Age and growth of bluespine unicornfish (Naso unicornis): a half-century life-span for a keystone browser, with a novel approach to bomb radiocarbon dating in the Hawaiian Islands

Abstract

Bluespine unicornfish (Naso unicornis) from Hawaii were aged to >50 years using cross-sectioned sagittal otoliths. Fish length was a poor indicator of age because of rapid and variable early growth, exemplified by fish aged to be 4 years near maximum length. Growth was deterministic with adult ages decoupled from body length. Otolith mass and thickness were evaluated as proxies for age and both were encouraging; thickness explained more variance but mass was easier to measure. An age estimation protocol was validated through ontogeny using bomb radiocarbon (14C) dating. Use of the postbomb 14C decline period from a regional reference chronology enabled age validation of young fish — a novel approach for the Pacific Ocean. A probabilistic procedure for assigning bomb 14C dates (CALIBomb) was used for the first time to determine fish birth years. The age-reading protocol was generally validated, and it was possible to describe length-at-age despite difficulties in counting otolith annuli beyond 30–40 years. Growth curves differed between the sexes, and a four-parameter generalized von Bertalanffy growth function provided the best fit.

Age‐based life history of humpback red snapper, Lutjanus gibbus, in New Caledonia

“…The extended longevity observed for L. gibbus in southern New Caledonia relative to that reported for the species elsewhere is likely a function of environmental influences (including water temperature, food availability and competition), fishing pressure, genetics, or, most probably, a combination of factors (Conover et al ., ). The ability of individuals to reach greater longevity and larger body sizes at higher latitudes, where water temperature are generally cooler, has been documented in a number of shallow and deep‐water fish species with distributions spanning broad latitudinal and temperature ranges (Andrews et al ., ; Berumen et al ., ; Robertson et al ., ; Trip et al ., ; Williams et al ., ). At c .…”

Using optimised otolith sectioning to determine the age, growth and age at sexual maturity of the herbivorous fish Kyphosus bigibbus: with a comparison to using scales

“…Several fishes inhabiting shallow reef habitats have similar life history strategies, with long-term population recruitment (e.g. Stewart and Hughes 2005;Ewing et al 2007;Andrews et al 2016). This strategy reduces the risk of a population collapsing during long periods of environmental conditions that are unfavourable for successful recruitment (Leaman and Beamish 1984).…”

Standing Out in a Big Crowd: High Cultural and Economic Value of Naso unicornis in the Insular Pacific

“…Based on the evidence presented here, I posit that the species is presently underappreciated in the scientific literature regarding its cumulative value to commercial and artisanal coral reef fisheries. The species is noted to have a peculiar life history compared with many harvested tropical fishes [16][17][18], and regional declarations of overexploitation [19,20] are perplexingly not met with temporal declines in the fishery [6,21]. Clearly, the nexus between ecological and commercial value warrants enhanced research on the sustainable harvest of this species.…”