Allen H. Andrews

A complete bomb radiocarbon (14C) chronology — covering an 80-year period (1938–2018) and reflecting thermonuclear testing in the 1950s and 1960s — was established using known-date otolith material to trace the signal in the Baltic Sea and to establish a tool in validating the age of regional fishes. Of particular interest were Baltic herring (Clupea harengus) and sprat (Sprattus sprattus) that are estimated to live >20 years in the Baltic Sea, a longevity that is ∼2× greater than determined for other locations. The new 14C chronology was used to validate age estimates up to 22 years for herring and 18 years for sprat, although there was evidence of 14C emissions from nuclear facilities, as well as deficiencies from other environmental factors. This work confirmed the accuracy of high-confidence age reading protocols used for decades and is a first step in establishing a valid basis for observed growth differences between northern-southern Baltic Sea populations. An exploration of 14C in otoliths of coastal Baltic pike (Esox lucius), pikeperch (Sander lucioperca), and Baltic cod (Gadus morhua) lend support for broader use of bomb 14C dating on marine and freshwater organisms of the Baltic Sea basin.

Age estimates from bomb ¹⁴C dating conflict with a well-recognized age reading protocol (grinding, polishing and staining in the sagittal plane) for otoliths of European eel (Anguilla anguilla). Proper alignment of calculated hatch years for ¹⁴C measurements taken from the earliest otolith growth—among the smallest otolith extractions to date for successful ¹⁴C analysis due to the advent of gas-AMS—was not achieved using age estimates from an accepted method. The realignment of otolith ¹⁴C values to a tropical bomb ¹⁴C reference chronology, which is most applicable to the Sargasso Sea as the natal origin of European eel, led to an increase of the original age estimates by 8 to 32 years. A maximum age of approximately 46 years was determined for the European eel specimen with the most massive otolith, of which mass is a reasonable proxy for age and was instrumental in identifying age estimate discrepancies. By extending the otolith mass-to-age relationships from this study to the most massive otoliths available from archived otoliths of Norway, an increase of up to several decades from the original otolith age estimates was discovered, leading to support for a potential lifespan of 70–100 years in the natural environment.

Cardinal snapper Pristipomoides macrophthalmus is a commercially important, but commonly misidentified, deepwater species in artisanal and semi-industrial fisheries throughout the Caribbean Sea. As with many tropical deepwater fishes, little is known about the biology or ecology of the species. Bomb radiocarbon (¹⁴C) dating was applied to cardinal snapper sagittal otoliths collected from the waters of Belize and Honduras during 2015–2019 to investigate the lifespan of the species from thin-sectioned otoliths with an evaluation of otolith mass as a proxy for age. Ages estimated from 28 thin-sectioned otoliths ranged from 7 to 68 years for fish that covered the range lengths and otolith masses available. Radiocarbon values were measured for each cardinal snapper otolith core, and two fish (one each from Belize and Honduras) had ¹⁴C signatures consistent with pre-bomb values, effectively validating a lifespan of at least 60 years. A curvilinear relationship between otolith mass and estimated age was robust (r ² = 0.95) and is likely to produce age estimates with similar margins of error to traditional, more labor-intensive methods, such as counting increments from thin-sectioned otoliths. The otolith mass-to-age relationship is a well-supported method that provides a simple, low-cost approach that can be used by fishers, managers, and other stakeholders to assess the age composition of the cardinal snapper stock in the western Caribbean Sea for present and long-term monitoring.

Age-reading protocols for tuna species using annual growth zones in thin-cut transverse otolith sections have produced greater age estimates than previous methods. Lifespan estimates for yellowfin (YFT) and bigeye (BET) tuna (Thunnus albacares and T. obesus) were validated up to 16–18 years in the western North Atlantic Ocean using bomb ¹⁴C dating and the current study extends the approach to YFT and BET of the western and central Pacific Ocean (WCPO). Archived otoliths from young-of-the-year (YOY) tuna caught in the WCPO were analysed for ¹⁴C to establish a reference chronology covering 30 years (1989–2019). This YOY ¹⁴C time series exhibited strong concordance with existing coral-otolith ¹⁴C references for the tropical-subtropical Pacific Ocean and was combined as a single chronology. Otolith cores from YFT aged 1–14 years and BET aged 1–13 years from presumed annual counts were analysed for ¹⁴C. These measurements aligned with the reference chronology for the calculated hatch years for both species. These findings provide strong evidence that growth zones in thin-sectioned otoliths are deposited annually for YFT and BET of the WCPO and that age interpretation is correct using the current age reading protocol with little to no bias.

Context: The potential lifespan of alligator gar (Atractosteus spatula) is currently unknown. A previous study applied bomb radiocarbon (14C) dating to establish ages >60 years, but maximum age was limited by the rise of bomb-produced 14C in the 1950s. Aims: An exceptionally large specimen (2.6 m, 148 kg) was captured in Mississippi and otolith growth zones revealed an age estimate of 95 years. This specimen provided an opportunity to apply new technology to validate the lifespan of alligator gar. Methods: Developments in accelerator mass spectrometry (AMS) led to technology that measures 14C continuously from carbonates (laser ablation-AMS), as opposed to single sample 14C analysis. Key results: Use of laser ablation AMS on the 2.6-m alligator gar otolith, and two smaller fish aged >60 years, supported ages that were older than original estimates by 5–20 years. Conclusions: Our study indicates that alligator gar age can be underestimated for the largest fish, maximum recorded length is 2.6 m based on a historical photograph, and lifespan is at least 75–95 years with support for an age of 100 years for the 2.6-m fish. Implications: An increase in lifespan of this magnitude would affect our understanding of population dynamics and recovery efforts.

Chemical analysis of calcified structures continues to flourish, as analytical and technological advances enable researchers to tap into trace elements and isotopes taken up in otoliths and other archival tissues at ever greater resolution. Increasingly, these tracers are applied to refine age estimation and interpretation, and to chronicle responses to environmental stressors, linking these to ecological, physiological, and life-history processes. Here, we review emerging approaches and innovative research directions in otolith chemistry, as well as in the chemistry of other archival tissues, outlining their value for fisheries and ecosystem-based management, turning the spotlight on areas where such biomarkers can support decision making. We summarise recent milestones and the challenges that lie ahead to using otoliths and archival tissues as biomarkers, grouped into seven, rapidly expanding and application-oriented research areas that apply chemical analysis in a variety of contexts, namely: (1) supporting fish age estimation; (2) evaluating environmental stress, ecophysiology and individual performance; (3) confirming seafood provenance; (4) resolving connectivity and movement pathways; (5) characterising food webs and trophic interactions; (6) reconstructing reproductive life histories; and (7) tracing stock enhancement efforts. Emerging research directions that apply hard part chemistry to combat seafood fraud, quantify past food webs, as well as to reconcile growth, movement, thermal, metabolic, stress and reproductive life-histories provide opportunities to examine how harvesting and global change impact fish health and fisheries productivity. Ultimately, improved appreciation of the many practical benefits of archival tissue chemistry to fisheries and ecosystem-based management will support their increased implementation into routine monitoring.Graphical abstract

Coral skeletal structures can provide a robust record of nuclear bomb produced ¹⁴C with valuable insight into air-sea exchange processes and water movement with applications to fisheries science. To expand these records in the South Pacific, a coral core from Tutuila Island, American Samoa was dated with density band counting covering a 59-yr period (1953–2012). Seasonal signals in elemental ratios (Sr/Ca and Ba/Ca) and stable carbon (δ¹³C) values across the coral core corroborated the well-defined annual band structure and highlighted an ocean climate shift from the 1997–1998 El Niño. The American Samoa coral ¹⁴C measurements were consistent with other regional records but included some notable differences across the South Pacific Gyre (SPG) at Fiji, Rarotonga, and Easter Island that can be attributed to decadal ocean climate cycles, surface residence times and proximity to the South Equatorial Current. An analysis of the post-peak ¹⁴C decline associated with each coral record indicated ¹⁴C levels are beginning to merge for the SPG. This observation, coupled with otolith measurements from American Samoa, reinforces the perspective that bomb ¹⁴C dating can be performed on fishes and other marine organisms of the region using the post-peak ¹⁴C decline to properly inform fisheries management in the South Pacific.