Bomb radiocarbon

Bomb radiocarbon dating - New records for the Insular Pacific

Sustainable fisheries through validated life history information for the Insular Pacific: Bomb radiocarbon dating as a tool for maintaining healthy ecosystems.

There is currently a critical need for validated life history information for the marine fish and invertebrate fisheries of the Insular Pacific. It has become glaringly apparent that management practices that did not fully consider important aspects of population dynamics have led to fisheries in dire straits. Valuable recreational and commercial fisheries of the Insular Pacific are currently threatened by the affects of overfishing because of a lack of understanding the importance of validated age, growth, longevity, age at maturity, and lifetime productivity. Healthy ecosystems and the sustainable management require timely and accurate life history information and in some cases the time has long past (i.e. orange roughy (Hoplostethus atlanticus), Andrews et al. 2009). In most cases, fisheries have been managed using incomplete life history information and untested assumptions about life history parameters. Validated longevity has been overlooked for decades (commonly greatly underestimated) as an important aspect of understanding population dynamics, rebuilding of depleted stocks, and making accurate assessments of sustainability (Cailliet and Andrews 2008). Recent findings indicate that assumptions of age were incorrect for one of the most important bottom fish species, Hawaiian pink snapper or opakapaka (Pristipomoides filamentosus). Previous longevity estimates were 5 to 18 years, but empirical evidence was lacking for maximum age. An application of a novel age validation technique, bomb radiocarbon (14C) dating, revealed this species has a lifespan exceeding 40 years and that this species grows differently in other regions (older at a smaller size in Mariana Islands; Andrews et al. 2012). Because managers utilize metrics associated with age (e.g., age at maturity, lifetime productivity) to make regulatory decisions, these findings have led to a revised stock assessment (Brodziak et al. 2011).

Relative to the Insular Pacific, life history parameters for reef fisheries are either unknown or inadequately described. The decline of many fisheries can be directly linked to poorly understood life history characteristics, often associated with severely underestimated longevity. For example, complicated changes in reproductive demography (i.e. parrotfishes), possibly related to a loss of population age structure, have been observed for fished populations with unknown long-term ramification (e.g. Hamilton et al. 2008). Recent studies have provided estimates for greater longevity than previously expected for reef fishes and invertebrates (e.g. Bumphead parrotfish (Bolbometopon muricatum) and Napoleon wrasse (Cheilinus undulatus) >40 years; kala (Naso unicornis) >50 years), but these estimates have remained unvalidated until recently but are often not fully considered in management practices and stock assessments; proper management and accurate public perception of fishery status is long overdue. For this reason, important species of reef fishes and invertebrates from the Insular Pacific (Hawaiian Archipelago, Guam, CNMI, Saipan, American Samoa) are slated for bomb radiocarbon dating by the Pacific Islands Fisheries Science Center, but refined bomb radiocarbon reference records were not available until recently to make use of this state-of-the-art age validation method.

Application of bomb radiocarbon dating to marine organisms of a given region requires accurate documentation of how the bomb radiocarbon signal (liberated during the testing of thermonuclear devices in the 1950s and 1960s) was sequestered and transported by the marine environment (Kalish 1993). To facilitate the pursuit of validated life history information for the reef fish and invertebrate fisheries of the Insular Pacific, we have analyzed two coral cores from strategic locations to be used as a strong basis for extensive and long-term applications of bomb radiocarbon dating. Ultimately, bomb radiocarbon data from these coral cores will be will be made available to researchers across the Insular Pacific and will be used as a basis for ongoing life history work by PIFSC (listed above), as well as other species slated for analysis and investigation across the Insular Pacific.

Map of regions with bomb radiocarbon records (yellow) and two locations where we have established new records that are comprehensive (pre-bomb to post-bomb) in the Hawaiian Archipelago (Kure Atoll) and in the western Central Pacific (Guam).

Latest developments:

The coral cores from Kure Atoll and Guam have been fully processed (new and separate pages will be developed for each coral core). For the Kure Atoll core, I extracted samples for (1) strontium:calcium (Sr:Ca) ratios as a proxy for annual temperature changes to validate the annual band counting and (2) radiocarbon (C-14) measurements to document annual changes in C-14 and the rise of bomb produced C-14 as a tool in age determination of regional marine organisms. The same is true for the coral core at Guam, except that only C-14 analyses were necessary.

Pictured above is a close-up of a portion of the coral core slab from Kure Atoll with banding pattern visible as minor changes in color. Arcs of sample material are being extracted with the dentists drill bit attached to the chuck at the top. Sampling is focused on 4 per year to capture season variations in marine chemistry over time. All extractions were performed with New Wave Research micromilling machine (Elemental Scientific Lasers, Bozeman, MT, USA; http://www.nwrlasers.com/milling/micromill/).

Participants in research: Allen Andrews, Edward DeMartini, and Robert Humphreys (NOAA Fisheries - PIFSC), Daria Siciliano, Donald Potts and Stephannie Covarrubias (University of California, Santa Cruz), Ryuji Asami (University of Ryukyus, Okinawa, Japan) and Yasufumi Iryu (Tokyo University, Japan), and Frank Camacho (University of Guam).

New bomb radiocarbon records NOW ESTABLISHED

FOR Kure Atoll and Guam

Sample extractions underway on the New Wave micromilling machine

next >

< previous