Otolith Chemical Analysis Research Articles

High-resolution otolith elemental signatures in eteline snappers from valuable deepwater tropical fisheries.

Marine resources are often shared among countries, with some fish stocks straddling multiple Exclusive Economic Zones, therefore understanding the structure of populations is important for the effective management of fish stocks. Otolith chemical analyses could discriminate among populations based on differences in the chemical composition of otoliths. We used otoliths from two deepwater snappers (flame snapper Etelis coruscans and ruby snapper Etelis boweni) to examine the evidence for population structure across six Pacific Island countries using solution‐based inductively coupled plasma mass spectrometry (ICP‐MS) for otolith core and whole otolith samples and laser ablation ICP‐MS (LA‐ICP‐MS) for core and edge areas of a cross‐sectioned otolith. The inter‐species comparison of these methods is important as the two species are often managed under the same regulations. For both species, the two methods demonstrated separation among the locations sampled with high classification accuracy. Smaller laser ablation spot size gave greater temporal resolution over the life‐history transect. Comparing the early life‐history section of the otoliths (i.e., the core), one interpretation is that young fish experienced more uniform environments in the open ocean as larvae than adults, as the elemental fingerprints had greater overlap among multiple locations. LA‐ICP‐MS methods had some advantages over solution‐based ICP‐MS and generally better discrimination for the trace elements investigated. There were substantial differences between species, but both methods suggested nonmixing populations at the regional scale. Otolith chemistry can be an effective tool in discriminating variation for deepwater marine species in multispecies fisheries, and edge measurements from LA‐ICP‐MS provided the greatest resolution. Although caution should be taken in interpreting the results from relatively small samples sizes, otolith chemical analyses could be useful at these spatial scales to investigate population structure. This information on separate or overlapping populations could be used in future regional fishery management plans.

Population structure of the chub mackerel (Scomber colias) in the NE Atlantic inferred from otolith elemental and isotopic signatures

The Atlantic chub mackerel (Scomber colias) is one of the main small pelagic fish resources in the North-East (NE) Atlantic. At present, for fisheries management purposes, a single stock of this species in the NE Atlantic is considered. Over the last years, fishing pressure has greatly increased in this species, but the information regarding its population structure, necessary in order to maintain a sustainable fishery, is still limited. One hundred and eighty individuals of S. colias were collected off the Portugal mainland (Matosinhos, Sesimbra and Portimão) and in the Atlantic Oceanic Islands (Azores, Madeira and Canaries) from January to March 2018. Following age estimation by counting the annual growth increments, 30 pre-selected individuals of the same age group (2 years old) from each sampling location were used for further otolith chemical analyses. Data were analysed by univariate and multivariate statistics to assess the degree of separation between the individuals of these geographic regions. Overall reclassification accuracy rate, obtained from a quadratic discrimination function analysis, was 80 % suggesting that fish passed through their life enough time in heterogeneous water masses to have a distinct chemical signature. Moreover, fish from the islands were fully discriminated (100 % reclassification rate). Regional differences were driven mainly by Sr:Ca, Na:Ca, Ba:Ca, Mg:Ca, Li:Ca, Mn:Ca, δ13C and δ18O, showing a clear separation of four population-units of S. colias in the NE Atlantic, namely Azores, Madeira, Canaries and Portugal mainland. The hereby results provide support for treatment of these fisheries as different regional management units.

Otolith‐Chemistry‐Based Discrimination of Wild‐ and Hatchery‐Origin Steelhead across the Lake Michigan Basin

AbstractEffective conservation and management of mixed‐stock fisheries depends upon accurate stock identification of individual fish. We evaluated the utility of otolith chemical analysis as an approach to classify juvenile, premigratory steelhead Oncorhynchus mykiss collected in tributaries of Lake Michigan as either wild or hatchery origin. Two primary hypotheses proposed were that otolith chemistry can be used (1) to classify juvenile, hatchery‐origin steelhead to the correct hatchery of origin and (2) to correctly classify stream‐collected juvenile steelhead as wild or hatchery origin. Using laser‐ablation inductively coupled plasma mass spectrometry, we analyzed the concentrations of seven elements (using 25Mg, 55Mn, 65Cu, 66Zn, 88Sr, 137Ba, 208Pb) in the otoliths of juvenile steelhead collected from five hatcheries and 25 streams in the Lake Michigan basin. When discriminating among hatcheries, only 4.41% of fish misclassified to an alternate hatchery when subjected to the best random forest classification algorithm that included all elements as predictor variables. Distinct chemical signatures between fish of wild and hatchery origin supported 100% classification accuracies of known‐wild, age‐0 steelhead as wild origin for 19 of the 25 streams sampled. Misclassification of wild, age‐0, and hatchery‐origin fish, which tended to occur for streams that were located in close proximity to the hatchery, never exceeded 3.4% for a given stream. Our findings demonstrate highly successful discrimination of hatchery‐origin and wild juvenile steelhead across a broad geographic range. Applying the classification algorithms developed herein to unknown‐origin steelhead provides the ability to infer survival of year‐classes from specific hatcheries. Further, the ability to differentiate hatchery‐ and wild‐origin fish will assist in stock assessment efforts allowing for increased effectiveness of conservation and management of the species.

Population connectivity of southern flounder in the US South Atlantic revealed by otolith chemical analysis

Population connectivity of southern flounder in the US South Atlantic revealed by otolith chemical analysis

Use of Lagrangian simulations to hindcast the geographical position of propagule release zones in a Mediterranean coastal fish

The study of organism dispersal is fundamental for elucidating patterns of connectivity between populations, thus crucial for the design of effective protection and management strategies. This is especially challenging in the case of coastal fish, for which information on egg release zones (i.e. spawning grounds) is often lacking. Here we assessed the putative location of egg release zones of the saddled sea bream (Oblada melanura) along the south-eastern coast of Spain in 2013. To this aim, we hindcasted propagule (egg and larva) dispersal using Lagrangian simulations, fed with species-specific information on early life history traits (ELTs), with two approaches: 1) back-tracking and 2) comparing settler distribution obtained from simulations to the analogous distribution resulting from otolith chemical analysis. Simulations were also used to assess which factors contributed the most to dispersal distances. Back-tracking simulations indicated that both the northern sector of the Murcia region and some traits of the North-African coast were hydrodynamically suitable to generate and drive the supply of larvae recorded along the coast of Murcia in 2013. With the second approach, based on the correlation between simulation outputs and field results (otolith chemical analysis), we found that the oceanographic characteristics of the study area could have determined the pattern of settler distribution recorded with otolith analysis in 2013 and inferred the geographical position of main O. melanura spawning grounds along the coast. Dispersal distance was found to be significantly affected by the geographical position of propagule release zones. The combination of methods used was the first attempt to assess the geographical position of propagule release zones in the Mediterranean Sea for O. melanura, and can represent a valuable approach for elucidating dispersal and connectivity patterns in other coastal species.

Patterns of larval source distribution and mixing in early life stages of Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea

Effective and sustainable management depends on knowledge of spawning locations and their relative contributions to marine fish populations. Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea aggregate at discrete spawning locations but there is little information on patterns of larval dispersal and the relative contribution of specific spawning areas to nursery habitats. Age-0 Pacific cod from two cohorts (2006 and 2008) were examined to address the following questions: (1) does size, age, and otolith chemistry vary among known capture locations; (2) can variation in elemental composition of the otolith cores (early larval signatures) be used to infer the number of chemically distinct sources contributing to juvenile recruits in the Bering Sea; and (3) to what extent are juvenile collection locations represented by groups of fish with similar chemical histories throughout their early life history? Hierarchical cluster (HCA) and discriminant function analyses (DFA) were used to examine variation in otolith chemistry at discrete periods throughout the early life history. HCA identified five chemically distinct groups of larvae in the 2006 cohort and three groups in 2008; however, three sources accounted for 80–100% of the juveniles in each year. DFA of early larval signatures indicated that there were non-random spatial distributions of early larvae in both years, which may reflect interannual variation in regional oceanography. There was also a detectable and substantial level of coherence in chemical signatures within groups of fish throughout the early life history. The variation in elemental signatures throughout the early life history (hatch to capture) indicates that otolith chemical analysis could be an effective tool to further clarify larval sources and dispersal, identify juvenile nursery habitats, and estimate the contributions of juvenile nursery habitats to the adult population within the southeastern Bering Sea.

All in the ears: unlocking the early life history biology and spatial ecology of fishes.

Obtaining biological and spatial information of the early life history (ELH) phases of fishes has been problematic, such that larval and juvenile phases are often referred to as the 'black box' of fish population biology and ecology. However, a potent source of life-history data has been mined from the earstones (otoliths) of bony fishes. We systematically reviewed 476 empirical papers published between 2005 and 2012 (inclusive) that used otoliths to examine fish ELH phases, which has been an area of increasing attention over this period. We found that otolith-based research during this period could be split into two broad themes according to whether studies examined: (i) biological objectives related to intrinsic processes such as larval and juvenile age, growth and mortality, and/or (ii) spatial objectives, such as habitat use, dispersal and migration. Surprisingly, just 24 studies (5%) explored a combined biological-spatial objective by simultaneously exploiting biological and spatial information from otoliths, suggesting much more scope for such integrated research objectives to be answered via the use of multiple otolith-based techniques in a single study. Mapping otolith analytical techniques across these two approaches revealed that otolith structural analysis was mainly used to investigate biological processes, while otolith chemical analyses were most often applied to spatial questions. Heavy skew in research effort was apparent across biomes, with most (62%) publications specific to marine species, despite comparable levels of species richness and the importance of freshwater taxa (just 15% of papers). Indeed, around 1% (380 species) of a possible 31400+ extant species were examined in our surveyed papers, with a strong emphasis on temperate marine species of commercial value. Potential model species for otolith-based ELH ecology research are arising, with the eel genus Anguilla (24 studies) and the European anchovy Engraulis encrasicolis (14 studies) attracting more research effort than most other taxa. While there is a preponderance of common techniques (e.g. daily otolith increment counts, increment widths), novel techniques such as transgenerational marking and computed X-ray tomography, are increasingly being applied in published studies. The application of an integrative approach based on a combination of emerging techniques and traditional methods holds promise for major advances in our understanding of ELH fish ecology and to shine light into the 'black box' of fish ecology.

Recruitment sources and dispersal of an invasive fish in a large river system as revealed by otolith chemistry analysis

The contributions of nursery habitats to recruitment of non-native common carp (Cyprinus carpio) were estimated via analysis of water and otolith 87Sr/86Sr and otolith trace element concentrations (Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca) over 3 years in the Lachlan River, Australia. Water samples and otoliths of postlarval carp were analyzed to characterize 87Sr/86Sr and multi-elemental signatures of nursery habitats. Considerable temporal variation occurred in both water 87Sr/86Sr and otolith multi-elemental signatures, which limited our ability to directly match water and otolith 87Sr/86Sr in nurseries of the lower catchment. However, spatial variation in multi-elemental signatures was sufficient to allow accurate classification of nurseries within years. Assignment analysis of young-of-year fish suggested that several wetland and floodplain systems made significant contributions to young-of-year recruitment in the lower catchment. These contributions were strongly influenced by river flows and water management. Nurseries contributed fewer recruits to the main channel as distance from the nursery increased. Fish from the upper catchment originated from local sources, and there was no evidence of mixing of recruits between the upper and lower catchments. We conclude that identification of recruitment “hotspots” via otolith chemical analysis can assist in developing strategies to control invasive fishes in large river networks.

Use of otolith chemistry to examine patterns of diadromy in the threatened Australian grayling Prototroctes maraena

Otolith chemical analyses (proton‐induced X‐ray emission and laser ablation inductively coupled plasma mass spectrometry) were used to examine patterns of diadromy in Australian grayling Prototroctes maraena collected from three rivers in south‐eastern Australia. Concentrations of Sr:Ca and Ba:Ca were measured in the sagittal otoliths of 25 fish and in water samples collected on two occasions from multiple sites within freshwater, estuarine and marine reaches of the rivers. The results provide evidence of marine residency during the juvenile phase, with high Sr:Ca and low Ba:Ca in the inner region of the otoliths that were consistent across all three rivers. This general pattern was apparent for all individuals examined, suggesting that diadromous migration may be an obligate aspect of the life history. The chemical signatures of the outer regions of the otoliths were distinct between the three rivers, whilst there was no difference in the inner regions of the otoliths. This suggests that juveniles from different rivers may reside in a relatively homogenous chemical environment, such as the sea, and populations in coastal Victorian rivers may share a common marine recruitment source.

Use of otolith chemical signatures to estimate carp recruitment sources in the mid-Murray River, Australia

Recent research has suggested that the Barmah-Millewa forest (BMF) floodplain provides a particularly important spawning ground for carp in the Murray River and that there is a large export of juvenile carp from the BMF into other parts of the Murray River system. This study examined whether chemical analysis of otoliths (fish ear stones) represents a feasible technique for estimating the relative importance of particular sources of carp recruitment in the Murray River. Otolith chemical signatures were analysed for fish collected from three lakes on the BMF floodplain and from three major tributaries of the mid-Murray River. A single site downstream of these potential sources of carp recruitment (Torrumbarry Weir) was then examined to estimate the relative contribution of the BMF and the tributaries to carp recruitment at this site. The results of the study suggest that at least some of the lakes on the BMF floodplain are important sources of carp in the mid-Murray River. Using a maximum likelihood analysis of otolith chemical signatures, it was estimated that Barmah Lake and Moira Lake were the most likely recruitment sources for 98% of the fish collected from Torrumbarry Weir. The study demonstrates the potential application of otolith chemical analyses for determining the relative importance of potential recruitment sources of fish in rivers. Copyright © 2006 John Wiley & Sons, Ltd.

Testing larval fish dispersal hypotheses using maximum likelihood analysis of otolith chemistry data

Otolith chemical analyses enable researchers to follow the dispersal pathways of individual fish through time. Given that water masses have spatially or temporally variable chemical signatures (or correlates thereof) and that this variability can be modelled statistically, we have the potential to describe a fish’s dispersal history by examining a temporal transect of elemental concentrations throughout the otolith generated from laser ablation inductively coupled plasma mass spectrometry. Statistical analyses tend to focus on temporal trajectories of individual elements or analyse multiple elements at single points in time. We have developed a customised statistical technique allowing detailed exploration of elemental signatures using maximum likelihood methods. The benefit of this approach is the ability to model chronological series of otolith measurements for all sampled fish and all elements simultaneously, while providing explicit treatment of variability in the data. We used data from a Caribbean fish population to compare traditional analysis techniques with this likelihood-based approach, showing their relative capacities to test among alternative hypotheses regarding the dispersal trajectories of individual fish. By incorporating information specific to the species’ natural history and to the analytical techniques, we can explore more detailed models of fish movement than were possible using pre-existing approaches.