Bomb Radiocarbon

Gary Brennand, Brinsmead, Queensland

Indo-Pacific bomb radiocarbon dating - humphead wrasse

Publication year 2015

Bomb radiocarbon dating of an iconic Great Barrier Reef fish - humphead wrasse (Cheilinus undulatus) 

Refinements to the methodology of bomb radiocarbon dating made it possible to validate age estimates of the humphead wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum). Age for these species has been estimated from presumed annual growth zones in otoliths at ~30 and ~40 years respectively. The validity of these estimates was tested using bomb radiocarbon dating on the small and fragile otoliths of these species, and provided an opportunity to refine the method using advanced technologies. A regional Δ14C reference record from hermatypic coral cores from the Great Barrier Reef was assembled and Δ14C measurements from extracted otolith cores of adult otoliths were successful. Validated ages supported the accuracy of growth zone derived ages using sectioned sagittal otoliths.

Publication: Refined Bomb Radiocarbon Dating

Refined bomb radiocarbon dating of two iconic fishes of the Great Barrier Reef

Allen H. Andrews, John H. Choat, Richard J. Hamilton and Edward E. DeMartini 

Humphead wrasse are the largest of the wrasse family reaching lengths of up to 2 m (6 feet). These fish are thought to be capable of reaching an age exceeding 30 years, but these estimates are based on growth zone counting in otoliths and attempts to validate age have been complicated by various factors. Otoliths of this species are complex and fragile, but proper sectioning has revealed patterns that may be annual. Based on these data, fish otoliths have been selected for bomb radiocarbon dating to provide a temporal basis for these estimates. 

Otoliths from this species on the Great Barrier Reef appear to be relatively easy to age by counting growth zones visible in cross sections. The otolith section above was aged consistently to 17 years by counting the zones on each side. However, this estimate requires validation and this is a goal for the project. 

The latest in our work is the processing of an otolith set from fish market collections made in Guam. Eric Cruz (NOAA Fisheries - Guam) and I have sectioned and examined a series of otoliths for which I have radiocarbon measurements. These otoliths were very tricky to read and not as well developed as Great Barrier Reef otoliths. The picture above is of me grinding down the mounted otolith section on a glass slide (my left forefinger points to the small white otolith section). The process is tedious and takes a considerable amount of time to not only prepare, but to read for estimates of age. The growth zones in the otoliths from Guam are not as well developed as seen in the otolith section shown above.

The project currently underway was funded by the Species of Concern Program (Department of Protected Resources, NOAA Fisheries) to provide desperately needed age and growth information for this vulnerable species. For more information on what is known about the humphead wrasse and why there is concern, see SOC_humpheadwrasse_detailed.pdf.

Varivoce, local name of humphead wrasse , has been protected under 

Fiji’s Endangered and Protected Species Act since 2004, but remains threatened. 

IUCN has this species listed as Endangered.

This project is an international effort with colleagues at James Cook University (John Choat) and The Nature Conservancy (Richard Hamilton), as well as Eric Cruz of the NOAA Fisheries Bio-Sampling Program in Guam. Archival and recent collections from the Great Barrier Reef and Guam are being used to describe the age and growth of this species to provide a sound basis for preservation efforts. Age, growth and longevity must be understood to make proper management and protection measures throughout its range. This mircostructure was sampled with a series of extractions made with a New Wave Research micromilling machine (Elemental Scientific Lasers, Bozeman, MT, USA;

The species has the common name of Maori Wrasse in Australia. See the Australian Museum for some interesting information, photographs and video.