Bomb Radiocarbon

Onaga - A popular long-lived snapper of Hawaii

Published as popular article in Lawai’a Magazine No. 31 and with Marine and Freshwater Research

Onaga is one of the more important commercial fishes of Hawaii


A long-lived life history for onaga (Etelis coruscans) in the Hawaiian Islands


Allen H. Andrews, Jon Brodziak, Ryan S. Nichols, Edward E. DeMartini, and Eric Cruz


Onaga (Etelis coruscans) is an important component of the commercial deep-water handline fishery in Hawaii and is one of the more valuable species because of its local popularity. This species is part of a management unit called the Deep 7, a data-poor fishery comprising six snapper and one grouper species for which information about age, growth, longevity, and maturity is incomplete. Opakapaka (Pristipomoides filamentosus) is one of the snappers in this group and was shown to be underaged by more than 20–30 years with longevity exceeding 40 years. While some life history information is available for onaga, prior estimates of maximum age (~10–20 years) have suffered from the same problems as opakapaka. In this study, a refined age reading protocol revealed age estimates up to 55 years for an onaga near maximum size — this maximum age estimate and the age reading protocol was validated using bomb radiocarbon dating. Using an otolith reference-image, age reading protocol that relied on the validated otolith sections, almost all onaga otoliths covering nearly the full body size range were used to generate valid growth parameters. An empirical estimate of age-at-maturity (L50) is 11 years and fish near minimum retention size in Hawaii (1 pound or ~30 cm FL) may be just 2–3 years old. 


Popular Article: Red fish, Blue fish, Old fish, New fish — Onaga can live half a century in the Hawaiian Islands. DOWNLOAD:Andrews 2020 Lawaia No31 Onaga w Cover V2.pdf


Draft Manuscript - This work was completed last year before I left federal service. I have heard the work is being shelved and felt it prudent to share the information because we all put a lot of effort into the findings for this important and iconic regional species. DOWNLOAD:Onaga-V19.pdf


PUBLISHED! I decided it was my professional duty to publish this work. 

Accepted - https://www.publish.csiro.au/MF/justaccepted/MF20243


Onaga (Etelis coruscans) otolith images of (A) a transverse section of an adult viewed under transmitted light, (B) lateral views (distal side) of the original whole otolith of the section shown (A) with the smallest juvenile otolith available, and (C) a zoomed detail of the fine increment structure counted toward the outer edge. The adult section (A) was aged to 55 years (growth zone counts are marked by small white dots) — a Rosetta Stone in the age estimation of other sections that were not as well defined. The juvenile otolith (B) was aged to 2 years and was used as a template in determining core extraction protocol on a New Wave Research micromilling machine (Elemental Scientific Lasers, Bozeman, MT, USA; http://www.nwrlasers.com/milling/micromill/), coupled with observations for the surface location and dimension of the second-year sample in sectioned otoliths (A). The growth structure identified and counted for estimates of age was similar to that shown for E. coruscans in the South Pacific (Williams et al., 2015). 


Plot of the coral bomb 14C reference record (Kona, Hawaii Island; Andrews et al., 2016) that is relevant for the region with measured 14C values from the extraction of 12 otolith core samples from 7 fish (5 fish with both year-1 and year-2 cores; Table 1). The age of onaga (Etelis coruscans) was determined by counting growth zones in otolith sections for an estimated birth year (arrows project from collection date back to calculated birth year). The validity of age reading was determined from the alignment or misalignment of the measured F14C value with the reference record. Horizontal and vertical error bars represent the final estimate of age reading precision (D = 5.3%) and instrument precision (1 SD). 


Scatterplots of age-at-length data with von Bertalanffy growth curves for onaga (Etelis coruscans) of the Hawaiian Islands (sexes separate, lognormal (LN) and normal (N) parameters; Table 3). Empirical estimates of age-at-maturity from these curves for females using an L50 of 66.3 cm FL from Everson et al., (1989) corresponds with an age of 11 years, and an alternate L50 near length-at-maturity for similar deep-dwelling eteline lutjanids (~50% Lmax; Grimes 1987) corresponds to an age of 5–6 years. The age of a minimum retention sized onaga (1-pound, 0.45 kg) in Hawaii would be immature and 2–3 years old.