Age Validation and Reproduction - Onaga
Validated Life History of Onaga - A popular and commercially important deep-water snapper of Hawaii
Published in Marine and Freshwater Research and as a popular article in Lawai’a Magazine No. 31
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.
PUBLISHED: https://doi.org/10.1071/MF2024
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.
Effects of data sources and biological criteria on length-at-maturity estimates and spawning periodicity of the commercially important Hawaiian snapper, Etelis coruscans
Erin M. Reed, Nancy J. Brown-Peterson, Edward E. DeMartini and Allen H. Andrews
Reproductive characteristics of a fish stock provide important tools for assessing population health. Change in length-at-maturity (L50) is a potential indicator of exploited fish populations but when criteria for determining maturity classifications are inconsistent, it is difficult to accurately assess change over time and space. Etelis coruscans is a commercially important eteline snapper found throughout the Indo-Pacific, but its region-specific reproductive information in the main Hawaiian Islands (MHI) is sparse. The present study describes length-specific (fork length: FL) female reproductive characteristics of this deep water snapper in the context of a data-limited fishery. We explored the use of six maturity classification criteria based on a functionally mature (containing vitellogenic oocytes and capable of spawning within the season of collection) or physiologically mature (gonadotropin-dependent maturation initiation) designation combined with seasonality and inclusion of additional reproductive phases. Of these classifications, the largest and therefore most conservative estimate was for functional maturity during the spawning period, September-December (L50F = 65.8 cm). Progressively smaller L50 estimates occurred as we incorporated additional reproductive phases and seasonality, the smallest being for physiological maturity during the entire year (L50PY = 50.0 cm). Both functional and physiological maturity criteria are valid for estimating L50 but can yield drastically different parameter estimates based on the definition of mature or immature reproductive phases. Fish that are relatively slow growing, late to mature, and whose fisheries encompass a wide size range, such as E. coruscans, may be more subject to unreliability in the development of their reproductive indicators (length-at-maturity and spawning period) when inconsistent maturity classification criteria are executed over time. We discuss the reproductive characteristics of E. coruscans in the MHI, the use of alternative maturity classification criteria in L50 estimation, the impact on resultant parameters estimates, and the life history implications for the future fishery.
Published: https://doi.org/10.3389/fmars.2023.1102388
Figure 3 Etelis coruscans gonadal histology depicting reproductive phases. (A) immature, (B) developing, (C) spawning capable, (D) actively spawning sub-phase, (E) regressing, and (F) regenerating. The insert in B) is the early developing subphase and it is to scale with the other images. The scale bar of 500 µm applies to all images. Abbreviations for histological characteristics include: A, atresia; MA, macrophage aggregate; BV, blood vessel; CA, cortical aveoloar; GW, gonad wall; MB, muscle bundle; PG, primary growth; Vtg 1, primary vitellogenic; Vtg2, secondary vitellogenic; Vtg3, tertiary vitellogenic; H, hydrated oocyte.
[I cannot claim the amazing work in this image — truly revelational and proud to be a part of it.]
Personal Note: While I did not contribute heavily to the hands-on reproductive analyses, I did foster this line of work based on observations of age and growth for Onaga as presented above — it was clear to me at the time that existing reproductive information was deficient and a reassessment was necessary. Hence, we made it happen with requests for support and funding within PIFSC. As a result, we now have complete life history data for yet another one of the members of the Deep-7 in Hawaii. Other completed Deep-7: Opakapaka and Hapupupu.
