Correspondence between Scale Morphometrics and Scale and Otolith Chemistry for Interpreting Juvenile Salmon Life Histories

Abstract

Fish scales have long been used to reconstruct fine-scale habitat transitions such as the movement of juvenile fish from freshwater, estuary, and ocean environments. Despite the importance of life history information to fisheries management and conservation, few studies have validated that scale morphology accurately describes fish movement between these habitats. Therefore, we tested the accuracy of using scale morphometric criteria to identify the movement of juvenile Chinook Salmon Oncorhynchus tshawytscha from freshwater to marine portions of the Columbia River estuary by comparing scale morphometric classification, scale chemistry, and otolith chemistry. Nearly one-half of all fish collected in the saline portion of the estuary and approximately one-quarter in the freshwater portion exhibited morphometric patterns (i.e., scale checks and intermediate growth) often associated with periods of estuary rearing. Depending upon the criteria used to define scale checks, otolith chemical results indicated that 33–53% of fish would have been misclassified as estuary residents based solely on their scale patterns. Moreover, many individuals who had resided in strontium-rich estuary water did not form a visible check (37%) on their scales to coincide with estuary entry. We estimated from otolith chemistry that these fish had either entered at or near the size at which scale formation occurs (35–42 mm) or had recently migrated to the saline portion of the estuary (<30 d) before new scale material could be formed and calcified. Scale chemistry alone was a good indicator of entrance into the saline portion of the estuary. Scale chemistry responded to the strontium-enriched salt water, and explained 86% of the variation found in otolith chemistry. Scale morphometric classification did not provide the fine-scale resolution that scale and, even more so, otolith chemistry provided for describing the proportion of juvenile Chinook salmon using the saline portion of the Columbia River estuary.

Received December 26, 2013; accepted August 28, 2014

ACKNOWLEDGMENTS

This research was supported by the U.S. Army Corps of Engineers, Portland District; the Bonneville Power Administration; National Oceanic and Atmospheric Administration (NOAA) Fisheries, Northwest Fisheries Science Center; and the Washington Department of Fish and Wildlife. Special thanks to Steven Schroder for advice on most aspects of this manuscript. Additionally, we thank Gordon Reeves and the U.S. Forest Service, Forest Science Laboratory, for laboratory space. We thank the many people who collected and necropsied juvenile Chinook Salmon for scales and otoliths, especially Curtis Roegner, Susan Hinton, Jen Zamon, Paul Bentley, Regan McNatt, George McCabe, and Tom Campbell. We also thank Lang Nguyen and Dana Anderson of the Washington Department of fish and Wildlife Otolith Laboratory, for assistance in otolith sample preparation. We thank Adam Kent and Andy Ungerer at the Keck Collaboratory for Mass Spectrometry, Oregon State University, for assistance in microchemistry analysis. Lastly we thank Andrew Claiborne, Paul Chittaro, John Sneva, Brian Wells, and one anonymous reviewer for their thoughtful critiques that have improved this manuscript.