Abstract
The strontium (Sr) and barium (Ba) profiles in otoliths of juvenile sockeye salmon Oncorhynchus nerka from British Columbia are measured using a Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) system and analyzed. The highest possible measurement resolution (near-daily) was used to assess variability and repeatability of the breakpoint (marine entry) estimates inferred from Sr:Ca and Ba:Ca ratios. Such resolution for the otolith chemical composition (to an accuracy of 2 μm) was reached using the rotating slit, which width was close to the daily circulus width of the otoliths. So, daily or 2-day changes in the elemental composition were recorded during the period of transition to the marine environment. Sr profiles were generally similar among the fish, starting with low values of Sr:Ca in the fresh water and increasing sharply after the marine entry. The Ba:Ca signal was more complex, showing in most cases a dramatic increase immediately before the breakpoint. Besides, multiple peaks in the Ba profiles were recorded prior to the marine transition with a significant difference of their number between fish from different populations. A breakpoint was detectable in the Ba profiles 3–11 µm prior to its appearance in the Sr profiles. The complexity of Ba profiles may cause erroneous estimates of the marine entry date; thus, the Sr signal is a more reliable marker of marine transition for juvenile sockeye.
Highlights
Pacific salmonids are currently a focal point of scientific interest in the North Pacific [www.npafc.org]
The fresh-to-saline water transition and the subsequent early marine stage are considered a critical period in the life history of Pacific salmon and are associated with the highest mortality [Preikshot et al, 2012; Welch et al, 2013; Naydenko et al, 2016]
Life history reconstruction based on fish otolith microanalysis is a rapidly developing field of research [Barnes, Gillanders, 2013]
Summary
Pacific salmonids are currently a focal point of scientific interest in the North Pacific [www.npafc.org]. We considered commonly used Ba and Sr profiles inferred from an ultra-high-resolution LA-ICP-MS analysis of otoliths of juvenile sockeye salmon from three different stocks in order to evaluate how these elements in otoliths could be used to best estimate the marine entry point. Even with a smallest spot diameter (10 μm) used in otolith studies based on a raster scan (the offset of 1⁄2 of the diameter), the breakpoint appeared ~5 μm earlier than the actual signal Such small spot sizes are not common in otolith analysis due to high coefficients of variation (CVs) and low accuracy provides lower reliability of the 10 μm ablation line measurements [Chang et al, 2012]. Further research is expected to clarify whether the peaks in Ba signal indicate the beginning of marine transition or rather reflect physiological changes that occur before the marine entry
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
