Effect of analytical conditions in wavelength dispersive electron microprobe analysis on the measurement of strontium-to-calcium (Sr/Ca) ratios in otoliths of anadromous salmonids

The use of strontium-to-calcium (Sr/Ca) ratios in otoliths is becoming a standard method to describe life history type and the chronology of migrations between freshwater and seawater habitats in teleosts (e.g. Kalish, 1990; Radtke et al., 1990; Secor, 1992; Rieman et al., 1994; Radtke, 1995; Limburg, 1995; Tzeng et al. 1997; Volk et al., 2000; Zimmerman, 2000; Zimmerman and Reeves, 2000, 2002). This method provides critical information concerning the relationship and ecology of species exhibiting phenotypic variation in migratory behavior (Kalish, 1990; Secor, 1999). Methods and procedures, however, vary among laboratories because a standard method or protocol for measurement of Sr in otoliths does not exist. In this note, we examine the variations in analytical conditions in an effort to increase precision of Sr/Ca measurements. From these findings we argue that precision can be maximized with higher beam current (although there is specimen damage) than previously recommended by Gunn et al. (1992)

A method of mounting multiple otoliths for beam-based microchemical analyses

Beam-based analytical methods are widely used to measure the concentrations of elements and isotopes in otoliths. These methods usually require that otoliths be individually mounted and prepared to properly expose the desired growth region to the analytical beam. Most analytical instruments, such as LA-ICPMS and ion and electron microprobes, have sample holders that will accept only one to six slides or mounts at a time. We describe a method of mounting otoliths that allows for easy transfer of many otoliths to a single mount after they have been prepared. Such an approach increases the number of otoliths that can be analyzed in a single session by reducing the need open the sample chamber to exchange slides—a particularly time consuming step on instruments that operate under vacuum. For ion and electron microprobes, the method also greatly reduces the number of slides that must be coated with an electrical conductor prior to analysis. In this method, a narrow strip of cover glass is first glued at one end to a standard microscope slide. The otolith is then mounted in thermoplastic resin on the opposite, free end of the strip. The otolith can then be ground and flipped, if needed, by reheating the mounting medium. After otolith preparation is complete, the cover glass is cut with a scribe to free the otolith and up to 20 small otoliths can be arranged on a single petrographic slide

Ecological relation of sympatric steelhead and resident rainbow trout in the Deschutes River, Oregon

Sympatric steelhead and resident rainbow trout (Oncorhynchus mykiss) are known to exist in many rivers throughout the Pacific Rim. Whether sympatric steelhead and resident rainbow trout are polymorphisms within a single gene pool or two reproductively isolated populations has significant implications concerning the study and conservation of this polytypic species. I examined population structure and use of spawning and rearing habitats by steelhead and resident rainbow trout in the Deschutes River, Oregon. I used otolith microchemistry to determine the maternal origin (steelhead verses resident) of adult steelhead and resident rainbow trout based on Sr/Ca ratios in primordia and freshwater growth regions of otoliths. Only steelhead of steelhead origin and resident rainbow trout of resident origin were encountered. In the Babine River of British Columbia, however, steelhead of resident origin and resident rainbow trout of steelhead origin were present. Temporal and spatial segregation of spawning habitat served to limit breeding between steelhead and resident rainbow trout in the mainstem Deschutes River. The timing of 50% spawning by steelhead occurred 9 to 10 weeks earlier than by resident rainbow trout. Steelhead spawning sites were deeper and of larger substrate than those used by resident rainbow trout. There was an overlap in the timing of emergence by steelhead and resident rainbow trout fry in the mainstem Deschutes River, but higher levels of aggression and territoriality characterize newly emerged steelhead fry. Determination of maternal origin based on otolith microchemistry indicated that young-of- year 0. mykiss in small hydrologically unstable tributaries to the Deschutes River were exclusively the progeny of steelhead. Progeny of resident rainbow trout numerically dominated mainstem-rearing habitats. Based on the degree of segregation between steelhead and resident rainbow trout, the two life history forms act as two separate species in the Deschutes River. This relationship has significant implications concerning the restoration and conservation of steelhead and resident rainbow trout. Where steelhead and resident rainbow trout constitute reproductively isolated populations, conservation of both life history forms within the species cannot be achieved unless both populations are maintained

Population structure of coastal cutthroat trout (Oncorhynchus clarki clarki) in the Muck Creek Basin, Washington

The relationship of coastal cutthroat trout (Oncorhynchus clarki clarki) populations in the Muck Creek basin, a 238 km² southern Puget Sound stream basin in western Washington, was examined using starch gel electrophoresis and meristic analysis. Coastal cutthroat trout were collected from six sites throughout the basin including tributaries, portions of the mainstem, and a lake. Four sites contained only resident trout, the lower mainstem contained resident and anadromous trout, and the lake contained only mature anadromous trout based on size and appearance. Patterns of allelic and meristic variation suggest a significant structuring and separation of coastal cutthroat trout populations in the basin. The lake population was distinguished from the other populations by significant differences in allele frequencies and meristic characters. The other sites grouped more closely together with significant variation among and between sites meristically and at several loci

Use of glacier river-fed estuary channels by juvenile Coho Salmon: transitional or rearing habitats?

Abstract Estuaries are among the most productive ecosystems in the world and provide important rearing environments for a variety of fish species. Though generally considered important transitional habitats for smolting salmon, little is known about the role that estuaries serve for rearing and the environmental conditions important for salmon. We illustrate how juvenile coho salmon Oncorhynchus kisutch use a glacial river-fed estuary based on examination of spatial and seasonal variability in patterns of abundance, fish size, age structure, condition, and local habitat use. Fish abundance was greater in deeper channels with cooler and less variable temperatures, and these habitats were consistently occupied throughout the season. Variability in channel depth and water temperature was negatively associated with fish abundance. Fish size was negatively related to site distance from the upper extent of the tidal influence, while fish condition did not relate to channel location within the estuary ecotone. Our work demonstrates the potential this glacially-fed estuary serves as both transitional and rearing habitat for juvenile coho salmon during smolt emigration to the ocean, and patterns of fish distribution within the estuary correspond to environmental conditions

Gravitomagnetism in the Kerr-Newman-Taub-NUT spacetime

We study the motion of test particles and electromagnetic waves in the Kerr-Newman-Taub-NUT spacetime in order to elucidate some of the effects associated with the gravitomagnetic monopole moment of the source. In particular, we determine in the linear approximation the contribution of this monopole to the gravitational time delay and the rotation of the plane of the polarization of electromagnetic waves. Moreover, we consider "spherical" orbits of uncharged test particles in the Kerr-Taub-NUT spacetime and discuss the modification of the Wilkins orbits due to the presence of the gravitomagnetic monopole.Comment: 12 pages LaTeX iopart style, uses PicTex for 1 Figur

Calcification-driven CO2emissions exceed blue Carbon sequestration in a carbonate seagrass meadow

Long-term Blue Carbon burial in seagrass meadows is complicated by other carbon and alkalinity exchanges that shape net carbon sequestration. We measured a suite of such processes, including denitrification, sulfur, and inorganic carbon cycling, and assessed their impact on air-water CO2 exchange in a typical seagrass meadow underlain by carbonate sediments. Eddy covariance measurements reveal a consistent source of CO2 to the atmosphere at an average rate of 610 ± 990 μmol m-2 hour-1 during our study and 700 ± 660 μmol m-2 hour-1 (6.1 mol m-2 year-1) over an annual cycle. Net alkalinity consumption by ecosystem calcification explains \u3e95% of the observed CO2 emissions, far exceeding organic carbon burial and anaerobic alkalinity generation. We argue that the net carbon sequestration potential of seagrass meadows may be overestimated if calcification-induced CO2 emissions are not accounted for, especially in regions where calcification rates exceed net primary production and burial

Species and Life History Affect the Utility of Otolith Chemical Composition for Determining Natal Stream of Origin for Pacific Salmon

To test the utility of otolith chemical composition as a tool for determining the natal stream of origin for salmon, we examined water chemistry and otoliths of juvenile and adult Chum Salmon Oncorhynchus keta and Coho Salmon O. kisutch from three watersheds (five rivers) in the Norton Sound region of Alaska. The two species are characterized by different life histories: Coho Salmon rear in freshwater for up to 3years, whereas Chum Salmon emigrate from freshwater shortly after emergence. We used laser ablation (LA) inductively coupled plasma (ICP) mass spectrometry (MS) to quantify element: Ca ratios for Mg, Mn, Zn, Sr, and Ba, and we used multicollector LA-ICP-MS to determine Sr-⁸⁷:Sr-⁸⁶ ratios in otolith regions corresponding to the period of freshwater residence. Significant differences existed in both water and otolith elemental composition, suggesting that otolith composition could be used to discriminate the natal origin of Coho Salmon and Chum Salmon but only when Sr-⁸⁷:Sr-⁸⁶ ratios were included in the discriminant function analyses. The best discriminant model included Sr-⁸⁷:Sr-⁸⁶ ratios, and without Sr-⁸⁷:Sr-⁸⁶ ratios it was difficult to discriminate among watersheds and rivers. Classification accuracy was 80% for Coho Salmon and 68% for Chum Salmon, indicating that this method does not provide sufficient sensitivity to estimate straying rates of Pacific salmon at the scale we studied.Keywords: Plasma mass spectrometry, Fish otoliths, Stock identification, Chemistry, Oncorhynchus tshawytscha, Population structure, Microchemistry, Elemental analysis, Describe movements, Trace element