Otoliths are remarkable recorders that continuously store visual and chemical information about fish phenotype, life history and environment. This review highlights the coupling between fish physiology and otolith characteristics with a focus on questions that are fundamental, unanswered and with the potential to yield significant new insights into the variability in life history traits among individuals and the importance of this variability in a fluctuating and changing environment.

The aim of this study was to investigate the role of otolith biomineralisation in the relationship between otolith chemistry and microstructure at a fine scale in order to understand the mechanism of elemental uptake. The results indicate that strontium incorporation may be assisted, in part, by the organic composition during otolith mineralisation, which potentially has implications for the interpretation of otolith strontium.

The daily growth patterns of juvenile and adult Peruvian anchovies in northern Chile for the recruitment and fishery seasons of 2009 and 2010 show high growth for the entire life history, maximising growth in the first year of life to reach a mean length at the first year of 16.3-cm total length.

It is assumed that fish otoliths grow in direct proportion to the body during discrete life stages. This assumption was violated for juvenile Chinook salmon subjected to variable seasonal water temperatures and food rations, wherein food-deprived fish in 21°C water had larger otoliths than equivalently sized fish in 15°C water and fed an unlimited ration. This breakdown could have implications for accurately estimating fish growth from otoliths in natural populations.

Many past attempts to age deep-water redfish (Sebastes mentella) and Acadian redfish (S. fasciatus) in the north-west Atlantic have been stymied by the use of inaccurate ageing methods, which have led to stock collapse in other deep-water species. Herein we report substantial improvements in methods for ageing Sebastes spp. through a combination of sectioning, burning and image enhancement. Bomb radiocarbon assays and microsatellite DNA confirmed both the accuracy of the ages and species identity, and demonstrated significant growth differences between both species and stocks to an age of 70 years.

To evaluate the method for age determination of Greenland halibut, a deep-water flatfish, juvenile fish were injected with a chemical compound that produces a time stamp in the otoliths. After up to 6 years at large, age readers identified the number of annual zones with a mean bias of 6 months or less, thus indicating that the current age reading protocol produces near-accurate age estimates.

Traditionally, the age of the European anchovy has been determined on the basis of interpretation of annual growth increments. Based on otolith microstructure analysis, this study confirms that the first annulus is composed of an opaque band, which is deposited during spring and summer, and a translucent band, which is formed during autumn and winter. Consequently, the study validates age determination based on these structures and shows that otolith macrostructure analysis is a reliable tool for age determination of anchovy.

Validation of the age determination using otoliths of European anchovy is presented along with a historical corroboration of the method and a summary of the annual growth in length. The paper also describes the three key pieces of information required, given a date of capture, for age determination: the typical annual growth pattern of otoliths, their seasonal edge formation by ages and the most typical checks.

Chemical signatures in fish otoliths have the potential to reconstruct fish movement patterns and habitat use of Arctic marine fish. A fish occupying different demersal habitats resulted in 76% correct classification of Arctic (or Polar) cod and 82% for Arctic staghorn sculpin into the habitat from which fish were captured. Chemical signatures were affected by water temperature, fish age and fish length.

The mixing dynamics between the two Baltic Sea cod stocks are unclear. Analysis of spatiotemporal patterns in quality flag distribution of cod otoliths showed that the Darß and Drogden sills separated readable otoliths in shallow western waters from more unreadable otoliths in deeper eastern waters. There were no temporal trends suggesting stable mixing and no increased spillover from the east since 2007.

Little information is available about the occurrence, distribution or habitat utilisation of red snapper juveniles in US Atlantic Ocean waters. Otolith chemical constituents were used to parameterise Markov Chain Monte Carlo models as a first-step approach in addressing questions about potential nursery sources contributing recruits to red snapper (Lutjanus campechanus) in waters from southern Florida to North Carolina.

In this paper we measured stable isotopes (δ¹³C and δ¹⁸O) and trace elements (Mg, Mn, Sr, Ba) in otoliths of North Atlantic albacore (Thunnus alalunga) collected from the Bay of Biscay and Atlantic offshore waters to explore the potential existence of population structuring and migratory patterns of albacore in the eastern North Atlantic Ocean.

The potential usefulness of vertebral chemistry to identify natal origin of blacktip sharks (Carcharhinus limbatus) in the northern Gulf of Mexico is demonstrated in this study. Regional differences in vertebral chemistry produced average classification accuracies of 81 and 85% for the 2012 and 2013 year-classes respectively. Important considerations are also discussed regarding the application of natural chemical tags to study connectivity of coastal elasmobranch populations.

Otolith shape analysis discriminated between western and eastern Atlantic bluefin tuna with an accuracy of 83% and indicated that samples from known mixing areas in the east Atlantic and Mediterranean were predominantly of eastern origin. Otolith shape descriptors could be used in combination with other population markers to improve the accuracy of stock discrimination and estimation of mixing rates for Atlantic bluefin tuna.

The shapes of sagittal otoliths of coastal fish assemblages of the north-west Mediterranean were described using geometric morphological analysis. Three morphological indices were estimated and compared with ecological, taxonomic, functional and morphological (from body fish shape) indices. The results revealed that otolith shape is a good variable for explaining the ecological structure of a fish assemblage and a useful tool for studying the diversity of fish assemblages.

The shape of the closed contour of fish ear stones (otoliths) has proven to contain important information useful for fish stock management. To reveal shape differences between fish stocks, classical Fourier methods have been the most frequently used approach. A simple modification has been developed that needs considerably fewer Fourier descriptors to obtain a good, large-scale description of the contour.

This paper presents a new method for compacting data from three-dimensional (3-D) otolith shapes. These shapes are defined by means of clouds of points across their surfaces and they are finally represented by a small set of parameters able to capture 3-D information relevant to classification of fish species. The use of these new parameters provides a greater percentage of correctly classified specimens compared with those obtained from two-dimensional analysis.

The element composition of fish ear bones (otoliths) is used extensively to reconstruct environmental histories of fish. Determining where elements are incorporated within otoliths is imperative to improving interpretations based on otolith chemistry. This study sought to determine whether elements were incorporated into the protein or mineral components of otoliths and the relative proportion of each element in each component.

The high variability of growth and longevity estimates for European hake (Merluccius merluccius) reflects the existence of two opposing hypotheses, a fast-growing hypothesis (FGH; with a longevity of ~15 years) and a slow-growing hypothesis (SGH; with a longevity of ~30 years). Bomb radiocarbon (¹⁴C) dating provided robust length-at-age measurements that are in agreement with the SGH.