Validating Fin Ray Microchemistry as a Tool to Reconstruct the Migratory History of White Sturgeon

Abstract

The objective of this study was to validate the use of fin ray strontium isotope ratios (⁸⁷Sr:⁸⁶Sr) via laser ablation (LA) to resolve fine-scale movement patterns in sturgeons (Acipenseridae) during freshwater rearing in early life stages. We conducted a laboratory experiment in which juvenile White Sturgeon Acipenser transmontanus were exposed to two water sources exhibiting distinctive ⁸⁷Sr:⁸⁶Sr isotope values (American River and Putah Creek, California) over weekly time periods to understand how water exposure histories are archived in pectoral fin rays. Using LA multicollector inductively coupled plasma mass spectrometry with a laser diameter of 65 µm, we detected distinct shifts in fin ray ⁸⁷Sr:⁸⁶Sr values to match a water source in fish that were exposed for 2, 4, 6, and 12 weeks. Fin ray ⁸⁷Sr:⁸⁶Sr values matched the new water source after 21.7 d (SD = 7.8; range = 11–36 d) of exposure. The lower limit of this estimate was constrained by the rate of fin ray growth as well as the LA spot size. Additionally, we assessed how diet affected fin ray ⁸⁷Sr:⁸⁶Sr values by feeding a marine-derived pellet feed commonly used in aquaculture to a subset of White Sturgeon, while others were fed a diet consisting of fish with ⁸⁷Sr:⁸⁶Sr values that matched their respective water source. Generally, we observed only a minor influence of diet, but there was some variability across individual fish in the effect of diet on the resulting fin ray ⁸⁷Sr:⁸⁶Sr value. As with any geochemical analytical technique, fin ray microchemistry has some limitations related to individual variability in fin ray growth and development; however, it is a promising approach to reconstructing sturgeon migratory history by using a nonlethal sampling method.

Received December 16, 2016; accepted April 13, 2017 Published online June 23, 2017

Acknowledgments

We thank D. Cocherell and the Fangue Lab for laboratory support; Jay Rowan (California Department of Fish and Wildlife, Rancho Cordova) and Michelle Workman (East Bay Municipal Utility District, Fisheries and Wildlife Office, Lodi, California) for providing fish for the sturgeon feed; Cramer Fish Sciences (West Sacramento, California) and U.S. Fish and Wildlife Service (Lodi) technicians for producing sturgeon feed and performing laboratory analyses; and G. Whitledge for input on study design and sturgeon physiology. The U.S. Fish and Wildlife Service funded this study (Grant Number F11AC01162). The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.