Relative contributions from exposed inshore and estuarine nursery grounds to the recruitment of stone flounder, Platichthys bicoloratus, estimated using otolith Sr:Ca ratios

In Sendai Bay, stone flounder larvae settle and spend their juvenile period in either shallow exposed inshore nursery grounds or estuarine nursery grounds. The purpose of this study is to examine the relative contributions of these two kinds of nursery grounds to the flounder population using otolith strontium:calcium ratios. Stone flounder juveniles were collected from both nursery grounds, and one- and two-year-old flounder were caught deeper in Sendai Bay. Sr and Ca content in the otoliths were measured by electron probe micro analysis. The Sr:Ca ratios in the otolith section corresponding to the early postsettlement period ranged from 3.06 to 3.85 for the exposed inshore areas with stable low temperature and high salinity conditions, and from 3.81 to 5.32 in brackish estuaries with high temperature and low salinity conditions but with large diel and tidal cyclical fluctuations. Values from an estuarine site with stable salinity ranged from 3.58 to 4.15 overlapping with both the above ranges. Rearing experiments supported our inference that the high otolith Sr:Ca ratios of juveniles inhabiting estuarine nursery grounds are attributable to higher temperature and physiological stress caused by the large diel temperature and salinity fluctuations within the estuaries. Estimation of the Sr:Ca ratio of recruited fish using the otolith section formed while in the nursery area showed that at least 20 out of 42 individuals examined originated from estuarine nursery grounds. The present study indicates that estuaries play an important role as nursery grounds for stone flounder, producing about half of the stock in spite of the small and restricted area compared with the wide expanse of the exposed inshore area.     

Evidence of diadromy in the French Polynesian Kuhlia malo (Teleostei: Percoidei) inferred from otolith microchemistry analysis

Abstract – Strontium/Calcium (Sr/Ca) and Barium/Calcium (Ba/Ca) ratios were measured in 60 otoliths of the French Polynesian flagtail Kuhlia malo. Both elemental ratios were needed to correctly distinguish residence in marine, brackish and fresh water. High Sr/Ca and low Ba/Ca around the nucleus of all otoliths provided evidence of marine residency during the early life of all individuals. At about 0.5 mm from the core, Ba/Ca increased rapidly and remained high in all otoliths. High and unstable Sr/Ca ratios were attributed to estuarine residency, whereas low and stable Sr/Ca ratios were attributed to freshwater residency. These chemical signatures inferred that following recruitment to rivers, some fish remained in the estuary, while others moved upstream. Some individuals shared their time between fresh and brackish waters later in life. The findings of this study have important implications for the protection of nearshore, brackish and freshwater environments for the conservation of this French Polynesian diadromous species.     

Unravelling the complex habitat use of the white mullet,Mugil curema,in several coastal environments from Neotropical Pacific and Atlantic waters

1. The white mullet, Mugil curema, is a widely distributed euryhaline species, the migratory behaviour of which is poorly understood. The objective of this work was to study the large-scale habitat use of this species for the first time. Several environments were considered, such as euryhaline and hypersaline lagoons, the sea, and a river, distributed in the Central Pacific (Mexico) and Atlantic (Gulf of Mexico, Caribbean Sea-Venezuela, and north-eastern Brazil).
2. Otolith core-to-edge Sr/Ca ratios of 163 fish, determined by laser ablation inductively coupled plasma mass spectrometry, were used to study the salinity-habitat migration history of the fish. Fish from Mexico (Tamiahua Lagoon, n = 4; Alvarado Lagoon, n = 2), Venezuela (n = 1), and Brazil (n = 12) (11.1% of the total) showed high Sr/Ca values at early life stages and were classified as marine estuarine opportunists. Two specimens (from Alvarado Lagoon and Balsas River, Mexico) showed Sr/Ca values consistently below the high salinity guide value (salinity < 33.5). For the rest of the fish (87.1%), the Sr/Ca ratio suggested a displacement from the estuary towards the sea or hypersaline environments, and so these fish were classified as estuarine migrants.
3. A change-point analysis identified six individuals with a single stable otolith Sr/Ca signature through ontogeny (three from Brazil, one from Venezuela, and two from Tamiahua Lagoon, Mexico), suggesting limited displacement between environments with different salinities. The rest of the individuals showed between two and 10 changes in stable Sr/Ca signatures (mean = 4.07 ± 1.85). The highest number of changes in Sr/Ca ratio (4.87 ± 1.1) was found in fish from Laguna Madre (Mexico) and the lowest was found in fish from Brazil (3.27 ± 1.70) (H = 19.8, p = 0.002).
4. Otolith Sr/Ca time series suggest that the migratory estuarine pattern is the most common throughout the study area. This work highlights that the sustainable use of M. curema depends on the conservation of estuaries and the corridors between them and other environments such as lagoons, rivers, mangroves and the sea.

     

基于耳石微化学的黄河垦利段刀鲚生活史初步研究

为研究黄河刀鲚(Coilia nasus)生境履历特征,利用电子探针微区分析技术(EPMA)对采集自黄河垦利段5尾刀鲚个体(D1、D2、D4、D5和D6)的矢耳石进行微化学特征研究。定量线分析结果显示,黄河口刀鲚生境履历较为复杂,所有个体核心区Sr/Ca值较低,表明其淡水孵化特征,但随着个体生长表现出不同的生活履历。个体D2生活史较复杂,其生长轨迹多次往返于淡水—半咸水生境,不具备洄游型刀鲚应有的规律性特征;个体D1、D4、D5和D6具有明显的洄游特征,不同的是个体D1和D4的Sr/Ca最大值分别为6.1和6.2,D5、D6生境已延伸至Sr/Ca值较高的区域,最大值分别达到8.44、8.63,但是由于调水、调沙对黄河口盐度变化影响较大,尚不能判断D5、D6个体生境已延伸至海水区域。分析的结果显示了同样的特征,个体D1、D4核心区表现为蓝色,外缘区域表现为蓝绿色;个体D2核心区表现为蓝色、绿色、黄色交替出现,个体D5、D6核心区域表现为Sr值较低的蓝色区域,随着生长耳石外围逐渐形成较为明显的黄色圆环。基于以上结果,本研究重新建立了黄河口刀鲚的生境履历,多数个体孵化和早期的生活主要在淡水生境完成,之后进入盐度较高的区域,往返于半咸水—海水生境中进行索饵、育肥,直至被捕获。以个体D2为代表的群体生活史较为复杂,推测可能是由于当年山东东平湖汛期放水而被动进入黄河的定居型刀鲚。     

Assessing the usefulness of otolith elemental compositions for evaluating the population structure of the Pacific herring <Emphasis Type="Italic">Clupea pallasii</Emphasis> in northern Japan

The present study examined whether the elemental compositions of whole otoliths and chronological transect profiles of otoliths covering the complete life history are useful for evaluating the population structure of Pacific herring. Eight elemental ratios, Li:Ca, Na:Ca, Mg:Ca, K:Ca, Mn:Ca, Cu:Ca, Sr:Ca, and Ba:Ca, were measured in whole otoliths and in a series of ablations across the life-history transects by laser ablation inductively coupled plasma mass spectrometry. We studied fish from three sample groups collected from Lake Obuchinuma, Miyako Bay, and Akkeshi Bay of northern Japan from March to May 2008. Significant differences were found in the Na:Ca, Mg:Ca, P:Ca, K:Ca, Mn:Ca, and Ba:Ca ratios of the whole otoliths and in the Li:Ca, Na:Ca, K:Ca, Mn:Ca, Sr:Ca, and Ba:Ca ratios of the otolith core among the three sample groups. Therefore, the present study showed clear differences in elemental composition among the three sample groups from different locations, suggesting that otolith elemental compositions reflect the habitats experienced by individual fish.     

Effect of salinity on strontium:calcium ratios in the otoliths of Sakhalin taimen, <Emphasis Type="Italic">Hucho perryi</Emphasis>

In order to determine the salinity effect on otolith strontium (Sr):calcium (Ca) ratios, the Sr and Ca contents of otoliths of Sakhalin taimen, Hucho perryi, reared for 60 days in four salinities (freshwater, one-third seawater, two-thirds seawater, and full seawater) were examined. The Ca and Sr contents and the resultant Sr:Ca ratios in the rearing water increased linearly with salinity. Otolith Sr:Ca ratios were also found to be positively correlated with salinity. However, the Sr:Ca did not correspond to temperature fluctuations during the experiment. These results indicate that Sr:Ca ratios in otoliths can be used to reconstruct the migratory history of the fish by differentiating when the fish migrated between freshwater and seawater.     

Importance of estuarine nursery areas for the adult population of the temperate seabass Lateolabrax japonicus,as revealed by otolith Sr:Ca ratios

Otolith Sr:Ca ratios were used to evaluate the contribution of estuarine nursery areas to the temperate seabass (Lateolabrax japonicus) population in Tango Bay, the Sea of Japan. Otolith Sr:Ca ratios of juveniles collected from freshwater, brackish and coastal areas were analysed to determine a criterion for distinguishing whether individuals used estuarine or coastal areas as nurseries. Otolith Sr:Ca ratios of adult seabass collected around Tango Bay were also analysed to detect the records of salinity that juveniles experienced and to estimate the contribution of each habitat. Sr:Ca ratios of the edges of otoliths of juveniles from freshwater areas were 2.4 × 10^?3 in average, which were significantly lower than those of juveniles collected from a coastal area (4.9 × 10^?3 in average) owing to differences in salinity conditions among these areas. Based on the threshold criterion determined by this difference, 39 out of 107 (36%) adult seabass were estimated to have used the estuary as a nursery during their juvenile stage according to their Sr:Ca chronologies. Despite the small area covered by estuarine nurseries compared with coastal waters, the Yura River estuary contributed considerably to the adult seabass population. This indicates estuaries play an important role as nurseries for seabass juveniles, and it should be noted that the estuaries are important nurseries to conserve the stocks of coastal fishes.     

Coexistence of anadromous and lacustrine life histories of the shirauo, Salangichthys microdon

The environmental history of the shirauo, Salangichthys microdon, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith, by means of wavelength dispersive X‐ray spectrometry on an electron microprobe. Anadromous and lacustrine type of the shirauo were found to occur sympatric. Otolith Sr concentration or Sr : Ca ratios of anadromous shirauo fluctuated strongly along the life‐history transect in accordance with the migration (habitat) pattern from sea to freshwater. In contrast, the Sr concentration or the Sr : Ca ratios of lacustrine shirauo remained at consistently low levels throughout the otolith. The higher ratios in anadromous shirauo, in the otolith region from the core to 90–230 μm, corresponded to the initial sea‐going period, probably reflecting the ambient salinity or the seawater–freshwater gradient in Sr concentration. The findings clearly indicated that otolith Sr : Ca ratios reflected individual life histories, enabling these anadromous shirauo to be distinguished from lacustrine shirauo.     

Colonisation tactics of three temperate catadromous species,eel Anguilla anguilla,mullet Liza ramada and flounder Plathychtys flesus,revealed by Bayesian multielemental otolith microchemistry approach

Daverat F, Martin J, Fablet R, Pécheyran C. Colonisation tactics of three temperate catadromous species, eel Anguilla anguilla, mullet Liza ramada and flounder Plathychtys flesus, revealed by Bayesian multielemental otolith microchemistry approach.
Ecology of Freshwater Fish 2011: 20: 42–51. © 2010 John Wiley & Sons A/S Abstract – The colonisation of Gironde (SW France) river catchment by juvenile, eel, Anguilla anguilla, flounder Platychtys flesus and thinlipp mullet Liza ramada was investigated comparatively using Sr:Ca and Ba:Ca composition of otolith. The relation between Sr, Ba and habitat was investigated based on Sr and Ba water composition sampled each month along the estuary‐river gradient. A total of 50 mullets, 30 eels and 47 flounders were collected in the Gironde river catchment. Analysis was performed with a Femtosecond LA‐ICPMS along a trajectory from the core to the edge. Sr and Ba water concentrations discriminated three habitats within the Gironde system, the lower estuary, the upper estuary and the freshwater sites. A signal processing method based on Gaussian hidden Markov models was applied to the multielemental life‐history data. The linear model used to allocate a Gironde habitat to coupled Sr, Ca values was parameterised with seasonal patterns and magnitude of Sr and Ba water values in the different habitats. The results showed that the three species used three different habitats and they had a large diversity of habitat use patterns with resident and nomadic tactics. Resident tactics were less frequent than nomadic tactics that suggested individual fish used two or more habitats. Mullet used a wider range of habitats in the lower part of the estuary than eel and flounder and switched habitats more frequently. Flounders tended to colonise initially freshwater, and then estuarine habitats later in life while mullets used the entire range of available catchment habitats throughout their life.     

An additional life-history tactic of masu salmon: Migration of parr to coastal habitats

Alternative life-history tactics of masu salmon Oncorhynchus masou are well documented. Subsequent to the freshwater parr stage (age ≥ 1 + years), an anadromous form migrates to the sea after smolting, while a resident form matures without seaward migration. In addition to this typical migratory dimorphism, anecdotal reports based on field observations have indicated that some underyearling masu salmon use estuarine waters. However, no empirical evidence indicates saltwater utilisation and subsequent survival in the early parr stage. Here, we used otolith microchemistry to examine whether a portion of masu salmon parr in northern Japan enters coastal habitats. The otolith Sr:Ca ratios of most juveniles collected from six rivers had consistently low values, indicating that masu salmon parr inhabiting these rivers stay only in freshwater. In contrast, in individuals from a steep-gradient river the Sr:Ca ratios increased at about a 200-µm distance from the otolith core. These results suggest that some masu salmon parr might use brackish water or sea water temporarily. In addition, three masu salmon parr were found in another steep river where a culvert located only ten metres from the river mouth completely blocked upstream migration for spawning. The Sr:Ca ratios in these fish increased at about >200 µm from the otolith core, indicating the parr had immigrated to the non-natal river from the sea. Such flexible behaviour at an early life stage may contribute to the spatial expansion of masu salmon, and the movement could moreover help to stabilise its population dynamics.     

长江口及邻近海域凤鲚生境履历重建

利用 X-射线电子探针微区技术(EPMA)对长江口崇明和邻近吕四凤鲚(Coilia mystus)耳石 Sr 和 Ca 的微化学进行了分析。定量线分析和 Sr 含量面分布图谱显示,凤鲚耳石核区的 Sr/Ca 比值存在 Sr/Ca<3、37 这 3 种类型,分别对应的耳石核心面分布同心环区域颜色为蓝色、绿色和黄-红色,据此推断长江口及邻近海域凤鲚孵化场存在 3 种,即淡水孵化场、河口半咸水孵化场及海水孵化场。凤鲚个体耳石从核心到边缘的 Sr/Ca比值变化波动极为显著,有对应淡水生活的低值阶段(Sr/Ca<3,最小为 2.04±0.87),也有对应海水生活的高值阶段(Sr/Ca >7,最大为 7.81±0.91),可将凤鲚的生境履历类型分为 4 种类型:淡水河口半咸水型、河口半咸水定居型、河口半咸水海水型和淡水河口半咸水海水型。长江口邻近海域吕四凤鲚有淡水和河口半咸水孵化个体,其生境履历类型包括淡水河口半咸水型、河口半咸水海水型和淡水河口半咸水海水型,而长江口崇明岛海域有海水及河口半咸水孵化个体,其生境履历类型包括淡水河口半咸水型、河口定居型及淡水河口半咸水海水型,这反映了长江口崇明岛及邻近海域吕四 2 个海域凤鲚个体间的共性以及差异性。通过本次研究,首次证明了长江口及邻近海域凤鲚存在 3 种孵化场及 4 种生境履历类型,准确反映了凤鲚个体组成及其生活史的多样性和复杂性。     

Migration history of Sakhalin taimen <Emphasis Type="Italic">Hucho perryi</Emphasis> captured in the Sea of Okhotsk,northern Japan,using otolith Sr:Ca ratios

Sakhalin taimen Hucho perryi populations have decreased drastically to near extinction. It is urgent to establish an effective conservation strategy based on an understanding of the characteristics of migration and habitat use of this species. We examined the migration history of anadromous Sakhalin taimen captured off the Sarufutsu coast, northern Hokkaido, Japan, using otolith Sr:Ca ratios and also examined the relationship between their otolith Sr:Ca ratios during freshwater and seawater residence in a rearing experiment. Otolith Sr:Ca ratios of some fish from the Sarufutsu coast showed freshwater levels (0.5–4.0 × 10⁻³) near the core, which thereafter increased to brackish water levels (4.0–6.0 × 10⁻³), and then to seawater levels (6.0–10.0 × 10⁻³) in the outermost regions. Those findings indicate that specimens from the Sarufutsu coast migrated to the brackish water region or the sea and spent most of their lives there. The anadromous migration pattern including the timing of downstream migration seems to be flexible among individuals in the species. They migrate between freshwater and seawater or brackish water several times during their lives, showing extensive habitat use. It is essential to secure the continuity among the freshwater, brackish water, and seawater areas for their effective conservation.     

Migration of anadromous white-spotted charr <Emphasis Type="Italic">Salvelinus leucomaenis</Emphasis>, as determined by otolith strontium: calcium ratios

ABSTRACT:   The migratory history of anadromous white-spotted charr Salvelinus leucomaenis collected from Japanese coastal waters, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith, by means of wavelength dispersive X-ray spectrometry using an electron microprobe. Otolith Sr concentration or Sr : Ca ratios of anadromous S. leucomaenis , fluctuated strongly along the life history transect in accordance with the migration (habitat) pattern from sea to fresh water. The anadrmous S. leucomaenis showed phase L (low Sr : Ca ratio) from the core to the point 1000–2500 µm distant, averaging 1.3 × 10⁻³ to 2.7 × 10⁻³ and thereafter, the ratios increased sharply, being higher than 5.0 × 10⁻³ to 10.0 × 10⁻³. These findings indicated that otolith Sr : Ca ratios reflected individual life histories, enabling a sea habitat to be identified from a freshwater habitat in this species.     

长江南京江段长颌鲚生境履历的反演研究

利用电子探针显微分析技术(EPMA),对2009年和2014年采自长江南京段的长颌鲚耳石微化学进行了研究,反演了其生境履历.结果显示,这些长颌鲚耳石上元素Sr/Ca值的动态可分为两类.一类Sr/Ca值出现显著波动,不仅具有对应淡水生境的低值(1.87±0.36),而且有对应于河口半咸水生境的较高值(4.80±0.80),甚至出现了外海高盐度生境的高值(7.85±0.57),反映了溯河洄游的生境履历特征.另一类Sr/Ca值稳定3.0以下(14NJC09和14NJCE10),仅反映出在淡水生境中生活的履历.上述结果均得到了耳石Sr面分布的验证.上述“反演”的结果首次发现,传统上认为的一定是溯河洄游的长颌鲚,也可能存在有淡水定居个体.单纯利用上颌骨的长短并不能作为有效判别长江刀鲚资源群体中溯河洄游个体和淡水定居个体的标准.     

长江短颌鲚耳石Sr/Ca值变化特征及其江海洄游履历

为确证长江刀鲚生殖洄游季节的短颌刀鲚是否为江海洄游个体,采用X射线电子探针微区分析技术(EPMA)研究了2013年4月27日采自长江靖江段的1尾短颌鲚(XGC-A)和1尾长颌鲚(XGC-B)矢耳石的锶(Sr)和钙(Ca)的微化学特征,同时将实验结果与确认是江海洄游型长江刀鲚矢耳石的Sr和Ca的微化学特征进行了比对分析。定量线分析结果显示,短颌鲚和长颌鲚个体的Sr/Ca值均波动显著,不仅具有对应淡水生活的低值(1.59±0.80、1.55±0.74),而且出现了对应于海水生活的高值(4.38±1.33、3.56±0.94),显示出其溯河洄游的履历;耳石元素面分布分析结果同时验证了短颌鲚和长颌鲚均参与江海洄游的事实。研究表明,目前长江中存在参与江海洄游的短颌鲚个体。     

Non‐diadromous life history and limited movement in northern lineages of Australian smelt: Evidence from otolith chemistry analysis

A comprehensive knowledge of migratory behaviour is paramount for the effective management and conservation of fishes in coastal drainages. The Australian smelt (Retropinna semoni) is a common fish distributed throughout coastal and inland drainages in south‐eastern Australia. Multiple life history patterns (potamodromy, facultative diadromy, estuarine residence) in the southern regions of its geographic distribution have been reported, and it is possible that some of these differences reflect characteristic behaviours of cryptic species within the group. To elucidate the life history patterns of smelt at the northern extent of their range and to identify any differences in migratory behaviour between two genetically distinct lineages (“SEQ‐N”, “SEQ‐S”) in this region, the movement patterns of Australian smelt were assessed using otolith chemistry. No evidence of marine residence was found based on otolith Sr:Ca and Ba:Ca transects for either group, suggesting that both are non‐diadromous. Significant differences in multi‐elemental otolith chemistry signatures were found among rivers and between paired sites within some rivers, suggesting no connectivity among drainages and limited dispersal of individuals over large spatial scales within rivers. These findings provide key insights into the migratory patterns of northern Australian smelt populations and, in combination with previous research, suggest that life history variation in the Australian smelt complex may occur primarily at the intra‐population level rather than among genetically distinct lineages. Conservation and management strategies for Australian smelt should take limited dispersal and individual life history variation into consideration in order to protect the components of this important species complex.     

Occurrence of estuarine and sea eels <Emphasis Type="Italic">Anguilla japonica</Emphasis> and a migrating silver eel <Emphasis Type="Italic">Anguilla anguilla</Emphasis> in the Tokyo Bay area,Japan

Otolith microchemical analyses of the strontium (Sr) and calcium (Ca) concentrations in the eels Anguilla japonica and A. anguilla caught in Tokyo Bay were undertaken to reconstruct the eels’ migratory histories. A. japonica in the yellow stage (immature stage) were caught in a bay without any adjacent rivers or streams. A. anguilla was in the silver stage (early maturing stage), and the eel was confirmed to have just begun spawning migration to the open ocean from Tokyo Bay based on the otolith Sr:Ca ratios, which showed a typical catadromous life history with low Sr:Ca ratio values throughout the eel’s life after recruitment. The mean Sr:Ca ratios in A. japonica from the elver mark to the otolith edge indicated the eels belonged to several general categories of migratory histories, including sea eels (average Sr:Ca ratio ≥6.0 × 10⁻³) and estuarine eels (average Sr:Ca ratio 2.5 to 6.0 × 10⁻³) based on the criteria reported previously in A. japonica. All eels had a certain freshwater life period, although the period was highly variable among fish. These results indicate that A. japonica has a flexible pattern of migration, with the ability to adapt to various habitats and salinities.     

Low-fidelity homing behaviour of Biwa salmon <Emphasis Type="Italic">Oncorhynchus</Emphasis> sp. landlocked in Lake Biwa as inferred from otolith elemental and Sr isotopic compositions

Biwa salmon Oncorhynchus sp. is endemic to Lake Biwa, Japan, where it is an important commercial and recreational fisheries species. However, no information is currently available on its population structure and migration ecology. Therefore, here we evaluated whether otolith Sr/Ca, Ba/Ca and ⁸⁷Sr/⁸⁶Sr ratios can be used as natural signatures in Biwa salmon and then used these to determine the natal origins of lake-migration-phase individuals and spawning adults, and the homing ability of spawning adults in the Lake Biwa water system. Quadratic discriminant function analysis demonstrated that the lake-migration school comprised individuals with multiple origins, including rivers to the east, west and north of Lake Biwa, and that the homing rate of spawning adults was low (18 out of 80 individuals), with ca. 78% of fish straying into non-natal rivers. However, this straying behaviour was not spatially random, with fish tending to migrate upstream in rivers neighbouring their natal rivers. The high rate of straying in spawning adults is considered important for establishing and maintaining this species, which is highly adapted to life in the Lake Biwa water system where environmental disturbances often occur.     

Discrimination of wild and hatchery trout by natural chronological patterns of elements and isotopes in otoliths using LA‐ICP‐MS

Abstract The potential to discriminate between wild and hatchery trout [Salmo trutta f. fario L. and Oncorhynchus mykiss (Walbaum)] by chronological microchemical patterns of different otolith regions was tested. Central and rim regions of otoliths were analysed for life stage specific elemental patterns of strontium (Sr), sodium (Na) and calcium (Ca) as well as of ⁸⁷Sr/⁸⁶Sr ratios using laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). Classification to life stage specific habitats was achieved with 100% accuracy by ⁸⁸Sr/⁴³Ca, ²³Na/⁴³Ca and ⁸⁷Sr/⁸⁶Sr ratios resulting in a discrimination of hatchery fish from wild fish. ⁸⁷Sr/⁸⁶Sr ratios and Sr concentration in otoliths were positively correlated with the ratio and amount in the water. Na content in otoliths did not directly reflect the concentration in the water, although the ²³Na/⁴³Ca ratio in otoliths contributed to the discrimination. Clear differences in otolith chemistry were found for fish experiencing different geological units or a groundwater‐fed environment in a hatchery. Natural chronological microchemical patterns in otoliths proved to be a valuable tool for discriminating wild and hatchery fish without the necessity to use marking methods. LA‐ICP‐MS is well suited for this application because of its limited need for sample preparation, its potentially high sample throughput and the possibility of simultaneous measurement of multiple elemental and isotopic fingerprints.     

Site fidelity and movements of an amphidromous goby revealed by otolith multi‐elemental signatures along a tropical watershed

Otolith microchemistry can provide crucial information to address gaps of knowledge in spatio‐temporal ecology of fish species. However, understanding the seasonal variability of water chemistry and its effect on otolith signatures is needed to interpret fish movements. Otolith multi‐elemental signatures were used to examine the diadromous migration and small‐scale movements of a tropical goby (Sicyopterus lagocephalus) within a watershed in La Réunion Island, Indian Ocean. The elemental ratios Sr:Ca, Ba:Ca and Sr:Ba recorded monthly in the water of nine sampling sites varied between localities and were correlated with otolith signatures, whereas the Mg:Ca signature was not. The incorporation of some trace elements in otoliths was influenced by the size of fish and site where they were caught, reflecting an effect of endogenous and exogenous factors. Despite these sources of variation, the elemental signatures did not overlap for three river sections distributed along the 26‐km‐long watershed. The diadromous migration and fish lifetime movements between these river sections were reconstructed using an original process based on random forest analysis. This approach revealed distinct migratory behaviours after fish entered in the river, with some individuals progressing slowly in the watershed whereas other rapidly reached the upper localities. As adults, S. lagocephalus showed a restricted exploratory behaviour and a strong site fidelity to a particular part of the watershed. The detection of adult movement was typically only between adjacent locations and is possibly explained by shifts in local intraspecific hierarchies and/or displacement during extreme discharge caused by cyclones.