Relationships between fish size and otolith size of four bathydemersal fish species from the south eastern Arabian Sea,India

The objective of this study was to estimate a prey body size from the hard parts (e.g. otoliths) of a fish species frequently found in the guts of predators. Length–weight relationships between otolith size (length, height, weight and aspect ratio) and fish size (total length and weight) were determined for four fish species captured in the Arabian Sea by bottom trawl (2015 survey on‐board FORV Sagar Sampada, 200–300 m depth), off the west coast of India: Psenopsis cyanea, Pterygotrigla hemisticta, Bembrops caudimacula and Hoplostethus rubellopterus. No significant differences were noted between the size of the left and right otoliths (t test) in any of the four species. The length–weight relationship of the otolith in all four species showed a negative allometric growth pattern (t test, p < .05). The data fitted well to the regression model for otolith length (OL), otolith height (OH) and otolith weight (OW) to total length (TL) and total weight (TW). Results showed that these relationships are a helpful tool in predicting fish size from the otoliths and in calculating the biomass of these less‐studied fish species during feeding studies and palaentology.     

Using the otolith sulcus to aid in prey identification and improve estimates of prey size in diet studies of a piscivorous predator

Diet studies are fundamental for understanding trophic connections in marine ecosystems. In the southeastern US, the common bottlenose dolphin Tursiops truncatus is the predominant marine mammal in coastal waters, but its role as a top predator has received little attention. Diet studies of piscivorous predators, like bottlenose dolphins, start with assessing prey otoliths recovered from stomachs or feces, but digestive erosion hampers species identification and underestimates fish weight (FW). To compensate, FW is often estimated from the least affected otoliths and scaled to other otoliths, which also introduces bias. The sulcus, an otolith surface feature, has a species‐specific shape of its ostium and caudal extents, which is within the otolith edge for some species. We explored whether the sulcus could improve species identification and estimation of prey size using a case study of four sciaenid species targeted by fisheries and bottlenose dolphins in North Carolina. Methods were assessed first on otoliths from a reference collection (n = 421) and applied to prey otoliths (n = 5,308) recovered from 120 stomachs of dead stranded dolphins. We demonstrated in reference‐collection otoliths that cauda to sulcus length (CL:SL) could discriminate between spotted seatrout (Cynoscion nebulosus) and weakfish (Cynoscion regalis) (classification accuracy = 0.98). This method confirmed for the first time predation of spotted seatrout by bottlenose dolphins in North Carolina. Using predictive models developed from reference‐collection otoliths, we provided evidence that digestion affects otolith length more than sulcus or cauda length, making the latter better predictors. Lastly, we explored scenarios of calculating total consumed biomass across degrees of digestion. A suggested approach was for the least digested otoliths to be scaled to other otoliths iteratively from within the same stomach, month, or season as samples allow. Using the otolith sulcus helped overcome challenges of species identification and fish size estimation, indicating their potential use in other diet studies.     

Heterogeneity of otolith chemical composition from two-dimensional mapping: Relationship with biomineralization mechanisms and implications for microchemistry analyses

Although otoliths are widely used as archives to infer life-history traits and habitat use in fishes, their biomineralization process remains poorly understood. This lack of knowledge is problematic as it can lead to misinterpretation of the different types of signals (e.g., optical or chemical) that provide basic data for research in fish ecology, fisheries management, and species conservation. Otolith calcification relies on a complex system involving a pericrystalline fluid, the endolymph, whose organic and inorganic compositions are spatially heterogeneous for some constituents. This property stems from the particular structure of the calcifying saccular epithelium. In this study, we explored the spatial heterogeneity of elemental incorporation in otoliths for two species of high economic interest, European hake Merluccius merluccius (L. 1758) and European sea bass Dicentrarchus labrax (L. 1758). Two-dimensional mappings of chemical elements were obtained using UV high-repetition-rate femtosecond laser ablation (fs-LA) system coupled to a high-resolution inductively coupled plasma sector field mass spectrometer analyses on transverse sections of sagittae. Results highlighted a clear asymmetry between proximal (sulcus) and distal (antisulcus) concentrations for elements such as magnesium (Mg), phosphorus (P), manganese (Mn), and potassium (K) with concentration gradient directions that varied depending on the element. Strontium (Sr) and barium (Ba) did not show a proximo-distal gradient. These results are discussed in light of current knowledge on the endolymph composition and the mechanisms that lead to its compartmentalization, highlighting the need for further research on otolith biomineralization. Operational implications for studies based on otolith chemical composition are also discussed with emphasis on advice for sampling strategies to avoid analytical biases and the need for in-depth analyses of analytical settings before comparing otolith signatures between species or geographical areas.     

Biometric relation between body size and otolith size of seven commercial fish species of the south‐western Atlantic

Given the importance and applicability of these biometric relations, the present work aimed to verify the existence of correlations between the length of saggitae otoliths and the body size of seven south‐western Atlantic marine fish species and to generate equations to estimate the body size of these species through otolith measurements. Fifty otoliths of Centropomus parallelus, Centropomus undecimalis, Lutjanus analis, Lutjanus jocu, Lutjanus synagris, Chaetodipterus faber and Mugil curema were collected for analysis. Significant relations between otolith length and total length and otolith width and total length were found for all the species. The highest coefficient of determination was observed for Centropomus undecimalis and Lutjanus synagris, for both relations, and the lowest was observed for Mugil curema. The results show that estimates of body size of the species through biometric analyses of otoliths are reliable. Based on this, the equations generated to obtain the total length of the fish using biometric otolith data can be used in dietary studies of top predators and in paleontological recostructions of modern fish.     

Saccular otolith mass asymmetry in adult flatfishes

A dimensionless measure of otolith mass asymmetry, χ, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass asymmetry was studied in eight flatfish species (110 otolith pairs) and compared with data from a previously published study on roundfishes. As in the case of symmetrical fishes, the absolute value of χin flatfishes does not depend on fish length and otolith growth rate, although otolith mass and the absolute value of otolith mass difference are correlated with fish length. The values of χwere between ?0·2 and +0·2 in 96·4% of flatfishes studied. The mean ±s .e . value of χin flatfishes was significantly larger than in standard bilaterally symmetrical marine fishes (‘roundfishes’), respectively 0·070 ± 0·006 and 0·040 ± 0·006. The most prominent distinction is the existence of downside prevalence of saccular otolith mass in flatfishes, which contrasts with no right–left prevalence in roundfishes found in a previous study. In the right‐eyed flatfishes (Soleidae), the left saccular otoliths are heavier than the right otoliths. In the left‐eyed flatfishes (Bothidae and Citharidae), the right saccular otoliths are heavier than the left otoliths. Not all flatfishes, however, fit in this design: 11·8% of flatfishes studied had the heavier saccular otoliths in the upside labyrinth and 5·4% of flatfishes had no otolith mass asymmetry (within the accuracy of the analysis). At the same time, the more mobile flatfishes (bothids and citharids) have more symmetrical and, hence, more precisely organized saccular otolith organs than the bottom‐associated flatfishes (soleids). It is possible to assume that the value of the otolith asymmetry is not only correlated with flatfish placement in a particular family, or position of eyes, but also may correlate with general aspects of their ecology. Mathematical modelling indicated that for most flatfishes one‐side saccular prevalence had no substantial significance for sound processing. On the other hand, calculations showed that 49% of flatfishes (but only 14·5% of roundfishes) have |χ| which exceed the critical level and, in principle, could sense the difference between the static displacement of the large and small paired otoliths. At that, the number of the soleids that could sense this difference is greater than the number of the bothids and citharids, 84 and 27%, respectively.     

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.

     

Validation of a simple and well‐suited chemical cleaning method for fish otoliths

In marine biology, many research fields are based on use of fish otoliths. All the studies dealing with otoliths need as starting point a perfectly clean otolith. Dissection is difficult when working on small or highly jagged otoliths. A common problem is that during otolith preparation some fish tissue may remain stuck to it, even after a mechanical cleaning. Then, supplementary cleaning with chemicals is needed. Classical methods are known to possibly alter otolith's structure and/or composition. Here, we present a chemical cleaning method using only sodium hydroxide. We have validated the method on two different fish species, Oblada melanura and Dicentrarchus labrax. Observation and analyses of morphological measurements have confirmed significant suppression of residual tissues. We propose this method as a good alternative to previously published mono‐ or multichemical methods.     

Ageing Belanger's croaker,Johnius belangerii (Cuvier, 1830), based on otolith shape analysis

The use of morphological characters and otolith weight as predictors of fish age has proven to be an efficient, objective and precise method, but studies were heretofore focused primarily on fast‐growing fish species. In the present study, Belanger's croaker, Johnius belangerii (Cuvier, 1830), is presented as a model species for slow‐growing fish where it is hypothesized that age has a significant effect on the otolith shape, and that the otolith weight has the potential to predict individual fish age as an alternative and objective method. Discriminant function analysis (DFA) of shape variables and cross‐validation were applied to a total of 359 sagittal otoliths in the age groups 0, 1 and 2. The shape variables demonstrated 64.1% correct age classification, and a 93.5% correct age classification with the inclusion of otolith weight in the discriminant function. Results show that a combination of shape variables and otolith weight work well in age determination of Belanger's croaker, and demonstrate its application potential for sciaenids that are distributed throughout the coastal waters of China.     

Dietary histories of herbivorous loricariid catfishes: evidence from δ<Superscript>13</Superscript>C values of otoliths

The ecology of many Neotropical fishes is difficult or often impossible to study during rainy seasons. Thus, ecological studies of tropical fishes are usually performed on fish captured only during dry seasons. Because otoliths preserve a record of life history, this study evaluated the utility of otolith stable isotope values for the investigation of trophic ecology of Neotropical fishes (specifically herbivorous loricariid catfish) throughout their lives. Because plant dietary materials have δ¹³C values that are determined by their photosynthetic pathways, metabolism and environmental conditions, different plants may impart different isotope values on fish otoliths that reflect consumption of these plants. The δ¹³C_(otolith) values of xylophagous Panaque nigrolineatus captured in the field were significantly lower than those of algivorous Hypostomus regani from a nearby region. A laboratory experiment wherein Hypostomus sp. had δ¹³C_(otolith) values that reflected the δ¹³C values of their plant diet and additional evidence indicate that δ¹³C_(otolith) values in loricariid catfish otoliths can record dietary history.     

Enigmatic ear stones: what we know about the functional role and evolution of fish otoliths

Otoliths in bony fishes play an important role in the senses of balance and hearing. Otolith mass and shape are, among others, likely to be decisive factors influencing otolith motion and thus ear functioning. Yet our knowledge of how exactly these factors influence otolith motion is incomplete. In addition, experimental studies directly investigating the function of otoliths in the inner ear are scarce and yield partly conflicting results. Herein, we discuss questions and hypotheses on how otolith mass and shape, and the relationship between the sensory epithelium and overlying otolith, influence otolith motion. We discuss (i) the state‐of‐the‐art knowledge regarding otolith function, (ii) gaps in knowledge that remain to be filled, and (iii) future approaches that may improve our understanding of the role of otoliths in ear functioning. We further link these functional questions to the evolution of solid teleost otoliths instead of numerous tiny otoconia as found in most other vertebrates. Until now, the selective forces and/or constraints driving the evolution of solid calcareous otoliths and their diversity in shape in teleosts are largely unknown. Based on a data set on the structure of otoliths and otoconia in more than 160 species covering the main vertebrate groups, we present a hypothetical framework for teleost otolith evolution. We suggest that the advent of solid otoliths may have initially been a selectively neutral ‘by‐product’ of other key innovations during teleost evolution. The teleost‐specific genome duplication event may have paved the way for diversification in otolith shape. Otolith shapes may have evolved along with the considerable diversity of, and improvements in, auditory abilities in teleost fishes. However, phenotypic plasticity may also play an important role in the creation of different otolith types, and different portions of the otolith may show different degrees of phenotypic plasticity. Future studies should thus adopt a phylogenetic perspective and apply comparative and methodologically integrative approaches, including fossil otoliths, when investigating otoconia/otolith evolution and their function in the inner ear.     

The use of otolith chemistry to characterize diadromous migrations

Chemical constituents in otoliths have become a valuable tool for fish ecologists seeking to reconstruct migratory patterns and life-history diversity in a wide range of species worldwide. This approach has proved particularly effective with fishes that move across substantial salinity gradients over the course of their life, including many diadromous species. Freshwater endmembers of several elemental and isotope ratios (e.g. Sr:Ca, Ba:Ca and (87)Sr:(86)Sr) are typically identifiably distinct from marine values, and often differ among freshwater tributaries at fine spatial scales. Because these chemical tags are generally incorporated in proportion to their ambient dissolved concentrations, they can be effective proxies for quantifying the presence, duration and frequency of movements between freshwater and marine habitats. The development of high precision probe-based analytical techniques, such as laser ablation inductively coupled plasma mass spectrometry (ICP-MS) and microbeam methods, has allowed researchers to glean increasingly detailed life-history profiles of these proxies across otoliths. Researchers are also combining multiple chemical proxies in an attempt to refine interpretations of habitat residence patterns. A thorough understanding of the spatial and temporal variation in water chemistry as well as environmental and physiological controls on incorporation of specific elements into otoliths is required for confident estimation of lifetime salinity experience. First some assumptions, methodological considerations and data processing options that are particularly relevant to diadromous otolith chemistry studies are discussed. Insights into diadromous migrations obtained from decades of otolith chemistry research, highlighting the increasingly recognized importance of contingent behaviour and partial migration are then discussed. Finally, areas for future research and the need to integrate otolith chemistry studies into comprehensive assessments of the effects of global environmental change are identified.     

Morphology and microchemistry of abnormal otoliths in the ayu, <Emphasis Type="Italic">Plecoglossus altivelis</Emphasis>

The sagittal otolith morphology and microchemistry of reared juvenile ayu, Plecoglossus altivelis, were examined to describe the occurrence and microchemical characteristics of the abnormal otoliths in this species. Juvenile ayu (N = 31) were collected in June 2004 at three different locations, Wakayama, Kumamoto, and Biwa Lake in Japan, where they were being reared in freshwater aquaculture ponds after having been collected in the wild as larvae. Otolith abnormality was found in the sagittae of 26% (N = 8) of the individuals examined, of which five fish had abnormal otoliths only on one side, while the otolith on the other side was normal. Abnormal otoliths were more transparent and crystalline in appearance with irregular shapes compared to normal ones that were more opaque and less irregular. Abnormal otoliths were divided into two types, semi-abnormal (Type 1) with a normal part in the center, and fully-abnormal (Type 2) that were completely crystalline in appearance. The line transects and whole otolith concentration maps showed that the contents of Sr, Na and K were lower in the abnormal otolith regions compared to the normal ones, while those of Ca and S were almost constant in both. The appearance and microchemical properties of the abnormal ayu otoliths were similar to the abnormal otoliths in other species in which vaterite replaces the aragonite. Abnormal formation of otoliths occurred in ayu from Biwa Lake (30%) and Kumamoto (45%), while the Wakayama samples had no abnormality. The microchemical analyses of the normal and abnormal otoliths indicated that some abnormal otoliths had formed before the fish were captured and transferred to the hatchery, so the possible causes of otolith abnormality in ayu are discussed.     

Factors affecting morphological development of the sagittal otolith in juvenile and adult small yellow croaker (Larimichthys polyactis Bleeker, 1877)

The morphology and morphometrics of the sagittal otoliths of small yellow croaker (Larimichthys polyactis) from the southern Yellow Sea were investigated. Study objectives were to evaluate the shape variability and morphometric variables of sagittae of juveniles and adults as related to developmental changes and habit shift. A total of 152 fish were sampled from April to June of 2012 and 2013, along the coastal waters of the Lüsi spawning ground in the southern Yellow Sea. Changes in otolith shapes from the juvenile to the adult were presented with the rim development through the entire‐lobed‐entire transition and with the curvature of the cauda toward the ventral margin. The otolith elongation in the juvenile stage occurred at 10–20 mm standard length (SL) and was likely associated with the formation of otolith accessory growth centers from larvae to juvenile. The L. polyactis sagittal otoliths acquired their definitive shape at 130 mm SL maturity. Ontogeny on otolith shape might be related, for example, to the factors of metamorphic development, feeding habitat, and ambient water salinity, which varied throughout the growth of L. polyactis.     

Using otolith shape and morphometry to identify four Alburnus species (A. chalcoides,A. escherichii,A. mossulensis and A. tarichi) in Turkish inland waters

Asteriscus otolith shapes as well as their morphometry and shape contours were investigated in order to identify four allopatric Alburnus species: A. chalcoides (Güldenstädt, 1772) (Ordu), A. escherichii Steindachner, 1897 (Eski?ehir), A. mossulensis Heckel, 1843 (Tunceli), and A. tarichi (Güldenstädt, 1814) (Van) in Turkish inland waters. These were compared using the shape indices (form factor, roundness, circularity, ellipticity, rectangularity and aspect ratio), and the morphological characters [otolith weight (OWE), otolith length (OL), otolith width (OW), otolith perimeter (OP), and otolith area (OA)]. The overall canonical discriminant analysis (CDA) classification score was 93.8%, with the lowest score for A. escherichii (82.5%) and the highest for A. chalcoides (100%). The otolith shapes, morphology and shape contours of all sampled fish were a clear species differentiator, thereby demonstrating that the otolith shape is species‐specific. The current study presents for the first time comprehensive variation information on interspecific left‐right asteriscus otoliths in males and females of each Alburnus species: A. chalcoides from Ordu, A. escherichii from Eski?ehir, A. mossulensis from Tunceli and A. tarichi from Van, based on a total of 307 individuals. Scanning electron microscopy (SEM) images, shape contours and other otolith characters vary within the same genus; these differences should be investigated not only in other freshwater fish species or genera but also in the same species living in different habitats. In addition, further investigation is required not only with respect to the morphometry, biometry, shape, geometry, and shape contours of the otoliths, but also regarding the genetic methods for robust identification of various sympatric and allopatric fish populations.     

Reconstructing migratory patterns of fish based on environmental influences on otolith chemistry

The analysis of elements in calcifiedstructures of fish (e.g., otoliths) todiscriminate among fish stocks and determineconnectivity between populations is becomingwidespread in fisheries research. Recently, theconcentrations of elements in otoliths arebeing analysed on finer scales that allow thedetermination of a continuous record of otolithchemistry over a fish's entire life history.These elemental concentrations can potentiallybe used to reconstruct migration patterns,based upon the influence that water chemistry,temperature, and salinity have on otolithchemistry. In doing so, assumptions are madeabout how environmental and biological factorsinfluence the concentration of elements in fishotoliths. However, there have been fewexperiments that have tested crucialassumptions regarding what influences elementaluptake and incorporation into fish otoliths.Specifically, knowledge regarding interactionsamong environmental variables, such as theambient concentration of elements in water,temperature, and salinity, and how they mayaffect otolith chemistry, is limited.Similarly, our understanding of the rate atwhich elements are incorporated into otolithsand the implications this may have forinterpretations is lacking. This reviewdiscusses methods of determining movement offish, the development of otolith research, andsome physiological aspects of otoliths (e.g.,pathways of elemental uptake). The types ofanalysis techniques that will lead to reliableand accurate migratory reconstructions areoutlined. The effects that have on otolith chemistry arereviewed with the specific aim of highlightingareas lacking environmentalvariables in experimental data. Theinfluences of the rate of elementalincorporation and ontogeny on otolith chemistryare also addressed. Finally, future researchdirections are suggested that will fill thegaps in our current knowledge of otolithchemistry. Hypotheses that need to be tested inorder to reconstruct the migratory histories offish are outlined, in a bid to clarify thedirection that research should take beforecomplex reconstructions are attempted.     

Lesser Sandplover,Charadrius mongolus,in Turkey

Sagittal otoliths are widely used to determine taxon, age and size of the teleost fishes, and are useful tools for studies of prey-predator relationships, population dynamics and ichthyo-archaeology. They can also be used to estimate the size of the prey. We examined the relationships between otolith measurements (length, height and weight) and fish size (total length and weight) for two species of Argentinidae (Argentina sphyraena and Glossanodon leioglossus) from the Southern Aegean Sea, Turkey. Length, height and mass of sagittae were shown to be good indicators for the length and weight of fish in both species. Glossanodon leioglossus has relatively larger sagittae than Argentina sphyraena. Linear and exponential functions provided the best fit for relations between otolith and fish measurements. No significant differences were found between left and right otolith sizes.     

Morphometric analysis of otoliths of juvenile crucifix sea catfish Sciades proops (Valenciennes, 1840)

The objective of this study was to analyze the morphometry of otoliths for Sciades proops juveniles by testing the hypothesis of equality in morphometric relationships for the right and left otoliths, which could then be interchangeably used to estimate fish size or weight. Samples were obtained monthly directly from anglers after each event that took place off the state of Sergipe from March/2014 to April/2015. Anglers used rod and reel during these events, with no restriction on hook size or line thickness. Each fish specimen sampled had their total weight (W, g) and total length (TL, cm) measured and their lapillus otoliths removed and stored separately. Each otolith had its length (OL), width (OWi), and thickness (OT) measured (all in mm) under a stereomicroscope. Otoliths were weighed using a precision scale (OW, g). A total of 883 specimens were sampled: TL = 12.0–60.5 cm and W = 9.8–1880 g. The weight‐length relationship for the juvenile fishes was W = 0.0052TL^3.086 and for their otoliths was OW = 0.0002OL^3.177. The weight‐length and length‐length relationships fitted for each otolith (right and left) were not statistically different and thus all relations were estimated for grouped otoliths. The length‐length relationships for the otoliths were: OWi = 0.947OL?0.205 and OT = O.484OL?0.698. The relationship estimated for juvenile fish and otolith weight was Wj = 1076.1OW?9.120. For juvenile fish total length and otolith length, width and thickness, the following relationships were estimated: TLj = 4.028OL?3.199, TLj = 4.208OWi?2.091, and TLj = 7.824OT + 3.659, respectively. Relationships between fish and otolith size, and between fish and otolith weight indicated a change in slope close to L_m50, which should be better explored when more adult specimens are available.     

Relationships between fish and otolith size of nine deep‐sea fishes from the Andaman and Nicobar waters,North Indian Ocean

The study presents for the first time the otolith morphology of nine species of deep‐sea fishes. This study was based on sampling carried out on‐board FORV Sagar Sampada (Cruise No 349) during March‐April 2016, along the continental margin of the Andaman and Nicobar Islands in the Bay of Bengal using high speed demersal trawl. Unbroken (complete) otoliths from Polymixia fusca Kotthaus, 1970, Neoepinnula orientalis (Gilchrist & von Bonde 1924), Chlorophthalmus nigromarginatus (Kamohara, 1953), Cubiceps baxteri (McCulloch, 1923), Bembrops caudimacula (Steindachner, 1876), Neoscopelus microchir (Matsubara, 1943), Ostracoberyx dorygenis Fowler, 1934, Synagrops japonicus (Döderlein, 1883), and Bathyclupea hoskynii Alcock 1891) were used for this study. Length–weight relationships (LWR) and the regression between otolith size (width, weight, area and perimeter) and fish length (TL) of nine deep‐sea Fishes were considered. Numerical relationships derived from the relationship between otolith size and the fish can be used as predictors to estimate the prey size as well as to understand trophic relations and food web dynamics of these hitherto unexamined deep‐sea ichthyofauna. LWR showed negative allometric otolith growth in five species; four species showed positive allometric growth. Otolith size to fish size (TL) relation is explained by a simple linear regression considering otolith width (OW), otolith weight (OWe), otolith area (OA) and otolith perimeter (OP). Stronger r² values (>.76) indicate robustness, except for Cubiceps baxteri (r² = .65), and give better estimates for the TL of the fish.     

Comparison of spatial variation in otolith chemistry of two fish species and relationships with water chemistry and otolith growth

Spatial variation in the chemistry (Mg, Mn, Sr and Ba) of recently deposited otolith material (last 20–30 days of life) was compared between two demersal fish species; snapper Pagrus auratus (Sparidae) and sand flathead Platycephalus bassensis (Platycephalidae), that were collected simultaneously at 12 sites across three bays in Victoria, south-eastern Australia. Otolith chemistry was also compared with ambient water chemistry and among three sampling positions adjacent to the proximal otolith margin. For both species, variation in otolith chemistry among bays was significant for Ba, Mn and Sr; however, differences among bays were only similar between species for Ba and Mn. Only Ba showed significant variation at the site level. Across the 12 sites, mean otolith Ba levels were significantly positively correlated between species. Further, although incorporation rates differed, mean ambient Ba levels for both species were positively correlated with ambient Ba levels. Spatial variation in multi-element otolith chemistry was also broadly similar between species and with multi-element water chemistry. Partition coefficients clearly indicated species-specific incorporation of elements into otoliths. Mg and Mn were consistently higher in snapper than sand flathead otoliths (mean ±s .d ., Mg snapper 22·1 ± 3·8 and sand flathead 9·9 ± 1·5 μg g⁻¹, Mn snapper 4·4 ± 2·6 and sand flathead 0·5 ± 0·3 μg g⁻¹), Sr was generally higher in sand flathead otoliths (sand flathead 1570 ± 235 and snapper 1346 ± 104 μg g⁻¹) and Ba was generally higher in snapper otoliths (snapper 12·1 ± 12·8 and sand flathead 1·8 ± 1·4 μg g⁻¹). For both species, Mg and Mn were higher in the faster accreting regions of the otolith margin, Sr was lower in the slower accreting region and Ba showed negligible variation among the three sampling regions. This pattern was consistent with the higher Mg and Mn, and generally lower Sr observed in the faster accreting snapper otoliths. It is hypothesized that the differences between species in the incorporation of these elements may be at least partly related to differences in metabolic and otolith accretion rate. Although rates of elemental incorporation into otoliths appear species specific, for elements such as Ba where incorporation appears consistently related to ambient concentrations, spatial variation in otolith chemistry should show similarity among co-occurring species.