Variation in migratory history of Dolly Varden in a stream with an artificial dam in the Shiretoko Peninsula,Hokkaido, Japan

The variation of migration patterns in Dolly Varden Salvelinus malma in a stream with an artificial dam (erosion-control-dam) in the Shiretoko Peninsula, Hokkaido Island, Japan, at the southernmost part of its distribution, was examined by otolith Sr:Ca ratio analysis. All specimens from the above-dam area showed consistently low Sr:Ca ratios (<5.0 × 10⁻³) throughout the otolith. In contrast, many specimens from the below-dam area had higher ratios (>5.0 × 10⁻³) throughout the otolith or only at the outer part than do those from the above-dam area. This higher ratio is probably due to salinity effects. Specimen from the below-dam area could be divided into three types: (1) Consistently low Sr:Ca ratios throughout the otolith, being freshwater residents. (2) Low Sr:Ca ratios around the inner part of the otolith, and thereafter higher ratios toward the outer part, being typically anadromous. (3) Relatively higher Sr:Ca ratios throughout many or in some parts of the otolith, indicating that these have migrated from the freshwater to brackish water or seawater from the early life stage. These findings suggest that Dolly Varden has a high degree of plasticity in its migratory behavior.     

Diversity of life strategies of pikepech <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.) in the Lower Volga (by the data of microelement composition of otolithes)

Strontium (Sr) and calcium (Ca) contents and Sr/Ca ratios in otoliths of pikeperch Sander lucioperca have been studied by X-ray fluorescent microanalysis. A sample of 95 specimens from the Lower Volga region are studied. The fish were obtained in a section of the Akhtuba River at a distance of 250–279 km upstream from the Caspian Sea. Some specimens in the sample have low strontium content throughout the otolith. The other fish have increased both Sr content and Sr/Ca ratios in core zones of otolith or near its outer edge: the Sr/Ca ratio is over 6.00 × 10^–3, with a maximum at 10.02 × 10^–3. The fish with a low Sr/Ca ratio live in freshwater and demonstrate a resident life history strategy. Pikeperch that have increased ratios of Sr/Ca in outer zones of otolith demonstrate a migratory life history strategy. These fish leave the freshwater of the Volga and feed in brackish water of the Northern Caspian Sea. Some migratory fish migrate to the sea as underyearlings, stay in a brackish water for 1 year or less, and then return back to fresh water for the rest of its life. The other group migrates back and forth from freshwater to the sea several times during their life. Finally, some fish leave freshwater for 1–2 years, spending this time in the Northern Caspian Sea. The conclusion is that the pikeperch stock in the Lower Volga has a complicated composition and consists of freshwater (residents and rheodromic ones) and migratory (anadromous and semianadromous) fish.     

Elemental signatures of Acanthochromis polyacanthus otoliths from the Great Barrier Reef have significant temporal, spatial, and between-brood variation

We evaluated the spatial and temporal scales over which otolith signatures varied in a reef fish on the Great Barrier Reef (GBR) using the non-dispersing damselfish Acanthochromis polyacanthus. We found a robust multi-element separation in otolith signatures from reef clusters in the northern and southern GBR. Variance components indicated that this spatial scale accounted for the majority of the variation in two elemental ratios (Ba/Ca and Sr/Ca) over the 2 years of the study. There was also significant variation in elemental signatures between otoliths collected over two consecutive years, as well as within a season. Individual reefs within clusters were less distinguishable based on otolith chemistry and were probably observed by differences within reefs (among sites and broods within sites). These results indicate that it may be difficult to determine the reef of origin for individual fish using otolith chemistry, while determining natal region seems a realistic goal.     

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.     

Using otolith weight to estimate the age of haddock (Melanogrammus aeglefinus): a tree model application

In this study, we investigated whether otolith weight can be used to estimate fish age with the same level of accuracy as that of the traditional annuli counting technique in a commercially important species such as haddock (Melanogrammus aeglefinus). Results indicate that this method is highly effective for young fish (around 97% correct classification), whereas its powers of prediction decrease with the increasing age of the fish. For older fish, the otolith weight cannot be an accurate estimator of fish age if the weight overlap between the different age classes is too large. Nevertheless, the otolith weight technique is strictly dependent on correct age determination through the counting of annuli of those individuals used in the calibration. Hence, an increase in the accuracy of ageing obviously determines an increase of the power of otolith weight to estimate fish age. Therefore, we suggest that otolith weight could represent a routine technique for determination of the age structure of haddock populations. This technique has the merit to be objective, fast, 100% repeatable and has the same level of accuracy as that of annuli counting.     

Cathodoluminescence Microscopy: A Useful Tool for Assessing Incremental Chemical Variation in Otoliths

Otoliths taken from fish from Eden Lake, Manitoba show yellow–green and red cathodoluminescence of varying intensity that corresponds to their annular structure. Proton-induced X-ray emission analysis shows manganese (Mn) concentrations of between 2 and 205ppm, zinc (Zn) concentrations between 2 and 290ppm and strontium (Sr) concentrations up to 1500ppm in the otoliths. The distribution of luminescence correlates with the distribution of Mn. The Mn, Zn and Sr are likely derived from the monzonitic rocks surrounding the lake. Variations in the distribution of cathodoluminescence may be a useful tool for evaluating changes in environmental chemistry and fish life histories.     

Temperate Utah chub form valid otolith annuli in the absence of fluctuating water temperature

Utah chub Gila atraria , a temperate freshwater minnow, formed valid otolith annuli (annual growth rings), even when raised in a constant‐temperature desert spring environment. This suggests that factors other than seasonal variation in water temperature control annual otolith marking.     

鲤稚鱼耳石锶标记效果

对鲤稚鱼开展了不同浸泡浓度和不同标记时间梯度的SrCl₂·6H₂O暴露标记试验,以确认其耳石Sr标记的可行性及基本条件.首先,基于4个浓度(0、4、8、12 mg·L^-1)水平的SrCl₂·6H₂O溶液,浸泡标记2 d来筛选基本浸泡标记浓度.然后,在SrCl₂·6H₂O为8 mg·L^-1浓度下,基于5个浸泡时间(1、2、3、4、5 d)来筛选基本浸泡标记时间.电子探针分布分析结果显示:对照组(0 mg·L^-1)耳石Sr/Ca比值低且稳定,标记组均出现了高Sr/Ca比值区.对照组耳石剖面为均一的低Sr蓝色图谱,而标记组耳石上均有高Sr红色标记环带,且标记成功率为100%.试验期间,标记组和对照组的死亡率、平均全长和平均体质量无显著差异,表明Sr标记对供试鱼无不良影响.由于耳石上清晰、完整的高Sr红色标记环带出现在标记浓度为8 mg·L^-1及以上,标记时间为2 d及以上,故建议分别选择8 mg·L^-1和2 d为基本浸泡标记浓度和基本浸泡标记时间.本研究证实耳石Sr标记技术对鲤稚鱼具有很好的可行性.     

The effect of otolith storage methods on the concentrations of elements detected by laser-ablation ICPMS

Otoliths of male (1+ year old) Terubok, tropical shad Tenualosa toli from the Lupar River, Sarawak, were treated in different ways to assess the effect of post-capture storage on element concentrations in the otolith core and edge detected by laser-ablation inductively coupled plasma mass spectrometry (ICPMS). Five treatments were compared: rapid removal and dry storage; fish kept 5 h after capture then otoliths removed; rapid removal and stored in alcohol; fish rozen for 24 h then otoliths removed; and storage of intact head in alcohol for several weeks. Seven elements were detected at the core and edge of otoliths (Li, Na, Mg, Mn, Co, Sr, Ba). Of these, Na, Mg, Co and Ba differed among treatments, being highest in treatments where the otolith remained in the head. Variation in element measurements due to treatment effects was similar to within-otolith variation for the other elements and was least variable in the fresh treatment. The variation in concentration between the core and edge was more significant than other sources of variation (up to 100 times) for some elements. These differences were probably due to physiological factors (ontogenetic) or to yearly changes in water chemistry. The results indicate that the method of otolith storage, especially freezing whole fish, can have a small, but measurable, effect on the concentrations of Na, Mg, Co and Ba.     

Flexible seaward migration of Dolly Varden <Emphasis Type="Italic">Salvelinus malma</Emphasis> in the Shiretoko Peninsula,Hokkaido, Japan

The migratory history of Dolly Varden Salvelinus malma was investigated in 30 streams in the Shiretoko Peninsula, Hokkaido, Japan, which is in the southern part of their distribution. Captured Dolly Varden were classified into two categories by their body coloration: silvery fish were thought to be an anadromous form, and non-silvery fish a fluvial form that remains in freshwater throughout its life. Forty-seven of 1,739 Dolly Varden collected in the spring and ten of 2,126 Dolly Varden collected in the autumn were silvery fish. Twenty silvery fish and 120 non-silvery fish were examined by analysis of otolith Sr:Ca ratio. Three silvery fish from autumn and 15 non-silvery fish had migrated to salt water or brackish water. The other specimens of silvery fish were regarded as smolt or pre-smolt before seaward migration. The present study suggests that Dolly Varden in the Shiretoko Peninsula have a flexible migratory history, where some of the non-silvery fish utilize marine environments while some individuals follow an anadromous life history.     

Electron microprobe analysis of juvenile walleye pollock,Theragra chalcogramma,otoliths from Alaska: a pilot stock separation study

Synopsis The incorporation of dissolved oceanic constituents in the otoliths of fish has potential as a chemical tracer for reconstructing the early life history of marine fish. Wavelength dispersive spectrometers on an electron microprobe were used to measure Na, Mg, P, S, Cl, K, Ca, and Sr concentrations on the outer margins of 57 juvenile walleye pollock, Theragra chalcogramma, otoliths from five locations in the Gulf of Alaska and Bering Sea. Discriminant analyses that used various combinations of Na, P, K, Sr, and fish standard length and/or age showed that 60–80% of the samples could be assigned to the correct capture locality. While the concentrations of some of the measured elements correlated with standard length or age of the fish, there are measurable differences among localities when concentrations are length or age corrected, mainly due to differences in Na and K concentrations. Elemental composition of otoliths potentially could be used to assign fish from a mixed stock fishery to original stocks, information that is greatly needed for the effective management of fish stocks.     

Fish otolith chemistry influenced by exposure to multiple environmental variables

There is an increasing desire for researchers to use the elemental concentrations in fish otoliths to reconstruct environmental histories of fish. These reconstructions may be plausible due to the unique incorporation of elements into discrete layers of otolith material that correspond to daily growth, and because environmental variables of temperature, salinity, and water chemistry can influence otolith chemistry. However, it is essential to establish exactly how temperature, salinity, and the ambient concentration of elements influence otolith chemistry in order to interpret environmental histories of fish. Using a controlled laboratory experiment we tested the relative and interactive effects of temperature, salinity, and ambient concentration of strontium (Sr) and barium (Ba) on the resulting concentration of Sr and Ba in otoliths of black bream Acanthopagrus butcheri (Munro 1949). Salinity and concentration, and temperature and concentration interacted to affect the elemental concentration of Sr:Ca and Ba:Ca in otoliths. Regression analysis revealed that temperature and ambient concentration contributed most to the trend in otolith chemistry for both elements. Importantly, this is the first experiment to combine three environmental variables and assess their effect on otolith chemistry. Based on these results, it should be possible to use changes in the elemental concentration in otoliths to better reconstruct previous environments of temperature, salinity, and ambient water chemistry, which is especially useful when determining occupancy in habitats such as estuaries that display variable environmental characteristics.     

Otolith Trace Elemental Analyses of South American Austral Hake,Merluccius australis (Hutton, 1872) Indicates Complex Salinity Structuring on their Spawning/Larval Grounds

Trace element signatures of otolith edges and cores from 335 austral hake (Merluccius autralis) were analysed using LA-ICPMS from samples collected in Chilean and Falkland Islands'' waters, in order to provide potential insights into stock discrimination and migrations. Fish were caught in two locations in Chile and four locations in the south-west of the Falkland Islands Shelf. Univariate and multivariate analyses of trace element signatures in the edges of otoliths, representing adult fish, were not able to distinguish between samples collected in Chile and the Falkland Islands. Cluster analyses based on Ward’s similarity/distance metric suggested that it was possible to identify two groups from core signatures. Further analyses of this perceived clustering of the core concentrations revealed that this was largely due to the wide spread of Sr/Ca ratios in the otoliths’ cores. Gaussian finite mixtures using MCMC methods confirmed that Sr/Ca ratios form two separate distributions with significantly different mean values while concentrations of other elements showed no evidence of the presence of two or more distributions. The results suggest that there is only one spawning stock of austral hake with spawning situated in and around the Chilean fjords (43°30’S– 47°S) and the variation in Sr/Ca ratios likely suggests complex salinity structuring in this area.     

Migratory patterns of anadromous white-spotted charr Salvelinus leucomaenis in Eastern Hokkaido, Japan: The solution to a mystery?

We evaluated the migratory patterns of white-spotted charr in eastern Hokkaido, Japan using: (1) field observation of fish, (2) salinity-recording archival tags, and (3) analysis of otolith Sr and Ca concentrations. Field observations suggest that the majority of anadromous white-spotted charr outmigrate to the sea in spring (April to June) and ascend the river between late summer and autumn (August to November). Salinity records from archival tags revealed a fluctuating pattern consisting of both low and high values within a month, indicating frequent short-term movements between freshwater (including non-natal rivers) and brackish/salt water habitats. Otolith Sr:Ca ratios exhibited a sharp rise at about 40–50% of the otolith radius, which was followed by several spikes consisting of both low and high values, indicating that fish migrated between freshwater and marine environments multiple times during their life history. However, the peaks in Sr:Ca ratios were generally associated with annulus zones on the otolith, indicating that the anadromous migration was generally an annual event.     

Demographic Variation between Colour Patterns in a Temperate Protogynous Hermaphrodite,the Ballan Wrasse Labrus bergylta

Fish populations are often treated as homogeneous units in typical fishery management, thereby tacitly ignoring potential intraspecific variation which can lead to imprecise management rules. However, intraspecific variation in life-history traits is widespread and related to a variety of factors. We investigated the comparative age-based demography of the two main colour patterns of Labrus bergylta (plain and spotted, which coexist in sympatry), a commercially valuable resource in the NE Atlantic. Individuals were aged based on otolith readings after validating the annual periodicity of annuli deposition. The relationships between the otolith weight and fish age and between otolith length and fish length were strong but differed between colour patterns. The fit of the growth models to the age and length data resulted in divergent growth curves between colour morphotypes and between sexes. Males and spotted individuals attained larger mean asymptotic sizes (L_inf) than females and plain individuals, respectively, but converged to them more slowly (smaller k). Estimates of mortality based on catch curves from two independent datasets provided a global total mortality (Z) of 0.35 yr^–1, although Z was larger in plain and female individuals. Overall, the results of this research have direct implications for management of L. bergylta and, as a precautionary measure, we recommend considering both colour patterns as two different management units.     

Factors influencing otolith strontium/calcium ratios in Anguilla japonica elvers

The effects of temperature and salinity on the concentration ratios of strontium (Sr) to calcium (Ca) within the sagittal otoliths of elvers of the Japanese eel, Anguilla japonica, were studied by spot analysis using a wavelength dispersive X-ray electron microprobe. A total of 340 elvers were used: 100 elvers were reared for 15 days under various salinity conditions (freshwater, one-third seawater, two-thirds seawater and pure seawater at 22 °C; 240 elvers were reared for 58 days under various water temperature conditions (12, 17, 22, 27 °C) in either freshwater or pure seawater. Otolith Sr/Ca ratios were found to be positively correlated with water salinity. On the other hand, the Sr/Ca ratios were not found to be significantly different among the various temperature groups. The above results strongly suggest that the physiological mechanism of incorporation of Sr and Ca within the otolith of an eurythermal fish, Japanese eel, does not change within this range of temperatures (12–27 °C).     

Identifying migratory contingents of fish by combining otolith Sr:Ca with temporal collections of ambient Sr:Ca concentrations

Ambient strontium:calcium (Sr:Ca) concentrations were determined at the temporal scales of months, weeks and days, in summer and winter at two estuarine sites, and experimentally derived correlations between ambient and otolith Sr:Ca were used to estimate the otolith Sr:Ca concentrations of 'resident' black bream Acanthopagrus butcheri . Wild black bream were collected in summer and winter at the end of the temporal water sampling, and their otolith Sr:Ca concentrations were examined. Wild fish were classified as 'resident' if their otolith Sr:Ca matched the predicted concentrations of resident fish, and 'migrant' if this did not occur. In winter, all fish were classified as resident. In summer, all fish were classified as migrants, with fish spending an average of only 16·8% (estuary 1) and 61·1% (estuary 2) of their time at each estuarine location.     

Contribution of water chemistry and fish condition to otolith chemistry: comparisons across salinity environments

This study quantified the per cent contribution of water chemistry to otolith chemistry using enriched stable isotopes of strontium (⁸⁶Sr) and barium (¹³⁷Ba). Euryhaline barramundi Lates calcarifer, were reared in marine (salinity 40), estuarine (salinity 20) and freshwater (salinity 0) under different temperature treatments. To calculate the contribution of water to Sr and Ba in otoliths, enriched isotopes in the tank water and otoliths were quantified and fitted to isotope mixing models. Fulton's K and RNA:DNA were also measured to explore the influence of fish condition on sources of element uptake. Water was the predominant source of otolith Sr (between 65 and 99%) and Ba (between 64 and 89%) in all treatments, but contributions varied with temperature (for Ba), or interactively with temperature and salinity (for Sr). Fish condition indices were affected independently by the experimental rearing conditions, as RNA:DNA differed significantly among salinity treatments and Fulton's K was significantly different between temperature treatments. Regression analyses did not detect relations between fish condition and per cent contribution values. General linear models indicated that contributions from water chemistry to otolith chemistry were primarily influenced by temperature and secondly by fish condition, with a relatively minor influence of salinity. These results further the understanding of factors that affect otolith element uptake, highlighting the necessity to consider the influence of environment and fish condition when interpreting otolith element data to reconstruct the environmental histories of fish.     

Extrinsic factors affecting otolith chemistry – implications for interpreting migration patterns in a diadromous fish

Much has been revealed about fish migration, including diadromous behaviour, through the use of otolith chemistry. Manipulative experiments assist with unravelling information on otolith chemical composition and incorporation thereby answering specific questions on diadromous movements. In this study, a laboratory-based experiment was used to determine the relative and interactive effects of salinity and water temperature on the composition of three key elements (Sr, Ba and Mg) within the otolith of a catadromous fish, Percalates novemaculeata, endemic to south-eastern Australia. Otolith incorporation of Sr and Ba was positively related to ambient water concentration, whereas Mg incorporation was not. Sr and Ba increased and decreased significantly across salinity gradients, respectively, with minor positive effects of temperature also being detected. Salinity and temperature interacted to significantly affect the elemental concentration ratios for Ba: Ca in otoliths. Discrimination between fresh water and marine environments shows promise for interpreting P. novemaculeata residency based on these elements alone. However, deciphering finer scale movements within estuarine environments may be difficult. Our data highlights the importance of multifactorial validation experiments and suggests complementary use of multiple approaches for unravelling species-specific patterns of fish movement and habitat use.     

Environmental signature in the otolith elemental fingerprint of the tapertail anchovy, Coilia mystus, from the Changjiang estuary, China

The ontogenetic patterns of habitat use and the migratory history of the tapertail anchovy, Coilia mystus, collected in the Changjiang estuary around Chongming Island, China, were studied by examining the environmental signature in the otolith strontium (Sr) and calcium (Ca) fingerprints using electron probe microanalysis (EPMA). Our results suggest that the migration strategy of C. mystus is much more flexible than supposed in the literature to date. The spring spawning population of C. mystus from the studied area was found to consist of individuals with different migration histories. Although the tapertail anchovy seems to be an anadromous fish that spawns and hatches in a freshwater habitat, it can also use a freshwater environment in non‐spawning seasons. The otolith EPMA of the elemental fingerprint (Sr x‐ray maps and Sr : Ca ratios) is an environmental indicator that can be applied to the migratory ecology of other important diadromous species in China.