Documentation of Unusual, Fall Spawning by Coastal Cutthroat Trout in the Elwha River System, Washington

Abstract

The timing of breeding is a key trait, reflecting selective forces acting on the adults and offspring in the population, contributing to reproductive isolation, and affecting the population's success during rapid environmental change. Salmon and trout populations vary greatly in the peak and range of breeding dates, and timing is a defining trait for salmonid populations. This study reports the occurrence and details of spawning by Coastal Cutthroat Trout Oncorhynchus clarkii clarkii in Indian Creek in the Elwha River, Washington, in October and November. This is unusually early in the season for this characteristically spring-spawning species and is much earlier than conspecifics elsewhere in the river system and the region. We hypothesize that the stream's low gradient and lake-dampened hydrologic regime reduced the depth of gravel scouring in the fall, and thus permitted the evolution of such an early breeding date by these small-bodied (ca. 20–35 cm) fish. The exclusion of otherwise sympatric, fall-spawning Coho Salmon O. kisutch for the past century from the habitat by Elwha Dam may also have contributed to this adaptation, and the recolonization by the larger and later-spawning Coho Salmon may have affected the Coastal Cutthroat Trout through redd disturbance.

Received April 24, 2014; accepted August 27, 2014

ACKNOWLEDGMENTS

We thank Wilson Wells, Lower Elwha Klallam Tribe (LEKT), for his assistance in field work, Randall McCoy, LEKT, for his GIS expertise in drafting the Indian Creek map, Sam Brenkman, Olympic National Park, for sharing his knowledge of Cutthroat Trout, and Polly Hicks, NOAA, Northwest Fisheries Science Center (NWFSC), for support. Funding was partly provided through a grant to Thomas Quinn from Washington Sea Grant, University of Washington, pursuant to NOAA Award NA10OAR4170075, Project R/LME-7. We also thank Sarah Morley, Todd Bennett, and Phil Roni at NOAA–NWFSC and the anonymous reviewers and the journal's editorial staff for reviews and suggestions that improved the manuscript. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its subagencies.