Otolith Structure Research Articles

Stock identification of sympatric Atlantic cod populations in the Gulf of Maine and mixed stock fishery analysis using otolith-based techniques

Sympatric populations of Atlantic cod with distinct spawning times in winter and spring have been identified within the Gulf of Maine. A new western Gulf of Maine stock assessment unit in U.S. waters lumps winter and spring spawning populations into a single stock unit and future monitoring and assessment of their abundance will require mixed stock analysis. The goal of this study was to evaluate the utility of otolith-based stock identification techniques to discriminate spawning populations. Significant differences in otolith structure and microchemistry were identified between winter and spring spawners with the highest degree of classification accuracy based on both features. Mixed stock analysis applied to fishery samples of unknown origin indicated the contemporary (2015-2016) commercial fishery is dominated by winter spawners. Exploratory classification of historical fishery samples suggested a change over time with spring and winter spawners present in near equal proportion in the early 1990s and winter spawners dominating in the early 1980s. Otolith-based stock composition analysis has the potential to support monitoring and assessment of cod populations in the Gulf of Maine.

Migratory behavior and maternal origin of anadromous brown trout in the Baltic Sea

In the Baltic Sea, brown trout have been shown to make extensive use of the marine ecosystem; however, little is known regarding their movements between freshwater and marine environments or the interactions between individuals at different life history stages within a population. First, we analyzed the otolith structure and chemistry of hatchery origin (n = 26) anadromous brown trout with known life history and maternal origin to evaluate the efficacy of otolith microchemistry to distinguish between freshwater habitat in northern Sweden and marine rearing in the northern Baltic Sea. We then described the maternal origin and migration patterns of wild anadromous brown trout (n = 59) originating from the Ume and Vindel River catchment in Northern Sweden. Otolith microchemistry revealed that the majority (73%) of fish made 3 or more (up to 5) migrations to the marine environment prior to capture, presumably to feed. We observed a high degree of life history diversity, where trout first migrated to sea from age-1 to age-4 and either migrated back to freshwater once each year (presumably to spawn) or spent more than 1 yr in the marine environment before returning to freshwater. While 42% of the wild anadromous trout were judged to be the progeny of a resident mother, sex ratio, age, and inter-habitat migrations were similar for resident and anadromous progeny, highlighting the role of resident life histories in producing anadromous adults. Results reported here provide managers with new information to support the protection and enhancement of brown trout populations in places where they have declined.

Age and growth of the Pacific hake, Merluccius productus (Actinopterygii: Gadiformes: Merlucciidae), in the Gulf of California: A multimodel approach

Over the past decade, the fishery of Pacific hake, Merluccius productus (Ayres, 1855), has increased in the Gulf of California, Mexico; therefore, any biological–fisheries information is highly relevant for the management of this fishery, and information on age and individual growth would be fundamental to evaluate populations. The objective of the presently study was to assess age, based on otolith structure, and estimate growth parameters through a multimodel approach. Specimens were collected during research cruises of BIP XI from 2014 to 2019. Pacific hake from the Gulf of California ranged in length from 12.5 to 105 cm TL, reaching a maximum age of 13 years, and females were four years older than males. The logistic model was the best model to describe age–size data for both sexes. Females reached 50% of the maximum length at five years old and males reached that length at four years old.

Biological parameters of juveniles of Gadus morhua Linnaeus, 1958 and Pollachius virens (Linnaeus, 1958) in the fjords affected by anthropogenic load, by the example of the Kola Bay, the Barents Sea

The paper continues the series of studies aimed on analyzing the biological processes taking place in the coastal zone of the Barents Sea. The size and weight parameters, age and sex structure, as well as the feeding of juveniles of Atlantic cod and saithe in the intertidal zone. There are pronounced seasonal changes in the studied parameters. Gammaridae play a large role in nutrition, but cannibalism is well-pronounced. Malformation of the otolith structure is recorded. The data obtained may be used for further monitoring or applied for the ecosystem modeling.

Physicochemical mechanisms of FT-NIRS age prediction in fish otoliths

Context Fourier transform near-infrared spectroscopy (FT-NIRS) is of interest to fisheries managers for rapid age prediction in fish otoliths, yet the underlying prediction mechanism is unknown. Aims To better understand drivers of FT-NIRS age prediction, we evaluated FT-NIRS spectra and age prediction models for otoliths of red snapper, Lutjanus campechanus, related to otolith structure, mass, and constituents (calcium carbonate (CaCO3) and protein). Methods Spectra were collected from a set of whole otoliths (n = 84, 0–28 years) and again sequentially after grinding to powder and subsampling a fixed mass of each ground otolith. Protein content was also measured (n = 26) and related to spectra. Key results Age prediction was diminished in ground and fixed-mass otolith models, but remained within 2 years of traditional ages. Protein content (0.43–0.92% weight) increased significantly with age, implying a concomitant decrease in CaCO3 content. FT-NIRS models predicted protein content to within 0.04%, but protein variability hindered modelling. Spectral characteristics of both CaCO3 and protein are evident in otolith spectra and are implicated in age-prediction models. Conclusions Changes in otolith composition, mass, and structure underlie FT-NIRS age prediction, but compositional changes inform the majority of age prediction. Implications These results provide a foundation for understanding FT-NIRS age prediction.

New evidence for the establishment of coastal cod Gadus morhua in Svalbard fjords

The Arctic is experiencing increasing water temperatures, leading to a northward shift of Atlantic species into Arctic waters. Arctic marine ecosystems are therefore subject to substantial changes in species distributions and occurrence due to anthropogenic climate change. Atlantic cod is one of the most important commercial fish species in the northern seas. The largest known stock is the migrating Northeast Arctic cod (NEAC) that is distributed along the Norwegian coast, the Barents Sea and off Svalbard. Atlantic cod in Svalbard waters are generally reported in the literature as belonging to the NEAC ecotype. The more stationary coastal cod (CC) spawn together with NEAC in the Lofoten region and several other areas along the Norwegian coast. The aim of this study was to investigate the population structure of Atlantic cod in Svalbard waters. We used single nucleotide polymorphic (SNP) markers, the pantophysin locus (Pan I) and otolith structure to categorize the 2 cod ecotypes collected in Svalbard fjords between 2017 and 2019. Our results show that both NEAC and CC appear in Svalbard fjords and revealed that 0-group and adult CC individuals caught in Svalbard fjords differ genetically from those along the Norwegian coast, indicating a separation into a local Svalbard CC population. The establishment of CC in Svalbard fjords may be another keystone of the ongoing borealization of the Arctic, with consequences for the local Arctic fjord ecosystem.

​Discrimination of Five Gobid Species (Family: Gobiidae) based on Otolith Morphometry

Background: The fishes of family Gobiidae are one of the least studied fishes, especially for otolith structure. The otoliths were possess species specific features. Hence, traits of sagittal otolith of gobid species studied. Methods: Five gobid species Odontamblyopus roseus (Valenciennes, 1837), Trypauchen vagina (Bloch and Schneider, 1801), Glossogobius giuris (Hamilton, 1822), Parachaeturichthys polynema (Bleeker, 1853) and Boleophthalmus dussumieri (Valenciennes, 1837) were investigated by three methods including morphological, shape indices and step wise discriminant function analysis (SDFA). Result: Interrelationship between shape indices investigated, at 95% level of confidence (P less than 0.05), revealed that perimeter of P. polynema and area of T. vagina have isometric growth with their length (b = 3.0071, 2.90, respectively) and otolith area of B. dussumieri have positive allometric growth (b = 4.23077). SDFA, based on otolith morphometry, discriminated species up with 97.18% accuracy. Hence, the results of present investigation can be used for discrimination of the species and as a tool in predicting fish size from the otoliths and in calculating the biomass of these less studied fish species.

Age, growth, mortality, and exploitation rate of blueline snapper, Lutjanus coeruleolineatus (Actinopterygii: Perciformes: Lutjanidae), from Dhofar Governorate, Sultanate of Oman

The blueline snapper, Lutjanus coeruleolineatus (Rüppell, 1838), is a significant commercial fish species harvested from the traditional fishery in the Sultanate of Oman. Deficient data on this species, however, make the management strategies challenging, especially in fisheries ecology. A total of 978 specimens were obtained from Dhofar Governorate off the coast of the Arabian Sea during the period between February 2015 and March 2016. In total, 296 sectioned otoliths were analyzed and growth was estimated from non-seasonal growth by using von Bertalanffy method. The parameters of von Bertalanffy growth function, total mortality (Z), natural mortality (M), fishing mortality (F), and exploitation rate (E) were determined and compared with those for Lutjanidae fishes elsewhere. The age structure of male fishes was between 1 and 14 years for males while the age of females ranged from 1 to 18 years. Growth rate (K) was 0.21 y–1 and 0.16 y–1 for males and females, respectively. The hypothetical length of female (L∞ = 46 cm) was relatively higher than that of male (L∞ = 42 cm). The natural mortality (M) was 0.296, total mortality (Z) was 0.372, fishing mortality was 0.076, and exploitation rate (E) was estimated as 0.2. The presently reported study is conducted to examine this fish in relation to growth parameters by analyzing otolith structure. The results of the presently reported study will contribute towards planning the regional fishery management policies in Oman.

Evidence on Otolith Structure and some Ecological Features of Three Small Foraging Species along the Southern Black Sea Coast

In this study, we aimed to describe otoliths to provide information about the stomach contents of three small foraging species and to contribute to the currently limited biological and ecological evidence about the species. Seasonal experimental bottom trawl surveys were conducted along the shelf areas of the Kızılırmak-Yeşilırmak and Melet Rivers to collect investigation materials which were abundant in the bycatch composition of the target catch. The information about body size measurements, abundance values, depth, season, and locality of samplings was recorded for further evaluations. Otolith shapes were defined as discoidal to ovate for the Aphia minuta, discoidal for the Pomatoschistus marmoratus, and square for the Arnoglossus kessleri. The mean length and weight values of the Aphia minuta, which was abundant along shallow coastal waters (0-30 m), were significantly different between localities and sampling season, but no difference was found between depth ranges. Pomatoschistus marmoratus, whose distribution varied significantly between depths and seasons had dense distributions along with the depth range of 30-60 m. Arnoglossus kessleri was most abundant along with the depth range of 0-30 m and had no samples in depths of over 60 m. It was found that the mean values of length and weight of this species were only significantly different among seasons but similar over the depth ranges and localities.

Differences in otolith shape and fluctuating-asymmetry between reared and wild gilthead seabream (Sparus aurata Linnaeus, 1758).

Otolith structure is a useful tool in discrimination among fish populations as it is a permanent record of the influence of endogenous and exogenous factors. In the present study we examined otolith morphology and fluctuating asymmetry (FA) for differences between wild-caught (by bottom trawl) and reared specimens of Gilthead seabream (Sparus aurata). Based on the frequency of regenerated scales (degree of scale regeneration, SRD) on each specimen, a threshold of 30% SRD was used to assign wild-caught fish individuals as wild (≤30% SRD, LR group) or as possible aquaculture escapees (>30% SRD, HR group). Based on the analysis of elliptic Fourier descriptors, significant differences were found in otolith shape between reared (Rr) and the wild-caught groups (LR, HR). Reared fish had otoliths with significantly larger perimeter (OP ) than wild-caught fish. Furthermore, FA was significantly higher in the Rr than the LR group for OP and all except one shape descriptors (harmonics 2-7). The HR group exhibited intermediate levels of FA between the low and high FA levels observed in the LR and Rr groups. Results are discussed in terms of the value of combining otolith and scale morphology for the identification of escapees in wild Gilthead seabream stocks.

Estimating Migratory Behavior and Age for Anadromous Coastal Cutthroat Trout in South Puget Sound: Evaluation of Approaches Based on Fish Scales versus Otoliths

AbstractImportant variability exists in life history attributes among localized populations of Coastal Cutthroat Trout Oncorhynchus clarkii clarkii in relation to geographic and environmental factors. Describing the life history of locally adapted populations is critical to successful fishery management and conservation. The number of annuli and distance between circuli in scales (i.e., scale analysis) are often used to describe migratory behavior and age of Coastal Cutthroat Trout, but the accuracy of these estimates is largely unknown. In this study, we compared estimates of age (based on analyses of scale and otolith structure) and migratory patterns (based on scale structure and otolith structure and chemistry) for anadromous Coastal Cutthroat Trout in South Puget Sound, Washington State. We compared 48 paired scale and otolith samples (age range = 1–5 years), and age estimates agreed 79% of the time (average percent error [APE] = 5%; CV = 6%), supporting historical age estimates that were generated using scales. However, the number of migrations between freshwater and marine environments estimated using scales and otoliths agreed 44% of the time (n = 50; APE = 25%; CV = 35%). Comparisons of scales and otoliths indicated that more individuals overwinter in marine waters than previously thought based on scale analysis. The majority of fish in this study (68%) were the progeny of females that matured in marine waters and may be vulnerable to fisheries in the marine environment. Current management actions that prohibit the harvest of Coastal Cutthroat Trout in marine waters may be important for the conservation of small localized populations in South Puget Sound.

Insights into fish auditory structure–function relationships from morphological and behavioural ontogeny in a maturing sciaenid

Knowledge of the relationship between auditory form and function is necessary to understand the role of hearing in fish ecology, as well as the potential impacts of anthropogenic noise and environmental change on hearing-mediated functions. We explored the functional significance of otolith (ear stone) morphology in a large predatory sciaenid, Argyrosomus japonicus (Temminck and Schlegel), by comparing ontogenetic changes in otolith structure to changes in habitat, diet and swimming activity. We examined an otolith metric that has previously been linked to habitat use and activity in fishes, the relative sensory area (sulcus to otolith area ratio, S:O), and a new metric that quantifies the protuberant structure (calcareous concrescence) found on the distal surface of sciaenid otoliths (otolith perimeter to area ratio, P:SA). Strong allometric growth of the sulcus acusticus was detected in the sagitta of A. japonicus ranging from 7 to 80 cm TL. Both S:O and P:SA changed rapidly until A. japonicus reached 50 cm TL, after which only a gradual increase in relative sensory area was detected. The aspect ratio of the caudal fin (CAR, an index of swimming activity) abruptly increased in A. japonicus at 41–50 cm TL. These changes coincide with an observed shift in diet from benthic invertebrates to pelagic fish, a shift in foraging habitat and an increase in foraging activity.

Analysis of cod otolith microchemistry by continuous line transects using LA-ICP-MS

Fish otoliths, also called ear stones or statoliths, are calcified structures functioning as movement and equilibrium indicators in the inner ear of fish (Fig. 1). From hatching to death these structures grow incrementally, with new material accreted daily (Pannella 1971) in successive layers of protein (1–8%, Degens et al. 1969) and calcium carbonate. The accretion rate of otoliths varies with fish growth, and in temperate species it is usually lowest during the winter season (Hüssy et al. 2010). This results in concentric growth resembling the ringed structure in trees (Fig. 1D), enabling the use of dendrochronological techniques to approximate the age and growth history of fish. During growth, certain elements are incorporated into the otolith structure, some associated with proteins and some with the calcium carbonate component (Thomas et al. 2017), supplying a valuable record of different aspects in fish life history and serving as a potential environmental record. Previous studies show that trace element and isotopic compositions of otoliths can be used as a proxy for reconstructing water chemistry, temperature and salinity (Patterson et al. 1993; Thorrold & Shuttleworth 2000). Other studies demonstrate that elemental histories can be used to investigate fish spawning and migration patterns (e.g. Sturrock et al. 2012), and more recent studies use elements such as Zn, Cu and Mg as indicators of seasonality (Hüssy et al. 2016; Limburg et al. 2018). Combining this knowledge of elemental variation with the micro-beam capabilities of laser ablation inductively coupled plasma mass spectrometry (LAICPMS) turns otolith microchemistry into a powerful tool for studying important parameters fundamental for establishing modern, sustainable fisheries management policies (e.g. stock identification, migration, pollution indicators, spawning habitats, duration of larval and juvenile stages, and magnitude and timing of spawning). We present an analytical method developed by the Geological Survey of Denmark and Greenland (GEUS) in collaboration with the National Institute of Aquatic Resources, Technical University of Denmark (DTU Aqua), for element abundance analysis in otoliths. Analyses of otoliths from Baltic Cod (Gadus morhua; Fig. 1) are used as an example for its application.

Otolith Microchemistry of Coastal Cutthroat Trout from the Marys and Willamette Rivers

Abstract We sampled the water chemistry and otolith chemistry and structure of juvenile Cutthroat Trout collected in the Marys River and adults collected in the Willamette River to evaluate the potential to identify life-history variation in this population. Differences in water chemistry between the Marys and the Willamette Rivers during the sampling period were reflected in otolith chemistry. We differentiated 2 life-history patterns: juveniles whose mothers appeared to be resident in the Marys River, and juveniles that likely had fluvial mothers from the Willamette River. Otolith elemental composition of both juveniles and adults showed maternal effects on core chemistry, movement, or changes in elemental incorporation related to changes in ontogeny, growth, or seasonal changes in temperature. Water and otolith edge 87Sr/86Sr were consistently lower in the Willamette River than in the Marys River. Mean otolith 87Sr/86Sr during early life provided evidence that some adults reared in tributaries and migr...

Systematics and biology of the blue lanternfish, Diaphus coeruleus from the south-eastern Arabian Sea

The paper presents the first detailed study on systematics, otolith structure and biology of Diaphus coeruleus, from the south-eastern Arabian Sea. The closely related and co-inhabiting species D. coeruleus and D. watasei are distinguished on the basis of morphometric, meristic and otolith characters. Analysis of gut content revealed that these fishes mainly feed on deep sea squids and shrimps. Six maturation stages of gonads are identified in males (immature, quiescent, mature, ripe, spawning and spent) and five stages (immature, quiescent, mature, ripening and spawning stages) in females. Overall sex ratio deviated in favour of males (1 male: 0.2 female) and the mean fecundity was 2150 ± 353 eggs. The length-weight relationship shows an overall isometric growth in males with N = 76 and b = 3.13 and for females with N = 17 and suggests negative allometric growth (b = 1.719). Otolith length (LO) and otolith weight (WO) are positively correlated to standard body length (LS) and body weight (BW).

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

AbstractIn 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.

Diet is correlated with otolith shape in marine fish

Previous studies have shown that the amount of food influences fish otolith structure, opacity and shape and that diet composition has an effect on otolith chemical composition. This study investigated the potential correlation between diet and otolith shape in 5 wild marine fish species by addressing 4 complementary questions. First, is there a global relationship between diet and otolith shape? Second, which prey categories are involved in this relationship? Third, what are the respective contributions of food quantity and relative composition to diet-otolith shape co-variation? Fourth, is diet energetic composition related to otolith shape? For each species, we investigated how otolith shape varies with diet. These questions were tackled by describing diet in the analysis in 4 different ways, while also including individual-state variables to remove potential confounding effects. First, besides the strong effect of individual-state, a global relationship between diet and otolith shape was detected for 4 out of 5 fish species. Second, both main and secondary prey categories were related to variability in otolith shape, and otolith outline reconstructions revealed that both otolith global shape and its finer details co-varied with these prey categories. Third, the contribution of relative diet composition to diet-otolith shape co-variation was much higher than that of ingested food quantity. Fourth, the energetic composition of diet was related to otolith shape of only 1 species. These results suggest that diet in marine fish species may influence the quantity and composition of saccular endolymph proteins which play an important role in otolith biomineralization and their resulting 3D structure.

Evaluation of Back‐Calculated Size and Timing Estimates for Juvenile Chinook Salmon Using Otolith Structure and Chemistry

AbstractOtolith chemistry is often used to reconstruct origin, life history, and migratory pathways in anadromous fishes. Although the accuracy and precision of back‐calculated size at a particular life history transition (such as when anadromous fish move from fresh to saline water) is often not estimated. We evaluated back‐calculated size and timing estimates based on otolith ratios of strontium to calcium (Sr:Ca) in Chinook Salmon Oncorhynchus tshawytscha marked with elevated concentrations of strontium chloride (SrCl). We used a combination of laser‐ablation, inductively coupled, plasma mass spectrometry (LA‐ICPMS), back‐calculation models, and daily increments to evaluate the accuracy of such estimates. Overall, back‐calculated size at marking was underestimated by <2 mm using direct and proportional back‐calculations of FL based on otolith Sr:Ca. Proportional back‐calculations of fish length were underestimated on average by 2.60 mm (SD, 2.09) when somatic growth (%/d) was less than otolith growth (%/d) and overestimated by an average of 4.89 mm (SD, 3.19) when somatic growth was greater than otolith growth. However, when somatic and otolith growth were equal, proportional back‐calculations were more accurate than direct estimates. Overall, the number of otolith daily increments since Sr:Ca inflection underestimated the actual days since marking by a median of 1 d (SD, 0.57) and was similar for individuals sampled 8–79 d after marking. Results from this study suggest that life history parameters for Chinook Salmon estimated using LA‐ICPMS, back‐calculation models, and daily increments are robust estimates suitable for ecological field studies.Received September 22, 2015; accepted December 29, 2015 Published online April 18, 2016

Three-dimensional rendering of otolith growth using phase contrast synchrotron tomography.

A three-dimensional computer reconstruction of a plaice Pleuronectes platessa otolith is presented from data acquired by the Diamond Light synchrotron, beamline I12, X-ray source, a high energy (53-150 keV) source particularly well suited to the study of dense objects. The data allowed non-destructive rendering of otolith structure, and for the first time allows otolith annuli (internal ring structures) to be analysed in X-ray tomographic images.

Where do elements bind within the otoliths of fish?

Otolith element analyses are used extensively to reconstruct environmental histories of fish based on the assumption that elements substitute for calcium within the CaCO3 otolith structure. However, elements may also be incorporated within the protein component of the otolith in addition to the direct substitution for calcium in the mineral component, and this could introduce errors in environmental reconstructions. The aim of the present study was to determine whether elements were incorporated into the protein or mineral components of otoliths and the relative proportion of each element in each component. Element concentrations from whole ground otoliths and the isolated protein component were quantified using solution inductively coupled plasma mass spectrometry (ICP-MS). Of the 12 elements investigated, most were found in both the proteinaceous and mineral components, but always in greater concentrations in the latter. Elements considered ‘non-essential’ to fish physiology with Ca-like properties (i.e. alkaline metals) were present in the mineral component in relatively high concentrations. Elements essential to fish physiology with smaller atomic radii than Ca (i.e. transition metals) were distributed throughout the protein and mineral components of the otolith. These findings enhance our understanding of element incorporation in the otolith and, ultimately, improve interpretations of otolith-based environmental reconstructions.