| 1. |
- Florin, Ann-Britt, et al.
(författare)
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How old are you-Evaluation of age reading methods for the invasive round goby (Neogobius melanostomus, Pallas 1814)
- 2018
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Ingår i: Journal of Applied Ichthyology. - : Hindawi Limited. - 0175-8659 .- 1439-0426. ; 34, s. 653-658
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic, the first observation of the round goby (Neogobius melanostomus, Pallas 1814) was made in 1990. Within the past decade the species became invasive and spread rapidly throughout the Baltic Sea. Studies about the fishes potential impacts on resident species promote the need for an increasing knowledge of their basic stock structures such as growth rates, longevity and mortality, which all rely on accurate estimates of age. Former studies on the round goby have used several different age reading techniques. In this study, we compared three standard otolith preparation methods for ageing and present the best procedure for the invasive round goby. The results showed significant differences in age estimates of the same fish between the different preparation methods and between readers. The estimation of the first annulus, the first year, was the most problematic. The overall agreement was lowest when reading the whole otoliths while the best performance was achieved with sectioned and stained preparation method. Depending on method used the growth estimates also differed. The results question comparability between previous studies and highlight the importance of harmonised aging procedures for the round goby for obtaining correct estimates of population parameters such as growth rate, age at maturity, and longevity.
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| 2. |
- Heimbrand, Yvette
(författare)
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Losing track of time : causes and solutions for the problematic determination of Baltic cod age
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Cod (Gadus morhua) is a key fish species of the Baltic Sea, economically as well as ecologically. Stocks declined during recent decades due to factors such as high fishing pressure, loss of spawning and feeding habitats caused by eutrophication, changing climate and widespread hypoxia. The growing seal population preys on cod and increased contact has resulted in the transmittance of parasites to cod, causing additional stress. In order to manage fisheries, age distribution and growth history of fish are needed to run stock assessment models. Based on these biological references, decisions are made for fishing quotas and restricting catches. Fish age is usually determined from counting annual growth zones in otoliths, calcium carbonate structures situated in the skull of the fish. Otoliths grow incrementally, depositing layers of material, forming annual rings reflecting growth, like a tree’s rings. Baltic cod otolith readability has always been somewhat difficult; today the poor condition of Baltic cod has worsened the problem. Unclear seasonal growth zones in otoliths have made age data unreliable, resulting in an uncertain forecast for stock size and suspended Marine Stewardship Council (MSC) certificate for sustainable seafood. However, invisible to the eye, the chemistry of the otolith contains a “hidden code” that could validate conventional ageing methods. The otolith takes up trace elements and isotopes from the surrounding water; hence the fish’s seasonal migration among areas with different environmental conditions is recorded in the otolith. Microchemical analyses enable us to track seasonal changes in trace elemental and isotopic composition in the otolith throughout the fish’s life. The aim of this thesis is to (1) explore the potential use of otolith chemistry as an age validating tool, (2) provide alternative ways to age fishes when other methods fail, as well as (3) provide novel information for aquatic monitoring.
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| 3. |
- Heimbrand, Yvette
(författare)
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Provenance of whitefish in the Gulf of Bothnia determined by elemental analysis of otolith cores
- 2018
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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. ; 417, s. 86-90
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Tidskriftsartikel (refereegranskat)abstract
- The strontium concentration in the core of otoliths was used to determine the provenance of whitefish found in the Gulf of Bothnia, Baltic Sea. To that end, a database of strontium concentration in fish otoliths representing different habitats (sea, river and fresh water) had to be built. Otoliths from juvenile whitefish were therefore collected from freshwater ponds at 5 hatcheries, from adult whitefish from 6 spawning sites at sea along the Finnish west coast, and from adult whitefish ascending to spawn in the Tome River, in total 67 otoliths. PIXE was applied to determine the elemental concentrations in these otoliths. While otoliths from the juveniles raised in the freshwater ponds showed low but varying strontium concentrations (194-1664 mu g/g,), otoliths from sea spawning fish showed high uniform strontium levels (3720-4333 mu g/g). The otolith core analysis of whitefish from Tome River showed large variations in the strontium concentrations (1525-3650 mu g/g). These otolith data form a database to be used for provenance studies of wild adult whitefish caught at sea. The applicability of the database was evaluated by analyzing the core of polished otoliths from 11 whitefish from a test site at sea in the Larsmo archipelago. Our results show that by analyzing strontium in the otolith core, we can differentiate between hatchery-origin and wild-origin whitefish, but not always between river and sea spawning whitefish.
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| 4. |
- Limburg, Karin, et al.
(författare)
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Making the Otolith Magnesium Chemical Calendar-Clock Tick: Plausible Mechanism and Empirical Evidence
- 2018
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Ingår i: Reviews in Fisheries Science & Aquaculture. - : Informa UK Limited. - 2330-8249 .- 2330-8257. ; 26, s. 479-493
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Tidskriftsartikel (refereegranskat)abstract
- The incorporation of a number of readily measured trace elements into otoliths is considered to be under some sort of physiological control, but rarely are explicit mechanisms proposed. Studies of the incorporation of the trace element magnesium reveal that in some taxa there exists strong seasonal patterning, taking on the characteristics of a ''chemical calendar-clock.'' However, Mg/Ca and the isotopic ratio Mg-26/24 are less ''clock-like'' in taxa that are not as metabolically active. Herein, it is hypothesized that Mg uptake and incorporation are related to metabolic activity. Further, a two-step process of Mg incorporation is proposed: (1) limited entry into the otolith-bearing chamber through ion channels and (2) association with water-soluble proteins within the chamber. Supporting data from a range of taxa and life histories are provided; the authors' aim is to stimulate discussion and encourage physiologists to test these and alternative mechanistic hypotheses.
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