Ear Stones Research Articles

Otoliths, bones, teeth, and more: Development of a new polishing wheel for calcified structures

AbstractBiochronological information stored in the calcified structures of organisms provide fundamental organismal, environmental, and ecological data. Bones, teeth, statoliths, corals, and otoliths are widely used to answer a myriad of questions related to trophic position, migration, age and growth, environmental variation, and historical climate. Many calcified structures, particularly the ear stones of fishes (otoliths), are small (50 μm to 5 mm) and require precise preparation methods, which vary depending on the structure and research question but commonly include embedding, sectioning, and polishing prior to structural or chemical analysis. Globally, management agencies rely on the precise polishing of millions of otoliths each year to obtain vital demographic data, such as age and growth. However, this process is time consuming, labor intensive, and ergonomically strenuous. Since the early 1970s, there has been limited advancement in preparation methods with many still using manual approaches or costly, and at times inefficient, equipment. Therefore, we designed and fabricated an affordable, adjustable speed, multi‐wheel polisher, which can be powered with alternating or direct current. Sample preparation time is reduced, and sample consistency is notably improved compared to manual approaches. While specifically designed for consistent and relatively rapid preparation of otolith thin sections, the polisher is readily adaptable to a variety of applications. Designs and manufacturing for these wheels are publicly available through the iLab at Oregon State University.

A nitrogen isotopic shift in fish otolith–bound organic matter during the Late Cretaceous

The nitrogen isotopes of the organic matter preserved in fossil fish otoliths (ear stones) are a promising tool for reconstructing past environmental changes. We analyzed the 15N/14N ratio (δ15N) of fossil otolith-bound organic matter in Late Cretaceous fish otoliths (of Eutawichthys maastrichtiensis, Eutawichthys zideki and Pterothrissus sp.) from three deposits along the US east coast, with two of Campanian (83.6 to 77.9 Ma) and one Maastrichtian (72.1 to 66 Ma) age. δ15N and N content were insensitive to cleaning protocol and the preservation state of otolith morphological features, and N content differences among taxa were consistent across deposits, pointing to a fossil-native origin for the organic matter. All three species showed an increase in otolith-bound organic matter δ15N of ~4‰ from Campanian to Maastrichtian. As to its cause, the similar change in distinct genera argues against changing trophic level, and modern field data argue against the different locations of the sedimentary deposits. Rather, the lower δ15N in the Campanian is best interpreted as an environmental signal at the regional scale or greater, and it may be a consequence of the warmer global climate. A similar decrease has been observed in foraminifera-bound δ15N during warm periods of the Cenozoic, reflecting decreased water column denitrification and thus contraction of the ocean's oxygen deficient zones (ODZs) under warm conditions. The same δ15N-climate correlation in Cretaceous otoliths raises the prospect of an ODZ-to-climate relationship that has been consistent over the last ~80 My, applying before and after the end-Cretaceous mass extinction and spanning changes in continental configuration.

The incorporation of strontium and barium into the otoliths of the flounder Paralichthys olivaceus at early life stages demonstrates resilience to ocean acidification.

Ocean acidification could modify the bioavailability and chemical properties of trace elements in seawater, which could affect their incorporation into the calcareous structures of marine organisms. Fish otoliths, biomineralized ear stones made by aragonite, are suspended within the endolymph fluid of teleosts, indicating that the elemental incorporation of otoliths might also be susceptible to ocean acidification. In this study, we evaluated the combined effects of CO2-induced ocean acidification (pH 8.10, 7.70, and 7.30, corresponding to ocean acidification scenarios under the representative concentration pathway 8.5 model as projected by the Intergovernmental Panel on Climate Change) and water elemental concentrations of strontium (Sr) and barium (Ba; low, medium, and high) on elemental incorporation into otoliths of the flounder Paralichthys olivaceus at early life stages. Our results revealed that the elemental incorporation of Sr and Ba into otoliths was principally dependent on the corresponding water elemental concentrations rather than on ocean acidification. Moreover, the partition coefficients (DMe) of Sr and Ba may stabilize after dynamic equilibrium is reached as the water elemental concentration increases, but are not affected by ocean acidification. Therefore, the incorporation of Sr and Ba into otoliths of the flounder at early life stages may not serve as an effective indicator of ocean acidification. In other words, the findings suggest that ocean acidification does not impact the incorporation of Sr and Ba incorporation into otoliths when tracing the temperature or salinity experiences of the flounder. Our findings will provide new knowledge for understanding the potential ecological effects of ocean acidification on the recruitment dynamics of fish species.

Fish age reading using deep learning methods for object-detection and segmentation

Abstract Determination of individual age is one essential step in the accurate assessment of fish stocks. In non-tropical environments, the manual count of ring-like growth patterns in fish otoliths (ear stones) is the standard method. It relies on visual means and individual judgment and thus is subject to bias and interpretation errors. The use of automated pattern recognition based on machine learning may help to overcome this problem. Here, we employ two deep learning methods based on Convolutional Neural Networks (CNNs). The first approach utilizes the Mask R-CNN algorithm to perform object detection on the major otolith reading axes. The second approach employs the U-Net architecture to perform semantic segmentation on the otolith image in order to segregate the regions of interest. For both methods, we applied a simple postprocessing to count the rings on the output masks returned, which corresponds to the age prediction. Multiple benchmark tests indicate the promising performance of our implemented approaches, comparable to recently published methods based on classical image processing and traditional CNN implementation. Furthermore, our algorithms showed higher robustness compared to the existing methods, while also having the capacity to extrapolate missing age groups and to adapt to a new domain or data source.

Otoliths of Caspian gobies (Teleostei: Gobiidae): Morphological diversity and phylogenetic implications.

Otoliths (ear stones) of the inner ears of teleost fishes, which develop independently from the skeleton and are functionally associated with hearing and the sense of equilibrium, have significantly contributed to contemporary understanding of teleost fish systematics and evolutionary diversity. The sagittal otolith is of particular interest, since it often possesses distinctive morphological features that differ significantly among species, and have been shown to be species- and genus-specific, making it an informative taxonomic tool for ichthyologists. The otolith morphology of the Caspian Sea gobiids has not been thoroughly studied yet, with data available for only a few species. The aim of the present paper is to examine the qualitative and quantitative taxonomic and phylogenetic information in the sagittal otoliths of these species. A total of 118 otoliths representing 30 gobiid species (including 53.5% of the Caspian gobiofauna) in three gobiid lineages (i.e., Gobius, Pomatoschistus, and Acanthogobius) and 11 genera (i.e., all Ponto-Caspian gobiid genera except Babka) were analysed at taxonomic levels using an integrated descriptive and morphometric approach. The results indicated high taxonomic efficiency of otolith morphology and morphometry at taxonomic levels for the Ponto-Caspian gobiids. Our qualitative and quantitative otolith data also (i) support the monophyly of neogobiin gobies, (ii) along with other morphological and ecological data, offer a new perspective on the systematics of Neogobius bathybius, (iii) suggest the reassignment of Hyrcanogobius bergi to the genus Knipowitschia, and (iv) question the phylogenetic integrity of the four phenotypic groups previously defined in the tadpole-goby genus Benthophilus; however, more studies are needed to complete these evaluations and confirm our otolith study findings.

The Role of Intrinsically Disordered Proteins in Liquid-Liquid Phase Separation during Calcium Carbonate Biomineralization.

Some animal organs contain mineralized tissues. These so-called hard tissues are mostly deposits of calcium salts, usually in the form of calcium phosphate or calcium carbonate. Examples of this include fish otoliths and mammalian otoconia, which are found in the inner ear, and they are an essential part of the sensory system that maintains body balance. The composition of ear stones is quite well known, but the role of individual components in the nucleation and growth of these biominerals is enigmatic. It is sure that intrinsically disordered proteins (IDPs) play an important role in this aspect. They have an impact on the shape and size of otoliths. It seems probable that IDPs, with their inherent ability to phase separate, also play a role in nucleation processes. This review discusses the major theories on the mechanisms of biomineral nucleation with a focus on the importance of protein-driven liquid–liquid phase separation (LLPS). It also presents the current understanding of the role of IDPs in the formation of calcium carbonate biominerals and predicts their potential ability to drive LLPS.

Fish Ear Stones Offer Climate Change Clues In Alaska’s Lakes

Otoliths, also known as ear stones, are small body parts that help fish with hearing and balance. Like tree rings, otoliths form one light and one dark band per year, creating rings. These rings can be measured to understand fish growth. The wider the ring, the greater the growth. In our study, we used otoliths to understand how one fish species—lake trout—responds to rising temperature in the state of Alaska. We found that warmer spring air temperature and earlier lake ice melt were related to faster lake trout growth. This finding is consistent with other studies that link warmer water temperature and earlier lake ice melt to increased plankton in Alaska’s lakes. Together, these findings suggest that climate-driven increases at the bottom of the food web might benefit top predators like lake trout. However, the relationship between warmer temperature and faster growth may not last.

'Ear stones' in crocodylians: a cross-species comparative and ontogenetic survey of otolith structures.

The vestibular system of the inner ear is a crucial sensory organ, involved in the sensation of balance and equilibrium. It consists of three semicircular canals that sense angular rotations of the head and the vestibule that detects linear acceleration and gravity. The vestibule often contains structures, known as the otoliths or ‘ear stones’. Otoliths are present in many vertebrates and are particularly well known from the fossil record of fish, but surprisingly have not been described in detail in most tetrapods, living or extinct. Here, we present for the first time a survey of the otoliths of a broad sample of extant crocodylian species, based on computed tomography scans. We find that otoliths are present in numerous crocodylian species of different growth stages, and they continue to increase in size during ontogeny, with positive allometry compared to skull length. Our results confirm that otoliths are a common component of the crocodylian vestibular system, and suggest they play an important role in sensory detection. Otoliths are likely common, but overlooked, constituents of the inner ear in tetrapods, and a broader study of their size, shape and distribution promises insight into sensory abilities.

Molecular mechanism of calcium induced trimerization of C1q-like domain of otolin-1 from human and zebrafish

The C1q superfamily includes proteins involved in innate immunity, insulin sensitivity, biomineralization and more. Among these proteins is otolin-1, which is a collagen-like protein that forms a scaffold for the biomineralization of inner ear stones in vertebrates. The globular C1q-like domain (gC1q), which is the most conserved part of otolin-1, binds Ca2+ and stabilizes its collagen-like triple helix. The molecular details of the assembly of gC1q otolin-1 trimers are not known. Here, we substituted putative Ca2+-binding acidic residues of gC1q otolin-1 with alanine to analyse how alanine influences the formation of gC1q trimers. We used human and zebrafish gC1q otolin-1 to assess how evolutionary changes affected the function of the protein. Surprisingly, the mutated forms of gC1q otolin-1 trimerized even in the absence of Ca2+, although they were less stable than native proteins saturated with Ca2+. We also found that the zebrafish gC1q domain was less stable than the human homologue under all tested conditions and became stabilized at higher concentrations of Ca2+, which showed that specific interactions leading to the neutralization of the negative charge at the axis of a gC1q trimer by Ca2+ are required for the trimers to form. Moreover, human gC1q otolin-1 seems to be optimized to function at lower concentrations of Ca2+, which is consistent with reported Ca2+ concentrations in the endolymphs of fish and mammals. Our results allow us to explain the molecular mechanism of assembly of proteins from the C1q superfamily, the modulating role of Ca2+ and expand the knowledge of biomineralization of vertebrate inner ear stones: otoliths and otoconia.

Zebrafish stm is involved in the development of otoliths and of the fertilization envelope.

SummaryUsing an in vivo assay, we selected 11 genes that were highly upregulated during the induction of ovulation in zebrafish using microarray analysis and RNA sequencing. The starmaker gene (stm) was one of these genes. Although stm has been previously reported to be involved in otolith formation during the early development of zebrafish, we detected its expression in eggs and showed that stm was related to fertilization by establishing an stm gene knockout strain using the CRISPR/Cas9 system. Further phenotypic analysis of stm knockout fish was conducted in this study. With a higher nonfertilization rate, the stm mutant strain showed an extremely low survival rate. Otoliths of stm homozygous mutant zebrafish showed abnormal morphology in embryos and adult fish. However, fish did not show any abnormalities in swimming behaviour in either embryos or adults. Stm proteins were detected on the chorion of ovulated eggs before spawning. Fibre-supported knob-like structures on the fertilization envelope (FE) also showed abnormal structures in stm mutants. The Stm protein is necessary for otolith formation, and a lack of Stm causes abnormal otolith formation. The partial defect of otolith formation does not cause defects in swimming behaviour. The Stm protein is expressed in the chorion and is responsible for the formation of fibre-supported knob-like structures on the FE. It was suggested that a lack of Stm caused a lower fertilization rate due to inadequate formation of the FE.Lay summaryIn zebrafish, the protein Starmaker (Stm) was identified as having a role in ovulation. Stm is also known to be required for the formation of ear stones (otoliths) which are needed to keep the body in balance. Zebrafish lacking Stm were produced by genome editing. As expected, Stm-deficient fish formed abnormal otoliths. To investigate the role of Stm in ovulation, fertilization and early development, we tried mating of Stm mutants and observed their juveniles. Although no problem found in ovulation, we found low fertilization rate and abnormal structure of knob-like structure (small pit) on the egg membrane. Survival rate of embryos with abnormal egg membrane was extremely low. It was demonstrated that Stm protein is necessary to form the functional egg membrane to protect embryos from the outside environment.

Quantitative assessment of the oxygen isotope composition of fish otoliths from Lake Mungo, Australia

AbstractThe Willandra Lakes region is a series of once interconnected and now-dry lake basins in the arid zone of southeastern Australia. It is a UNESCO World Heritage Site of cultural, archaeological, and geological significance, preserving records of Aboriginal occupation and environmental change stretching back to at least 50 ka. Linking the archaeology with the commensurate palaeoenvironmental information is complicated by the millennial time spans represented by the past hydrological record preserved in the sediment vs. the subdecadal evidence of each archaeological site. Oxygen isotope records across annual growth rings of fish otoliths (ear stones) can elucidate flooding and drying regimes on subannual scales. Otoliths from hearth sites (fireplaces) link lake hydrology with people eating fish on the lakeshore. Oxygen isotopic trends in hearth otoliths from the last glacial maximum (LGM) were previously interpreted in terms of high evaporation under dry conditions. However, this ignored hydrology-driven changes in water δ18O. Here, a mass balance model is constructed to test the effect lake desiccation has on water δ18O and how this compares with the LGM otolith records. Based on this modelling, we suggest that Lake Mungo otolith signatures are better explained by evaporation acting on full lakes rather than by lake drying.

Explaining decisions of deep neural networks used for fish age prediction.

Age-reading of fish otoliths (ear stones) is important for the sustainable management of fish resources. However, the procedure is challenging and requires experienced readers to carefully examine annual growth zones. In a recent study, convolutional neural networks (CNNs) have been demonstrated to perform reasonably well on automatically predicting fish age from otolith images. In the present study, we carefully investigate the prediction rule learned by such neural networks to provide insight into the features that identify certain fish age ranges. For this purpose, a recent technique for visualizing and analyzing the predictions of the neural networks was applied to different versions of the otolith images. The results indicate that supplementary knowledge about the internal structure improves the results for the youngest age groups, compared to using only the contour shape attribute of the otolith. However, the contour shape and size attributes are, in general, sufficient for older age groups. In addition, within specific age ranges we find that the network tends to focus on particular areas of the otoliths and that the most discriminating factors seem to be related to the central part and the outer edge of the otolith. Explaining age predictions from otolith images as done in this study will hopefully help build confidence in the potential of deep learning algorithms for automatic age prediction, as well as improve the quality of the age estimation.

An open-source database model and collections management system for fish scale and otolith archives

Scales and otoliths (ear stones) from fish are routinely sampled for age estimation and fisheries management purposes. Growth records from scales and otoliths can be used to generate long-term time series data, and in combination with environmental data, can reveal species specific population responses to a changing climate. Additionally, scale and otolith microchemical data can be utilized to investigate fish habitat usage. A common problem associated with biological collections, is that while sample intake grows, long-term physical storage is rarely a priority, and much of the sampling took place before the advent of open-access digital infrastructure. Material is often collected to meet short-term objectives and resources are seldom committed to maintaining and archiving collections. As a consequence, precious samples are frequently stored in many different and unsuitable locations, and may become lost or separated from associated metadata. The Marine Institute's ecological research station in in Newport, Co. Mayo, Ireland, holds a multi-decadal (1928–2020) collection of scales and otoliths from various fish species, gathered from many geographic locations. Here we present an open-source database model and archiving system to consolidate and digitize this collection, and show how this case study infrastructure could be used for other biological sample collections. The system utilizes the FAIR (Findable Accessible Interoperable and Reusable) open-data principles, and includes a physical repository, sample metadata catalogue, and image library.

INFLUENCES OF UPPER FLORIDAN AQUIFER WATERS ON RADIOCARBON IN THE OTOLITHS OF GRAY SNAPPER (Lutjanus griseus) IN THE GULF OF MEXICO

ABSTRACTThe otoliths (ear stones) of fishes are commonly used to describe the age and growth of marine and freshwater fishes. These non-skeletal structures are fortuitous in their utility by being composed of mostly inorganic carbonate that is inert through the life of the fish. This conserved record functions like an environmental chronometer and bomb-produced radiocarbon (14C)—a 14C signal created by atmospheric testing of thermonuclear devices—can be used as a time-specific marker in validating fish age. However, complications from the hydrogeology of nearshore marine environments can complicate 14C levels, as was the case with gray snapper (Lutjanus griseus) along the Gulf of Mexico coast of Florida. Radiocarbon of these nearshore waters is influenced by freshwater input from the karst topography of the Upper Floridan Aquifer—estuarine waters that are 14C-depleted from surface and groundwater inputs. Some gray snapper likely recruited to this kind of environment where 14C levels were depleted in the earliest otolith growth, although age was validated for individuals that were not exposed to 14C-depleted waters to an age of at least 25 years with support for a 30-year lifespan.

Experimental support towards a metabolic proxy in fish using otolith carbon isotopes.

Metabolic rate underpins our understanding of how species survive, reproduce and interact with their environment, but can be difficult to measure in wild fish. Stable carbon isotopes (δ13C) in ear stones (otoliths) of fish may reflect lifetime metabolic signatures but experimental validation is required to advance our understanding of the relationship. To this end, we reared juvenile Australasian snapper (Chrysophrys auratus), an iconic fishery species, at different temperatures and used intermittent-flow respirometry to calculate standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS). Subsequently, we analysed δ13C and oxygen isotopes (δ18O) in otoliths using isotope-ratio mass spectrometry. We found that under increasing temperatures, δ13C and δ18O significantly decreased, while SMR and MMR significantly increased. Negative logarithmic relationships were found between δ13C in otoliths and both SMR and MMR, while exponential decay curves were observed between proportions of metabolically sourced carbon in otoliths (Moto) and both measured and theoretical SMR. We show that basal energy for subsistence living and activity metabolism, both core components of field metabolic rates, contribute towards incorporation of δ13C into otoliths and support the use of δ13C as a metabolic proxy in field settings. The functional shapes of the logarithmic and exponential decay curves indicated that physiological thresholds regulate relationships between δ13C and metabolic rates due to upper thresholds of Moto Here, we present quantitative experimental evidence to support the development of an otolith-based metabolic proxy, which could be a powerful tool in reconstructing lifetime biological trends in wild fish.

Natal origin of Pacific bluefin tuna from the California Current Large Marine Ecosystem.

Natal origin of subadult (age-1) Pacific bluefin tuna (PBT, Thunnus orientalis) from the California Current Large Marine Ecosystem (CCLME) was determined using natural tracers in ear stones (otoliths). Age-0 PBT collected from the two known spawning areas in the western Pacific Ocean (East China Sea, Sea of Japan) were used to establish baseline signatures from otolith cores over 4 years (2014–2017) based on a suite of trace elements (Li, Mg, Mn, Sr, Zn and Ba). Distinct chemical signatures existed in the otolith cores of age-0 PBT collected from the two spawning areas, with overall classification accuracy ranging 73–93% by year. Subadult PBT collected in the CCLME over the following 4 years (2015–2018) were then age-class matched to baselines using mixed-stock analysis. Natal origin of trans-Pacific migrants in the CCLME ranged 43–78% from the East China Sea and 22–57% from the Sea of Japan, highlighting the importance of both spawning areas for PBT in the CCLME. This study provides the first estimates on the natal origin of subadult PBT in this ecosystem using otolith chemistry and expands upon the application of these natural tracers for population connectivity studies for this species.

Wide-Ranging Temporal Variation in Transoceanic Movement and Population Mixing of Bluefin Tuna in the North Atlantic Ocean

Uncertainty regarding the movement and population exchange of Atlantic bluefin tuna (Thunnus thynnus) from the two primary spawning areas (Gulf of Mexico, Mediterranean Sea) is increasingly implicated as a major impediment for the conservation of this species. Here, two mixture methods were applied to natural chemical markers (18O and 13C) in otoliths (ear stones) to comprehensively investigate the nature and degree of transoceanic movement and mixing of eastern and western populations in several areas of the North Atlantic Ocean that potentially represent mixing hotspots. Areas investigated occurred on both sides of the 45W management boundary as well as waters off the coast of Africa (Morocco, Canary Islands) where both populations are known to occur. Projections of population composition (i.e., natal or nursery origin) from a multinomial logistic regression (MLR) classification method with different probability thresholds were generally in agreement with maximum likelihood estimates from the commonly used mixed-population program HISEA; however, predicted contributions for the less abundant population were occasionally higher for MLR estimates. Both MLR and HISEA clearly showed that mixing of Atlantic bluefin tuna in the Central North Atlantic Ocean was highly variable from year to year with expatriates of eastern or western origin commonly crossing into the other management area. Pronounced transoceanic movement and mixing of western migrants was also present off the coast of Africa, with the occurrence of western migrants in the Canary Islands and Morocco ranging from zero to the majority of the individuals assayed for the years examined. Results indicate highly variable rates of movement and population exchange for Atlantic bluefin tuna, highlighting the need for temporally resolved estimates of natal origin in mixing hotspots to improve population models used to evaluate the status of this threatened species.

Polyketide Synthase Plays a Conserved Role in Otolith Formation.

Otoliths (ear stones) are biomineralized complexes essential for the balancing and hearing function of the inner ears in fish. Their formation is controlled by a genetically programmed biological process that is yet to be defined. We have isolated and characterized a spontaneous genetic mutant zebrafish with a complete absence of otoliths, named no otolith 1 (not1). not1 mutants are unable to develop otoliths during embryonic stages and fail to respond to acoustic stimuli, indicating an inner ear defect. We identified a deleterious mutation (G239R) that altered a highly conserved amino acid residue in the zebrafish ortholog of type I polyketide synthase (pks1) to underlie these phenotypes and showed that expression of the polyketide synthase gene of Japanese medaka fish could rescue the otolith deficiency in not1 mutant zebrafish. Our finding highlights a critical and conserved role of type I polyketide synthase in the initiation of otolith formation. Given the functional homology between otoliths in teleost fish and otoconia in mammals and humans, not1 mutants provide a new animal model for the study of human otoconia-related diseases.

Shifting habitat mosaics and fish production across river basins.

Watersheds are complex mosaics of habitats whose conditions vary across space and time as landscape features filter overriding climate forcing, yet the extent to which the reliability of ecosystem services depends on these dynamics remains unknown. We quantified how shifting habitat mosaics are expressed across a range of spatial scales within a large, free-flowing river, and how they stabilize the production of Pacific salmon that support valuable fisheries. The strontium isotope records of ear stones (otoliths) show that the relative productivity of locations across the river network, as both natal- and juvenile-rearing habitat, varies widely among years and that this variability is expressed across a broad range of spatial scales, ultimately stabilizing the interannual production of fish at the scale of the entire basin.

Significance of otolith calcium carbonate crystal structure diversity to microchemistry studies

Otoliths, calcium carbonate (CaCO3) ear stones of fish, contain a wealth of information about fish life and environmental history yet the CaCO3 polymorph form the otolith is made of is a critical, but seldom considered, piece of information during otolith analysis. Otolith trace element chemistry data increasingly informs management decisions, but recent work has shown that CaCO3 polymorphs—aragonite, vaterite, and calcite—can bear on incorporation of trace elements in a non-trivial way. Most fishes are thought to have otoliths of the aragonite CaCO3 form, but this construct is potentially outdated with many recent literature reports showing otherwise. Our study used previously unpublished neutron diffraction data and reports from published literature to address three objectives: (1) summarize the relative effects of otolith CaCO3 polymorphism on otolith microchemistry, (2) summarize reports of otolith polymorphs to gain a better understanding of the extent of non-aragonite otoliths among fishes, (3) outline future research needed to align interpretations of microchemistry with our current understanding of otolith polymorph diversity. We found that while aragonite otoliths are the most common, so are exceptions. For example, the ostensibly rare (among species) CaCO3 form vaterite was reported in at least some otoliths of 40% of the species surveyed. Our work suggests that examination of the CaCO3 polymorph composition of otoliths should become more common particularly in studies where results will or may be used to inform management decisions. Future research should work to attribute controls on otolith CaCO3 polymorph expression using a combination of -omics and material characterization approaches to enrich the life history and environmental information output from otoliths and increase our understanding of the assumptions made in otolith trace element chemistry studies.