Incorporation of bomb-produced¹⁴C into fish otoliths. An example of basin-specific rates from the North Pacific Ocean

Abstract

Sagittal otoliths from juvenile Pacific halibut (Hippoglossus stenolepis) of known age were used to create a bombproduced radiocarbon reference chronology for the eastern Bering Sea (EBS) by fitting a coupled-function model to ⌬ 14 C values from each specimen's birth year. The newly created EBS reference chronology was then compared with a reference chronology previously created for Pacific halibut from the Gulf of Alaska (GOA). Adult Pacific halibut age-validation samples from the EBS were also analyzed for 14 C and modeled to validate age-estimation accuracy. A Bayesian model was developed and Markov chain Monte Carlo simulation was used to estimate model parameters and adult Pacific halibut ageing bias. Differences in reference chronologies between ocean basins were reflected in a large deviance information criterion (⌬DIC) between models, supporting the hypothesis that two separate coupled-function models were required to adequately describe the data, one each for the EBS and GOA. We determined that regionally specific GOA and EBS oceanography plays a considerable role in the ⌬ 14 C values and must be taken into consideration when selecting a reference chronology for bomb-produced 14 C age-validation studies. The age-validation samples indicated that the current ageing methodology used in Pacific halibut assessments is accurate and has provided accurate age assignments for Pacific halibut in the EBS.Résumé : Des otolites sagittaux de flétans du Pacifique (Hippoglossus stenolepis) juvéniles d'âges connus ont été utilisés pour établir une chronologie de référence au radiocarbone dérivé d'explosions pour la mer de Behring orientale (EBS) en calant un modèle de fonctions couplées sur les valeurs de ⌬ 14 C pour l'année de naissance de chaque spécimen. Cette nouvelle chronologie de référence pour l'EBS a ensuite été comparée à une chronologie de référence déjà établie pour le flétan du Pacifique du golfe d'Alaska (GOA). Des échantillons de validation de l'âge de flétans du Pacifique adultes de l'EBS ont également été analysés pour le 14 C et modélisés pour en valider l'exactitude des estimations de l'âge. Un modèle bayésien a été mis au point et une simulation de Monte Carlo par chaîne de Markov a été utilisée pour estimer les paramètres de modèle et le biais associé à la détermination de l'âge de flétans du Pacifique adultes. Des différences des chronologies de référence entre les deux bassins océaniques se reflétaient par une grande variation du critère d'information associé à la somme des carrées des écarts (⌬DIC) entre les modèles, appuyant l'hypothèse voulant que deux modèles de fonctions couplées distincts soient nécessaires pour décrire adéquatement les données, soit un modèle pour l'EBS et un autre pour le GOA. Nous avons établi que l'océanographie régionale respective du GOA et de l'EBS joue un rôle important dans la détermination des valeurs de ⌬ 14 C et doit être prise en compte dans la sélection d'une chronologie de référence pour les études de validation des âges reposant sur le 14 C dérivé d'explosion...

Age structure of the Australian lungfish (Neoceratodus forsteri)

“…The reduced amplitude of the peak F 14 C within the scale is most likely due to time–averaging of the F 14 C scale signal because of the scale sample size (widths/time) needed for the 14 C measurement. We used a coupled–function model in order to develop a reference curve to use radiocarbon to age lungfish based on fish otolith research [21–22, 30]. The model used is shown in Eq 1.…”

Validating blueline tilefish Caulolatilus microps ages in the U.S. South Atlantic using bomb radiocarbon (F14C)

“…The conflicting results of the ageing methodology validation, depending on the reference chronology used for comparison, highlight the importance of using a reference chronology from the same, or similar, environments with respect to 14 C availability. Cross-basin (Kastelle et al, 2016) and even within-basin (Wischniowski et al, 2015) comparisons have revealed chronologies with distinctly different properties between a validation and a reference data set, demonstrating how misapplication may lead to ageing error. While our study provides a more appropriate bomb radiocarbon reference chronology for use within deeper waters of the SAB, the development of a true region-specific chronology in the SAB consisting of known-age specimens remains necessary to unequivocally distinguish between ageing error and effects of oceanographic processes (Piner & Wischniowski, 2004), and should be a future research goal.…”

Radiocarbon in otoliths of tropical marine fishes: Reference Δ14C chronology for north Caribbean waters

“…Early on in the history of research utilizing bomb radiocarbon for fish ageing validation, Δ 14 C reference chronologies were limited, but in the past 20 years additional datasets have been developed for multiple regions, so fisheries investigators are no longer extremely limited to a few reference chronologies. The sources of Δ 14 C reference data for ageing validation work are varied, and consist of Δ 14 C measured directly from the atmosphere [ 33 ], from known-age otoliths [ 20 ], from otolith core Δ 14 C with validated ages [ 30 , 34 , 35 ], and from Δ 14 C reported from corals [ 19 , 20 ]. To explain our findings within the context of past research involving the use of temporal Δ 14 C trends and to emphasize the applicability of the north Caribbean reference chronology we established in this study, we identified three main considerations that future ageing validation studies should evaluate to strengthen their findings: 1) evaluation of the applicability of the original goal/objectives and study design of potential Δ 14 C reference studies; 2) evaluation of the applicability of potential Δ 14 C reference data to the region/location where fish samples under evaluation were obtained; and 3) determination of the location of habitat in which the fish species under investigation spends at least the juvenile period that was recorded in the otolith core material extracted for Δ 14 C analysis.…”