| 1. |
- Heimbrand, Yvette, et al.
(författare)
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Information depths of analytical techniques assessing whitefish otolith chemistry
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 477, s. 104-108
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Tidskriftsartikel (refereegranskat)abstract
- The elemental composition of otoliths provides historical information on migration and provenance of fish. Due to the complex structure of the otoliths, the depth from which the elemental information originates has to be considered. In this work, three analytical methods often used to assess otolith chemistry are compared. The information depths are calculated for mu-XRF and PIXE and measured for LA-ICP-MS. The information depth in PIXE depends on the energy of the incident particles and on the element to be analysed while in XRF it depends mostly on the element to be analysed as the energy of the incident X-rays usually is high enough to excite atoms at depths of several hundreds of micrometres. If we assume that the otolith is exposed to X-rays from a Rh-tube (20.16 keV) about 50% of the detectable Sr(K alpha) X-rays will be emitted from a depth ranging from 0 to 114 mu m. In the case of PIXE with 3 MeV protons the corresponding range is 0-15 mu m. The information depths in LA-ICP-MS were determined by measuring the depth of the laser-ablated craters or trenches that remained on the otolith surface. The depths measured with a scanning white light interferometer (SWLI) were found to be about 40 mu m (spots) and 11 mu m (trenches).The correlation between strontium concentrations obtained by spot analysis of whitefish otoliths with PIXE and LA-ICP-MS was excellent (92%), although different spot sizes were used. A comparison of strontium concentration profiles measured with mu-XRF and LA-ICP-MS showed that the higher information depth of mu-XRF in combination with the 52 degree angle of the incident X-rays smoothens out the sharp edges seen in the LA-ICP-MS profiles. Otoliths from whitefish captured in the Baltic Sea (n = 30) were analysed in this comparison of methods. Among these whitefish there are sea spawners, river spawners and stocked fish with different life history and different otolith chemistry.
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| 2. |
- Heimbrand, Yvette, et al.
(författare)
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Prevalence of stocked whitefish in River Kemijoki, Finland, inferred by micro X-ray fluorescence analysis of otoliths
- 2020
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Ingår i: Fisheries Management and Ecology. - : Wiley. - 0969-997X .- 1365-2400. ; 27, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- Micro X-ray fluorescence (mu-XRF) analysis of otoliths was evaluated as a method to estimate the proportion of stocked one-summer-old whitefish Coregonus lavaretus L. in catches of adult fish (n = 20) ascending the River Kemijoki to spawn. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis was applied as control. Polished otoliths were scanned with mu-XRF to obtain strontium maps that were used to infer visually the provenance of the whitefish. Thirteen of the fish showed signs of being stocked as one-summer-old fingerlings. LA-ICP-MS was applied to determine the elemental composition in a spot outside the core of the otolith. The results were largely consistent with the visual inspection of the mu-XRF mapped otoliths. In conclusion, mu-XRF mapping successfully identified whitefish stocked as one-summer-old fingerlings. The vast majority of whitefish returning to the River Kemijoki to spawn were stocked fish.
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| 3. |
- Heimbrand, Yvette, et al.
(författare)
-
Seeking the true time: Exploring otolith chemistry as an age-determination tool
- 2020
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 97, s. 552-565
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Tidskriftsartikel (refereegranskat)abstract
- Fish otoliths' chronometric properties make them useful for age and growth rate estimation in fisheries management. For the Eastern Baltic Sea cod stock (Gadus morhua), unclear seasonal growth zones in otoliths have resulted in unreliable age and growth information. Here, a new age estimation method based on seasonal patterns in trace elemental otolith incorporation was tested for the first time and compared with the traditional method of visually counting growth zones, using otoliths from the Baltic and North seas. Various trace elemental ratios, linked to fish metabolic activity (higher in summer) or external environment (migration to colder, deeper habitats with higher salinity in winter), were tested for age estimation based on assessing their seasonal variations in concentration. Mg:Ca and P:Ca, both proxies for growth and metabolic activity, showed greatest seasonality and therefore have the best potential to be used as chemical clocks. Otolith image readability was significantly lower in the Baltic than in the North Sea. The chemical (novel) method had an overall greater precision and percentage agreement among readers (11.2%, 74.0%) than the visual (traditional) method (23.1%, 51.0%). Visual readers generally selected more highly contrasting zones as annuli whereas the chemical readers identified brighter regions within the first two annuli and darker zones thereafter. Visual estimates produced significantly higher, more variable ages than did the chemical ones. Based on the analyses in our study, we suggest that otolith microchemistry is a promising alternative ageing method for fish populations difficult to age, such as the Eastern Baltic cod.
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