New Study Finds Age and Growth of Popular Recreational Fish

The Journal of Fish Biology published the first robust age and maturity study on ulua aukea and omilu by Hawai‘i fishery scientists. These two jacks are the most important nearshore species targeted recreationally throughout Hawai‘i, with many fishing clubs and tournaments devoted to them.

Poseidon Fisheries Research (PFR) scientists studied ulua aukea, or giant trevally (Caranx ignobilis), and omilu, or bluefin trevally (Caranx melampygus), to find their growth rate, longevity and maturity. Researchers collected more than 100 samples of each species from recreational fishermen at fishing tournaments, and from the Pacific Islands Fisheries Group and the Hawai‘i Division of Aquatic Resources.

Scientists found that, just as in humans, as these fish age, their size and weight can vary. The oldest ulua aukea weighed 50 pounds and was 31 years old, while the heaviest (80 pounds) was 24 years old. The oldest omilu was 24 years old at nearly 14 pounds.

Scientists also found that the average size at maturity, a key population metric, differed between males and females. Female ulua aukea matured at 594 mm (about 23 inches) and 4.4 years, while males matured at 465 mm (about 18 inches) and 2.8 years. Omilu reached maturity at 372 mm (about 14.5 inches) and 4.1 years for females and 329 mm (13 inches) and 2.9 years for males.

“The collected age and maturity data will be important for future management of these highly prized and ecologically important predatory species in Hawai‘i,” said Cassie Pardee, study co-author and PFR fishery biologist. Fishers can be found camping along the coast ready to battle one of the toughest fighting fish and hoping to land a fish that can be upwards of 100+ pounds. “Ensuring that the best scientific data for ulua and omilu are available for stock assessments will allow fishermen to continue fishing sustainably,” added John Wiley, a PFR fishery biologist and co-author on the study.

Poseidon Fisheries Research scientists extract the gonads from an ulua aukea provided by fishermen at the East Maui Casting Tournament in Hana.

Photo: PFR.

The study is available in the June 2021 issue of the Journal of Fish Biology: https://onlinelibrary.wiley.com/doi/10.1111/jfb.14828.

For more information about Poseidon Fisheries Research, visit www.poseidonfisheriesresearch.org or follow on Facebook (/poseidonfisheriesresearch) and Instagram (@poseidon.fisheries).