a store or restaurant.
“U.S. fisheries are among the most sustainable in the world because of our strong science, engagement with partners and stakeholders, responsive management, and effective enforcement of ocean stewardship and protection laws,” said Kamikawa. “Fishermen can contribute to a healthy ecosystem by following state, territorial and federal rules and regulations, using responsible fishing practices, and getting involved in monitoring the health of our oceans and fish resources.”
For information on participating in the study, email keith.kamikawa@noaa.gov.